Cswip 3.1 Test

WELDING INSPECTION(WISS)

Section

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2)

3)

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9)

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11)

12)

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16)

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21)

22)

23)

Title

Terms & Definitions V

Duties & Responsibilities

Welding Imperfections 1/Mechanical Testing

Welding ProcedureslWelder approval

Materials Inspection

Codes and Standards

Welding Symbols on Drawings

Introduction to Welding Processes

Manual Metal Arc Welding

Tungsten Inert Gas Welding

Metal InertlActive Gas Welding

Submerged Arc Welding

Welding Consumables

Non Destructive Testing V'Weld Repairs

Residual Stress & Distortion

Heat Treatment of Steels \.I

Oxy-Fuel Gas Welding & Cutting

Arc Cutting Processes

Welding Safety

Weldability of steels

Visual Inspection Section

TWIV!lfll. THE WELDING INSTITUTE

Terms and Definitions:

/

A Weld:/'

! /!~/)Cr

JI

OF gy fi;Jfh_/' ./

C-J'e--C- 0,/S

A Joint:

Welding Inspection - Terms & DefinitionsCopyright © 2002 TWI Ltd

1.1 Rev 09-09-02

TWIV/lDI. THE WELDING INSTITUTE

Types of common welds:

Welds.

Welds.

2 - ? (' 1i)/1]I ~. I J '/'- "

r- ! '.--:- t' liie" '1 ( (l fc(:;;;, {,iu.:,C ,- -

///0I v-'tt/ I;ct ,\ c(( ,r-ellf)

ly~s-.su;-cI '

Welds.

! /J 1./~t Welds.

Ttt-,(,,>k/~:~.£-:~~,--(~.'- . /

Welds.

Welding Inspection - Terms & DefinitionsCopyright © 2002 TWl Ltd

1.2 Rev 09-09-02

TWIV!lfl#. THE WELDING INSTITUTE

Types of common joints:

Joints.--------

__~)~J=f_!~-(-(k_1_J__Joints.

CkC~1


Joints.

1.3 Rev 09-09-02

TWIVflDI. _

Weld Preparations:

THE WELDING INSTITUTE

When welding, we need to fuse the entire width of the faces of both members. Mosttimes we need to prepare, or remove metal from the joint to allow access for theprocess, for full fusion of the faces. We can use grinding, flame/arc cutting, or machiningfor this operation, but grinding back 1 or 2 mm may be required after flame or arccutting.

The purpose of a weld preparation is to allow access for the welding process, penetrationand fusion through the complete area of the joint and its faces. The function of the rootgap is to allow penetration. The function of the root face is to remove excess heat and actas a heat sink. The higher the arc energy of the process, then generally the wider is theroot face, as in SAW.

The simple rule is this: The more taken out then the more must be replaced.This has a major effect on both economics, and distortion. The root face, root gap andangle of bevel values, choice of single or double sided preparations, is solely dictated bythe choice of welding process, the welding process parameters, the position andaccessibility of the joint.


1.4 Rev 09-09-02

TWIrofll. THE WELDING INSTITUTE

Single Butt Weld Preparations:

Single

Single

Single

Single

v

J

u

'-----v I

\\1 I

,-----U I

I l) I

Single sided preparations are normally made on thinner materials, or when access fromboth sides is restricted.

The selection may be also influenced by the capability of the welding process and theposition of the joint, or the positional capability of available welding consumables, or theskill level available.


1.5 Rev 09-09-02

TWIV!lOI. THE WELDING INSTITUTE

Double Butt Weld Preparations:

Double

Double

Double

Double

v

J

u

L---K I

I x_Double sided preparations are normally made on thicker materials, and when access fromboth sides is unrestricted.

They may also be used to control the effect of distortion, and in economics, whenwelding thicker sections.


1.6 Rev 09-09-02

TWIroOI. THE WELDING INSTITUTE

Welded Butt Joints:/~, ;!

.:>- ,;/ -.( ·{2,

Welded Butt Joint.

A Welded Butt Joint.

{:Of~Welded Butt Joint.


1.7 Rev 09-09-02

TWIrvO#. THE WELDING INSTITUTE

Welded T Joints:

A ft(~f

A

Welded T Joint.

Welded T Joint.

A Welded T Joint.


1.8 Rev 09-09-02

TWIfllfll. THE WELDING INSTITUTE

Welded Lap Joints:

A Welded Lap Joint.

A Welded Lap Joint.

A Welded Lap Joint.


1.9 Rev 09-09-02


Welded Closed Corner Joints:

A

A

Welded Closed Corner Joint.




1.10 Rev 09-09-02

Welded Open Corner Joints:

TWIV/lfll. THE WELDING INSTITUTE

rtk PH T/&-/i< I'-/~ (jC~1-

t{/~ r- f-" U6L' "-

r (£ /_r tiC_-/--It<hr e r.r ~t Welded Open Corner Joint.

An awt--sioLe- I/Mwelded Open Corner Joint.

A~ t/fJ3z;f- Welded Open Comer Joint.v


1.11 Rev 09-09-02

TWIV!lDI. THE WELDING INSTITUTE

Terms of a Butt Welded Butt Joint:

,TJ~

A & B ": fl.~ Weld Metal.


1.12 Rev 09-09-02


Terms of a Fillet Welded T Joint:

&~ wd.d meke])e&' Tky~ Tk'aAc~.

ndu~ nv~-f 7k/dk~.

In visual inspection it is usually the leg length that is used to size fIllet welded joints. Itis possible to find the design throat thickness easily by multiplying the leg length by 0.7

The excess weld metal can be measured by taking the measurable throat reading, then bydeducting the design throat thickness calculated above.

Example:

If the leg length of a convex fillet weld is measured at 10 mm, then the design throatthickness = 10 x 0.7 which is 7mm.

If the actual throat thickness is 8.5 mm then the excess weld metal is calculated as:8.5 - 7mm = 1.5mm excess weld metaL


1.13 Rev 09-09-02


'Nominal' and 'Effective' Design Throat Thickness:

Same leg length

-.J -.- ---.I -.-I I I II I I II II II II II II II II

"a" = 'Nominal' design throatthickness

"s" = 'Effective' design throat thickness(deep penetration fillets)

When using deep penetrating processes with high current density it is possible to createdeeper throat dimensions.

This may be used in design calculations to carry stresses and is a big advantage byreducing overall weight ofwelds in a large welded structure.

Deep throat fillet welds are possible when using high penetration (High current density)processes, such as FCAW & SAW.

This throat notation "a" or "s" is used in BSEn 22553 for weld symbols on drawingsthroughout Europe.


1.14 Rev 09-09-02

TWIfllfll. THE WELDING INSTITUTE

FiDet Weld Profdes:

In joints that are to be dynamically loaded with cyclic stresses, concave fillet weld arepreferred to minimise any stress concentrations or sites for fatigue crack initiation.

In critical applications it may be a requirement of the welding procedure that the toes arelightly ground, or even flushed in with a TIG run, to remove any notches that are present.


1.15 Rev 09-09-02

TWIVDDI. THE WELDING INSTITUTE

Duties of a Welding Inspector:

\/

It is the duty of a welding inspector to ensure that all operations concerning welding arecarried out in strict accordance with written, or agreed practices, or specifications.

This will include monitoring or checking a number ofoperations including:

Before welding:

Safety:

Ensure that all operations are carried out in complete compliance with local, company, orNational safety legislation (Le. permits to work are in place).

Documentation:

Specification. (Year and revision)

Drawings. (Correct revisions)

Welding procedure specifications and welder approvals.

Calibration certification. (Welding equipment/ancillaries and all inspection instruments)

Material and consumable certification

Welding Process and ancillaries:

Welding equipment and all related ancillaries. (Cables, regulators, ovens, quivers etc.)

Incoming Consumables:

All pipe/plate and welding consumables for Size, Type and Condition.

Marking out preparation & set up:

Correct method of cutting weld preparations. (pre-Heat for thermal cutting if applicable)

Correct preparation. (Relevant bevel angles, root face, root gap, root radius, land, etc.)

Correct pre-welding distortion control. (Tacking, bridging, jigs, line up clamps, etc.)

Correct pre heat applied prior to tack welding.

All tack welding to be monitored and inspected

Welding Inspection - Duties ofa Welding InspectorCopyright © 2002 TWI Ltd

2.1 Rev 09-09-02

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During welding:

Pre-heat values. (Heating method, location and control)


In-process distortion control. (Sequence or balanced welding)

Consumable control. (Specification, size, condition, and any special treatments)

Process type and all related variable parameters. (Voltage, amperage, travel speed)

Purging gases. (Type, pressure/flow and control method)

Welding conditions for root run/hot pass and all subsequent run, and inter-run cleaning.

Minimum, or maximum inter-pass temperature. (Temperature and controlling method)

Compliance with all other variables stated on the approved welding proced~re.

Mter welding:

Visual inspection ofthe welded joint. (Including dimensional aspects)

NDT requirements. (Method and qualification ofoperator, and execution)

Identify repairs from assessment ofvisual or NDT reports. (Refer to repairs below)

Post weld heat treatment (pWHT) (Heating method and temperature recording system)

Re-inspect with visual/NDT after PWHT. (If applicable)

Hydrostatic test procedures. (For pipelines or pressure vessels)

Repairs:

Excavation procedure. (Approval and execution)

Approval ofthe NDT procedures (For assessment of complete defect removal)

Repair procedure. (Approval ofre-welding procedures and welder approval)

Execution ofapproved re-welding procedure. (Compliance with repair procedure)

Re-inspect the repair area with visual inspection and approved NDT method.

Submission of inspection reports, and all related documents to the Q/C department.


2.2 Rev 09-09-02

TWIVOI. THE WELDING INSTITUTE

Responsibilities of a Welding Inspector:

To Observe

To observe all relevant actions related to weld quality throughout production.This will include a :final visual inspection of the weld area.

1,--:;_O_R_e_co_r_d_£__!iJ_~

To record, or log all production inspection points relevant to quality, including a finalmap and report sheet showing all identified welding imperfections.

IL--;,_a~_c_o_m_p_a_re__""

To compare all reported information with the acceptance levels/criteria and clauseswithin the applied application standard.

Submit a fmal inspection report of your findings to the QAlQC department foranalysis and any remedial actions.


2.3 Rev 09-09-02

TWIV!lOI. _

Mechanical Testing:


Mechanical tests are generally carried out to ensure that the required levels of certainmechanical properties have been achieved.When metals have been welded, the mechanical properties of the plates may havechanged in the HAZ due to the thermal effects of the welding process.It is also necessary to establish that the weld metal itself reaches the minimum specifiedvalues.

The mechanical types of properties or characteristics most commonly evaluated are:

Hardness:

Toughness:

Strength:

Ductility:

The ability of a material to resist indentation.

The ability of a material to absorb impact energy and resist fracture.

The ability of a material to resist a force. (Normally tension)

The ability of a material to plastically deform under tension.

To carry out these evaluations we require specific tests. There are a number ofmechanical tests available to test for these specific mechanical properties, the mostcommon ofwhich are:

1) Hardness testing. (VickerslBrinelllRockwell)

3) Tensile testing. (ReducedlRadius IAII weld metal)

2) Toughness testing. (Charpy VlIzod/CTOD) Used to measureQuantity.

Tests 1- 3 have units and are termed quantitative tests.

We use other tests to evaluate the quality ofwelds

4) Macro testing.

7) Butt weld Nick-break testing.

5)

6)

Bend testing. (SidelFacelRoot)

Fillet. weld fracture testing.

Used to measureQuality.

Tests 4 -7 have no units and are termed qualitative tests.

Welding Inspection - Mechanical TestingCopyright © 2002 TWl Ltd

4.1 Rev 09-09-02

TWIV!lfll. _THE WELDING INSTITUTE

1) Hardness tests: Used to check the level ofhardness across the weld.

Types ofhardness test are:

a) Rockwell scale.

b) Vickers pyramid. VPN

c) Brinell. BHN

d) Shore Schlerescope.

(Diamond or steel ball)

(Diamond)

(5 or 10 mm diameter steel ball)

(Measures resilience)

Most hardness tests are carried out by (1) impressing a ball, or a diamond into thesurface of a material under a fixed load, (2) then measuring the resultant indentation andcomparing it to a scale of units (BHNNPN etc.) relevant to that type of test. Hardnesssurveys are generally carried out across the weld as shown below. In some applications itmay also be required to takes hardness readings at the weld junction/fusion zone.

A shore schlerescope measures hardness by dropping a weight from a height onto thesurface of a metal and measuring the height of the rebound. The higher the rebound ofthe weight, the harder is the material. Early equipment was cumbersome, but moreportable compared to other hardness testing methods. Equipment is now available whichworks on the resilience principle, and is the size of a ballpoint pen. This equipment isgenerally scaled to give hardness values in all of the above scales.

Plate

1 +o

Welding Inspection - Mechanical TestingCopyright © 2002 TWI Ltd

4.2 Rev 09-09-02

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2) Toughness tests: Used to check the resistance to impact loading.

Types of toughness test are:

a) Charpy V. (Jollies) Specimen held horizontally in test machine, notch to the rear.

b) Izod. (Ftlbs) Specimen held vertically in test machine, notch to the front.

c) CTOD or Crack Tip Opening Displacement testing. (mm)

There are many factors that affect the toughness of the weldment and weld metal. One ofthe important effects is that of testing temperature. In the Charpy V and Izod test, thefracture toughness is assessed by the amount of impact energy absorbed by a smallspecimen of 10 mm2 during fracture by a swinging hammer. A graph can be producedusing temperature as the base. The notch is 2mm deep, 0.25 root radius, and notch e45 0

I··.·"'·._~~~----=:J~ 10 x 10 mm

Machined notch

Graduated scale of Joulesabsorbed energy


4.3

Fusion zone & HAZ

Release lever

/Pendllium locked inposition

Specimen

Rev 09-09-02

TWIVOI. _THE WELDING INSTITUTE

DuctilelBrittle transition curve for a typical ferritic steel

Temperature range~

I

Transition range

47 Joules

14--.-----.. DuctilelBrittle transition point

28 Joules

Energy absorbed(Joules)

-50 -40 -30 -20 -10 0 10Degrees Centigrade

20 30 40

The curve can be moved by many factors, including alloying & heat input:

a) Alloying:

The curve can be moved to the left by additions of manganese of up to 1.6 %. In otherwords the addition of manganese of up to 1.6%·has a positive effect on improving thetoughness of plain ferritic steels. Nickel also has a very positive effect on lowtemperature toughnessof steels, however nickel is a very expensive metallic element andis used only where low temperatures are severe. Steels containing 9% nickel haveexcellent low temperature toughness. Fully austenitic stainless steels show measurabletoughness at -270 °C, or a few degrees above absolute zero.

b) Heat input:

The curve can be moved to the right by too high a heat input during the welding cycle.This happens because of the effect called grain growth. At high temperatures, grainsgrow and fuse together to form larger grains. The amount of energy needed to fracture alarge grain structure is much less than a fme grain structure. Hence the need to controlinter-pass temperatures.


4.4 Rev 09-09-02

TWIVflUI. _THE WELDING INSTITUTE

3) Tensile Test: Used to measure tensile strength (N/mm2) (Ductility as E %)

Types oftensile tests are:

a) Transverse tensile test:Reduced section: Used to test the strength of the weldment.Radius reduced section: Can be used to assess the strength of the weld metal.

b) All weld metal tensile test:Used to test weld metal for UTS, yield point and elongation, or E %.

Transverse tensile tests are taken across the weld to test the value of tensile strength inthis area. A reduced tensile test is the standard test where the specimen is first cut andthen reduced to allow a gripping area for the machine with a very low stressconcentration. A radius may be cut into the weld to assess the weld metal strength.

A transverse tensile test specimen

Test gripping area/

Weld Radius (For radius reduced test specimens only)

Plate material~I<: 50mm

Elongation marks

.... 'Reduced Section

Failure is generally expected in the plate material, though failure in the weld or HAZ isnot reason to fail the test if the minimum specified tensile stress has been reached.

In a Radius reduced tensile test the weld metal is turned down, and so failure would beexpected in the weld, due to a smaller CSA. It is sometimes used to show the tensilestrength of the weld metal, but it is not very accurate due to the local stressconcentrations that are produced.

All weld metal tensile tests are carried out by electrode manufacturers to determineweld metal strength, and also ductility as elongation (E%). A deep weld is made in aplate and then a tensile specimen is cut along the length of the weld, which shouldcontain 99.9% undiluted, or pure weld metal. Prior to the test, marks are made 50 mmapart along the length of the specimen. As the test is being carried out yield stress andfracture stress are recorded and documented. After fracture, the pieces are placed backtogether and the elongation is calculated from the original gauge length and given as E%


4.5 Rev 09-09-02

TWIVfl!7I. _THE WELDING INSTITUTE

4) Macro examination tests: Used to check the intemallevel ofquality in theweld.

A macro specimen is normally cut from a stop/start position in the root, or hot pass of awelder approval test. The start/stop position is marked out during a welder approval testby the welding inspector. Once cut, the specimen is polished using progressively fmergrit papers and polishing at 90° to previous polishing direction, until all the scratchescaused by the previous polishing direction have been removed. It is then etched in anacid solution which is normally 5 -10% Nitric acid in alcohol (carbon steels). Care mustbe taken not to under-etch or over-etch the specimen, as this will mask the elements thatcan be observed on a correctly etched specimen. After etching for the correct time, thespecimen is then washed and dried. A visual examination should be carried out at allstages of production to observe any imperfections that are visible. Finally, a report isthen produced on the visual fmdings, then compared and assessed to the levels ofacceptance in the application standard.Macro samples may be sprayed with clear lacquer after inspection, for storage purposes.

Macro Assessment Table

1) Excess weld metal height. 2)

3) Slag with lack of inter-run fusion. 4)

5) Root penetration bead height. 6)

7) Undercut

Slag with lack of sidewall fusion.

Angular misalignment.

Segregation bands.


4.6 Rev 09-09-02

TWIrofll. _THE WELDING INSTITUTE

5) Bend tests: Used to check weld ductility & fusion in the area under stress.

The fonner is moved through a guide (guided bend test), or rollers, and the specimen isbent to the desired angle.Types of bend test are:

a) Face bends b) Root bends c) Side bends d) Longitudinal bends

Fonner.

. . Before testing

After testing

A guided side bend test

Specimen

Guide

Specimen is bent through pre-determined angle

Generally, bend tests are carried out for welder approval tests, though they may also beused during procedure approval to establish good sidewall, root, or weld face fusion.Inspection of the test face is made after the test to check the integrity of the area in test.

For materials of greater than 12mm thickness, a slice of 1O-12mm is nonnally cut outalong the length and the material is side bend tested. Bend testing is a qualitativemethod of mechanical testing. Ductility may be observed but is not measured.


4.7 Rev 09-09-02

TWIrofll. THE WELDING INSTITUTE

6) Fillet weld fracture tests. Used to assess root fusion in fillet welds.

A fillet weld fracture test is normally only carried out during a welder approval test.The specimen is normally cut by hacksaw through the weld face to a depth (usually 1-2mm) stated in the standard. It is then held in a vice and fractured with a hammer blowfrom the rear. Once fracture has been made, both fractured surfaces are inspected forimperfections.

Finally the vertical plate X is moved through 90° and the line of root fusion is observedfor continuity. Any straight line would indicate a lack of root fusion. In most standardsthis is sufficient to fail the welder.

Hammer blow

Fracture line t

X

B

1

y

Saw cut

Full fracture

~3

1I

Line of fusion

c

"Lack of root fusion"

After inspection of both fractured surfaces for imperfections, turn fracture piece Xthrough 90° vertically and inspect the line ofroot fusion. (Line 2)

A Fillet weld fracture test is a qualitative mechanical test, as we are observing weldquality.


4.8 Rev 09-09-02


TWIVOOI. _7) Nick-break tests:

Used to assess root penetration and fusion in double-sided butt welds, and the internalfaces of single sided butt welds. A Nick-break test is normally carried out during awelder approval test.

The specimen is normally cut by hacksaw through the weld faces to a depth stated in thestandard. It is then held in a vice and fractured with a hammer blow from the rear. Oncefracture has been made then both fractures are turned horizontally through 90° and maythen be inspected for imperfections on the fracture faces, as shown below in C.

Saw Cuts Hammer blow

A Fracture line

B

Lack of root penetration, or fusion Inclusions on the fracture line

A butt Nick-break test is a qualitative test, as we are observing quality.


4.9 Rev 09-09-02


Quantitative and Qualitative Mechanical Testing:

TWIVl7fll. _

Quantitative:

We test weldments mechanically to establish the level of mechanical properties of theweld. In such a case we may use the following types of tests:

1) Hardness:Vickers (VPN) Brinell (BHN) Rockwell (Scale C for steels)

2) Toughness:Charpy V (Joules) Izod (Ftlbs) CTOD(mm)

3) Tensile Strength:N/mm2 (UK) & PSI (USA)

Transverse reduced & radius reduced. Longitudinal all weld metal.

Elongation E% may be measured during tensile testing.

(The ductility value often given as a % reduction in area mainly in transverse and shorttransverse tensile tests)

All the above tests 1 - 3 have units, and are thus termed quantitative tests.

They are used only in welding procedure approvals.

Qualitative:

We also test weldments mechanically to establish the level of quality in the weld.In such a case we may use the following types of test:

4) Macro testing.

5) Bend testing. (Face. Root. Side. & Longitudinal)

6) Fillet weld fracture testing.

7) Butt nick-break testing.

All the above tests 4 - 7 have no units, and are thus termed qualitative tests.

They are mainly used in welder approvals.

Some of the qualitative tests may be used during procedural approval to establishgood fusion/penetration etc.


4.10 Rev 09-09-02

TWIVllfl#. _

Summary of Mechanical Testing:


Name Property Qualitative Units, if Used mainly forIf applicable or applicable

QuantitativeRockwell scale Hardness Quantitative Scale C is used Welding

for Steels Procedure testsVickers pyramid Hardness Quantitative VPN Welding

Procedure testsBrinell Hardness Quantitative BHN Welding

Procedure testsShore Schlerescope Hardness Quantitative Measures Measuring

Resilience mm Stock materialsCharpyV Toughness Quantitative Joules. Energy Welding

absorbed Procedure testsIzod Toughness Quantitative Ft.lbs Welding

Procedure testsCTOD Notch Ductility Quantitative 0.0000 mm + a Welding

Toughness detailed report Procedure testsTransverse Reduced Tensile Strength Quantitative N/mm.lor PSI WeldingTensile Ductility % Reduction Area Procedure testsAll Weld Metal Tensile Strength Quantitative N/mm.lor PSI WeldingTensile Ductility Elon2ation % Consumable testsRadius Reduced Tensile Strength Quantitative N/mm~ or PSI WeldingTransverse Tensile of weld metal Procedure testsMacro N/A Qualitative N/A Welder Approval

or Procedure tests

IBends Ductility may be Qualitative N/A Welder ApprovalFace Root or Side observed or Procedure testsFillet Weld Fracture N/A Qualitative N/A Welder ApprovalT & Lap Joints or Procedure testsNick Break Test N/A Qualitative N/A Welder ApprovalButt Joints or Procedure tests


4.11 Rev 09-09-02


Welding Procedures:

What is a welding procedure?

A welding procedure is a systematic method of producing a sound weld. For productionpurposes this is generally held as a written, or a computer generated document.

Testing a weld sample:

Most production welding procedures are approved. (They have been thoroughly tested)Having carried out a test weld using the preliminary Welding Procedure Specification(pWPS), the welded specimen is generally sent for visual inspection and non-destructivetesting to assess the level ofquality.

If the test weld passes these tests it may then be sent for any required mechanical testing.The test coupons are cut from the welded test piece from locations that are generallyspecified in the application standard, and are then sent to a test house for testing.

These tests may include quantitative tests such as hardness, toughness or tensile tests, andany required qualitative tests such as macros, bends, or fracture tests.

Documentation:

If all the tests have met the requirements of the standard, the procedure will becomeapproved. The Welding Procedure Approval Record *(wpAR) will include all thevarious welding parameters and test record data.*Also commonly referred to as a Procedure Qualification record (PQR)

From this data a workable document for production welding is prepared and called aWelding Procedure Specification (WPS).

Generally the approved Welding Procedure Specification will have an "Extent ofapproval" which may include the following variable parameters:

1) Thickness of plate. 2) Diameter of pipe.

3) Welding position. 4) Material groups.

5) Amperage range. 6) Number of runs.

7) Consumables. 8) Heat input range. (kJ/mm)

A CSWIP 3.2 Senior Welding Inspector would generally witness the welding of theprocedure and supervise the subsequent testing of the weld.

Welding Inspection - Welder & Procedure ApprovalCopyright © 2002 TWI Ltd

5.1 Rev 09-09-02


Welder Approval:

A welder approval test is a test of the level of skill attained by the welder.

Once a welding procedure has been approved it is then important to ensure that allwelders employed using the procedure on a project can meet the level of quality setdown in the application standard. Welder approvals are therefore carried-out, where thewelders are directed to accurately follow the approved WPS by the welding inspector.

The test plate, or pipe is then tested for quality using NDE/NDT and some qualitativemechanical tests. In general a visual examination is carried out, followed by radiographyor ultrasonic testing (depending on the level of skill demanded from the welder) to lookfor internal imperfections. The specimen may then be cut into coupons for the variousqualitative mechanical tests. These tests generally require simple equipment such as ahacksaw, hammer, vice, polishing equipments, and bend testing machine.

The mechanical tests ofa welder approval may include:

a) Bend tests. (Side. Face. Root)

c) Nick Break tests.

b)

d)

Fillet weld fracture tests.

Macro Assessments.

When supervising a welder test the welding inspector should:

\

1)

2)

3)

4)

5)

6)

7)

8)

9)

10)

11)

12)

Check the welding process, condition of equipment and test area for suitability.

Check that extraction systems, goggles and all safety equipment are available.

Check grinders, chipping hammers, wire brush and all hand tools are available.

Check materials to be welded are correct and stamped correctly for the test.

Check welding consumables specification, diameter, and treatment with WPS.

Check the welder's name and stamp details are correct.

Check that the joint has been correctly prepared and tacked, or jigged.

Check that the joint and seam is in the correct position for the test.

Explain the nature ofthe test and check that the welder understands the WPS.

Check that the welder carries out the root run, fill and cap as per the WPS.

Ensure welders identity and stop start location are clearly marked.

Supervise or carry out the required tests and submit results to Q/C department.

A CSWIP 3.1 welding inspector may be called upon to witness/conduct a welderapproval test, and supervise, or carry out the subsequent testing of the weld.


5.2 Rev 09-09-02

THE WELDING INSTITUTEA typical welder approval certificate to BS 4872 would contain the following data:

TWIVllDI. _

Organization's Symbol Logo: Welder approval test certificate Test record No

& (BS 4872: Part 11982) 321

Manufacturers name: Welders name & Identity No Issue NoXYZ Fabrications Ltd. Mr. A Welder. Stamp 123 001

Test piece details: Date of test9th September 2002

Welding process: MMA IIIParent material: Ferritic steel Extent of approval:Thickness: 5mmJoint type: Single V butt. Welding Process: MMAPipe outside 0: 150mm Materials Range: Ferritic steels.Welding position: Overhead. Vertical up. Thickness range: 2.5-10mm.

Horizontal vertical. Flat. Joint types: Butt welds inTest piece position: Axiso inclined 45 plate & pipe.Fixed/rotated: Fixed Pipe outside 0: 75 -30Omm

Welding consumables:Welding Position: All except

Vertical down.Consumables: Rutile & Basic.

Filler metal: BOC Fortrex 7018(Make & type) Weld preparation (dimensioned sketch)

Composition: Ferritic steel.

'~OiSpecification: E 50 5 B 12 H5 1.5-2mmShielding gas: N/ASpecification number: BSEn4991994 ... 1.5-2mm

1~~

Visual examination & Test results:

Visual Inspection:Contour: l1"'ftaJfe, Penetration (No bac~g) l1"'ftaJ&Undercut: l1"'ftaJfe, Penetration (with backing) Not Of/llellfe,Smoothness of joins: l1"'ftaJfe, Surface defects l1"'ftaJ&Destructive tests:

Macro I Side Bend I Root Bend I Fillet fracture I Butt Nick breakNot l'ejD/iwi I Not I'ejwI'd I Xc:' l1"'ftaJfe, I Not l'ejD/iwi I Not I'ejwiwI

Remarks: Tk Nlel' «lOG ~/)(J.tte~ I""' 1JIr' ia'apo' Of/~lJIree lJIr'toe JleI(d.

The statements in this certificate are correct. The test weld was prepared inaccordance with the requirements of BS 4872: Part 11982.

Manufacturers Representative: Inspecting authority, or test house:Mr. A Representative ABC Inspection Ltd. ......................... . .

::::::A'" 'roved::::::11 Re!l"UeI(tatiue Ie PleI(t, .... PP. ........Position. Witnessed by: .:CSWlP 3~t:rio:123:'..............................

. . Mr'ICPlinlY ..Quality Manager Mr. I C Plenty.. .. .. .. ............ ....... .. .. .. .. .. .. .. .. .. .. .. .. .. ..

Date: 9th September 2002 Date: 9th September 2002


5.3 Rev 09-09-02

TWIVllOI. _

Materials Inspection:

All materials arriving on site should be inspected for:

1) Size.2) Condition.3) Type/Specification.


In addition, other elements may need to be considered depending on the materials fonnor shape. Most plate materials begin life as a casting, which is then rolled out into plate.Plate is sometimes rolled into pipe and then welded with a longitudinal, or helical seam.Some imperfections associated with rolling are shown below:

Direction of rolling

I------------------~~

············z··········. . . . . . . . . . . . . . .. . .. --.-

Segregation and

Laminations contain impurities and major inclusions such as slags that solidify in theingot.When rolled out these major inclusions may exist throughout the plate thickness.Gas pores in the solidified ingot can also cause laminations when rolled out but willgenerally 'close up' during the hot rolling process.Laminations will become thinner as the plate is rolled into thinner sections and willeventually become invisible to the naked eye in thinner sheet or plate.

Segregation bands occur in the centre of the plate and are low melting point impuritiessuch as sulphur or phosphorous which have segregated to the centre of the ingot as thatis the last place to cool. Great care needs to be taken when welding low quality steel assulphur levels may be present in the steel which cannot be detected by non destructivetesting.Segregation bands can only be found on etched surfaces and have an appearancesimilar to that ofa weld HAZ.

Laps are caused during rolling when overlapped metal does not fuse to the basematerial due to insufficient temperature, and or pressure.

Welding Inspection - Materials InspectionCopyright © 2002 TWI Ltd

6.1 Rev 09-09-02

TWIV!llll. _THE WELDING INSTITUTE

Plate Inspection:

Condition:

Corrosion, Mechanical damage, Laps and Laminations.

Size:

Length

... ,;.'

, ;;-.'

Width

I--------------~

Thickness

Other checks need to be made such as heat treatment condition, distortion,tolerance, quantity, storage and identification.


6.2 Rev 09-09-02

TWIV!7DI. _

Pipe Inspection:

Condition:


Corrosion, Mechanical damage, Wall thickness, Ovality, Laps, Laminations.

Type/Specification:

Welded seam

Length

Size:

Other checks also need to be made, such as heat treatment condition, distortion,tolerance, quantity, identification and storage.


6.3 Rev 09-09-02


Codes and Standards:

A code of practice is generally a legally binding document containing the rules and lawsrequired to design, and test a specific product, whereas a standard will generally contain,or refer to all the relevant optional and mandatory manufacturing, testing and measuringdata. The definitions given in the English dictionary state:

A code of practice:A set of law's, or rules that shall be followed when providing a service or product.

An applied standard:A level of quality, or specification too which something must be tested.

We use codes and standards to manufacture many things that have been built many timesbefore. The lessons of failures, or under-design are generally incorporated into the nextrevised edition.

Typical design/construction codes and standards used in industry include:

Pipe lines carrying low, and high-pressure fluids.Oil storage tanks.Pressure vessels.Offshore structures.Nuclear installations.Composite concrete and steel bridge construction.Vehicle manufacture.Nuclear power station pipe work.Submarine hull construction.Earth moving equipment.Building construction etc.

Generally; the higher the level of quality required then the more specific is thecode/standard in terms of the manufacturing method, materials, workmanship, testingand acceptable imperfection levels.

The application code/standard gives important information to the welding inspectoras it determines the inspection points and stages, and other relevant criteria that must befollowed, or achieved by the contractor during the fabrication process.

Most major application codes and standards contain 3 major sections, which arededicated to:

1) Design.2) Manufacture.3) Testing.

Welding Inspection - Codes and StandardsCopyright © 2002 TWI Ltd

7.1 Rev 09-09-02

TWIVllOI. _THE WELDING INSTITUTE

Application codes/standards may not contain all the relevant data required formanufacture, but may refer to other applicable standards for special elements. Examplesof these are given below:

1) Materials specifications.2) Welding consumable specifications.3) Welding procedure and welder approvals.4) Personnel qualifications for NDT operators.5) NDT Methods.

On many occasions the application code/standard will contain it own levels ofacceptance, which are drawn up by a board of professional senior engineers, who operatein that specific industrial area.

Codes and standards are' revised periodically to take into account new data, newmanufacturing methods, or processes that may come into being. If no local legalobligations exist then it is the year of the application code/standard within the contractdocuments, which becomes the legally binding version.

The main areas of responsibility within an application standard is generally divided into:

1) The client, or customer.2) The contractor, or manufacturer.3) The third party inspection authority, or client's representative.

The applied code/standard will form hub of the contract documents hence any deviation,or non-conformance from the code/standard must be applied for by application from thecontractor to the client as a concession. Once a concession has been agreed, it must thenbecome a signed and written document, which is then filed with the fabrication qualitydocuments.

Welding Inspection - Codes and StandardsCopyright © 2002 TWl Ltd

7.2 Rev 09-09-02

TWIVllOI. _

Weld Symbols on Drawings:


We use weld symbols to transfer infonnation from the design office to the workshop.

It is essential that a welding inspector can interpret weld symbols, as a large proportionof the welding inspectors time will be spent checking that the welder is correctlycompleting the weld in accordance with the approved fabrication drawing. Thereforewithout a good knowledge of weld symbols, a welding inspector is unable to carry outhis full scope of work. Standards for weld symbols do not follow logic, but are based onsimple conventions.

There are many different standards for weld symbols, as most major manufacturingcountries have their own. Basically a weld symbol is made of 5 different components,and the following is common to all major standards:

1) The arrow line:The arrow line is always a straight and unbroken line, (With the exception of instancesin AWS AlA) and has only 1 of 2 points on the joint where it must touch, as shownbelow:

2) The reference line:The reference line must touch the arrow line, and is generally parallel to the bottom ofthe drawing page. There is therefore always an angle between the arrow line andreference line. The point of the joint of the 2 lines is referred to as the knuckle.

~,-.----- Either/or

3) The symbol:The orientation of the symbol on the line is generally the same in most standards,however the concept of arrow side and other side is shown differently in somestandards. This convention is explained within the following text for UK, European, andISO standards. (AWS Al.4 convention for arrow and other side follows that ofBS 499)

4) The dimensions:Basically, all cross sectional dimensions are given to the left, and all linear dimensionsare given to the right hand side of the symbols in most standards.

5) Supplementary information:Supplementary information, such as welding process, weld profile, NDT, and any specialinstructions may differ from standard to standard.

The following section gives a guide to the standards used in UK and Europe.

Welding Inspection - Weld Symbols on DrawingsCopyright © 2002 TWI Ltd

8.1 Rev 09-09-02

TWIV!llll. THE WELDING INSTITUTE

1) Convention ofBS 499 (UK):

The Arrow Line:

a) Shall touch the joint intersection.b) Shall not be parallel to the drawing.c) Shall point towards a single plate preparation.

The Reference Line:

a) Shall join the arrow line.b) Shall be parallel to the bottom ofthe drawing.

The Weld Symbol:

a) Welds done from this side (Arrow side) ofjoint, go underneath the reference line.

b) Welds done from the other side ofthe joint, go on top ofthe reference line.

c) Symbols with a vertical line component must be drawn with the vertical line drawnto the left side ofthe symbol.

d) All cross sectional dimensions are shown to the left ofthe symbol.Fillet throat thickness is preceded by the letter a and the leg length by the letter b

When only leg length is shown the reference letter (b) is optional.

The throat thickness for partial penetration butt welds is preceded by the letter s

e) All linear dimensions are shown on the right ofthe symbol

I.e. Number ofwelds, length ofwelds, length ofany spaces.

Example:

X Length (Space)a Throat. b. Leg

Example: a.7 b.10 x 50 (100)

Welding Inspection - Weld Symbols on DrawingsCopyright © 2002 TWI Ltd.

8.2 Rev 09-09-02


Examples of BS 499 ISO 2553 and BSEn 22553

Double-sided butt weld symbols

Double bevel Double V DoubleJ Double U

Supplementary & further weld symbols to BS 499:

Weld all around Weld on site Square butt weld

/ Profile offillet weld/ C\10l~ ~

111 (Welding process to ISO 4063

'SPOt weld

Compound weld (Single bevel and double fillet)

Intermittent welds in BS 499 and BSEn 22553 are given as shown as below withnumber ofwelds x length ofeach weld, with gap length given in brackets i.e. 3 x 20 (50)

A staggered intermittent weld may be shown with a Zdrawn across the axis betweenthe weld length and gap.


3 No's 20mm length

~~

3x20

Staggered

8.3

/(50)

(50)

50 mm gap

Rev 09-09-02


2) Convention of ISO 2553 and BSEn 22553: (Has now replaced BS 499 in UK)

The Arrow Line: (As per BS 499)

a)b)c)

Shall touch the joint intersection.Shall not be parallel to the drawing. IShall point towards a single plate preparation.

The Reference Line:

a) Shall join the arrow line. J- As per BS 499b) Shall be parallel to the bottom ofthe drawing.c) Shall have a broken line placed above, or beneath the reference line.

------

or

The Symbol: As per BS 499 with the following exceptions:

The other side of the joint is represented by the broken line, which shall be shownabove, or below the reference line, except in the case where the welds are totallysymmetrical about the central axis ofthe joint.

Fillet weld leg length shall always be preceded by the letter z.Nominal fillet weld throat thickness shall always be preceded by the letter a.Effective throat thickness shall always be preceded by the letter S for deep penetrationfillet welds and partial penetration butt welds.

Unbroken line representing the arrow side of the joint

Broken line indicatingother side of the joint

Welding process to BSEn 24063

L JI' Reference information

1310-------------~---

..8 ..10 Z.10~

\ Weld toes to beground smoothly

Removable backing strip

/I MR I s.10


8.4 Rev 09-09-02

TWIV!7fll. _Table 10 * Numerical indication of process


No. Process1 Arc welding11 Metal-arc welding without gas protectionIII Metal-arc welding with covered electrode112 Gravity arc welding with covered electrode113 Bare wire metal-arc welding114 Flux cored metal-arc welding115 Coated wire metal-arc welding118 Firecracker welding12 Submerged arc welding121 Submerged arc welding with wire electrode122 Submerged arc welding with strip electrode13 Gas shielded metal-arc welding131 MIG welding: (With an inert shield gas)

135 MAG welding: (With an active gas shield)

136 Flux cored arc welding (With an active gas shield)

14 Gas-shielded welding (Non-consumable electrode)

141 TIG welding149 Atomic-hydrogen welding15 Plasma arc welding18 Other arc welding processes181 Carbon arc welding185 Rotating arc welding

2 Resistance welding21 Spot welding22 Seam welding221 Lap seam welding225 Seam welding with strip23 Projection welding24 Flash welding25 Resistance butt welding29 Other resistance welding processes291 HF resistance welding

3 Gas welding31 Oxy-fuel gas welding311 Oxy-acetylene welding312 Oxy-propane welding313 Oxy-hydrogen welding32 Air fuel gas welding321 Air-acetylene welding322 Air-propane welding

4 Solid phase welding: Pressure welding41 Ultrasonic welding42 Friction welding43 Forge welding44 Welding by high mechanical energy441 Explosive welding45 Diffusion welding47 Gas pressure welding48 Cold welding

No.77172737475751752753767778781782

99191191291391491591691791891992392493949419429439449459469479489499519529539549697971972

ProcessOther welding processesThermit weldingElectroslag weldingElectrogas weldingInduction weldingLight radiation weldingLaser WeldingArc image weldingInfrared weldingElectron beam weldingPercussion weldingStud weldingArc stud weldingResistance welding

Brazing, soldering & braze weldingBrazingInfrared brazingFlame brazingFurnace brazingDip brazingSalt bath brazingInduction brazingUltrasonic brazingResistance brazingDiffusion brazingFriction brazingVacuum brazingOther brazing processesSolderingInfrared solderingFlame solderingFurnace solderingDip solderingSalt bath solderingInduction solderingUltrasonic solderingResistance solderingDiffusion solderingFlow solderingSoldering with soldering ironFriction solderingVacuum solderingOther soldering processesBraze weldingGas braze weldingArc braze welding

* This table complies with International Standard ISO 4063 (Now BSEn 24063)

Welding Inspection - Weld Symbols on DrawingsCopyright © 2002 TWl Ltd.

8.5 Rev 09-09-02

HAI-BANG

Highlight

HAI-BANG

Highlight

HAI-BANG

Highlight

HAI-BANG

Highlight

HAI-BANG

Highlight

HAI-BANG

Highlight

HAI-BANG

Highlight

TWIVlJDI. THE WELDING INSTITUTE

Complete a symbols drawing for the welded cruciform joint given below:

All butt weld are welded with the MIG process and fillet welds with MMA.

35

15

20

30

All fillet weld leg lengths are 10 mm

Use the sheets overleaf to transcribe the information shown above into weld

symbols complying with the following standards:

BS 499 Part IIBSEn 22553

Use the drawings provided overleaf

The course lecturer will present the solutions, after you have completed theexercise.

Welding Inspection - Weld Symbols on DrawingsCopyright © 2002 TWl Ltd.

8.6 Rev 09-09-02

TWIV!7fll. THE WELDING INSTITUTE

BS499Partll

\

~

BSEn 22553

-----------------------~


8.7 Rev 09-09-02


Introduction to Welding Processes:

A welding process: Special equipment used with method, for producing welds.

The 4 main requirements of any fusion welding process are:

Adequateproperties

Heating:

Protection:

Cleaning:

Adequate:properties

Ofhigh enough intensity to cause melting of base metals and filler metals.

Of the molten filler metal in transit and base metal from oxidation, and toprotect the heat source and metals from ingress of gases such as hydrogen& oxygen.

Ofthe weld metal to remove oxides and impurities, and refine the grains.

Adding alloying elements to the weld, to produce the desired mechanicalproperties.

Welding Inspection - Introduction to Welding Processes 9.1Copyright © 2002 TWl Ltd.

Rev 09-09-02

TWIV!l!7I. _Heating:


There are many heat sources used for welding. In fusion welding, the main requirementis that the source must be of sufficient temperature to melt the materials being welded.

Combustion of gases:Oxygen & acetylene will combust to produce a temperature of 3,200 °C. Other fuelgases may be used for oxy fuel gas cutting. The intensity of the flame is not as high asother heating methods and so longer time has to be spent to bring the material to itsmelting point.

Electrical resistance:The heat generated by electrical resistance between 2 surfaces is used to produce over95% of all welds made, in the resistance spot welding process. Electrical resistance isalso used as a heat source in the Electro Slag welding process where the resistance isgiven by the molten slag. This process is classed as a resistive heating process.

High intensity energy beams:We use 3 types ofconcentrated high intensity energy beams, which are:

I) Laser. (Light Amplification by Stimulated Emissions of Radiation)2) Electron Beam. (Concentrated beam of electrons, generally in a vacuum)3) Plasma. (A gas forced through an electric arc to create an ionised gas)

All these welding processes use beams of high energy creating extremely hightemperatures. These energy beams also enable very high welding speeds, which reducethe amount of overall distortion with increased productivity.

Friction:We can use the heat generated by friction (and pressure) to weld components together.The joint is made with the materials faces in the plastic state.

The Electric Arc:By far the most common heat source for fusion welding, the electric arc is utilised inmost of the common welding processes. The electric arc can produce heat of> 6000 °Cwith extreme levels of ultra-violet, infrared and visible light. Heat is derived from thecollision of electrons and ions with the base material and the electrode. An electric arcmay be defined as the passage of current across an ionised gap. All gases are insulatorsand thus sufficient voltage, or pressure needs to be available to enable an electron to bestripped from an atom into the next. Once this conducting path or plasma has beencreated, a lower voltage can maintain the arc. The voltage required to initiate the arc istermed the open circuit voltage or OCV requirement of the process/consumable. Thevoltage that maintains the arc once it is created is termed the welding, or arc voltage.The conducting path produced is termed the plasma column.

Welding Inspection- Introduction to Welding Processes 9.2Copyright © 2002 TWl Ltd.

Rev 09-09-02

TWIV!7!lI. _

Protection:


In MMA welding, the gas shield is produced from the combustion of compounds in theelectrode coating. The gas produced is mainly C02 but electrodes are available thatproduce hydrogen gas, which give a very high level of penetration.

In Submerged Arc welding the gas shield is again produced from the combustion ofcompounds, but these compounds are supplied in a granulated flux, which is suppliedseparately to the wire. MMA electrodes or SAW fluxes containing high levels of basiccompounds are used where hydrogen controlled welding is required.

In MIGIMAG & TIG welding the gas is supplied directly from a cylinder, or bulk feedsystem and may be stored in a gaseous, or liquid state. In TIG & MIG welding wegenerally use the inert gases argon or helium. In MAG welding we generally use C02 ormixtures of C02 or 0 2 in argon.

Cleaning (of surface contaminants):

The cleaning, refIning and de-oxidation of the weld metal is a major requirement of allcommon fusion welding processes. As a weld can be considered as a casting, it ispossible to use low quality wires in some processes, and yet produce high quality weldmetal by adding cleaning agents to the flux. This is especially true in MMA welding,where many cleaning agents and de-oxidants may be added directly to the electrodecoating. De-oxidants and cleaning agents are also generally added to FCAW & SAWfluxes. For MIGIMAG & TIG welding wires, de-oxidants, such as silicon, aluminiumand manganese must be added to the wire during initial casting. Electrodes and wires forMIG & TIG welding must also be refIned to the highest quality prior to casting, as theyhave no flux to add cleaning agents to the solidifying weld metal.

Adequate properties (from alloying):

As with de-oxidants, we may add alloying elements to the weld metal via a flux in someprocesses to produce the desired weld metal properties. It is the main reason why there isa wide range of consumables for the MMA process. The chemical composition of thedeposited weld metal can be changed easily during manufacture of the flux coating. Thisalso increases the electrode efficiency. (Electrodes of> 160% are not uncommon). InSAW, elements such as Ferro-manganese may be added to agglomerated fluxes. It ismuch cheaper to add alloying elements to the weld via the flux as an ore, or compound.

As with the cleaning requirement described above, wires for MIGIMAG & TIG must bedrawn as cast, thus all the elements required in the deposited weld metal compositionmust be within the cast and drawn wire. This is the main reason why the range of theseconsumables is very limited. With the developments of flux core wires, the range ofconsumables for FCAW is now very extensive, as alloying elements may be easily addedto the flux core in the same way as MMA electrodes fluxes.

Welding Inspection - Introduction to Welding Processes 9.3Copyright © 2002 TWI Ltd.

Rev 09-09-02

TWIVlll. _Special Terms Related to Welding Safety:

Duty cycle:


A Duty Cycle is the amount of current that can be safely carried by a conductor in aperiod of time. The time base is normally 10 minutes and a 60% duty cycle means thatthe conductor can safely carry this current for 6 minutes in 10 and then must rest andcool for 4 minutes. At a 100% duty cycle equipment can carry the current continuously.Generally 60% & 100% duty cycles are given on welding equipment.

Example: 350amps at 60% duty cycle and 300amps 100% duty cycle.

This should not be confused with the term Operating Factor, often wrongly used forDuty Cycle, as they are both measured as a percentage. Operating Factors are mainlyused in economic calculations to calculate the amount of time required from a weldingprocess to deposit an amount ofweld metal. A typical Operating Factor for MMA wouldbe only 30%

Occupational, and Maximum Exposure Limit (OEL and MEL):

Operational, and Maximum Exposure Limits may be defmed as a safe, or maximumworking limit of exposure to various fume, gases or compounds during certain timelimits, as calculated by the Health and Safety Executive or HSE in the UK. The branchof the executive that holds responsibility for this function is known as COSHH orControl of Substances Hazardous to Health. Examples of levels of some fume and gasesthat workers may be exposed to, taken from Guidance Note EHl40 2002, are given inthe table below:

Fume orgas Exposure Limit Effect on Health

Cadmium 0.025Mg/mjExtremely toxic

General Welding Fume 5Mg/mj Low toxicityIron 5Mg/mj

Low toxicityAluminium 5Mg/mj Low toxicity

Ozone 0.20 PPM Extremely toxicPhosgene 0.02 PPM Extremely toxic

Argon NoOELValue Very low toxicity0 2 air content to be controlled

*Note MEL/OEL values given in Guidance Note EHl40 may change annually.

The toxicity of these examples can be gauged by the value of exposure limit. Any of theabove examples may be present in welding under certain conditions, which will beexpanded upon by your course lecturer at the relevant time, though Welding Safety willbe discussed fully as a separate subject area.

Welding Inspection - Introduction to Welding Processes 9.4Copyright © 2002 TWl Ltd.

Rev 09-09-02


Arc Characteristic for MMA & TIG:

In MMA & TIG welding, the arc length is controlled by the welder. Whilst anexperienced and highly skilled welder can keep the arc length at a fairly constant length,there will always be some variation.

When the arc length is increased, the voltage or pressure required to maintain the arc willalso need to increase. This would also reduce the current supplied in a normal electricalcircuit, where the supplied voltage is proportional to a drop in current.

Thus we need to find a way of reducing a large drop in current for the variation in arcvoltage. This is achieved by the use of special electrical components within theequipment that produce sets of curves as shown below.

The graph below shows amperage curve (A) selected @ 100 amps, with the effect ofvariation in the arc gap and voltage.Note how an increase in arc length increases the area under the graph, whichappears to give an increase in overall heat input. The extra heat is, however,generally lost in the arc and is not transferred to the weld pool.

Constant Current (Drooping) Characteristic

Output Curves for current selector settings:A: 100 Amps. B: 140 Amps. C: 180 Amps

OCV50-90 volts 1P--............

Arc Voltage

Short arc gap

Normal arc gap~LW:UliI~~~W._+---+~\

Long arc gap

Welding Amperage ABC

A large variation in voltage = A smaller variation in amperage

Welding Inspection - Manual Metal Arc WeldingCopyright © 2002 TWI Ltd.

10.1 Rev 09-09-02

TWIroDI. THE WELDING INSTITUTE

Manual Metal Arc Welding:

MMA is a welding process that was first developed in the late 19th century using barewire electrodes.

Definitions:

MMA:

SMAW:

Manual Metal Arc Welding. (UK)

Shielded Metal Arc Welding. (USA)

Introduction:

MMA is simple process in terms of equipment and consumables, using short flux coveredelectrodes. The electrode is secured in the electrode holder and the leads for this, and thepower return cable are placed in the + or - electrical ports as required. The processdemands a high level of skill from the welder to obtain consistent high quality welds, butis widely used in industry, mainly because of the range of available consumables, itspositional capabilities and adaptability to site work. (photograph 1)

The electrode core wire is often of very low quality, as refining elements are easily addedto the flux coating, which can produce high quality weld metal relatively cheaply.

The arc is struck by striking the electrode onto the surface of the plate and withdrawingit a small distance, as you would strike a match. The arc should be struck in the directarea of the weld preparation avoiding arc strikes, or stray flash on the plate material. Careshould also be taken to maintain a short and constant arc length and speed of travel.

Photograph 2 shows a trainee dressed in the correct safety clothing, whilst photograph 3indicates the level of process-produced fume, and the use of a flexible hose extractionsystem. Little has changed with the basic principles of the process since it was developed,but improvements in consumable technologies occur on a very regular basis.


10.2 Rev 09-09-02

TWIV!71l1. THE WELDING INSTITUTE

Manual Metal Arc WeldingBasic Equipment Requirements:

1) Power source TransformerlRectifier. (Constant current type)

2) Holding oven. (Temperature up to 200°C)

3) Inverter power source.

4) Electrode holder.

5) Power cable.

6) Welding visor with correct fIlter glass rating.

7) Power return cable.

8) Electrodes.

9) Electrode oven. (Bakes up to 350 °C)

10) Control panel. (Amperage & polarity)


10.3 Rev 09-09-02


Variable Parameters:

1) Voltage:

The Arc Voltage of the MMA welding process is measured as close to the arc aspossible. It is variable only by changes in arc length.

The OCV (Open Circuit Voltage) is the voltage required to initiate, or re-ignite theelectric arc and will change with the type of electrode being used. Most basic coatedelectrodes require an OCV of 70 - 90 volts. Most rutile electrodes require only 50 volts.

2) Current & Polarity:

The type and value of current used will be determined by the choice of electrodeclassification, electrode diameter, material type and thickness, and the welding position.

Electrode polarity is generally determined by the operation i.e. surfacing/joining and thetype of electrode, or electrode coating being used. Most surfacing and non-ferrous alloysrequire DC - for correct deposition, although there are exceptions to this rule. Electrodeburn off rates will vary with AC or DC + or - depending on the coating type and thechoice of polarity will also affect heat balance of the electric arc.

Important Inspection Points/Checks when MMA Welding:

1) The Welding Equipment:A visual check should be made to ensure the welding equipment is in good condition.

2) The Electrode:Checks should be made to ensure that the correct specification of electrode is being used,that the electrode is of the correct diameter and that the flux coating is in good condition.A check should be made to ensure that any basic coated electrode being used has beenpre-baked to that specified in the welding procedure. A general pre-use treatment forbasic coated electrodes would typically be:

a) Baked at 350°C for 1 hour.b) Held in holding ovens at 150 °Cc) Issued to the welder in a heated quiver (Normally around 70°C)

Vacuum pack pre-baked electrodes do not need to undergo this pre-baking treatment.If the vacuum seal appears be broken at the point of opening the carton, users shouldfollow the manufacturers advice and instructions to maintain the hydrogen level specifiedon electrode cartons.The date and time ofopening must be recorded to enable re-baking as required.


10.4 Rev 09-09-02

TWIVOOI. THE WELDING INSTITUTE

Cellulosic and rutile electrodes do not require this pre-use,treatment, but should be storedin a dry condition. Rutile electrodes may require "drying only when damp" and shouldtherefore be treated as damp unless evidence dictates otherwise and dried at specifiedtemperature.

3) OCVA check should be made to ensure that the equipment can produce the OCV required bythe consumable and that any voltage selector has been moved to the correct position.

4) Current & Polarity.A check should be made to ensure the current type and range is as detailed on the WPS.

5) Other Variable Welding Parameters:Checks should be made for correct angle of electrode, arc gap distance, speed of traveland all other essential variables of the process, given on the approve,d welding procedure.

6) Safety Checks:

Checks should be made on the current carrying capacity, or duty cycle of equipment, andthat all electrical insulation is sound.

A check should also be made that correct eye protection is being used when welding andchipping slag and that an efficient extraction system is in use, to avoid over exposure totoxic fumes and gases.

A check should always be made to ensure that the welder is qualified to weld theprocedure being employed.

Typical Welding Imperfections:

1) Slag inclusions caused by poor welding technique or insufficient inter-runcleaning.

2) Porosity from using damp, or damaged electrodes or welding contaminatedmaterial.

3) Lack of root fusion or penetration caused by in-correct settings of amps, rootgap or face.

4) Undercut caused by too high amperage for the position or by a poor weldingtechnique e.g. travel speed too fast or too slow, arc length (therefore voltage)variations during weaving in particular.

5) Arc strikes, caused by incorrect arc striking procedure, or lack of skill.These may be also caused by incorrectly fitted/secured power return lead clamps.

6) Hydrogen cracks caused by the use of incorrect electrode type, or incorrectbaking procedure and/or control of basic coated electrodes.


10.5 Rev 09-09-02

TWIV!l!ll. _

Summary of MMAISMAW:

Equipment requirements:


1) A Transformer/Rectifier, generator, inverter. (Constant amperage type).2) A power and power return cable. '-, -'-3) Electrode holder.4) Electrode.5) Correct visor/glass, all safety clothing and good extraction.

Parameters & Inspection Points:

1)3)5)7)9)

Amperage.AC/DC & Polarity. Dy-fElectrode type & diameter.Electrode condition.Insulation/extraction.

2)4)6)8)10)

Voltage.Speed of travel.Duty cycles.Connections.Any special electrode treatment.


1) Slag inclusions. 2)3) Lack of root fusion or penetration. 4)5) Arc Strikes. (q L<D+) 6)

Advantages & Disadvantages:

Advantages:

Porosity.Undercut.H2 Cracks. (Electrode treatment)

Disadvantages:

1) Field or shop use.2) Range of consumables.3) All positional.4) Very portable.5) Simple equipment.

1)2)3)4)5)

High skill factor requiredArc strikes/Slag inclusions.* Low Operating Factor.High level of generated fumes.Hydrogen control.

* Comparatively uneconomic when compared with some other processes Le. MAGFACW&SAW'

~<:'L---

r f 0 j {)I(.~ '[)


10.6 Rev 09-09-02

TWIV!lDI. _THE WELDING INSTITUTE

Tungsten Inert Gas Welding:~~~~~~~~~~~

TIG welding was first developed in the USA during the 2nd world war for weldingaluminium alloys. As helium was used as the gas, the process was known as Heliarc.

Definitions:

TIG:

GTAW:

Tungsten Inert Gas Welding. (UK)

Gas Tungsten Arc Welding. (USA)

Introduction:

TIG welding is a process that requires a very high level of welder skill, which can begauged in the degree of concentration of the welder shown in photograph 1 above. It is aprocess synonymous with high quality welds, as shown in application of the offshorepowerboat repair in photograph 2. It is considered a comparatively slow process, butwith the development of hot-wire TIG (Photograph 3) TIG welding may produce highquality welds with deposition rates higher than SAW.

The ari may be struck by using a number of methods,but in cheaper equipment the arcis struck (Scratch start) in a similar way to MMA welding. This can easily causecontamination of the tungsten and weld metal and to avoid this high frequency arcignition is often used in most equipment to initiate the are, however high frequency maycause interference with hi-tech electrical equipment and computer systems. To overcomethis, Lift arc has been developed where the electrode is touched onto the plate and iswithdrawn slightly. An arc is produced with very low amperage, which is increased tofull amperage as the electrode is extended to the normal arc length. In contrast with otherarc processes, the filler wire is added directly into the pool separately by the welder,which requires a very high level ofhand dexterity and artisan craft skill.

TIG is a far more complex process than MMA, with more variable parameters to adjust,and parts to check, and therefore more inspection points for the inspector to meet.

Welding Inspection - Tungsten Inert Gas WeldingCopyright © 2002 TWI Ltd.

11.1 Rev 09-09-02

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Tungsten Inert Gas WeldingBasic Equipment Requirements:

1)

2)

3)

4)

5)

6)

7)

8)

9)

Power source. TransformerlR~ctifier (Constant Amperage type)

Inverter power source.

P\Jwer control panel.•Power cable hose.

Flow-meter.

Tungsten electrodes.

Torch assemblies.

Power return cable.

Power Control panel. (Amperage & polarity)

Welding Inspection - Tungsten Inert Gas WeldingCopyright © 2002 TWl Ltd.

11.2 Rev 09-09-02

TWIVOI._------------- THE WELDING INSTITUTE

The TIG Torch Head Assembly:

1) Tungsten electrodes.

2) Spa~e ceramic shield.

3) Gas lens.

4) Torch body.

5) Spare ceramic shield.

6) Gas diffuser.

7) Split copper collett. (For securing the tungsten electrode)

8) On/off or latching switch.

9) Tungsten housing.

Welding Inspection - Tungsten Inert Gas WeldingCopyright © 2002 TW1 Ltd.

11.3 Rev 09-09-02

TWIVf7!lI. THE WELDING INSTITUTE


1) Voltage:The voltage of the TIG welding process is variable only by the type of gas being used,and changes in arc length as in MMA.

2) Current & Polarity:The current is adjusted proportionally to the diameter of the tungsten being used. Thehigher the level of the current, then the higher is the level of penetration and fusion that isobtained.

The polarity used for steels is always DC -ve as most of the heat is concentrated at the +pole in TIG welding. This is required to keep the tungsten as cool as possible duringwelding. AC is used when welding aluminium and its alloys.

When welding aluminium alloys withAC, the tungsten end is chamfered, andforms a ball end during welding.

vr!' bOD

The tungsten vertex angle e/

/ / (/e/y--I-t;A~")1U-l, l) j7 '-f:'~~

~~) 10A--/V~fOJLJ j, '~,}.,. ,~' y t2//Ct ! '/ Jj .. -

gl(,((£ ) (, ,'- c i y"/i :/ "-'

v 4) Gas type and flow rate:Generally 2 types of pure gases are used for TIG welding; namely argon and helium,though nitrogen is sometimes added for welding copper and hydrogen additions may bemade for austenitic stainless steels (increasing welding speed). The gas flow rate is afurther essential variable of the welding procedure. This will change on joint type andwelding position.

3) Tungsten type and vertex angle:The tungsten diameter, type of tungsten, and vertex angle, are all critical factorsconsidered as essential variables of a welding procedure. The most common types oftungsten used are thoriated or ceriated fOl"~d zirconiated with AC (aluminiumalloys) The vertex angle is measured as shownbelo~ IV~. Ii. f/u~ 10 fr r: ILLX~.

Too fine an angle will promotemelting of the tungsten tip

TIG gases are produced in purity of 99.99% and though argon is cheaper than heliumand has higher density than air, it has low ionisation potential, giving relatively shallowpenetration. Helium is more expensive than argon and has a lower density than argonand air, and higher ionisation potential, giving higher penetration and a hotter arc. Thismeans practically that the flow rate of helium must be increased in the down-handposition, and argon increased in the overhead position, for a similar joint design in orderto maintain adequate gas cover of the weld zone. We sometimes mix argon and heliumgases to combine the useful features ofeach gas Le. gas cover and penetration.


11.4 Rev 09-09-02

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TWIV/lfll. THE WELDING INSTITUTE

5) Slope in and slope out:Slope in and slope out are variables available on some TIG welding equipments, whichcan regulate the current climb and decay. This is very beneficial in avoiding crater pipesat the end of weld runs. The slope in and slope out control may be shown on theequipment as below:

Slopein /

During welding it is used to control the rise and decay of the current at the start and endof a weld as shown below:

weldFinish~Weld Start(Slope out) ~ (Slope In)

6) Gas cut off delay:The gas cut off delay control delays the gas solenoid shut off time at the end ofthe weld,and is used to give continued shielding of the solidifying and cooling weld metal at theend of a run. It is often used when welding materials that oxidise at high temperaturessuch as stainless and titanium alloys. It may be shown on the welding equipment asfollows:

7) Pulsed TIG welding variables:The pulse parameters ofpulsed TIG are generally adjustable as follows:

a)b)

Pulse background current.Pulse duration.

c)d)

Pulse peak current.Pulse frequency.

Welding Inspection - Tungsten Inert Gas WeldingCopyright © 2002 TWI Ltd.

11.5 Rev 09-09-02

_________________ THE WELDING INSTITUTE

Important Inspection Points/Checks when TIG Welding:


2) The Torch Head Assembly:Check the diameter and specification of the tungsten, the required vertex angle has beencorrectly ground, and that a gas lens has been fitted. Check the tungsten protrudes thecorrect length from the ceramic, the ceramic is the correct type, and is in good condition.

3) Gas type and Dow rate:Check the correct gas, or gas mixture is being used and the flow rate is correct for thegiven joint design and position as stated on the approved welding procedure.

4) Current & Polarity:Checks should be made to ensure that the type of current and polarity are correctly set,and that the current range is within that given on the procedure. These values will becontrolled by, the material type, thickness, and diameter and type oftungsten being used.

5) Other Variable Welding Parameters:Checks should be made for correct angle of torch, arc gap distance, speed of travel and allother essential variables of the process given on the approved welding procedure.In mechanised welding checks will need to be made on the speed of the carriagemechanism and the speed of the filler wire. Additionally when welding reactive materialschecks will need to be made on purging, or backing gas type and pressures.

6) Safety Checks:Checks should be made on the current carrying capacity, or duty cycle of equipment, andthat all electrical insulation is sound. Correct extraction systems should be in use to avoidexposure to ozone and other toxic fumes.

A Check should always be made to ensure that the welder is qualified to weld theprocedure being employed.


1) Tungsten inclusions, caused by a lack of welder skill, too high current setting,andlor incorrect vertex angle.

2) Surface porosity, caused by a loss of gas shield particularly when site welding, orincorrect gas flow rate for the joint design and/or welding position.

3) Crater pipes, caused by poor weld finish technique, or incorrect use of currentdecay.

4) Weld/root oxidation ifusing insufficient gas cut-off delay, or purge pressure whenwelding stainless steels or titanium alloys.


11.6 Rev 09-09-02

TWIV!ll. THEWELDING INSTITUTE

Summary ofTIG/GTAW:


1) A Transfonner/Rectifier. (Constant amperage type)2) A power and power return cable.3) An inert shielding gas. (Argon or Helium)4) Gas hose, flow meter, & gas regulator.5) TIG torch head with ground tungsten, collets, and ceramics.6) Method of arc ignition. (High frequency, lift arc, or scratch start.)7) Correct visor/glass, all safety clothing and good extraction.8) Optional filler metal in rod fonn, to correct specification.


1) Amperage.3) ACfDC & Polarity.5) Tungsten type & diameter.7) Tungsten vertex angle.9) Gas type & flow rate.11) Ceramic condition, size and type.


2) Arc voltage.4) Speed of travel.6) Duty cycles.8) Connections.10) Insulation/extraction.12) Gas lens.

1) Tungsten Inclusions.3) Crater pipes.


Advantages:

1) High quality.2) Good control.3) All positional.4) Lowest H2 arc welding process.5) Low inter run cleaning.

2)4)

1)2)3)4)5)

Surface porosity.Weld/root oxidation.

Disadvantages:

High skill factor required.Small range of consumables.Protection for site work.Low productivity (o/f).High ozone levels.

Utl--V

llCf2f--:;I

!/-tC

Welding Inspection - Tungsten Inert Gas WeldingCopyright © 2002 TWILtd.

11.7 Rev 09-09-02

TWIVIlDI. THE WELDING INSTITUTE

Arc Characteristic for MIG & SAW:

In MIGIMAG & SAW welding we require different welding equipment than usedfor MMA & TIG, as the arc length is controlled by voltage.

To achieve this we require a Constant Voltage (Flat) characteristic power source.

Constant Voltage (Flat) Characteristic

.4~

......'r

~r.

"p

....... ......... ~

.......

OCV

Arc Voltage

Large arcga

Normal are gap

Small arc ga

Welding Amperage

Small change in voltage = Much larger change in amperage.i.e. 2 volts = 100 amps

When pre.calculating the welding arc voltage from the OCV setting it is considered that1-2 Open Circuit Volts are lost for every 100 amps ofwelding current being used.

Welding Inspection - Metal Inert!Active Gas WeldingCopyright © 2002 TWI Ltd.

12.1 Rev 09-09-02

TWIV!lll#. THE WELDING INSTITUTE

Metal Inert Gas Welding:

MIG welding was initially developed in the USA in the late 4O~s for the welding ofaluminium alloys structures, using argon, or helium gas shielding.

Definitions:

MIG: Metal Inert Gas (Using an inert shielding gas Le. argon or helium)

MAG: Metal Active Gas (Using active gases Le. pure C(h, Ar/C02 or Ar/Oz mixtures)

GMAW: Gas Metal Arc Welding (Used to describe the MIG/MAG process in USA)

FCAW: Flux Cored Arc Welding (Used to describe the flux cored arc process in USA) i

Introduction:

The basic equipment requirements ofMIG/MAG welding differ from MMA and TIG as adifferent type of power source characteristic is required and a continuous wire (from aspool) is supplied at the welding torch head automatically. The shielding gas is suppliedexternally from a separate cylinder. A separate wire feed unit, or internal wire drivemechanism is also required to drive the wire electrode.

The arc is struck by short circuit of the wire on contact with the work piece, as it isdriven by the drive rolls through the liner, and then out through the contact tip. The typeof metal transfer that occurs is entirely dependant on gas type being used andamperage/WFS and voltages set. As the electric arc length is controlled by the powersource the process is classified as a semi automatic welding process, which may be usedmanually, fully automated by robotics, or can be simply mechanised by using trackingand/or weaving system. Photograph 1 and 2 show the basic process components andphotograph 3 shows simple mechanisation in the overhead position.

Welding Inspection - Metal Inert/Active Gas WeldingCopyright © 2002 TWI Ltd.

12.2 Rev 09-09-02

TWIV!llll. _

Metal Inert Gas WeldingBasic Equipment Requirements:


1) Power source. TransformerlRectifier (Constant Voltage type)

2) Inverter power source.

3) Power hose assembly. (Liner. Power cable. Water hose. Gas hose)

4) Liner.

5) Spare contact tips.

6) Torch head assembly.

7) Power-return cable & clamp.

8) 15kg wire spool. (Copper coated & uncoated wires)

9) Power control panel.

10) External wire feed unit.


12.3 Rev 09-09-02


The MIGIMAG Wire Drive Assembly1) An internal wire drive system

2) Half groove bottom drive roller. 3) Wire guide.


12.4 Rev 09-09-02

TWIV!7!lI. THE WELDING INSTITUTE

The MIG Torch Head Assembly

1) Torch body.

2) On/off or latching switch.

3) Spot welding spacer attachment.

;~ ~:m;::. (10gf' (J( 0 00Il,J ) ,6) Sparesbrouds.

7) Torch head assembly. (Less the shroud)

/1,), ili/2_ Vdl t

Welding lnspection- Metal Inert/Active Gas WeldingCopyright © 2002 TWI Ltd.

12.5 Rev 09-09-02

TWIV!lDI. _THE WELDING INSTITUTE

Immediately on pressing the torch on/off Oatching) switch, the following occurs:

a) The gas solenoid opens and delivers the shielding gas.b) The wire begins to be driven from the reel and through the contact tip.c) The contactor closes and delivers current to the contact tip.d) The water pump circulates the cooling water. (If required)

Types of Metal Transfer:

1) Dip Transfer:In dip transfer the wire short-circuits the arc between 50 - 200 times/second. This type oftransfer is normally achieved with C02 or mixtures of C02 & argon gas + low amps &welding volts < 24 volts. Dip transfer is all positional, but with a low deposition rate,penetration and fusion. This is because of the time when the arc is extinguished and onlyresistance heating takes place. It is mainly used for thin sheet steel < 3mm(and may alsobe used for positional welding in thicker section). The weld metal is deposited during theshort circuit part of the welding cycle.

2) Spray Transfer:In spray transfer a continuous electric arc and spray metal transfer is produced. This isusually achieved with pure argon, or argon C02 mixtures and higher amps & volts> 24volts. With steels it can be used only in down-hand butts and HIV fillet welds, but giveshigher deposition rate, penetration and fusion than dip transfer because of the continuousarc heating. It is mainly used for plate steel > 3mm but may be have limited use forpositional welding due to the potential large weld pool involved.

3) Pulsed Transfer:Pulse transfer uses pulses of current to fire a single globule ofmetal across the arc gap ata :frequency between 50 -300 Pulses/second. Pulse transfer is a development of spraytransfer, that gives positional welding capability for steels, combined with controlled heatinput, good fusion, and high productivity. It may be used for all sheet steel thickness>Imm, but is mainly used for positional welding of steels> 6mm.As all the parameters require extremely fme adjustment synergic equipment is nonnallyused for pulse transfer.

4) Synergic Pulsed Transfer:Synergic MIGIMAG was developed in the 1980's and uses microprocessor control toadjust the parameters of the electric are, in maintaining an optimum conditions for aselection of wire type & diameter, material and gas. The microprocessor control willchange all other pulse parameters automatically and immediately, for any change in WFS(Wire feed speed). Equipment may also be used for standard dip, spray and globulartransfer.

5) Globular Transfer:Globular transfer occurs between dip & spray, but is not normally used for solid wireMIG-MAG welding, but is sometimes used in FCAW. (Flux cored arc welding)


12.6 Rev 09-09-02

TWIVI7/lI. THE WELDING INSTITUTE


1) Wire Feed Speed:Increasing the wire feed speed automatically increases the current in the wire.Wires are generally produced in 0.6/0.8/1.0/1.2/1.4 & 1.6 mm diameter.

2) Voltage:The voltage setting is the most important setting in spray transfer as it controls the arclength. In dip transfer it also effects the rise of current and the overall heat input into theweld. An increase of both WFS/current and voltage will increase heat input. The weldingconnections need to be checked for soundness, as any slack connections will give a hotjunction where voltage will be lost from the circuit and will affect the characteristic of thewelding arc greatly. The voltage will affect the type of transfer achievable, but this is alsohighly dependant on the type of gas being used.

3) Gases:C02 gas cannot sustain spray transfer, as the Ionisation Potential of the gas is too high.Because of this high ionisation potential it gives very good penetration, but also a veryunstable arc and lots of spatter. Argon has a much lower Ionisation potential and cansustain spray transfer above 24 welding volts. Argon gives a very stable arc and littlespatter, but lower penetration than C02. We mix both argon and C02 gas in mixtures ofbetween 5 - 20% C02 in argon to get the benefit of both gases i.e. good penetration witha stable arc and very little spatter. C02 gas is much cheaper than argon or its mixtures.

4) Inductance:Inductance causes a backpressure ofvoltage to occur in the wire and operates only whenthere is a changing current value. In dip transfer welding the current rises as the electrodeshort circuits on the plate and it is then that the inductance resists the rapid rate of rise ofcurrent at the tip of the electrode. This has a main effect of reducing the level of spatter.

Important Inspection Points/Checks when MIGIMAG Welding:


2) The Electrode WireThe diameter, specification and the quality of the wire are the main inspection headings.The level of de-oxidation of the wire is an important factor with Single, Double & Triplede-oxidized wires being available. The quality of the wire winding is also important.

The higher the level ofde-oxidants in the wire, then the lower is the chance ofoccurrenceof porosity in the weld. The quality of the copper coating, and the quality of the wiretemper and winding are also important factors in minimizing wire feed problems.

Quality ofwire windings and increasing costs

(a) Random wound. (b) Layer wound. c) Precision layerwoun


12.7 Rev 09-09-02

TWIVllL7I. _THE WELDING INSTITUTE

3) The Drive Rolls and Liner.Check the drive rolls are of the correct size for the wire and that the pressure is only handtight, or just sufficient to drive the wire. Any excess pressure will deform the wire to anovular shape. This will make the wire very difficult to drive through the liner and result inarcing in the contact tip and excessive wear ofthe contact tip and liner.

Check that the liner is the correct type and size for the wire. A size of liner will generallyfit 2 sizes of wire Le. (0.6 & 0.8) (1.0 & 1.2) (1.4 & 1.6) mm diameter. Steel liners areused for steel wires and Teflon liners for aluminium wires.

4) The Contact Tip.Check that the contact tip is the correct size for the wire being driven, and check theamount of wear frequently. Any loss of contact between the wire and contact tip willreduce the efficiency of current pick. Most steel wires are copper coated to maximise thetransfer of current by contact between 2 copper surfaces at the contact tip, this alsoinhibits corrosion. The contact tip should be replaced regularly.

5) The Connections.The length of the electric arc in MIGMAG welding is controlled by the voltage settings.This is achieved by using a constant voltage volt/amp characteristic inside the equipment.Any poor connection in the welding circuit will affect the nature and stability of theelectric arc, and is thus is a major inspection point.

6) Gas & Gas Flow Rate.The type of gas used is extremely important to MIG/MAG welding, as is the flow ratefrom the cylinder, which must be adequate to give good coverage over the solidifying andmolten metal to avoid oxidation and porosity.

7) Other Variable Welding Parameters.Checks should be made for correct WFS, Voltage, Speed of travel, and all other essentialvariables of the process given on the approved welding procedure.

8) Safety Checks:Checks should be made on the current carrying capacity, or duty cycle of equipment andelectrical insulation. Correct extraction systems should be in use to avoid exposure toozone and fumes.A check should always be made to ensure that the welder is qualified to weld theprocedure being employed.


1) Silica inclusions, (on ferritic steels only) caused by poor inter-run cleaning.2) Lack of sidewall fusion during dip transfer welding thick section vertically down.3) Porosity caused from loss ofgas shield and low tolerance to contaminants4) Burn through from using the incorrect metal transfer mode on sheet metal.

Welding Inspection - Metal Inert/Active Gas WeldingCopyright © 2002 TWl Ltd.

12.8 Rev 09-09-02


Advantages of Flux Cored Arc Welding:

In the mid 80's the development of self-shielded and dual-shielded FCAW was a majorstep in the successful application of on-site semi automatic welding, and has also enableda much wider range ofmaterials to be welded.

The wire consists of a metal sheath containing a granular flux. This flux can containelements that would normally be used in MMA electrodes and so the process has a verywide range of applications.

In addition we can also add gas producing elements and compounds to the flux and so theprocess can become independent of a separate gas shield, which restricted the use ofconventional MIG/MAG welding in many field applications. "Dual Shield" wires obtaintheir gas shielding from a combination of flux and separate shielding gas.

Most wires are sealed mechanically and hermetically with various forms of joint. Theeffectiveness of the joint of the wire is an inspection point of cored wire welding,particularly with wires containing basic fluxes, as moisture can easily be absorbed into adamaged or poor seam.

It is the accepted practise when using basic wires that the first few meters of wire fromthe reel is stripped off and discarded as moisture can be absorbed up the length of thewire through the core of flux if incorrectly stored. Baking of cored wires is ineffectiveand will do nothing to restore the condition of a contaminated flux within a wire.

A major advantage of fluxed cored wires is that they produce extremely good penetration.This is caused by the amount of current density in the wire, or in other words the amountofcurrent carried in the available CSA ofthe conductor.

This area is very small in flux-cored wires, in comparison with other welding processes.

MMA

3.25 mm 0 @125 Amps

Solid MIG Wire

1.2 mm 0 @180 Amps

Flux Cored Wires

2.0mm 0 @180 Amps

Wire sheath -----i.carrying current

Flux core centre

------------~~Increasing Current Density & Penetration Power


12.9 Rev 09-09-02

TWIVflL _THE WELDING INSTITUTE

Equipment requinmumts:

1) l!t.:L TransfcrmerlR.ectifier~ (Constant voltage t)rpe)A power and power rett-UTI cable.An Tn",rt ""t;,r", or ..";v,,,r'l .,}"",lr'l;nn n"., (A rnon nr r{)2'1

.L.Jo..I..x. .L.L.LV.L", u..VIl,..I,,,,,,,,, 'V.L .L.L.L.L.n..~ ~"'~""''''''''''''.L.a..J.O f:>........u'. \.1. .J,..].O....,.J..1. V.L ................. I

4) Gas hose, flow meter, & gas regulator.5) ~lIIG torch \~lith hose, liner, difftJSer:') contact tip & nozzle..6) ·Wire feed unitwiih correct drive rolls.7'1 Pl",,,tror'l,,, ur;..", tn "n...."'''t .,n",,,if'1,,,,t'nn "nrl A'".."",t",rI} ,LJ........V\..LV1o.I-..... y~.L.LV '-" VV.L.LV_'" ~P"""''''''''''''''I.......u..'''.L'V'.L.L U..L.l."-I.- ....,. ........... .1. .......... " ........&..

8) Correct visor/glass, all safety clothing and good eAi:raction.


1)3),,)vI

7)9)11)

'\lfSIi~J11perage.'''ir a 'P ~vv Ire type"" UiamCIer.Contact tip size and condition.Liner size.In.sulationlextraction.D-aty eyclcs.

')'1"'1

4)h\'JI

8)1m~V}

1 '""\'\1£)

r"' ....... 4--............. 0... -t:1 "" ...............+ ....vu::; lYlJ'" "" HUW lULl,;.

Roller t)rpe~ size and pressure"Inductance settings.Connections. ('lo1tage drops)Travel specd, direction & angles.

1'1~I

3)Siiica inclusions.Sfu"i:ace Porosity.

')'1"'1

4)Lack offJSion" ~1airJydip transfer)":"'"\. ~,. "'- CD ... r- 't .:\.bum mrougn 'smg spray ror snccI)


Advantages: Disadvantages:

1'1LI

2)'.noJI

4)5)

l-i'n}, prnAll"tl'"'t,, (n/i)-L ......e ...... .Lv..... \,.1...... '" '1'''''''J VI"" ..

Easily automatcd.LAJl positional. (Dip & Pulse)Matcrial thickness range.Continuous electrode.

1)2)':t'lJI

4)5)

T <If'lr nf'fug'nn (D'n T""nsf':er).I....J""'.......a:ll.. VL .L 1'-".1.. 11-'.L.I.\4I..L

Small range ofconsumabks.Prot",,,t'nn f'nr "'t,,, urnrlr'nn.... 1 ~""'''-'.LI..I.'''.1. f>3.L......, VTV.I..I.'1o...1.1...Lz:,"

Complex equipment.High ozonc levels.

Welding Inspectiofi.- Metalillett/Active Gas WeldingCopytight © 2002 TWi Ltd.

i2.10n n,n. 1\1"\ 1"'\ ...

KI;;V \I:t-V:-.r-U...

TWIV!l!ll. THE WELDING INSTITUTE

Submerged Arc Welding:

SAW or Submerged arc welding was developed in the Soviet Union during the 2Dd

world war as an economical means ofwelding thick steel sections.

Definitions:

SAW: Submerged Arc Welding. (UK & USA)

Introduction:This welding process is normally mechanised and uses a constant voltage power source,as it is the voltage that controls the arc length. Amperages can range from 100 up to andover 2,000 amps, which gives very high current density in the wire and deep penetrationand dilution into the base metal.

The arc is struck in the same manner as MIG, which is generally aided by the linearmovement of the electrode tip across the surface of the run on tab, though HIF arcstriking is also possible on some equipment. As its name suggests the arc is submergedbeneath a covering of flux, which is ofa granular nature.

A flux delivery system must be incorporated into the equipment, which may also beaccompanied by a flux recovery system. It is restricted in position and is generally usedfor thickness of over 10mm. Run-on and run-off tabs are normally used on weldedseams, as this allows the welding arc to settle to its required conditions prior to thecommencement of the actual welding seam. The run off plate allows a similar set ofconditions to occur at the end ofthe weld. Both run-on and run-off tabs are removed afterthe weld seam has been completed. The arc is normally formed as the point of the wirecomes into moving contact with the plate. The flux blanket protects the arc fromatmosphere and decompose, in the heat of the arc adding alloying elements and deoxidants to the molten weld metal. The flux also provides a slag, which forms aprotective barrier to the cooling weld in a similar manner to MMA.

Photographs 1 and 2 show a stationary SAW head with rotated pipe, and photograph 3shows a mobile tractor/carriage assembly, which may be used for welding deck plates.

Welding Inspection - Submerged Arc WeldingCopyright © 2002 TWI Ltd

13.1 Rev 09-09-02

TWIVO#. _

Submerged Arc WeldingBasic Equipment Requirements:


1) Welding carriage control panel.

2) Welding carriage assembly.

3) Reel ofwire.

4) Granulated DUL

5) Transfonner rectifier.

6) Power source control panel.

7) Power return cable.

8) Flux hopper.


13.2 Rev 09-09-02

TWIfllDI._- THE WELDING INSTITUTE

Immediately on pressing the switch, the following occurs:

a) The flux is released fonning a layer beneath the torch head.b) The wire begins to feed and strikes the arc.c) The contactor closes and delivers current to the contact tip.d) The tractor begins to move. (If mechanised)

Because of the nature of the granular flux, the use of Submerged Arc Welding forpositional welding has been restricted to the flat position. However the process has beencontinually developed and is now capable of certain degree of positional welding, with anaddition of some simple extra equipment (Le. flux dams).

Submerged arc welding has many applications, but certain limitations exist other than thepositional capability of the process, as with the restriction of full penetration welds fromone side without the use of a backing bar or backing strip. One of the most popularapplications for SAW is in the welding of "Spirally welded pipe" where a fixed unit isstationed inside the pipe to weld the internal seam with an additional fixed unit placed onthe top of the pipe for the outer seam. Full penetration welding takes place as the pipe isspiralled through. Other factors that may need to be taken into consideration are thetoughness requirements of the joint, as the arc energy input is comparatively high.

Arc blow can also be a major problem as its occurrence due to magnetic field isproportional to the current used and in SAW currents of over 1,500 amps are notuncommon. Arc blow can be minimised by the use of tandem wire systems with theleading wire on DC+ and the trailing wire on AC producing opposing magnetic fields.The use of double, or multi run techniques also has effects on the properties of the weldmetal and HAZ. Multi run techniques tends to nonnalise previous weld deposits andHAZ, giving superior properties. The resultant SAW weld metal is difficult to predict, asthe weld is made up from 3 elements. A typical set ofvalues is given below, but this canchange dramatically with any changes in the welding parameters:

1) The Electrode. (25%)

2) Elements in the flux. (15%)

3) Dilution. (60%)

SAW Weld Metal Analysis

~1

02EJ3

The proportion of these elements in the final weld deposit will vary depending on thewelding parameters set and a variation in arc voltage will change the arc length and thusaffect the amount of flux being melted and overall % of alloying elements in the finalweld.


13.3 Rev 09-09-02

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1) Wire Feed Speed:Increasing the wire feed speed automatically increases the current in the wire. Thedensity of the current in the wire is dependant on the cross section area of the wire. Thehigher the density of the current, then the higher is the level ofpenetration and fusion thatis obtained.

2) Voltage:The voltage setting is a critical variable in SAW affecting the bead shape and penetrationprofile and is an essential variable of a SAW welding procedure. It also governs arclength beneath the flux layer and any changes in arc length will radically alter weld metalcomposition due to more or less elements from the flux being alloyed in the weld metal.

3) Electrode stick out:This variable parameter is adjusted by adjusting the distance of the welding headassembly from the work surface. It will affect the arc amperage, as power will beconsumed in the resistance heating ofthe wire from the tip of the contact tip to the end ofthe wire. The electrode stick out dimension should be given on the approved weldingprocedure specification sheet.

4) Flux depth:The flux depth is controlled by the flux. feed rate and the distance from the feeding headto the work surface. The flux. depth needs to be sufficiently high to cover the arc.

5) Travel Speed:As SAW is most often a mechanised process the travel speed can be considered as animportant variable parameter affecting penetration and bead profile.

The correct travel speed for the joint should be given on the approved welding procedurespecification sheet.

Important Inspection Points/Checks when Submerged Arc Welding:


2) The Welding Head Assembly & Flux Delivery System:Checks should be made that the diameter, specification of the electrode wire and thespecification and mesh size of flux. being used is correct to the approved WPS.Checks should also be made to ensure the wire drive system has correct rollers diameterand that the flux delivery system is operational. A check should be made that theelectrode stick out dimension is correct, and if using run on and run off plates that theseare fitted and tacked in place correctly.

Welding Inspection - Submerged Arc WeldingCopyright © 2002 1WI Ltd

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40-50 0

3) Current & Polarity:Checks should be made to ensure that the type of current being used is correct and if DCthat the polarity is correct and that the current range is within that given on theprocedure. Multi wire welding may use both types of current Le. DC + leading wire withan AC trailing wire as this improves welding times and offsets the effects of "arc blow"If using multi wire process the angle of the trailing wire must also be checked. Allparameters should be given on the approved WPS.

4) Other Variable Welding Parameters:Other procedural parameters may include the use of backing bar or backing stripsparticularly when welding from a single side. In addition to the inspection pointsmentioned previously checks should also be made to ensure that arc voltage and speed oftravel are within the acceptable limits. All these parameters should be given on the WPS.

A typical single sided weld preparation for SAW could look like this:

A broad root facewith no root gap

A permanently welded backing bar.

5) Safety Checks:Checks should be made on the current carrying capacity, or duty cycle of equipment, andthat all electrical insulation is sound. Correct extraction systems should be in use to avoidexposure to toxic fumes.


1) Porosity from the use of damp welding fluxes or improperly cleaned plates.2) Centreline cracks caused by high dilution and sulphur pick up or deep and

narrow welds (Le. depth/width ratio of>3/2)3) Shrinkage cavities caused by a weld depth/ratio of > 3/24) Lack of fusion caused by the effects ofarc blow.

Welding Inspection - Submerged Arc WeldingCopyright © 2002 TWl Ltd

13.5 Rev 09-09-02


Summary of Sub Arc Welding:


1) A Transformer/Rectifier. (Constant voltage type)2) A power and power return cable.3) A torch head assembly.4) A granulated flux ofthe correct type/specification and mesh size.5) A flux delivery system.6) A flux recovery system.7) Electrode wire to correct specification and diameter.8) Correct safety clothing and good extraction.


1) AC/DC WFS/Amperage.3) Flux type and mesh size.5) Electrode wire and condition.7) Flux delivery/recovery system.9) Insulation/duty cycles.11) Contact tip size/condition.

2) DCV & Welding Voltage.4) Flux condition. (Baking etc.)6) Wire specification.8) Electrode stick-out.10) Connections.12) Speed oftravel.


1) Lack offusion.3) Shrinkage cavities.

2)4)

Solidification, or centreline cracks.Porosity.

Restricted in positional welding.High probability of arc-blow. (DC+/-)Prone to shrinkage cavities.Difficult penetration control.Variable compositions. (Arc length)

1)2)3)4)5)

Advantages & Disadvantages: t-o L i

01>J .!Disadvantages:Advantages:

1) Low weld-metal costs/2) Easily mechanised.3) Low levels ofozone production.4) High productivity (o/f).5) No visible arc light.


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Summary of Arc Welding Processes:


Process MMA TIG MIGIMAG SAWTransformer! Transformer! Transformer! Transformer!Rectifier. Rectifier. Rectifier. Rectifier.Power!power Head assembly. Head assembly. Head assembly.return cables. Hose assembly. Hose assembly. Hose assembly.Electrode holder. Power return cable. Wire Liner. Power return cable.

Basic Visor with lens. Torch head Power return cable. Wire feed unit.Equipment Fume extraction. assembly. Wire feed unit. Flux hopper.Requirements. Gas cylinder. Gas cylinder. Flux delivery system.

Gas hoses. Gas hoses. Flux recovery system.Gas regulators. Gas regulators. Run on/off tabs.

I Gas flow meter. Gas flow meter. Tractor carriage.Visor with lens. Visor with lens. Fume extraction.Fume extraction. Fume extraction.

The Arc is struck Scratch Start. Wire contact is made Wire contact is madeArc Striking. striking the core (Low quality) by the advancement by the advancement

wire onto the plate HIF or Lift Arc. of the wire by the ofthe wire by theand withdrawing. (High quality) mechanical drive. mechanical drive.

Arc and weldGas for the Arc, Cylinder fed inert Cylinder fed inert Gas for Arc, and Slag

shielding.and Slag for Weld. Gas shield for Arc & !active Gas shield for for the weld. DerivedDerived from flux. Weld. Arc & Weld. from 2ranular flux.

Weld RefiningCompounds and Very clean, high Very clean, high Compounds within

and Cleaning.cleaning agents quaHty drawn wire. quaHty drawn wire. flux + higher qualitywithin the flux. wire than MMA.OCV. Amperage. OCV. OCV.Amperage. Polarity. Arc voltage. Arc voltage.Polarity (ACIDC +1-) (DC -ve for steels) AmperagelWFS. AmperageIWFS.

Process Full electrode (AC for Aluminium) Polarity DC +ve Polarity (ACIDC +!-)Variable specification. Inert gas type. Gas type. Electrode stick-out.Parameters. Electrode 0. Gas flow rate. Gas flow rate. Flux type.

,Electrode pre-use Tungsten type. Inductance. Flux mesh-size.baking treatments! Tungsten 0. Electrode wire type. Electrode wire type.specified holding Wire type. Electrode wire 0. Electrode wire 0.conditions. Wire 0. Tip/drive roller sizes. Wire/flux specification.Speed oftravel. Speed of travel. Speed oftravel. Speed oftravel.

Consumables.Short flux coated High quality drawn High quality drawn High quality drawnelectrodes. wire + inert 2as. wire + inert/active gas. wire + granular flux.

2 x Typical Arc Strikes. Tungsten Inclusions. Lack offusion. Shrinkage cavities.Imperfections. Slag inclusions. Crater pipes. Porosity. Solidification cracks.2 x General Shop and Site use. High quality welds. High Productivity. Low weld-metal costs.Advantages. Electrodes range. Low H2 content. Easily Automated. No visible arc light.

2 x General High skill factor. AvaUable wires. AvaUable wires. Penetration control.Disadvant32es. Low productivity. High Ozone level. Il.i2h Ozone levels. Arc blow.

PositionalAll positional, but All positional. Dip: All positional. Flat only, but may be

Capabilities. very dependant on Spray: Flat only. adapted for weldingconsumable types. Pulse: All Positional. HIV butt welds.

Welding Inspection Arc Process SummaryCopyright © 2002 TWI Ltd

13a.l Rev 09-09-02

TWIVflfll. _

Welding Consumables:


Welding consumables are defmed as all those things that are used up in the production ofa weld.

This list could include many things including electrical energy, however we normallyrefer to welding consumables as those things used up by a particular welding process.

These are namely:

Electrodes wires Fluxes Gases

When inspecting welding consumables arriving at site, it is important that they arechecked for the following:

1) Size.2) Type or Specification.3) Condition.

Welding Inspection -Welding ConsumablesCopyright © 2002 TWI Ltd

14.1 Rev 09-09-02

TWIVllfll. _

Consumables for MMA Welding:


Welding consumable for MMA consist ofa core wire typically between 350 and 450mmlength and from 2.5 - 6mm diameter. Other lengths and diameters are also available.

The wire is covered with an extruded flux coating. The core wire is generally of lowquality steel (Rimming Steel) as the weld can be considered as a casting, and thereforethe weld can be refined by the addition ofcleaning, or refining agents in the flux coating.

The flux coating contains many elements and compounds that all have a variety of jobsduring welding.

Silicon is mainly added as a de-oxidising agent (in the form of Ferro silicate), whichremoves oxygen from the weld metal by forming the oxide Silica. Manganese additionsofup 1.6% will improve the strength and toughness ofsteel.

Other metallic and non-metallic compounds are added that have many functions, some ofwhich are as follows:

1) To aid arc ignition.2) To improve arc stabilisation.3) To produce a shielding gas to protect the arc column.4) To refine and clean the solidifying weld-metal.5) To form a slag which protects the solidifying weld-metal.6) To add alloying elements.7) To control hydrogen content ofthe weld metal.8) To form a cone at the end ofthe electrode, which directs the arc.

Electrodes for MMA/SMAW are grouped depending on the main constituent in their fluxcoating, which in turn has a major effect on the weld properties and ease ofuse.

The common groups, are given below:

Group Constituent Shield eas Uses AWSA5.1Rutile Titania CO2 General purpose E6013Basic Calcium compounds CO2 HiJ];h Quality E7018Cellulosic Cellulose Hydrogen + CO Pipe root runs E 6010

Welding fuspectiOll-Welding ConswnablesCopyright © 2002 TWI Ltd

14.2 Rev 09-09-02

TWIrzJ/lI. THE WELDING INSTITUTE

A Typical BS 639 Specification: E 51 33 B 160 2 0 HReference given in box letter: A) B) C) D) E) F) G)

•.

A) Tensile streng1h:Symbol Min Yield Tensile Strength

N/mm2 N/mm2

43 330 430-55051 380 510-650

C) Covering types:B Basic

BB Basic High EfficiencyC Cellulosic0 OxidisingR Rutile Medium Coated

RR Rutile Heavy CoatedS Other Types

E) Welding position:Symbol Position

1 All positions

2 All positions exceptVertical Down

3 Flat Butt & Fillets + HVFillets.

4 Flat Butt & Fillets5 Vertical Down +

.

positions of symbol 39 Any position not

classified by the above.

B) Toughness:First Digit Second Digit Testing

28J 47 J Temperature0 0 Not specified1 1 +202 2 03 3 -204 4 -305 5 -40

D) Electrode Efficiency:% Recovery to the nearest 10% (> = 110)

F) Electrical characteristic:Symbol DC Polarity ACMin OCV

0 Polarity as Not recommendedrecommended

1 +or- 500CV2 - 500CV3 + 500CV4 + or- 700CV5 - 700CV6 + 700CV7 + or- 900CV8 - 900CV9 + 900CV

G) Hydro2en Control:H Indicates Low Hydrogen Potential


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TWIVf7fll. THE WELDING INSTITUTE

A Typical Electrode Specification to BSEn 499

A Typical Electrode Specification to AWS A5.1 & A5.5


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TWIV/lOI. _THE WELDING INSTITUTE

A Typical BSEn 499 Specification:Reference given in box letter:

E 46 3 INi B 5 4 H5A) B) C) D) E) F) G)

A) Tensile strenlrth:Symbol Min Yield Tensile Min

Strength Strength E%N/mm2 N/mm2

35 355 440-570 2238 380 470-600 2042 420 500-640 2046 460 530-680 2050 500 560-720 18

C) Alloying:(Deposited weld chemical composition) .

Symbol Mn Mo Ni

None 2.0 - -Mo 1.4 0.3-0.6 -

MnMo >1.4-2.0 .0.3-0.6 -INi 1.4 - 0.6-1.22Ni 1.4 - 1.8-2.63NI 1.4 - >2.6-3.8

MnlNi >1.4-2.0 - 0.6-1.2INiMo 1.4 0.3-0.6 0.6-1.2

Z Any other agreedcomposition

E) Electrical characteristic + recovery %Symbol Recovery % Current type

1 < 105 ac+dc2 < 105 dc3 > 105 < 125 ac+dc4 > 105 < 125 dc5 > 125 < 160 ac+dc6 > 125 < 160 dc7 > 160 ac+dc8 > 160 dc

G) Hydrogen Content ofdeposited weld metal:

Symbol Max H2 Contentml/100mgm

H5 5HIO 10Hl5 15

B) Toughness at minimumimpact ene~ 47 Joules:

Z No requirementA +200 02 -203 -304 -405 -506 -60

D) Coverin2 types:A AcidC CellulosicR Rutile

RR Rutile thick coveringRC Rutile/CellulosicRA Rutile/AcidRB Rutile/BasicB Basic

F) Welding position:Symbol Position

1 All positions

2 All positions exceptVertical Down

3 Flat Butt & Fillets + HVFillets.

4 Flat Butt & Fillets5 Vertical Down +

positions ofsymbol 3

The strength, toughness, coating ofBS 639 plus any light alloying elements ofBS EN499 (Ifapplicable) are the mandatory elements of information that shall be shown on allelectrodes. All other information is normally given on the electrode carton


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TWIVOOI. THE WELDING INSTITUTE

A Typical AWS A5.1 & A5.5 Specification E 80 1 8 GReference given in box letter: A) B) C) (D For A5.5 only)

A) Tensile Yield Strenlrth and E%: B) Weldin~ Position:Code I Min Yield Min Tensile MinE % 1 All Positional

PSI x 1000 PSI x 1000 In 2" min 2 Flat butt & HIV Fillet WeldsGeneral 3 Flat only

E60xx 48,000 60,000 17-22 Care should be taken when selecting anE70xx 57,000 70,000 17-22 electrode for Vertical Down, as not allE80xx 68-80,000 80,000 19-22 electrodes can weld in this position.E IOOxx 87,000 100,000 13-16

V Notch Impact RadiographicSpecific Electrode Information for E 60xx and 70xx Izod test (fUbs) Standard.E6010 48,000 60,000 22 20 tUbs at -200 F Grade 2E6011 48,000 60,000 22 20 tUbs at -200 F Grade 2E6012 48,000 60,000 17 Not required Not requiredE6013 48,000 60,000 17 Not required Grade 2E6020 48,000 60,000 22 Not required Grade 1E6022 Not required 60,000 Not required Not required Not requiredE6027 48,000 60,000 22 20 tUbs at -200 F Grade 2E7014 58,000 70,000 17 Not required Grade 2E7015 58,000 70,000 22 20 tUbs at -200 F Grade 1E7016 58,000 70,000 22 20 iUbs at -200 F Grade 1E7018 58,000 70,000 22 20 ft.lbs at -200 F Grade 1E7024 58,000 70,000 17 Not required Grade 2E7028 58,000 70,000 20 20 ft.lbs at 00 F Grade 2

C) Electrode Coating &Electrical Characteristic

Code Coating Current typeExxl0 Cellulosic/Organic DC + onlyExx11 Cellulosic/Organic ACorDC+Exx12 Rutile ACorDC-Exx13 Rutile + 30% Fe Powder ACorDC+/-Exx14 Rutile AC or DC +/-Exx15 Basic DC + onlyExx16 Basic ACorDC+Exx18 Basic + 25% Fe Powder ACorDC+Exx20 High Fe Oxide content ACorDC+/-Exx24 Rutile + 50% Fe Powder ACorDC+/-Exx27 Mineral + 50% Fe Powder ACorDC+/-Exx28 Basic + 50% Fe Powder ACorDC+

D) AWS A5.5 Low Alloy SteelsSymbol Approximate Alloy Deposit

Al 0.5%MoBl 0.5% Cr + 0.5% MoB2 1.25% Cr + 0.5% MoB3 2.25% Cr + 1.0% MoB4 2.0% Cr + 0.5% MoB5 0.5% Cr + 1.0% MoCl 2.5%NiC2 3.25% NiC3 l%Ni + 0.35%Mo + 0.15%Cr

D1/2 0.25 - 0.45%Mo + 0.15%CrG 0.5%Ni or/& O.3%Cr or/&

0.2%Mo or/& O.I%VFor G only 1 element is required

*The above tables giving data for BS 499. BSEn 639. AWS A5.1 and A5.5 are not fully complete,and are also subject to periodic changes. Thus latest revisions of the relevant standard shouldalways be consulted for full, and up to date electrode classification and technical data.

Welding Inspection -Welding ConswnablesCopyright © 2002 TWI Ltd

14.6 Rev 09-09-02

TWIVOI. THE WELDING INSTITUTE

Inspection Points for MMA Consumables

1: Size:

<

Wire Diameter & length.

>

2: Condition: Cracks, chips & concentricity.

3: Type (Specification): Correct specification/code.

Checks should also be made to ensure that basic electrodes have been through thecorrect pre-use procedure. Having been baked to the correct temperature (typically 300350°C) for 1 hour and then held in a holding oven at 150°C before being issued to thewelders in heated quivers. Most electrode flux coatings will deteriorate rapidly whendamp and care should be taken to inspect storage facilities to ensure that they areadequately dry, and that all electrodes are stored in conditions ofcontrolled humidity.

Vacuum packed electrodes may be used directly from the carton, only if the vacuum hasbeen maintained. Directions for hydrogen control are always given on the carton andshould be strictly adhered to.

The cost of each electrode is insignificant compared with the cost of any repair, thusbasic electrodes that are left in the heated quiver after the day's shift may potentially bere baked, but would normally be discarded to avoid the risk ofHz induced problems.


14.7 Rev 09-09-02

TWIV!l!ll. _

Consumables for TIG Welding:


Consumables for TIG/GTAW consist of a wire and gas, though tungsten electrodes mayalso be grouped in this. Though it is considered as a non-consumable electrode process,the electrode is consumed by erosion in the arc, and by grinding and incorrect weldingtechnique.

The wire needs to be of a very high quality as normally no extra cleaning elements canbe added into the weld. The wire is refined at the original casting stage to a very highquality where it is then rolled and finally drawn down to the correct size.

It is then copper coated and cut into 1m lengths. A code is then stamped on the wire witha manufacturer's, or nationally recognised number for the correct identification ofchemical composition. A grade of wire is selected from a table of compositions. Thewires are mostly copper coated which inhibits the effects of corrosion. Gases forTIG/GTAWare generally inert.

Pure argon or helium gases are generally used for TIG welding. The gases are extractedfrom the air by liquefaction. Argon is more common in air than helium and thus it isgenerally cheaper than helium.

In the USA vast pockets of naturally occurring helium are found and thus helium gas ismore often used in USA. Helium gas produces a deeper penetrating arc than argon. It isless dense (lighter) than air and needs 2 to 3 times the flow rate of argon gas to producesufficient cover to the weld area when welding down-hand. Argon on the other hand isdenser (heavier) than air and thus less gas needs to be used in the down-hand position.

We often use mixtures of argon and helium to balance the properties of the arc and theshielding cover ability ofthe gas. Gases for TIG/GTAW need to be ofthe highest purity(99.99% pure). Careful attention and inspection should be given to the purging of, andthe condition of gas hoses, as it is possible that contamination ofthe shielding gas can bemade through a worn, or withered hose.

Tungsten electrodes for TIG welding are generally produced by powder forgingtechnology. The electrodes contain other oxides to increase their conductivity, electronemission and also have an effect on the characteristics of the arc. Sizes of tungstenelectrodes are available offthe shelf between 1.6 - lOmm diameter. Ceramic shields mayalso be considered as a consumable item, as they are easily broken.

The size and shape ofceramic used depends on the type ofjoint design and the diameterofthe tungsten.


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Consumables for MIGIMAG Welding:


Consumables for MIG/MAG welding consist of a wire and gas. The wire specificationsused for TIG welding are also used for MIGIMAG welding, as a similar level of qualityis required in the wire.

The main purpose ofthe copper coating of steel MIGIMAG welding wire is to maximisecurrent pick-up at the contact tip and reduce the level of coefficient of friction in theliner, with protection against the effects ofcorrosion being a secondary function.

Wires are available that have not been copper coated as the effects of copper flaking inthe liner can cause many wire feed problems. These wires may be coated in a graphitecompound, which again increases current pick up and reduces friction in the liner. Somewires, including many cored wires are nickel coated.

Wires are available in sizes from 0.6 - 1.6 rom diameter with finer wires available on alkg reel though most wires are supplied on a 15kg drum.

Common gases and mixtures used for MIGIMAG welding include:

Gas Type Process Used for CharacteristicSpray or Pulse Very stable arc with

Pure Argon MIG Welding ofSteels and poor penetration andAluminium alloys low snatter levels.

Dip Transfer Good penetration

Pure CO2 MAG Welding ofSteels Unstable arc and highlevels of snatter.

Argon + Dip Spray or Pulse Good penetration

5 - 20%) CO2 MAG Welding ofSteels with a stable arc andlow levels of spatter.

Spray or Pulse Active additive gives

Argon + MAG Welding of good tluidity to the

1-2% O2Austenitic or Ferritic molten stainless, andStainless Steels Only imDroves toe blend.

Welding Inspection -Welding ConswnablesCopyright © 2002 TWl Ltd

14.9 Rev 09-09-02

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Consumables for Sub Arc Welding:


Cdnsumable for Submerged Arc SAW consist of an electrode wire and flux. Electrodewires are normally of high quality and for welding C/Mn steels are generally graded ontheir increasing Carbon and Manganese content, and the level ofde-oxidation.

Electrode wires for welding other alloy steels are generally graded by chemicalcomposition in a table, in a similar way to MIG and TIG electrode wires. Fluxes forSubmerged Arc Welding are graded by their manufacture and composition. There are 2normal methods ofmanufacture known as fused and agglomerated.

1) Fused fluxes:

Fused fluxes are mixed together and baked at a very high temperature where all thecomponents become fused together. When cooled the resultant mass resembles a sheet ofblack glass, which is then pulverised into small particles.

These particles again resemble small slivers of black glass. They are hard, reflective,irregular shaped, and cannot be crushed in the hand. It is impossible to incorporatecertain alloying compounds into the flux such as Ferro manganese, as these would bedestroyed in the high temperatures of the manufacturing process. Fused fluxes tend to beof the acidic type, which are fairly tolerant of poor surface conditions, but producecomparatively low quality weld metal in terms of the mechanical properties of tensilestrength and toughness.


14.10 Rev 09-09-02

TWIVllfll. _Agglomerated fluxes:


Agglomerated fluxes on the other hand are a mixture of compounds that are baked at amuch lower temperature and are essentially bonded together by bonding agents intosmall particles. The recognition points of these types of fluxes is easier, as they are dull,generally round granules, that are friable (easily crushed), and can also be very brightlycoloured, as colouring agents may be added in manufacture as a method of identification,unlike fused fluxes. Agglomerated fluxes tend to be of the basic type and will produceweld metal that is of much higher quality in terms of strength and toughness. This is atthe expense ofusability as these fluxes are much less tolerant ofpoor surface conditions.

It can be seen that the weld metal properties will result from using a particular wire, witha particular flux, in a particular weld sequence and therefore the grading of SAWconsumables is given as a function ofa wire/flux combination and welding sequence.

A typical grade will give values for:

1)2)

Tensile Strength.Toughness (Joules at temp)

2)3)

Elongation %.Toughness testing temperature.

The re-use or mixing of used and new flux will depend on the class of work beingundertaken and is generally addressed in the application standard. All consumables forSAW (wires and fluxes) should be stored in a dry and humid free atmosphere.

Basic fluxes may require baking prior to use, and the manufacturers instructions shouldbe strictly followed. On no account should different types of fluxes be mixed together.


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TWIrtlfll. _

Non-Destructive Testing:


NDT, or Non Destructive Testing is used to assess the quality of a component withoutdestroying it.

There are many methods ofNDT some ofwhich require a very high level of skill both inapplication and analysis and therefore NDT operators for these methods require a highdegree oftraining and experience to apply them successfully.

The four basic methods ofNDT are:

1) Penetrant testing.

2) Magnetic particle testing.

3) Ultrasonic testing.

4) Radiographic testing.

A welding inspector should have a working knowledge of an these methods, theirapplications, advantages and disadvantages.

NDT operators are examined to establish their level of skill, which is dependant on theirknowledge and experience, in the same way as welders and welding inspectors areexamined and tested to establish their level ofskill.

Various examination schemes exist for this purpose throughout the world. In the UK theCSWIP and PCN examination schemes are those that are recognised most widely.

A good NDT operator has both knowledge and experience, however some of the abovetechniques are more reliant on these factors than others.

Welding Inspection - Non-Destructive TestingCopyright © 2002 TWI Ltd

15.1 Rev 09-09-02

TWIVIIlI. THE WELDING INSTITUTE

Penetrant Testing:

Basic Procedure:

1) Surface preparation.Component must be thoroughly cleaned.

2) Penetrant application.Penetrant applied and allowed to dwell for a specified time. (Contact time)

3) Removal of excess penetrant.Once the dwell or contact time has elapsed, the excess penetrant is removed bywiping with a clean lint free cloth, finally wipe with a soft paper towelmoistened with liquid solvent. (solvent wipe)

4) Application of developer.Penetrant that has been drawn into a crack by capillary action will be drawn out ofthe defect by reverse capillary action.

5) Inspection.

6) Post cleaning and protection.

Method: (Colour contrast, solvent removable)

1) Apply Penetrant. 2) Clean then apply Developer. 3) Result.


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Advantage Disadvantages

1) Low operator skill level. 1) Careful surface preparationrequired.

2) Applicable to non-ferromagnetic 2) Surface breaking flaws only.materials.

3) Low cost. 3) Not applicable to porousmaterials.

4) Simple, cheap and easy to interpret. 4) No permanent record.

5) Portability. 5) Potentially hazardouschemicals.


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!WIrt7fll. THE WELDING INSTITUTE

Magnetic Particle Testing:

Basic Procedure:

1) Test method for the detection ofsurface and sub-surface defects in ferromagneticmaterials.

2) Magnetic field induced in component.(permanent magnet, electromagnet (Y6 Yoke) or current flow (Prods).

3) Defects disrupt the magnetic flux.

4) Defects revealed by applying ferromagnetic particles.(Background contrast paint may be required)

Method:1) Apply contrast paint. 2) Apply magnet & ink. 3) Result.


1) Pre-cleaning not as critical as with DPI. 1) Ferromagnetic materials only.

2) Will detect some sub-surface defects. 2) Demagnetisation may berequired.

3) Relatively low cost. 3) Direct current flow mayproduce Arc strikes.

4) Simple equipment. 4) No permanent record.

5) Possible to inspect through thin coatings. 5) Required to test in 2 directions.

Welding Inspection - Non-Destructive TestingCopyright © 2002 TWl Ltd

15.4 Rev 09-09-02

TWIWl. THE WELDING INSTITUTE

Ultrasonic Testing:

Basic Procedure:

1) Component must be thoroughly cleaned; this may involve light grinding to removeany spatter, pitting etc in order to obtain a smooth surface.

2) Couplant is then applied to the test surface. (water, oil, grease etc.)This enables the ultrasound to be transmitted from the probe into the componentunder test.

3) A range ofangle probes are used to examine the weld root region and fusion faces.(Ultrasound must strike the fusion faces or any discontinuities present in the weld at90° in order to obtain the best reflection ofultrasound back to the probe for displayon the cathode ray tube)

Method:

1) Apply Couplant. 2) Apply sound wave. 3) Result.

Signal rebound from thelack of sidewall fusion

Couplant

Advantage

I) Can easily detect lack of sidewall fusion. 1)

2) Ferrous & Non - ferrous alloys. 2)

3) No major safety requirements. 3)

4) Portable with instant results. 4)

5) Able to detect sub-surface defects. 5)Measures depth and through wall extent.

Disadvantages

High operator skill level.

Difficult to interpret.

Requires calibration.

No permanent record.(Unless automated)

Not easily applied to complexgeometry.


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Radiographic Testing:

Basic Procedure:

1) X or Gamma radiation is imposed upon a test object.

2) Radiation is transmitted in varying degrees dependant upon the density of thematerial through which it is travelling.

3) Variations in transmission detected by photographic film or fluorescent screens.(Film placed between lead screens then placed inside a cassette)

4) An IQI (image quality indicator) should always be placed on top of the specimen torecord the sensitivity of the radiograph.

Method:

DevelopedgraphRadioactive source

c) Developed graph.

Latent, or hidden image

b) Exposure to radiation.-!,Load film cassette.a)


1) Permanent record.

2) Most materials can be tested.

3) Detects internal flaws.

1)

2)

3)

Skilled interpretation required.

Access to both sides required.

Sensitive to defect orientation.(possible to miss planar flaws)

4) Gives a direct image of flaws.

5) Fluoroscopy can give real time imaging.

4)

5)

Health hazard.

High capital cost.


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Summary of Non Destructive Testing:


Discipline Application Advanta2es Disadvanta2esWelds/Castings. Low operator skill level Highly clean the materialSurface testing only. All non porous material

Penetrant All materials can be surfaces may be tested Surface flaws onlyTesting tested. Colour Low cost process Extremely messy

contrast & florescent. Simple equipment No pennanent recordWelds/Castings Low operator skill level Fe magnetic metals onlyFerrous metals only. Surface/Sub surface flaws De-magnetise after use

Magnetic Wet & Dry inks. Can cause arc strikes usingParticle Yolks. Permanent Relatively low cost straight current techniqueTesting magnets and straight Simple equipment No pennanent record

current ACIDCWelds/Castings. Can more easily fmd lack of High operator skill levelOne side access. sidewall fusion defects

Ultra Sonic Un-favoured for large A wide variety ofmaterials Difficult to interpretTesting grained structured can be tested

alloys. No safety requirements Requires calibrationi.e. Austenitic SIS Portable with instant results No pennanent recordWelds/Castings. Pennanent record of results High operator skill levelAccess from both A wide variety ofmaterials Difficult to interpretsides is required. can be tested

Radiographic All materials. Gamma Can assess penetration in Cannot generally identifyTesting and X-ray sources of small diameter, or line pipe lack of sidewall fusion**

radiation used. Gamma ray is very portable High safety requirements

** To identify planar or 2 dimensional defects such as lack of side wall fusion, or cracksetc, the orientation ofthe radiation beam must be in line with the orientation ofthe defectas shown below, hence if the radiation source is at the centre of the weld then noindication oflack of side wall fusion may be shown on the radiograph.

Lack ofsidewall fusion


15.7

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Radiation beam

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TWIVOI. _

Weld Repairs:

Weld repairs can be divided into two specific areas:

1) Production repairs

2) In service repairs

1) Production repairs:


The Welding Inspector, or NOT operator usually identify production repairs during theprocess of inspection, or evaluation of reports to the code or applied standard. A typicaldefect is shown below:

Before the repair can commence, a number ofelements need to be fulfilled:

1) An analysis of the defect may need to be made by the Q/A department todiscover the likely reason for the occurrence of the defect (MateriaVProcess orSkill related).

2) A detailed assessment needs to be made to fmd out the extremity of the defect.This may involve the use ofa surface or sub surface NDT method.

3) Once established the excavation site must be clearly identified and marked out.

4) An excavation procedure will need to be produced, approved and executed.

5). NDT should be used to provide confirmation that the defect has been located•

. 6) NDT used to establish total removal of the defect

7) A welding repair procedure will need to be drafted and approved.

8) Welder approval to the approved repair procedure.(Normally carried out during the repair procedural approval)

9) A fmal method of NDT will have to be identified and a procedure prepared toensure that the repair has been successfully carried out.

10) Any post repair procedures that need to be carried out i.e. Heat treatment

)

Welding Inspection - Weld RepairsCopyright © 2002 TWl Ltd

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Analysis:


As this defect has occurred in the HAZ the fault could be a problem with either thematerial or the welding procedure, however if the approved procedure was followed noblame can be apportioned to the skill ofthe welder.Assessment:

In this particular case as the defect is open to the surface, penetrant testing may be usedto gauge the depth and length ofthe defect.

Excavation:

As this defect is a crack it is likely that the ends of the crack should be drilled to avoidfurther propagation during excavation, particularly if a thermal method of excavation isbeing used.

The excavation procedure may also need approval, particularly if it will affect themetallurgical structure of the component Le. Arc Gouging.

Plan View ofdefect with drilled ends

Side View ofdefect excavation

Welding Inspection - Weld RepairsCopyright © 2002 TWI Ltd

16.2 Rev 09-09-02

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Confirmation ofexcavation:


At this stage NDT should be used to confIrm that the defect has been completelyexcavated from the area.

Re-welding of the excavation:

Prior to r~-welding of the excavation a detailed weld procedure will need to be draftedand approved. This is often carried out by the welder to be used in the repair who shouldthen become automatically approved, should the procedure become qualifIed.

NDT confirmation of successful repair:

After the excavation has been filled the weldment should then undergo a complete retestusing NDT to ensure no further defects have been introduced by the repair. NDT mayalso need to be further applied after any additional post weld heat treatment has beencarried out.

In service repairs:

Most in service repairs can be ofa very complex nature, as the component is very likelyto be in a different welding position and condition than it was during production. It mayalso have been in contact with toxic, or combustible fluids hence a permit to work willneed to be sought prior to any work being carried out. The repair welding procedure maylook very different to the original production procedure due to changes in these elements.

Other factors may also be taken into consideration, such as the effect of heat on anysurrounding areas of the component i.e. electrical components, or materials that maybecome damaged by the repair procedure. This may also include difficulty in carryingout any required pre or post welding heat treatments and a possible restriction of accessto the area to be repaired. For large fabrications it is likely that the repair must also takeplace on site and without a shut down ofoperations, which may bring other elements thatneed to be considered.

Repair of in service defects may require consideration of these and many other factors,and as such are generally considered more complicated than production repairs.

Welding Inspection - Weld RepairsCopyright © 2002 TWI Ltd

16.3 Rev 09-09-02

TWIV!lOI. _

Residual Stress and Distortion:


Residual stresses are defined as those stresses remaining inside a material after a processhas been carried out. The process used is welding, and the stresses are caused by the heatof welding producing local expansion and contraction to take place. If a block of metalwas heated uniformly to a temperature and then cooled under the same conditions nostresses would be left in the block, as expansion and contraction is uniform and equal.

Welding causes un-uniform heating and cooling conditions to exist and are compoundedby the fact that the material is increasingly restricted from freedom of movement as thewelder moves along the welded seam. The stresses that remain in the structure afterwelding are called residual stresses. Residual stresses may compound with appliedstresses to cause early failure, and may be reduced after welding by heat treatments.

The stresses caused by local expansion and contractional strain can be a very complexpattern in a welded construction, however we can say that they have three basicdirections.

Plan View of a welded plate.

Transverse

Longitudinal

End View of a welded plate.

Short transverse

One effect of welding stresses is to move the material from its original shape to producedistortion. Distortion is the movement of material in one area caused by expansion andcontraction, which misshapes the component.

Welding Inspection - Residual Stress and DistortionCopyright © 2002 TWI Ltd.

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TWIV!7!lI. _THE WELDING INSTITUTE

The degree of distortion that occurs is dependant on the ability of the material to resistthese stresses and defonnation.

It is this defonnation that produces distortion of a product. Distortion, like the overallpattern of residual stresses can be very complex, however we can show the three basicdirections of distortion exaggerated as follows:

Longitudinal distortion

Transverse distortion

t

Angular distortion


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TWIfl]fll. _THE WELDING INSTITUTE

The volume of weld metal in a joint will affect the amount of local expansion andcontraction, hence the more volume of weld metal then the overall amount of distortionwill be higher.

Preparation angle of600

Preparation angle of 400

Preparation angle of 00

The effect of expansion and contraction causing distortion during welding can begraphically seen when gas welding 2 free plates together, as the plates tend fIrst to moveapart and then back together and then apart again and finally change direction once againand move together. This effect is caused by what is called the reversal of stresses, whereexpansion and contraction are taking place as the weld cools and each weld element actsas a fulcrum for the following element upon contraction. As progression is made downthe weld the weld becomes fIXed in a fmal position and is restrained from furthermovement by the previous length ofweld, as shown below:

1) Plates are 2) Welding begins 3) Fulcrum effect. 4) Fulcrum reversal. 5) Final position.unrestrained. with contraction.

Welding Inspection - Residual Stress and DistortionCopyright © 2002 TWl Ltd.

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TWIV!lOI. _THE WELDING INSTITUTE

To counteract the effects of expansion contraction and distortion we can carry out one ofthe following techniques:

Offsetting:Offsetting means to offset the plates to a pre-determined angle to allow distortion to takeplace, with the final position of the weld being that required. Examples of this are shownbelow:

L tt .. .•' ~4#4#iJ?"....arip;Wt%'Ip>-;:] r .. :::J"\,../

.OJ' '

The amount of offsetting required is generally a function of trial & error, but if there aremany numbers of components to produce it can be an economical method of controllingdistortion.

Back-step welding and balance welding:These 2 methods of distortion control use a special welding technique, or weldingsequence to control the effects ofdistortion. Examples are given below:

Back-step welding Balance welding of a pipe butt weld

•


Weld 1 from A-BWeld 3 from B-C

17.4

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Weld 2 fromC-DWeld 4 fromD-A

Rev 09-09-02

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Clamping Jigging and Tacking:In clamping and jigging, the materials to be welded are prevented from moving by theclamp or jig. The advantage of using a jig is that elements in a fabrication can beprecisely located in the position to be welded and can be a very time saving method ofmanufacturing high volume products. On most occasions the components are accuratelypositioned by the jig and then tacked in position to prevent movement, then the jig isremoved to allow full access for welding. The use ofclamps, jigs, strong backs, bridgingpieces, and tack welds will severely restrict any movement of material, and so reducedistortion, this however will also increase the maximum amount of residual stresses.Pictorial examples of some ofthese methods are shown below:

Summary of Residual Stresses & Distortion:

1) Residual stresses are locked in elastic strain, which is caused by local expansion &contraction in the weld area.

2) Residual stresses should be removed from structures after welding as they maycause Stress Corrosion Cracking to occur, and can compound with applied stresses.They may also affect dimensional stability, when machining a welded component.

3) The amount ofcontraction is controlled by: The volume ofweld metal in the joint,the thickness, heat input, joint design, and the coefficient ofconduction.

4) Offsetting may be used to finalise the position ofthe joint

5) Ifplates or pipes are prevented from moving by tacking, clamping or jigging etc(restraint). then the amount of residual stresses that remain will be higher.

6) The movement caused by welding related stresses is called distortion.

7) The directions ofcontractional stresses and distortion is very complex, as is theamount and type offmal distortion, however we can say that there are 3 directions:

a) Longitudinal b) Transverse c) Short transverse

8) A high percentage ofresidual stresses can be removed by heat treatments.Ultrasound has also been used in the stress relieving offabrications.

9) The peening ofweld faces (With the use a pneumatic needle gun) will only redistribute the residual stress, and place the weld face in compression.

Welding Inspection - Residual Stress and DistortionCopyright @ 2002 TWI Ltd.

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TWIflllll. _THE WELDING INSTITUTE

Heat Treatment of Steels:

All heat treatments are basically cycles ofthree elements, which are:

a) Heating. b) Holding, or Soaking. c) Cooling.

c. Cooling

b. Holding

a. Heating

~

~~=.

! c-- ........

Time

We use heat treatments to change properties of metal, or as a method of controllingformation ofstructures, or expansion/contractional forces during welding.

In heat treating metals and alloys there are many elements for the welding inspector tocheck that may be of great importance, such as the rate of climb and any hold points inthe heating cycle. The holding or soaking time is generally calculated at 1hour for every25mm of thickness, but this can vary. Heat treatments that are briefly covered in thissection are as follows:

1) Annealing 2) Normalising

3) Hardening 4) Tempering

5) Stress relieving 6) Pre-heating

The methods/sources that may be used to apply heat to a fabrication may include:

a) Flame burners/heaters (Propane etc.). Preheating.b) Electric resistance heating blankets. Pre-heating & PWHT.c) Furnaces. Annealing. Normalising. Hardening. Tempering.

The tools that an inspector may use to measure the temperatures of furnaces and heatedmaterials may include.

a) Temperature indicating crayons (Tempil sticks). Pre-heating. PWHT.b) Thermo-couples. All heat treatments.c) Pyrometers (Optical. Resistance. Radiation.). Furnace heat treatments.d) Segar cones. Furnace heat treatments.

All heat treatment records are an important part of the quaDty documentation.

Welding Inspection - Heat Treatment ofSteelsCopyright @ 2002 TWI Ltd

18.1 Rev 09-09-02

TWIVllOI. - __THE WELDING INSTITUTE

1) Annealing:

Full AnnealingUCT

LCT

Annealing for steels

Annealing is a heat treatment process that may be carried out on steels, and most metalsthat have been worked hardened or strengthened by an alloying precipitant, to regain thesoftness and ductility. In the latter case we generally refer to solution annealing. Inwork hardened non-ferrous metals, annealing is used to re-crystallise work-hardenedgrains. When annealing most work hardened non-ferrous alloys the cooling rate is notalways critical, and cooling may be rapid without forming any hardened structures. Insteels we can carry out 2 basic kinds ofannealing:

a) Full Annealing (Including Solution Annealing)b) Sub Critical Annealing

In full annealing of steels the steel is heated above its UCT (upper critical temperature)and allowed to cool very slowly in a furnace. This slow cooling will result in a degree ofgrain growth, which produces a soft and ductile structure. There are no temperatures thatcan be quoted for annealing steels, as this will depend entirely upon the carbon content ofthe steel.

The UCT range ofPlain Carbon Steels is between 910 -723°C, however the temperatureis mostly taken to 50°C above the calculated UCT to allow for any inaccuracies in thetemperature measuring device. Plain carbon steel of carbon content of 0.2% would havean annealing temperature in the region of850 - 950°C

The solution annealing of some metallic alloys may require a rapid cooling rate.

In sub criti~1annealing the steel is heated to temperatures well below the lower criticaltemperature (723°C). This type of annealing is similar to that used with non-ferrousmetals as it is only the deformed ferritic grains that can be re-crystallised at these lowertemperatures.

The term annealing generally means to bring a metal, or alloy, to its softest and mostductile natural condition. In steels this also means a reduction in toughness, as theresultant large grain structure shows very low impact strength.

Welding Inspection - Heat Treatment of SteelsCopyright © 2002 TWI Ltd

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2) Normalising:

UCT

Cooling in still air

Normalising is a heat treatment process that is generally used for steels. The temperatureclimb and holding may be exactly the same as for annealing, however the steel isremoved from the furnace after the soaking period to be allowed to cool in still air.

This produces a much rmer grain structure than annealing and although the softness andductility is reduced, the strength and hardness is increased. Far more importantly thetoughness, or impact strength is vastly improved.

3) Hardening:

UCT

Rapid cooling

In the thermal hardening of steels the alloy must be taken above its UCT as with all theheat treatment processes discussed thus far, and soaked for the same period. The majordifference is in the cooling cycle where cooling is generally rapid.

For plain carbon steel, the steel must have a sufficiently high carbon content to behardened by thermal treatment, which is generally considered as > 0.3% carbon. Alloysteels containing carbon contents below 0.1% with added Mo. Cr. Mo. or Ni. Etc. can bemade much harder by thermal heat treatment

Some steels are specially designed to produce hardness even at very slow rates ofcooling, and are included in a group ofsteels called Air Hardening Steels.

The cooling media for quenching steels is very important; as if the steel is cooled tooquickly then the thermal shock may be too rapid and cause cracking to occur in the steel.Brine is considered to be the fasted cooling media followed by water and then oil.


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Tempering range 220· 723°C

......:.~~,.

220°C

Fe steel temper colours:

r----....,.... .22X~ - -

4) Tempering:

Tempering is a sub critical heat treatment process that is used only after hardening hasfIrst been carried out. Hardening will leave some steels very hard, but also very brittle.

Balance of properties, after Hardening.

Balance of properties after a temper at 350°C

Balance of properties after a temper at 720°C

Welding fuspection - Heat Treatment ofSteelsCopyright © 2002 TWI Ltd

18.4 Rev 09-09-02

TWIV/ll1I. _THE WELDING INSTITUTE

The softness, and far more importantly the toughness, is of very low values after thermalhardening, and the tenn temper really means to balance. When tempering steel we rebalance the properties of excessive hardness and brittleness by decreasing the hardnessand increasing the level oftoughness.

The process of tempering the hardness commences measurably at around 220°C andcontinues up to the LCT, or 723°C. At this point most of the extra hardness produced bythermal hardening has been removed, or fully tempered, but the fme grain structureproduced by the hardening process will remain, giving the steel good toughness andstrength. This is the mechanism used to give good toughness, and strength to Qff steels.

5) Stress relieving, or PWHT:

The purpose of stress relieving is to relieve internal elastic stress that has become trappedinside the weld during welding. The procedure of heat, hold and cool is the same as allother heat treatments however special heating curves are required when stress relievingsome types of steels, particularly Creep Resistant Steels.

In stress relieving the steel may be heated between 200-950 °C depending on the steeltype and the amount of stress that is to be relieved. To understand what happens duringstress relieving there are a number oftenns that require to be defmed:

Yield Point (Re)This is the point where steel can no longer support elastic strain and becomes plasticallydeformed i.e. plastic strain occurs. This means that the steel will no longer return to itsoriginal dimensions. The residual stresses that are contained within steels after weldingare all elastic, with the remaining stresses having been absorbed by plastic movement ofthe steel (Distortion). The stress/strain diagram of annealed low carbon steel belowshows this point:

Yield Point

Elastic strain Plastic Strain

When steel is heated the yield point is suppressed, which means that the elastic strainshown above will now start to become plastic strain. The higher the temperature, thengenerally the more elastic strain will be converted to plastic strain, or plastic movement.


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TWIV!7[JI. _THE WELDING INSTITUTE

It is generally accepted that up to 90% of residual welding stresses can be plasticallyrelieved during this process. This change is shown diagrammatically below:

••••••• /'" Failure pointNew Yield Point ••••••••• ••••• ¥

••..••••••

••••••

••••••f • ..• • •...

Plastic Strain

When the temperature is returned to ambient temperatures, the yield point returns topractically the same position as at the start ofthe heat treatment.

6) Pre-beating:

We can preheat metals and alloys when welding for a number of reasons._ Primarily weuse most pre-heats to achieve one or more ofthe following: \

1) To control the structure ofthe weld metal and HAZ on cooling.2) To improve the diffusion ofgas molecules through an atomic structure.3) To control the effects ofexpansion and contraction.

We can control the formation of un-desirable microstructures that are produced fromrapid cooling of certain types of steel. Martensite is produced by the entrapment ofcarbon in solution at temperatures below 300 °C. The function of a pre-heat withsusceptible steels is thus 2 fol~ the frrst being the suppression of martensite formation bydelaying the cooling rate, and secondly allowing the trapped hydrogen gas to diffuse outof the HAZ, or weld metal area back to the atmosphere. We may also control the effectof expansion and contraction in welds.

Summary:

We use heat treatments to change, or control the final properties of welded joints andfabrications. All heat treatments are cycles of3 elements, beating, bolding and cooling.

Tbe welding inspector sbould carefully monitor tbe beat treatment procedure, itsmetbod of application, and measuring system. All documents and graphs relating toheat treatments should be submitted to the Senior Inspector in the Q/C departmentto be logged in the fabrication quality document fdes.


18.6 Rev 09-09-02

TWIVll!ll. _Summary of Heat Treatments of Steels:


Treatment Method UsesThe steel is heated above its upper critical temperature Used to make steels softand soaked for 1 hour for every 25mm of thickness. and ductile.The furnace is then turned off and the steel remains in

Annealing the furnace to cool.This produces a large or course grain structure that issoft and ductile but has very low toughness.

The steel is heated above its upper critical temperature Used to make steelsas in annealing and soaked for 1 hour for every 25mm tougher and stronger

Normalising of thickness. Once the soaking time has elapsed thesteel is removed from the furnace to cool in still air.Produces a small, or fine grain structure that has hightoughness and strength, though ductility is lower thanannealed steel.

The steel is heated above its upper critical temperature Used to make mediumas in annealing and soaked for 1 hour for every 25mm or high plain carbon andof thickness. Once the soaking time has elapsed the most low alloy steels

Hardening steel is removed from the furnace to quench in a harder.cooling medium.Produces a fme grain martensitic structure that hasvery high hardness and strength, though ductility isalmost zero, with very low toughness.

The steel is re-heated after hardening, and the balance Used to rebalance theofhardness to toughness is adjusted as the temperature properties of thermallyis increased from 220° - 723°C hardened steels.

Tempering At 723 °C all martensite has been tempered removingbrittleness, and returning the ductility.The fme structure is retained giving high strength andfurther improving the toughness.

The steel is heated to a temperature dependant on the Used after welding totype of steel being heat-treated. relieve ths)rapped

Stress elastic streSses caqsed byRelieving Plastic flow of stresses increases as the temperature expansion/contraction.

rises relieving the locked in elastic stresses.

The steel is heated to a temperature dependant on the Used to control thePre-Heating type of steel being heat treated, but normally less than formation of Hz cracks.

350°C Also used to control theThis suppresses the formation ofMartensite and allows effects of expansion andtime/temperature for diffusion ofH2 contractional stresses.


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Oxy Fuel Gas Welding and Cutting:


The oxy fuel gas heating method has been used for many decades as a portable means ofapplying heat for many operations directly linked to welding, some of which are givenbelow:

1) Pre-heating.3) Cutting.S) Brazing.7) Fusion welding.

2)4)6)8)

PWHT.Soldering.Bronze welding.Straightening.

The equipment generally consists of2 cylinders, 1 containing acetylene and 1 containingoxygen. Acetylene gas is very unstable and will self detonate at very low pressure, henceit becomes a very dangerous gas to store in a cylinder under pressure.To enable storage to be achieved acetylene is dissolved in liquid acetone, which canabsorb around 25 times its own volume ofacetylene gas. The acetone is then absorbed ina charcoal and kapok mass, this makes the gas much more stable to store.

For this reason the cylinder should always be used in the vertical position, as liquidacetone will be expelled from the blowpipe if it is not used vertically. This will have asimilar effect to a flame-thrower, and is a very dangerous situation.

If transported, or stored horizontally the cylinder should be placed vertically and not usedfor a minimum of 1 hour to avoid this effect.

Oxygen may be supplied at pressures of up to 3,500 PSI and must therefore be treatedwith the greatest respect. Should the valve seat of an oxygen cylinder become fracturedby sudden impact the results would be horrific, with a high possibility of death foranyone in the vicinity.

Key safety factors that must be observed:

Cylinders must be secured in vertical positionOnly correct fittings must be used for connections*Oil and grease must not be used on connections**Left-handed threads must be used for fuel gassesColour coding of hoses must be adhered toFlash back arrestors must be used on oxygen and fuel gas suppliesOne way valves must be used on each hose/torch connectionThe correct start up and shutdown procedure must be foUowedAll equipment must be thoroughly leak tested

*Use of non-propriety grades of brass may contain a high % of eu which may formexplosive compounds on contact with pressurised acetylene.**Oxygen will readily spontaneously combust when in contact with oil and grease.

/ .'

Welding Inspection - Oxy - Fuel Gas Welding ICutting 19JCopyright © 2002 TWI Ltd .

Rev 09-09-02

TWIIll!ll.__------ THE WELDING INSTITUTE

A typical set of oxy-acetylene welding equipment is shown below:

CylinderI;On1enl$ gaUlle

/Flam,! tr'IP

/

Safety cradle cylinder standi

Oxy - Acetylene Fusion Welding:

The flame temperature of Acetylene combusted in air is 2,300 °c, whilst the flametemperature combusted with oxygen is 3,200 °c, which is the highest temperatureachievable from the normal combustion of industrial gases.

This is higher than all the metals with the exception of tungsten, which has a meltingpoint of over 3,410 °C. During the welding of metals and alloys it is required that thesurface oxide needs to be removed from the molten pool. In the arc welding processesthe heat of the arc is generally high enough to melt the surface oxides of the metal withthe exception of the TIG welding of aluminium as the surface oxide called alumina(aluminium oxide) has a melting point ofover 2000 °C

For this reason we often need to use a flux when gas welding many ferrous and nonferrous alloys, such as the fusion welding ofstainless steels and aluminium alloys. Whenwelding plain carbon steels we do not need a flux as the melting point of iron oxide isbelow that ofthe alloy.

Welding Inspection - Oxy - Fuel Gas Welding ICuttingCopyright © 2002 TWI Ltd

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Oxy - Acetylene Flame Types


Uses

A neutral flame used for the fusionwelding of most metals and alloys,including all types of steelsAlso used for cutting (nozzle difference)

An oxidising flame used mainly forbronze welding.

A carburising flame used mainly forhard facing, and the fusion welding andbrazing ofaluminium and its alloys.

Oxy - Fuel Gas Brazing and Bronze Welding:

Oxy fuel gas welding may be used very successfully as a heat source for brazing andbronze welding, the difference between the tenns being that the term brazing involves acapillary action of some kind within the joint, and bronze welding is simply a shape ofweld, which is generally a fillet or butt weld, made ofa bronze, or brass alloy. Cast ironsare very often brazed as the heat input is far less than fusion welding, and therefore thechances of cracking due to expansion forces is also less. 9% Nickel bronze filler wiresare mostly used for brazing of cast irons. (Nickel bronze has a tensile strength doublethat of low carbon steels) Aluminium and aluminium alloys may be brazed using anOxy-Acetylene flame heat source, with an aluminium braze filler metal containing>15%silicon.

In the correct application, a brazed, or bronze welded joint may be stronger than a fusionwelded joint, as the surface area ofbonding is much higher, as shown below:

Area of fusion welds Area ofbraze weld

Fusion welded T joint

Welding Inspection - Oxy - Fuel Gas Welding /Cutting 19.3Copyright © 2002 TWI Ltd

Brazed T joint

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TWIflJ!lI. _Oxy Fuel Gas Cutting:


In oxy-fuel gas cutting we do not need to melt the steel, but simply heat it until it reachesits ignition temperature. (Appears bright cherry red) At this temperature the iron willreact with pure oxygen to produce an exothermic chemical reaction, the product beingFE3 0 4 or magnetic oxide of iron. A jet of pure oxygen is sent from an orifice in thecentre of the nozzle that reacts with the iron at its ignition temperature. The velocity ofthe oxygen jet removes the magnetic iron oxide from the cut face (The kerf).

As we do not require to reach the high temperatures needed for fusion welding, we donot need to use acetylene gas. Therefore propane, butane and other cheaper gases may beused for oxy-fuel gas cutting. Temperature reached during the chemical exothermicreaction of oxygen with iron is sufficient to melt most metals, though a restriction ofoxy-fuel gas cutting is that it cannot be used successfully in its conventional form to cutmetals with high melting point oxides (i.e. Stainless Steels). By the addition of an ironpowder injection system, the iron-oxygen reaction can be produced ahead of thematerials surface by the exothermic reaction ofthe heated iron powder within the oxygenjet. The thickness of steel that may be cut using the Oxy-Fuel gas cutting method issolely dependant on the nozzle size and gas pressure available. The oxy-fuel gas cuttingsystem may be simply mechanised and used to cut plates (Photograph 1) andpreparations on pipe to be welded. (Photographs 2.3. & 4). It must be recognised that thecut face may be hardened up to a depth of 3mm, therefore dressing is normally requiredto remove this hardened region as well as removing oxide.

The main inspection points ofconventional oxy fuel gas cutting will include:

SAFETY POINTS +

1) Cutting nozzle type, and size. 2) Nozzle distance from work.3) Cutting{)xygen pressure. 4) Speed oftravel ofthe cutting head.5) Angle of cut. 6) Fuel gas type and flame setting.7) Pre-heat, if specified. 8) The condition of the kerf.

If all the above parameters are set correctly then the cnt face or kerf should appearas in photograph 4 below.

Welding Inspection - Oxy -Fuel Gas Welding ICutting 19.4Copyright © 2002 TWI Ltd ,.

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TWIVfllll. _

Arc and Plasma Cutting Processes:


All thermal cutting processes that we use in fabrication must satisfy 2 major functions tobe successfully used as a cutting/gouging process.

I)A high temperature. (Capable of melting the materials being cut)

2)A high Velocity. (Capable ofremoving the molten materials in the cut)

In oxy-fuel gas cutting described in the previous section the temperature is achieved bythe exothermic reaction of iron at its ignition temperature and pure oxygen. The productof iron oxide is removed from the cut edge, or kerf by the velocity ofthe oxygen gas jet.

Plasma Cutting:Plasma cutting utilises the temperatures reached from the production of the plasmas fromcertain types ofgases. Nitrogen gas plasma can reach a temperature ofover 20,OOO°C buttemperature of air plasma is much lower. Air however is freely available and thereforecheaper and can be compressed by a compressor in the equipment, but is restricted in thedepth ofcut attainable.

The velocity for plasma cutting is produced by the expansion of the plasma in the torchchamber, which is then forced through a constricting orifice at the torch head, producingthe velocity required.

There are 2 different types ofthe plasma cutting process, which are:

1) Transferred arc. (Used for cutting conductive materials)2) Non-transferred arc. (Used for cutting non-conductive materials)

Tungsten electrode

-~~.~~"._._" ~-ve

Powersource

Air Plasma Cutting Equipment

Water cooling

Plasma jet column

Welding Inspection - Arc and Plasma CuttingCopyright © 2002 TWI Ltd.

20.J Rev09-09"()2

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Arc Cutting & Gouging:


We can use the temperature attained by an electric arc in cutting processes to reach thetemperatures required to melt the metal or alloy to be cut. There are 3 types of processthat are generally used, the main differences being in the consumables and the gas usedin producing the velocity required.

1) Conventional cutting/gouging electrodes.

2) Oxy-Arc cutting/gouging.

3) Arc-Air cutting/gouging.

Conventional cutting/gouging electrodes:In conventional arc gouging there is no requirement for any additional equipment otherthan that required for MMAlSMAW welding. The consumables consist of a light alloycentral core wire. which is mainly to give rigidity. and a heavy flux coating. whichprovides elements that produce arc energy. The arc is struck in a conventional way toMMA welding, however the arc melts the base material, which is then pushed away byusing a pushing action with the electrode. The process generates a great volume ofwelding fume and is not very effective. but is suitable for the occasional need to removeold welds. or gouge grooves in base metal.

Oxy-Arc cutting/gouging:In oxy-arc cutting we require a special type of electrode holder. The consumables aretubular in section and are coated with a very light flux coating. The electrode is locatedin the special electrode holder to which is attached a power cable and gas hose. Thepower cable is attached to the power source and the gas hose is attached to a source ofcompressed oxygen. The arc is struck and the compressedoxygen may be activated at thetorch head. The heat of the electric arc will melt the base metal or alloy and the velocityto remove it is provided by the compressed oxygen. When cutting ferritic alloys, asimilar effect can be produced to the exothermic reaction found when using conventionaloxy-fuel gas cutting. This process is generally used for decommissioning/scrapping plantas the cut surface is generally not consistent.

Arc-Air cutting/gouging:Arc-air cutting is the most commonly used method of arc cutting/gouging and is usedextensively for gouging old welds and removing materials. The consumable is a coppercoated carbon electrode. The gas used is of course compressed air. The process isbasically a "melt and blow process" in that no exothermic reaction is involvedThe main disadvantages include the high level of high-pitched noise produced and thevolume of fumes generated. The cut face will require dressing due to potential carbonpick up and the rapid heating/ cooling cycle involved. A major safety inspection point inthe use ofall arc processes is that correct ear protection is in use and also that an efficientfully isolated breathing supply system is also being used.


20.2 Rev 09-09-02

Cross Section

Light flux coating


Tubular steel core wire containingcompressed oxygen

Gouged metal

TWIV!7!lI. _1) Oxy-Arc Gouging.

2) Arc-Air Gouging.

Jet of compressed airsupplied from holes inthe electrode holder --...

~ Gouged metal

~~ 0~

Copper covered carbon electrode


20.3 Rev 09-09-02

TWIVllOI. _

Welding Safety:


As a respected officer, it is a duty of a welding inspector to ensure that safe workingpractices are strictly followed. Safety in welding can be divided into several areas, someofwhich are as follows:

1) Welding/cutting process safety.

2) Electrical safety.

3) Welding fumes & gases. (Use & storage of gases.)

4) Safe use oflifting equipment.

5) Safe use of hand tools and grinding machines.

6) General welding safety awareness.

1) Welding/cutting process safety:

Consideration should be given to safety when using gas, or arc cutting systems by:

a) Removing any combustible materials from the area.

b) Checking all containers to be cut or welded are fume free. (permits to work etc.)

c) Providing ventilation and extraction where required.

d) Ensuring good gas safety is being practised.

e) Keeping oil and grease away from oxygen.

f) Appropriate PPE is worn at all times

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2) Electrical Safety:

Safe working with electrical power is essential. Ensure that insulation is used whererequired and that cables and connections are in good condition. Be especially vigilant inwet or damp conditions.Low voltage supply (110 v) must be used where appropriate for all power tools etc.All electrical equipment must be regularly tested and identified as such accordingly.

3) Gases & Fume Safety:

The danger of exposure to dangerous fumes and gases in welding cannot be overemphasised. Exposure to these welding fumes and gases may come from electrodes,plating, base metals and gases used in and produced during the welding process.

Dangerous gases that may be produced during the welding process include ozone,nitrous oxides, and phosgene (caused by the breakdown of Trichloroethlylene baseddegreasing agents in arc light); all of which are extremely poisonous and will result indeath when over-exposure occurs.

Other gases used in welding can also cause problems by displacing air, or reducing theoxygen content

Most gases are stored under high pressure, and therefore the greatest care should beexercised in the storage and use of such gases. All gases should be treated with respectand are considered a major hazard area in welding safety.

Cadmium, chromium, and other metallic fumes are extremely toxic and again willresult in death if over-exposure results. Know the effects of a coating fume and alwaysuse correct extraction or breathing systems, which are essential items in safe weldingpractice.

If in doubt stop the work! Until a health and safety officer takes full responsibility.

4) Lifting Equipment:

It is essential that correct lifting practices are used for slinging and that strops of thecorrect load rating are used for lifts. All lifting equipment is subject to regular inspectionaccording to national regulations in the country concerned. In the UK this is governed bythe HSE under the LOLER requirements, which are mandatory for all operations withinthe UK.Cutting comers is an extremely dangerous practice when lifting and often leads tofatalities. (Never stand beneath a load)

Welding Inspection - Welding Related SafetyCopyright © 2002 TWI Ltd

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TWIV!7fll. _THE WELDING INSTITUTE

5) Hand tools and grinding machines:

Hand tools should always be in a safe and serviceable condition (grinding machinesshould have wheels changed by an approved person) and should always be used in a safeand correct manner. Use cutting discs for cutting, and grinding discs for grinding only.

6) General:

Accidents do not just happen, but are usually attributable to someone's neglect, orignorance ofa hazard. Be aware ofthe hazards in any welding job, and always minimisethe risk. Always refer to your safety advisor ifany doubt exists.

f


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Exercise:Complete the table below, by inserting any specific safety issues that will need to beconsidered:

Material Process Other Information Issues to be considered

Stainless Steel MAG Vessel containedexplosive & toxic

compounds

Stainless Steel Silver braze Cd braze alloy

Steel Gas GalvanizedWelding

Steel MMA Cadmium plated

Steel TIG Degreased withTrichloroethylene,

but still damp

Steel Arc Air Confmed spaceGouging

Steel Overhead 500 tonnesLift

Steel MMA Site workWet conditions

Stainless Steel TIG Confmed space

Steel Oxy-Fuel In an area containingcutting combustibles


21.4 Rev 09-09-02

TWIV!7!lI. _

The Weldability of Steels:


In general, the tenn weldability ofmaterials can be defmed as:

"The ability of a material to be welded by most of the common welding processes, andretain the properties for which it has been designed"

The weldability of steels can involve many factors depending on the type of steel, theprocess and the mechanical properties required.

Welding engineers involved only with the welding ofC/Mn structural steel could probablydefine weldability as carbon equivalent, however this is a narrow application ofthe tenn.

Poor weldability generally results in the occurrence of some sort of cracking problem,though most steels have a degree ofweldability.

When considering any type of weld cracking mechanism, three elements must be presentfor it's occurrence:

I)2)3)

Stress.Restraint.Susceptible microstructure.

I. Residual stress is always present in weldments, through local expansion & contraction.2. Restraint may be a local restriction, or through plates being welded to others.3. The microstructure is often made susceptible to cracking by the process ofwelding.

The types of cracking mechanism prevalent in steels in which the CSWIP 3.1 WeldingInspector should have some knowledge are:

1. Hydrogen induced HAZ cracking. (elMo steels)

2. Hydrogen induced weld metal cracking. (lISLA steels)

3. Solidification cracking. (All steels)

4. Lamellar tearing. (All steels)

5. Inter-crystalline corrosion. (Stainless steels)

Welding Inspection - The Weldability of SteelsCopyright © 2002 TWI Ltd

22.1 Rev 09-09-02

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Definitions:


To compliment this section it is important to understand the following terms.

Solubility:

MaximumSolubility:

Steel:

PlainCarbon Steels:

LowCarbon Steel:

MediumCarbon Steel:

HighCarbon Steels:

LowAlloy Steels:

HighAlloy Steels:

Ferrite:

Austenite:

Martensite:

Diffusion:

To be able to dissolve one substance in another, like sugar in tea.

The maximum % ofa substance that can be dissolved in another.

An alloy of the iron with the non-metal carbon. (0.01-1.4% C)

Steels that contain only iron & carbon as main alloying elements.Traces ofMn, Si, A, P & S may be also present from refining.

Plain carbon steels containing between 0.01 - 0.3% C

Plain carbon steels containing between 0.3 - 0.6% C

Plain carbon steels containing between 0.6 - 1.4 %C

Steel containing iron and carbon, and other allying elements Le.Mn, Cr, Ni, Mo < 7% Total

Steel containing iron and carbon, and other alloying elements Le.Mn, Cr, Ni, Mo > 7% Total

A low temperature structure of iron & dissolved carbon, themaximum solubility of carbon occurring in this structure is 0.02 %

A high temperature structure of iron & dissolved carbon, themaximum solubility of carbon occurring in this structure is 2.06%

A hard structure produced in some steels by the rapid cooling fromhigh temperature austenite, generally to temperatures below 300°C

The movement of solute atoms, or molecules through a crystallinestructure. This can generally be accelerated with increasing levelsofheat energy in the material.

Welding Inspection - The Weldability of SteelsCopyright © 2002 "!WI Ltd

22.2 Rev 09-09-02

TWIVllOI. _Effect of alloying elements:


Elements may be added to steels to produce the properties required to make it useful foran application. Most elements can have many effects on the properties of steels.Below is a list ofmost common elements alloyed to steel, with some of their effects.

Aluminium:

Carbon:

Chromium:

Manganese:

Molybdenum:

Nickel:

Niobium:

Silicon:

Titanium:

Tungsten:

Vanadium:

Alloyed to steels mainly as a grain refiner, and is also used as a deoxidising agent in triple de-oxidised steel and welding consumables.

A prime and essential element in steel alloys. An increase in Carboncontent will increase hardness and strength, but reduces the ductility.

Alloyed in additions> 120/0 to produce stainless steels, but is oftenused in low alloy steels < 5% to increase hardness strength andgreatly increase the resistance to oxidation at higher temperatures.Chromium stabilises carbide formation, but promotes grain growthifadded in isolation. It is thus often alloyed together with Ni or Mo

Alloyed to structural steels < 1.6% to increase the toughness andstrength. It is also used to control solidification cracking in ferriticsteels. Alloyed up to 14% in wear/impact resistant Hadfield steel.

Alloyed to low alloy steels to control the effects of creep. It is alsoused as a stabilising element in stainless steels, and will a limit theeffects of grain growth. Alloyed in Cr/Ni/Mo low alloy steels tocontrol an effect called temper embrittlement.

Nickel is alloyed to produce austenitic stainless steels. It may alsobe added < 9% in the low temperature nickel steels. It promotesgraphitisation, but is good grain refiner, and is often used to offsetsome effects of Chromium. Nickel is very expensive, but improvesthe strength, toughness, ductility and corrosion resistance ofsteels.

Carbide former used to stabilise stainless, also in HSLA < .05%

Is alloyed in small amounts < 0.8% as a de-oxidant in ferritic steels.It is alloyed to valve and spring steels, and can also increase fluidity.

Used mainly to stabilise stainless steel, and < .05% in HSLA steels.

Mainly alloyed to high alloy High Speed Tool steels. This increasesthe high temperature hardness required of such steels, due to thetempering effect of frictional heat on other steels during cutting.

Used as a de-oxidant, or as a binary alloy as in HSLA steels < .05%

It should be remembered that most alloying additions increases the ability of a steel toharden by the thermal hardening process. This property is termed "hardenability"


22.3 Rev 09-09-02

TWIV!ll. _THE WELDING INSTITUTE

Crack type:

Location:

Steel types:

Susceptible microstructure:

Causes:

Hydrogen cracking (cold cracking)

a. HAZ. Longitudinalb. Weld metal. Transverse or longitudinala.AJlhardenablesteehb. HSLA steels & QT SteelsMartensite.

Hydrogen cracking may occur in the HAZ or the weld metal, depending on the type ofsteel being welded. Hydrogen may be absorbed into the arc from water on the plates,moisture in the air, paint or oil on the plates or the breakdown of gas shielding etc. AnE6010 cellulosic electrode uses hydrogen as a shielding gas.

Hydrogen will easily dissolve in the molten weld metal, and remain in solution onsolidification to austenite. The weld will cool down and transform to ferrite, where thehydrogen has less solubility and will want to diffuse to the HAZ, which will still beaustenitic.

This occurs rapidly as diffusion is increased with high temperatures. If the HAZ is unhardenable it will itself transform to ferrite and the hydrogen, which has some solubilityin ferrite, will eventually diffuse out of the weldment. If the HAZ has somehardenability, then the transformation of the HAZ will be from austenite to martensite,which has no solubility for hydrogen.

This will result in great internal stress, occurring in a microstructure, which is verybrittle. Cracks may occur at areas of high stress concentration, such as the toes of aweld, and move through the hardened HAZ and in extreme cases, the weld metal.

The four minimum critical factors and their values, where hydrogen cracking islikely to occur, are considered to be: .

a. Hydrogen content: > 15 mlll00 gm of deposited weld metal.

b. Hardness: > 350 VPN.

c. Stresses: > 0.5 of the yield stress.

d. Temperature: < 300°C.


22.4 Rev 09-09-02

TWIV!JOI. _THE WELDING INSTITUTE

Hydrogen may be absorbed into the arc zone and liquid weld metal from:

Rust, oil, grease, orpaint etc. on the plate. E 6010 electrodes produce

H 2 as a shielding gas.

A long, or an unstable arc.

'Y Austenite in HAZ

Weld metal changes

phase to a. ferrite and

H 2 diffuses into HAZ

H2 diffusion to HAZ

Martensitic HAZ

H2 HAZ Cracking a. Butt joints.

H2 HAZ Cracking

Martensitic HAZ

b. T joints.

Austenite in HAZ changes to

martensite at 300°C trapping H2and forcing it out of solution.

Stress concentrations

Stress concentrations


22.5 Rev 09-09-02

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Prevention of hydrogen HAZ cracking:


To control hydrogen cracking in the HAZ it may be necessary to pre-heat the weldment.Pre-heating retards the rate of cooling and suppresses the formation of martensite andother hard structures, which is formed on rapid cooling.

It will also allow some of the trapped hydrogen to diffuse back to the atmosphere.Elements that are to be considered when calculating pre-heat are:

a. Hardenability of the joint. (Le. Ceq)c. Arc energy input.

b. Thickness ofmetal and joint type.d. Hydrogen scale, or achievable limit.

Hydrogen induced weld metal cracking is found when welding HSLA (High strengthlow alloy) steels which are alloyed with micro amounts of titanium, vanadium and/orniobium. (Typically 0.05%)

In order to match the weld strength to plate strength, weld metal with increased carboncontent is used, as carbon content increases tensile strength. A graph showing the effectof carbon on the properties ofplain carbon steels is given below.

This results in a hardenable steel weld deposit, in which the austenite of the weldtransforms directly to martensite, causing the same conditions as found in the HAZpreviously and cracking may now occur within the weld metal.

Prevention of H2 for these steels is as per H2 HAZ cracking, by the preheating of theweld area, but this is principally to allow any trapped hydrogen the time at temperature todiffuse from the weld & HAZ area back to the atmosphere.

Both HAZ and weld metal H2 cracks are considered as cold cracks « 300°C) and fmalinspection is often delayed for up to 72 hours as these cracks may appear within thistime.

ITensile Strength

Hardness

DuctilityI

o 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.2 1.4 1.6 % Carbon


22.6 Rev 09-09-02

TWIVlllll. _THE WELDING INSTITUTE

It can be clearly seen from the graph that additions of carbon (up to O.83%C) willincrease the tensile strength of plain carbon steel dramatically. Whilst this will serve thepurpose of cheaply matching the weld metal strength to the base metal, it will also givethe weld metal much higher hardenability.

This may now result in H2 cracking in the weld metal, as the weld will transfonn fromaustenite - martensite trapping the hydrogen in weld, before it is able to diffuse to theHAZ. It can also be seen from the graph that higher carbon steels have very littleductility, which further complicates the problem.

Cracks tend to be transverse, as the main residual stresses are generally in thelongitudinal direction, though they may occasionally be longitudinal, or even at 45° tothe weld metal.

High strength low ductility weld metal. Hydrogen induced weld metal cracks.

Prevention of hydrogen cracking in the weld metal of HSLA, or Micro-alloyed steelsis very much the same as for hydrogen cracking in the HAZ of other low anoysteels.

Summary ofprevention methods:

a. Use a low hydrogen process and/or hydrogen controlled consumables.b. Maximise arc energy (taking HAZ and weld toughness into consideration).c. Use correctly treated H2 controlled consumablesd. Minimise restrainte. Ensure plate is dry and free from rust, oil, paint or other coatings.f. Use a constant and correct arc length.g. Ensure pre-heat is applied and maintained before any arc is struck.h. Control interpass temperaturei. Ensure welding is carried out under controlled environmental conditions


22.7 Rev 09-09-02

TWIVflll. _THE WELDING INSTITUTE

Crack type:

Location:Steel types:Susceptible microstructure:

Causes:

Solidification cracking (Hot cracking)

Weld centre. (longitudinal)AllColumnar grains.(In the direction of solidification)

Solidification cracking, is a hot cracking mechanism that occurs during solidification ofwelds in steels, having high sulphur content or contaminated with sulphur.

Another potential cause is the depth/width ratio of the weld, which in normal weldingsituations refers to deep narrow welds (cladding applications may produce shallow widewelds, which are also prone to this problem).

Therefore if we have a combination of deep narrow welds with a high incidence ofsulphur we are greatly increasing the likelihood ofhot cracking.

As with all cracking mechanisms stress plays a major role in susceptibility.

During welding, sulphur in or on the plate may be re-melted and will join with the iron toform iron sulphides. Iron sulphides are low melting point impurities, which will seek thelast point of solidification ofthe weld, which is the weld centreline.

It is here that they form liquid films around the hot solidifying grains, which arethemselves now under great stress due to the actions of contractional forces.

The bonding between the grains may now be insufficient to maintain cohesion and acrack will result running the length ofthe weld on its centreline.

Prevention of solidification cracking in ferritic steels: To prevent the occurrence ofsolidification cracking in ferritic steels that contain high levels of sulphur (these steelsare said to suffer from Bot Shortness), manganese is added to the weld via theconsumable.

Sulphur related:

Scrutiny ofMill sheets is essential to assess the materials Sulphur content.

A typical maximum level allowed in a low carbon steel specification is 0.05%. Even thisseemingly low figure may be excessive for certain high stress/higher carbon applications,or if the depth/width ratio is excessive.

Another potential source of Sulphur is paint, oil and grease. This is why temperatureCrayons always carry the statement "sulphur free".


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TWIVfl!ll. _THE WELDING INSTITUTE

This is a prime reason for thorough cleaning, which becomes of even greaterimportance when dealing with Austenitic Stainless Steels

If material availability dictates the necessity of welding high sulphur steels consumableswith a relatively high Manganese content are specified.

An example of steel with very high sulphur levels would be a free machining steel. Someofthe free machining steels could be considered not weldable in normal circumstances assulphur levels are so high.

Manganese has the effect of forming preferential manganese sulphides with the sulphur.MnIS are spherical, solidify at a higher temperature than iron sulphides and therefore aredistributed more evenly throughout the weld. The cohesion between the grains is thusmaintained and the crack will not occur.

Careful consideration must be given to the Mn/S ratio, which should be in the region ofabout 40:1. Increased carbon content can rapidly increase the required ratioexponentially; thus carbon must be reduced as low as possible, with low plate dilutionand low carbon, high manganese filler wires.

A summary of prevention methods:

a. Use low dilution processesc. Maintain a low carbon contente. Specify low sulphur content ofplateg. Thorough cleaning ofpreparation

b. Use high manganese consumablesd. Minimise restraint/stressf. Remove laminationsh. Minimise dilution

Solidification cracking (Sulphur related)

Direction of grain solidification

Weld centre line with liquid Iro__n=..=.:su.:IP:..=h=id:.:e..=.s_------~,~around the solidifying grains - ,"'lii=~


22.9 Rev 09-09-02

TWIVfl!ll. _

Effect of Manganese Sulphides formation

Direction ofgrain solidification

Spheroidal Mn sulphides form between thesolidifying grains, maintaining inter-granularstrength.

Depth/width ratio related


The shape of the weld will also contribute to the possibility of cracking. This may betotally independent from the sulphur aspect but is usually in combination.

Processes such as SAW and MAG (using spray transfer) may readily provide thesedeep/narrow susceptible welds.

However it is not the weld volume that is the prime factor but the weld shape as referredto previously. Therefore root runs and tack welds may readily provide the susceptibleprofile. As root runs are also areas of high dilution (therefore greater sulphur pick up)and more likely to be highly stressed these must always be inspected with solidificationcracking in mind.


22.10 Rev 09-09-02


Solidification cracking in Austenitic Stainless steels

Austenitic stainless steel is particularly prone to solidification cracking.

This is due to:A comparatively large grain size, which gives rise to a reduction ofgrain boundary areaHigh coefficient ofthermal expansion, with resultant high stress.An atomic structure that is very intolerant of contaminants, such as sulphur,phosphorous and additional elements such as boron.

The cause and avoidance may be regarded as the same as that of plain carbon steel butwith extra emphasis on thorough cleaning requirements prior to welding.

The welding procedure will have been written to control the balance of austenite andferrite in the weld metal. This balance will directly effect the structures tolerance ofcontaminants and the resultant grain boundary area. This is why the filler materialspecified often does not appear to match the parent material.Careful monitoring ofparameters is required to control dilution to ensure this balance ismaintained.


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TWIV!lO#. - _THE WELDING INSTITUTE

Crack type:


Lamellar tearing.

Parent materialAny steel typeLow through thickness ductility

Causes:When welding of joints where high contractional stresses are passed in the throughthickness direction of one ofthe plates in the joint.

This short transverse direction is lacking in ductility in cold rolled plates, but ductilityis required to accommodate the plastic strain caused by contraction.

A stepped like crack may initiate in the affected plate, just below the HAZ, in ahorizontal plane. Micro inclusions of impurities such as sulphides and silicates, whichoccur during steel manufacture, cause this poor through thickness ductility. Whensubjected to high short transverse stress this may lead to lamellar tearing

Lamellar tearing. (Ferritic steels)

a. Comer joints.

b. Butt joints.

Through thickness contractional strain. = ~


22.12 Rev 09-09-02

TWIVOI. _THE WELDING INSTITUTE

To assess the risk of a materials susceptibility to lamellar tearing through thicknesstensile tests are normally carried out.

There are 2 types of short transverse tensile tests that may be done:

1) Conventional short transverse tensile test.2) Compound welded cruciform joint tensile test.

Full penetration compoundwelded cruciform joint.

Plate to be tested.

In test 1 the observation is made on the level of through thickness ductility, whichshould show a certain minimum level.

In test 2 failure of the specimen would be expected at much lower levels than specifiediflamellar tearing were to be a problem.

Prevention of lamellar tearing:To reduce the risk oflamellartearing, the following steps may be taken:

a. Check the chemical analysis, and for laminations with UT & PT on plate edges.b. A buttering layer of high ductility weld metal may be deposited where the vertical

member is to be welded, which will enable the plastic strain to be absorbed.c. A gap can be left between the horizontal and vertical members enabling the

contractional movement to take place.d. Joint design may be improved, to reduce or change the direction ofstresses.e. A complete re-design of the welded joint may be required; using pre formed

T pieces.


22.13 Rev 09-09-02

TWIf[J[jI. _


Methods of controlling the occurrence of lamellar tearing:

1) Change ofweld design

2) Use weld metal buttering layers

3) Minimise restraint

Aluminium wire

A pre fanned T piece

4) Use pre formed T piece for critical joints


22.14 Rev 09-09-02

TWIVlJIJI. _THE WELDING INSTITUTE

"Crack" type:


Inter-crystalline corrosion

Weld HAZ. (longitudinal)Austenitic stainless steels.Sensitised grain boundaries.

Causes:During the welding of stainless steels, temperature gradients are met in the HAZ wherechromium carbides can be formed from the carbon and chrome.

This carbide formation depletes the affected grains of chromium, which will severelyreduce their corrosion resistance. Immediately after such an effect has occurred we cansay that the stainless steel has been sensitised, that is to say it has become sensitive tocorrosion.

If no further treatment is given, corrosion will appear parallel to the weld toes, within theHAZ. This corrosion will occur only when the weld is subsequently put in service. Thisis commonly known as weld decay. This corrosion initiates as localised pitting which instainless steel may lead to relatively rapid failure.

Prevention ofweld decay in stainless stee"'l~s:--

a. To prevent the occurrence ofweld decay, we can use parent material with a carboncontent below 0.03% C. This reduces the free carbon available to form chromiumcarbides. For example E316 stainless steel containing a low carbon content is designatedas E 316L.

b. Another option is to add other elements such as niobium and titanium to.the plateand electrodes to stabilise the steel. These are termed stabilising elements, and tie upany free carbon by forming preferential carbides, thus leaving chromium within thegrain, where it will perform its function in resisting corrosion.

c. The conversion of chromium and carbon into chrome carbides occurs betweenapproximately 500 - 8500 C. Most welding procedures are designed to reduce the amountof time that the HAZ is undergoing this temperature range. Therefore it is normal to seemaximum interpass temperature controls applied.

d. A sensitised stainless steel may be solution annealed after welding by heating tonoo°c and quenching. This dissolves the chromium carbides and inhibits their reassociation.


22.15 Rev 09-09-02

TWIV!7!lI. _THE WELDING INSTITUTE

Summary of Weldability of Steels:

Keywords:.

Hl HAZ cracks Process Consumables Paint, Rust, GreaseDelayed inspection. Solubility cr concentrations HAZDiffusion Transformation Martensite Critical factors =Hardness> 350VPN Hydrogen >15ml cr > 0.5 yield stress. Temp < 300°C

Hydrogen induced HAZ or weld metal cracks.Cause·

HSLA weld cracksWeld contraction

.Pre-heat Hydrogen control Bake consumable Use low H~ ProcessMinimise restraint Remove coatings Stable arc length y SIS Weld metalArc energy Use low Ceq plate Use hot pass ASAP Use low H~ Cons'

Prevention·

Keywords:

Weld centrelineLoss ofcohesion

ContractionHot shortness

Lamellar tearing in CIMo steels.Cause:

Keywords:

Short transversePlastic strain

ContractionPoor ductili

Inter - crystalline corrosion in stainless steels.Cause:

Keywords:

Chromium de letionParallel to weld

CrCarbideLoss ofresistance

SensitisationStabilised

Prevention:Low Carbon .03%Low heat in t

NiobiumSolution anneal


22.16 Rev 09-09-02

r

TWIVllfll. THE WELDING INSTITUTE

Practical Visual Inspection:

The CSWIP (Certification Scheme for Welding & Inspection Personnel) examinationscheme for welding inspectors consists at present of the following categories:

CSWIP 3.0 Visual Welding Inspector

CSWIP 3.1 Welding Inspector

CSWIP 3.2 Senior Welding Inspector

As this text is aimed at candidates attempting the entry level, the CSWIP 3.0 3.1 andAWS Bridge examination content only is given below:

Exam:

eSWIP3.0

Time

Practical butt welded plate (code provided) Ihour 45 minutes.

Practical fillet welded T joint (code provided) Ihour 15 minutes.

Total time: 3 hours.

eSWIP3.1

Practical butt welded plate (code provided) Ihour 15 minutes.

Practical butt welded pipe (to candidates supplied code) Ihour 45 minutes.

Practical assessment ofmacros (2 x macros to a code provided) 45 minutes.

Theory Specific. (4 from 6 questions) 1 hour 15 minutes.

Theory General. (30 Multi choice questions) 30 minutes.

Oral. (Questions on code and general inspection) 15 minutes.

Total time: 5 hours 45 minutes.

AWS eWI - eSWIP 3.1 Bridge

Practical butt welded pipe (code provided) Ihour 45 minutes.

Practical assessment ofmacro (1 x macro to code provided) 25 minutes.

Theory Specific. (llong answer + 9 short answer questions) 1 hour 20 minutes.

Total time: 3 hours 30 minutes.

Welding Inspection - Practical Visual InspectionCopyright © 2002 TWI Ltd

23.1 Rev 09-09-02

HAI-BANG

Highlight

HAI-BANG

Rectangle

TWIV!7f7l. THE WELDING INSTITUTE

To successfully attempt the practical inspection elements of these examinations willrequire a number of important tools:

1) Good eyesight.2) Specialist Gauges.3) Hand tools i.e. Magnifying glass, torch, mirror, graduated scale etc.4) Pencil/pen, report forms, acceptance criteria, and a watch.

1) Good eyesight:

To effectively carry out your scope of work as a CSWIP qualified Welding Inspector it isimportant that your close vision acuity is of an acceptable level, and thus a test certificateof your close vision acuity must be provided before your examination to any CSWIPWelding Inspection, or NDT subject area.

For colour contrast penetrant and fluorescent penetrant and magnetic particle inspection,inspectors must also be able to distinguish between these contrasting colours; therefore acolour blindness test for these colours is also required.

All candidates for CSWIP examinations must be tested; by a qualified optometrist.Alternatively tests may be conducted; by qualified personnel available at most TWIexamination centres.

It is also important to be aware that human visual ability may decay rapidly as the yearsprogress.

Holders of CSWIP Welding Inspection certificates should thus make every effort to havetheir vision professionally tested twice yearly. Up to date test certificates must be suppliedto the CSWIP examination board as proofofvision ability.

2) Specialist Gauges:

A number of specialist gauges are available to measure the various elements that need tobe measured in a welded fabrication including:

a) Hi - Lo gauges, for measuring mismatch between pipe wall and plate thickness.b) Fillet weld profile gauges, for measuring fillet weld face profile and sizes.c) Angle gauges, for measuring weld preparation angles.d) Multi functional weld gauges, for measuring many different weld measurements.


23.2 Rev 09-09-02


TWI CAMBRIDGE MULTI-PURPOSE WELDING GAUGE:

Angle of Preparation:

This scale reads 0° to 60° in 5° steps.The angle is read against the chamferededge of the plate, or pipe.

Fillet Weld Actual Throat Thickness:

The small sliding pointer reads up to20mm, or % inch. When measuring thethroat it is supposed that the fillet weldhas a 'nominal' design throat thickness,as an 'effective' design throat thicknesscannot be measured in this manner.

Fillet Weld Leg Length:

The gauge may be used to measure filletweld leg lengths ofup to 25mm, asshown on left.

Linear Misalignment:

The gauge may be used to measuremisalignment of members by placing theedge of the gauge on the lower memberand rotating the segment until the pointedfmger contacts the higher member.

Welding Inspection - Practical Visual InspectionCopyright © 2002 TWl Ltd

23.3 Rev 09-09-02

TWIVllUI. _THE WELDING INSTITUTE

Excess Weld MetallRoot penetration:

The scale is used to measure excessweld metal height or root penetrationbead height of single sided butt welds,by placing the edge of the gauge on theplate and rotating the segment until thepointed fmger contacts the excess weldmetal or root bead at its highest point.

Undercut:

The gauge may be used to measureundercut by placing the edge of thegauge on the plate and rotating thesegment until the pointed finger contactsthe lowest depth of the undercut.The reading is taken on the scale to theleft of the zero mark in mm or inches.

Fillet weld leg length size & profile gauge:

Excess weld metal can be easily calculated by measuring the Leg Length, andmultiplying it by 0.7 This value is then subtracted from the measured ThroatThickness =Excess Weld Metal.

Example: For a measured Leg Length of 10mm and Throat Thickness of 8 mm:. 10 x 0.7 = 7 :. 8 - 7 =1 mm of Excess Weld Metal.


23.4 Rev 09-09-02

TWIVflDI. - THE WELDING INSTITUTE

....1"~..;--

'/f- 7):;-/ ~/'{-, /' 7< /;

For Training Purposes Only IWIS 5 Acceptance Levels for Plate & Macro Inspection Practice

Specification Number TWI 09-09-02

All dimensions are given in millimetres

Key: 0 = diameter. t = plate thickness. d = depth. h = height

No Imperfection Comments Allowance1 Cracks --~._--_ .. Not permitted2 Porosity _.-_ ..-.--" Individual pore 0 1 mmMaximum3 Solid Inclusions 1/ Non metallic \/ 2mmMaximum4 Solid Inclusions ---- Metallic Not permitted5 Lack ofFusion II" Side wall/root/inter-run Not permitted6 Lack ofRoot Penetration / , Not permitted7 Overlap/Cold lap

-'

Weld face/Root Not permitted,

8 Incompletely filled Vi Not permittedgroove

9 Linear Misalignment V ----- 0.2t Maximum 4mm ?10 Angular Misalignment _. 10° Maximum11 Undercut \ / Smoothly blended 10%t up tolmm d

. 1'-'; Maximum -Sz/l;'//C/

12 Arc Strikes \,./ Seek advice \J-.

13 Laminations~

Not permitted14 Mechanical Damage \// Not permitted15 Cap Height - Shall not be less than Imm 1 -3mm h Maximum16 Penetration Bead (~<tes,((ve \ 2mm hMaximum17 Toe Blend \./ / Smooth18 Spatter \ --' Clean & Re-inspect Not permitted\/

19 Weld Appearance ! All runs shall blend smoothly Smooth20 Root concavity '. 10%tMaximum ?','

v~·rCt,! ce. T .> / 0 ~/;'iL~'Lx-1

T ./ //,./ if.;; It !i''-~~. ,'~


23.5 Rev 09-09-02

c

Joint type: Single V Butt

Date 1st January 2003

Test piece ident: 001

Undercutsmooth1.5 max

~ 30 I

Gas pore1.5 ()

~

IWELD FACE I

Welding process: MMAISMAW

Length & thickness of plate: 300mm. x 10 mm

EXAMPLE PLATE REPORT

22

flIt'2, Lack of sidewall fusion

87 ....r-_----,--.

Page 1 of3

A

Name: [Block capitals] Mr. I C Plenty Signature: I CPlenty

Code/Specification used: TWI09-09-02

Welding position: Flat IPA

a::~

>00o

"~-+~

=coa:: I-------- --&..__....L- -I- -'--__..l-- --j

t-3

= ~ 8 ~ Itlp.40 mr;, Arc Stril{eI-( -l00 ::I:

m

-+ Slag inclusion Centreline crack :?:241. m

~ 30 r> 25

0

t-3 z0 G>

~ a:: Cap height: 4mm. Z< ~0 Weld width: 12-14mm\0

Toe blend: Poor =iI0

~C\0

I HilLo: 2mm -I0~ mIV Spatter along weld length**~

~

\.l::E: Page 2 of3 EXAMPLE PLATE REPORT ~~o C1>'a_

~.S-

~~l§.f1Q@[N'gono ::toNO....,1:1

IWELD ROOT I;:51cl

~A C

Q. ::tone. ~

~ >tilr::: 00e. c::S'til ~'aC1>

~n::to0 Root concavityI:S

~ Lack of root fusion~

2 deep

~ 23247 ...

0 -+/ to/IV ..20w

~~

__.~ 1--__---112850

Penetration height: 4mm max~ Penetration width: 3 - 6mmt:::' Root toe blend: smooth~ Linear misalignment: 2mm~

Lack of penetration-I:J:m~mroZG)

zen-I=ic-Im

TWIVllfll. THE WELDING INSTITUTE

Weld Report Sheet: Page 3 of 3

EXAMPLE WELD INSPECTION REPORT/SENTENCE SHEET

PRINT FULL NAME I C Plenty

SPECIMEN NUMBER 001

EXTERNAL DEFECTS Defects Noted Code or Specification Reference

Defect Type ~/Plate Accumulat~e Maximum Section! AcceptlRejectSection Total/'" Allowance Table N°

1 2 < 3 4 5Excess weld meta(height ) A-C 4mm 3mm 15 RejectExcess weld me~ appearance') A-C Poor blend SMOOTH 19 RejectIncomplete fillin~ A-C NONE ------------- ------------ AcceptInadequate weld width A-C NQNE ------------- ------------ Accept

Sla~ Inclusions A-C Ix 8mmlong. 2mm 3 RejectUndercut A-C 1.5mm depth Imm 11 RejectSurface Porosity A-C 1.5mm0 Imm 2 RejectCracks/Crack-like defects A-C 40mm NONE 1 RejectLack of fusion A-C 22mm NONE 5 RejectArc strikes A-C 30x25 ------------- 12 Seek advise***Mechanical damage A-C NONE ------------- ------------ AcceptLapslLaminations A-C NONE ------------- ------------ AcceptMisalignment (Linear) A-C 2mm 2mm 9 AcceptLon~tudinal seams A-C NONE ------------- ------------ Accept

ROOT DEFECTSMisalignment A-C 2mm 2mm 9 AcceptExcessive Root Penetration A-C 4mm 2mm 16 Reject

,Lack ofRoot Penetration A-C 50mm NONE·· 6 RejectLack ofRoot Fusion A-C 20mm NONE 5 RejectRoot Concavity A-C 2mm depth Imm 20 RejectRoot Undercut A-C NONE ------------- ------------ AcceptCracks/Crack-like defects A-C NONE ------------- ------------ AcceptSlag inclusions A-C NONE ------------- ------------ AcceptPorosity A-C NONE ------------- ------------ AcceptLapslLaminations A-C NONE ------------- ------------ Accept

Thi ~ I h b . d th· f d / 'fi' TWI 09-09-02s '"'P7""p ate as een examme to e reqUIrements 0 co e speCl lcatlOn .and is .lIlp"~/rejectedaccordingly.

Signature ~~~ ..

*Delete which is not applicable.


1st January 2003Date .

Use the other side for any comments.

23.8 Rev 09-09-02

TWIV!lOI. _Weld Report Sheet: Page 3 of 3 Reverse Side

Comments:

*Request NDT testing to confirm crack and true length.

**Large amount of spatter on weld face.Recommend this is removed and re inspected


***Recommend arc strikes are ground flush prior to MPI testing for crack detection.Seek advice


23.9 Rev 09-09-02

TWIrzlOI. _

Effect of a Poor Toe Blend:

A very poor weld toe blend angle

6mm

An improved weld toe blend angle


Generally speaking, most specifications tend to quote that "The weld toes shall blendsmoothly"

This statement can cause problems as it is not a quantitative statement, and thereforevery much open to individual interpretation. To help in your assessment of theacceptance of the toe blend it should be remembered that the higher the angle at the toethen the higher is the concentration of stresses, which between 20° - 30° is almost at aratio of2:1

A poor toe blend will be present when the excess weld metal height is excessive,however it may be possible that the height is within the given limits, yet the toe blend isnot smooth, and is therefore a defect, and unacceptable.

It should be remembered, that a poor toe blend in the root of the weld has the sameeffect.


1.16 Rev 09-09-02

TWIVIlfll. _THE WELDING INSTITUTE

Summary of Weld and Joint Terms and Definitions:

A Weld:

A Joint:

A weld preparation:

Types of weld:

Types of joint:

Types of preparation:

Preparation terms:

Weldment terms:

Weld sizing (Butts):

Weld sizing (Fillets):

A Union of materials, produced by heat and/or pressure.

A Configuration of members.

Preparing a joint to allow access & fusion through the jointfaces.

Butt. Fillet. Spot. Seam. Edge.

Butt. T. Lap. Open Comer. Closed Comer.

Bevel's. V's. J's. U's. (Single & Double).

Bevel angle. Included angle. Root face. Root gap.

Weld face. Weld root. Fusion Zone. Fusion boundary.HAZ. Weld toes. Weld width.

Design throat thickness. Actual throat thickness. Excessweld metal. Excess root penetration.

Design throat thickness. Actual throat thickness.Excess weld metal. Leg length.


1.17 Rev 09-09-02

TWIV/lDI. THE WELDING INSTITUTE

Welding Imperfections:

What are welding imperfections?

Welding imperfections are material discontinuities caused by, or during, the process ofwelding.

All things contain imperfections, but it is only when they fall outside of a "level ofacceptance" that they should be termed defects, as they may render the productdefective, or unfit for its purpose.

As welds can be considered as castings they may contain all kinds of imperfectionsassociated with the casting of metals, plus any other particular imperfections associatedwith the specific welding process being used.

We can classify welding imperfections into the following groups:

1)3)5)7)

1) Cracks:

CracksSolid inclusionsSurface and profileMisalignment

2)4)6)

Gas pores and porosityLack of fusionMechanical damage

Cracks sometimes occur in welded materials, and may be caused by a great number offactors. Generally, we can say that for any crack like imperfection to occur in a material,

. there are 3 criteria that must be present:

a) Aforce b) Restraint c) A weakened structure

Typical types ofcracks that will be discussed later in the course are:

1) H2 Cracks 2) Solidification Cracks 3) Lamellar Tears

A Material's likelihood to crack during welding can be evaluated under the termWeldability. 1bis may be defined as:

"The ease with which materials may be welded by the common welding processes"

All cracks have sharp edges, which produce high stress concentrations. This generallyresults in rapid progression, however this also depends on the properties of the metal.Cracks are classed as planar imperfections as they generally have only 2 visible, ormeasurable dimensions Le. length and depth. Most fall into the defects category, thoughsome standards allow crater cracks.

Welding Inspection - Welding ImperfectionsCopyright © 2002 TWI Ltd

3.1 Rev 09-09-02

TWIVIlDI. _THE WELDING INSTITUTE

2) Gas pores, porosity and cavities: Ii i, _I

Jt'J I pI'" f/u~ (l -1-14',"V\.// - / v Il&""'j let 'Gas pores: 'Gas pores are defined as internal gas filled cavities smaller than 1.6mm diameter, whichare created during solidification by the expulsion of gases from solution in the solidifyingweld metal.

Porosity:These are gas pores < 1.6mm diameter which are generally grouped together, and may beclassified by their number, size and grouping. (Le. Fine, or coarse cluster porosity) Asingular gas filled cavity = or > 1.6mm diameter is termed a "blow hole" Porosity ismainly produced when welding improperly cleaned plate, or when using damp weldingconsumables. Gases may also be formed by the breakdown of paints, oil based products,corrosion or anti corrosion products that have been left on the plates to be welded.

Porosity can be frequently formed during the MIG or TIG process by the temporary lossof gas shield, and ingress of air into the arc column, which is caused by movement of thesurrounding atmosphere, or wind. Porosity may also be caused by improper settings ofshielding gas flow rate.Porosity may also found in deep Sub Arc welds due to the distance that trapped gasesformed in the root area need to travel to escape from the surface, and may also occurwhen using damp MMA welding electrodes, or damp Sub Arc Fluxes.Porosity may be prevented by correct cleaning of materials, correct setting and shieldingwhen using the TIG or MIG welding processes, and using dry welding consumables.Porosity may be identified on a radiograph as a spherical imperfection that has varyingdensity shades, from highest in the centre, decreasing to its outer edges Le.

Shrinkage cavities:These are voids created during solidification ofwelds ofhigh depth: width ratio.This may occur when the d:w ratio is> 2:1 and is often associated with SAW and can bedefined as a hot plastic tear, which has sharp edges and is treated as a crack., wr~,l~ 0 urface breaking porosity

Shrinkage cavity I ffJS Coarse cluster porosity

Fine cluster porosity~_-=-'• Blow hole> 1.6 mm 0

An isolated internal pore


3.2 Rev 09-09-02

TWIV!lD#. _4) Solid inclusions:


Solid inclusions include metallic and non-metallic inclusions that may be trapped in theweld during the process of welding. The type of solid inclusion that may be expected isreally dependant on the welding process being used. In welding processes that use fluxesto form all the required functions of shielding and chemical cleaning, such as MMA andSubmerged Arc welding, slag inclusions may occur. Other welding processes such asMIG and TIG use silicon, aluminium and other elements to de-oxidise the weld. Thesemay form silica, or alumina inclusions. Any of these non-metallic compounds may betrapped inside a weld during welding. This often happens after slag traps, such asundercut have been formed. Slag traps are mostly caused by incorrect welding technique.Metallic inclusions include tungsten inclusions that may be produced during TIGwelding by a poor welding technique, an incorrect tungsten vertex angle, or too highamperage for the diameter of tungsten being used. Copper inclusions may be causedduring MIGIMAG welding by a lack of welding skill, or incorrect settings inmechanised, or automated MIG welding. (Mainly welding Aluminium alloys)

Other welding phenomena such "arc blow" or the deviation of the electric arc bymagnetic forces, can cause solid inclusions to be trapped in welds. The locations of theseinclusions may be within the centre of a deposited weld, or between welds where theresult causes "Lack of inter-run fusion", or at the sidewall of the weld preparationcausing "Lack of side wall fusion" Generally solid internal inclusions may be caused by:

1) Lack ofwelder skill. (Incorrect welding technique)2) Poor manipulation of the welding process, or electrode.3) Incorrect parameter settings, i.e. voltage, amperage, speed of travel.4) Magnetic arc blow.S) Incorrect positional use of the process, or consumable.6) Incorrect inter-run cleaning.

Internal solid inclusion causinga lack of sidewall fusion

Solid inclusions caused by undercutin the previous weld run

}ht(ck..£ '

Surface breaking solid inclusion

Internal solid inclu~~~,j'YO \

d'b'f"y»@uJ 0 C!

'Z, ~~~' 0

Internal solid inclusion causinga lack of inter-run fusion


3.3 Rev 09-09-02

TWIVIlOI. THE WELDING INSTITUTE

3) Lack of fusion:

Lack of fusion imperfections, are defined as a lack of union between two adjacent areasof material. This may be accompanied, or caused by other imperfections as explained inthe last section. Lack of fusion can be considered a serious imperfection, as like cracks,they produce areas of high stress concentration. Lack of fusion, or overlap (a form oflack of fusion) may occur in the weld face area during positional welding caused by theaction of gravity and incorrect use ofthe process.

Arc blow is a prime cause of lack of fusion imperfections, particularly when using highcurrent processes, such as Sub Arc using high direct electric currents. (DC+ or DC -)Lack of fusion may also be formed in the root area of the weld where it may be found onone, or both plate edges. It may also be accompanied by incomplete root penetration.Lack of fusion is also a common imperfection in "Dip transfer MIG welding" of metalsover 3mm thickness, especially when welding vertically down. This is caused by theinherent coldness of this form ofmetal transfer, and the action of gravity.

Like solid inclusions, lack of fusion imperfections may be caused by:

1) Lack ofwelder skill. (Incorrect welding technique)2) Poor manipulation of the welding process, or electrode.3) Incorrect parameter settings, i.e. voltage, amperage, speed of travel.4) Magnetic arc blow.5) Incorrect positional use of the process, or consumable.6) Incorrect inter-run cleaning.

Mi)Overlap

!. Lack of sidewall fusion

Lack of root fusion

Lack of sidewall fusion (J_ wr/Ie-(Incompletely idled groove fllin some standards)

Lack of inter-run fusion


3.4 Rev 09-09-02

TWIV!7fll. THE WELDING INSTITUTE

4) Surface and profile:

Surface and profile imperfections are generally caused by poor welding techniques. Thisincludes the use of incorrect welding parameters, electrode/blowpipe sizes and/ormanipulation and joint set up.

1bis category may be split into two further groups ofweld face and weld root.

Surface and profile imperfections are shown pictorially in A & B below:

A:

Spatter is not a major factor in lowering the weldment strength, though it may maskother imperfections, and should therefore be cleaned ofIbefore inspection.Spatter may also hinder NDT and be detrimental to coatingsIt can also cause micro cracking or hard spots in some materials due to the localisedheating/quenching effect.

An incompletely filled groove may bring the weld below its DIT. It is a major stressconcentration when accompanied by lack of sidewall fusion.

Lack of root fusion causes a serious stress concentration to occur in the root.It may also render the root area more susceptible to corrosion in service

Spatter

Lack of root fusion

An Incompletely f'illed groove

L


3.5 Rev 09-09-02

TWIV!lOI. _

B:


A bulbous contour is an imperfection as it causes sharp stress concentrations at the toesof individual passes and may also contribute to overall poor toe blend

Arc strikes, Stray-arcing, or Stray flash may cause many problems including severaltypes of cracks to occur. They can also cause depressions in the plate bringing it belowits DTT. Arc strikes would normally be NOT inspected and then repaired.

Incomplete root penetration may be caused by too small a root gap, insufficientamperage, or poor welding technique. It also causes high stress concentrations to occur.It also generally produces a weld with less throat thickness than the DTT of the joint.

An irregular bead width is a surface imperfection, which is often referenced inapplication standards as. "The weld bead should be regular along its linear length"

Arc Strikes

Incomplete root penetration /

Bulbous, or irregular contour

Poor toe blend

Undercut:

Undercut can be defined as a depression at the toe of a weld in a previous depositedweld, or base metal, caused by welding. Undercut is generally caused by incorrectwelding technique, including the use of too high a current for the electrode being used,and the welding position. It is often caused in the top toe of fillet welds when attemptingto produce a large leg length fillet weld in one run. Undercut can also be considered aserious imperfection particularly if it is sharp, as again it causes high stressconcentrations. It is gaug~d in severity by its length, depth and sharpness. Fillet weldedstructures intended for fatigue loaded applications often require the toes to be lightlyground, or flushed in with a TIG run to remove any toe undercut.

Shrinkage grooves:

Shrinkage grooves may occur in the root area and are caused by contractional forcespulling on the hot plastic base metal in the root area It is often mistaken as root undercut.


3.6 Rev 09-09-02

Weld metal, surface undercut

Parent metal, "top toe?

Parent metal, surface undercut

Weld metal, surface undercut

TWIVflfll. I!IIII THE WELDING INSTITUTE

w~kr' <; 10{Lt-ef_.'

Root Run or "Hot pas~" undercut

Root concavity: (suck back)

This may be caused when using too high a gas backing pressure in purging. It may alsobe produced when welding with too large a root gap and depositing too thin a root bead,when the hot pass may pull back the root bead through contractional strains.

Root concavity


3.7 Rev 09-09-02

TWIVfl!ll. _THE WELDING INSTITUTE

Excess penetration:Often caused by using too high a welding current, and/or, slow travel speed, coupledwith a large root gap, and/or a small root face for the current or process being used. It isoften accompanied by bum through, which can be defmed as a local collapse of the weldpuddle causing a hole, or depression in the fmal weld root bead.

Root oxidation:Root oxidation may take place when welding re-active metals such as stainless steelswith contaminated, or inadequate purging gas flow.

Root oxidation in Stainless SteelExcess penetration, and burn through /

Crater pipes:Often occurs during TIG welding, at the end of the weld run, on [mal solidification. It iscaused by insufficient filler material to meet the solidification process. It can beeliminated by careful application of the filler metal, or using a slope out control.

Crater pipe r,' ,r-/e- )"---- ", /' ,

L~v/ 'c: .. c-:; ( :

!, /1/) I),,., '7 ,'7I .... ' ~r..<_.. f 'I...~-"'" '-

it'I

Incomplete root penetration.

Bulbous or irregular contour.

Poor toe blend.

Irregular bead width.

Undercut.

Root concavity.

Excess penetrationlBurn through.

Root oxidation.

Incompletely filled grove.

Spatter.

Arc strikes. (Stray arcs)

To summarize, we can list surface or profile welding imperfections as follows:

rn "t\!,~/p0-t'h "~{.,'V ;/ ItJ ;

ff,

1)

2)

3)

4)

5)

6)

7)

8)

9)

10)

11)


3.8 Rev 09-09-02


5) Mechanical damage:

Mechanical damage:This can be defmed as any surface material damage caused during the manufacturingprocess. This can include damage caused by:

1) Grinding.3) Hammering.5) Chiselling.

2)4)6)

Chipping.Braking off welded attachments by hammering.Using needle guns to compress weld capping runs.

As with the stray arcing, the above imperfections can be detrimental as they reduce thethrough thickness dimension of the plate in that area. They can cause local stressconcentrations and should be repaired prior to completing the job.

7) Misalignment:

There are 2 forms ofmisalignment, which are termed:

1) Linear misalignment 2) Angular misalignment.

Linear misalignment: can be controlled during weld set up by the correct use/control ofthe weld set up technique Le. tacking, bridging, clamping etc. Excess weld metal heightis always measured from the lowest plate to the highest point of the weld cap.

Linear misalignment measured in:: - - - - - - - - - - f 3mm

Angular misalignment: may be controlled by the correct application of distortioncontrol techniques, Le. balanced welding, offsetting, or use ofjigs, clamps, etc.

dJ~i/td"

b~.i_:== __ :::::t 150 i/ r

::

Angular misalignment measured in degrees 0

Good working practices and correct welder training will minimise the occurrence ofunacceptable welding imperfections, or welding defects.


3.9 Rev 09-09-02

124

MULTICHOICE PAPER FIVE

1. Generally the most suitable method of detecting lack of sidewall fusion would be:a. Ultrasonics.b. MPI.c. Radiography.d. Penetrant inspection.

2. Hot shortness is a term used to indicate:a. Lamellar tearing.b. Solidification cracking.c. Hydrogen cracking.d. None of the above.

3. Cobalt as an isotope would generally be used on:a. Thin material.b. Tee joints.c. Plate thicknesses greater than 25 mm.d. All the above.

4. In welding procedure terms, a change in essential variable means:a. Re-qualification of the weld procedure.b. Possible changes in the weld's microstructure.c. Possible changes in the mechanical properties.d. All the above.

5. Weld symbols placed on a dotted line in accordance with ISO requirements means:a. Weld on 'arrow' side.b. Weld on 'other' side.c. Weld on site.d. Full penetration required.

6. A welding inspector's main attributes include:a. Knowledge and experience.b. Literacy.c. Honesty and integrity.d. All th,e above.

7. Technically, a code ofpractice is:a. A standard.b. A 'set of rules' for the manufacture of a product.c. Related to welder and weld procedure approval.d. All the above.

8. The correct term for 'cap height' is:a. Reinforcement.b. Cap profile height.c. Excess weld metal.d. All the above.

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9. A tensile test will assess:a. Impact values.b. Stress.c. Strain.d. Both band c.

10. The important point of high temperature steels is that:a. They can withstand creep failure.b. They may suffer re-heat cracking problems.c. They may suffer loss of toughness.d. All the above.

11. An austenitic stainless steel may suffer:a. Weld decay.b. Sensitisation.c. Solidification cracking.d. All the above.

12. Carbon equivalent values are useful to determine:a. Weldability aspects.b. Crack sensitivity aspects.c. Typical mechanical properties.d. All the above.

13. A basic electrode would normally:a. Have superior mechanical properties.b. Require baking before use.c. Not be used on low carbon steels.d. Both a and b.

14. When referring to TIG welding, the shielding gas could be:a. Argon and hydrogen.b. Argon and helium.c. Argon and nitrogen.d. All the above.

15. When referring to MIG welding, the shielding gas would be:a. Argon.b. Argon + 1% oxygen.c. Argon + 20% carbon dioxide.d. None of the above.

16. Submerged arc utilises:a. Deep penetration characteristic.b. High deposition rates on DC+.c. Flat (PA) welding only.d. None of the above.

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17. Ultrasonics would be preferred over radiography due to:a. Ability to find most defects.b. Lower skill requirement.c. Ability to detect laminations.d. Both a and c.

18. The most serious defect types are:a. Planar.b. Cracks.c. Lack of fusion.d. All the above.

19. MMA welding of low alloy steels is more likely to be performed with:a. Rutile electrodes.b. Cellulosic electrodes.c. Iron powder electrodes.d. Basic hydrogen controlled electrodes.

20. Which of the following defects is more common to welds deposited by C02 welding thanwelds deposited by MMA?a. Slag inclusions.b. Excess penetration.c. Lack of sidewall fusion.d. Tungsten inclusions.

21. Which defect would you expect to get in TIG welds in non-deoxidised steel?a. Undercut.b. Porosity.c. Tungsten inclusions.d. Linear misalignment.

22. Which of the following can arise from copper inclusions in a ferritic steel weld?a. Weld metal cracks.b. HAZ cracks.c. Lamellar tearing.d. Porosity.

23. Which of the following is likely to give the highest impact strength in ferritic weld metal?a. Cellulosic electrodes.b. Submerged arc with acid flux.c. Spray transfer C02 welding.d. Basic coated MMA electrodes.

24. You suspect that ferritic steel plates contain cracks in the prepared edges. What NDTmethod would you use to check this?a. Radiography.b. Magnetic particle inspection.c. Penetrant inspection.d. Ultrasonic flaw detection.

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25. Which of the following defects would you not expect to find by visual inspection of welds?a. Linear slag inclusions.b. Undercut.c. Overlap.d. Linear misalignment.

26. Stress relieving is not helpful in which of the following cases?a. Improving resistance to stress corrosion cracking.b. Improving dimensional stability after machining.c. Lowering the peak residual stress.d. Softening the steel.

27. What is the maximum hardness usually recommended for the heat-affected zone of amedium strength ferritic steel weld?a. 100 DP Hv.b. 350 DP Hv.c. 500 DP Hv.d. 750 DP Hv.

28. What effect does mid thickness laminations in steel plate normally have when they arelocated within a weld heat affected zone?a. Cause lamellar tearing.b. Fuse together to form a bond.c. Affect the weld metal composition.d. Cause internal tearing on a micro scale.

29. The permanent backing material for MMA welding of low carbon steel should be madefrom:a. Copper.b. Low carbon steel.c. QT steel.d. Cast iron.

30. The overall length of a pipeline can be affected by:a. Transverse shrinkage.b. Longitudinal shrinkage.c. Angular shrinkage.d. Circumferential shrinkage.

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MULTICHOICE PAPER SIX

1. The weld dimension used to indicate the minimum strength of a fillet weld is:a. Leg length.b. Throat thickness.c. Width of bead.d. Length of weld element.

2. An electroslag weld requires what heat treatment to improve the grain structure?a. Annealing.b. Stress relieving.c. Normalising.d. Quench and tempering.

3. The most cornmon type of failure associated with sharp fillets, notches and undercut is:a. Crystallisation.b. Fatigue.c. Corrosion.d. Brittle fracture.

4. Weld decay in stainless steels can be avoided by:a. Stress relieving.b. Slow cooling after welding.c. Addition of more manganese to the steel.d. Addition of titanium to the steel.

5. An eutectoid mixture in steel is:a. A mixture of ferrite and austenite.b. A mixture comprising a substitutinal solid solution.c. Called pearlite.d. Called ledeburite.

6. Low alloy steels having a high carbon equivalent before welding will require:a. A reduction in carbon content.b. High pre-heat temperatures.c. Low pre-heat temperatures.d. No pre-heating.

7. The electrodes for welding low alloy steels should be:a. Used with a low current value.b. One size larger than for general purpose electrodes.c. Used for welding in the flat position only.d. Heated in a drying oven before use.

8. The purpose of pre-heating low alloy steel pipes before electric arc welding is to:a. Refine grain structure.b. Relieve internal stress.c. Retard rapid cooling.

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d. Regulate excessive expansion.9. Welder qualification tests are designed to:

a. Test the correctness of the welding procedure.b. Test the welder's skill.c. Prove the weldability of the parent material.d. All the above.

10. In positional MMA welding on pipework, welders are having difficulty in obtaining goodcapping profiles when welding in the overhead position. Would you:a. Advise them to increase the current.b. Advise them to increase the voltage.c. Ask for a new welding team.d. Suggest the use of a smaller diameter electrode.

11. You have a macro section of a 'T' butt joint that shows a step-like defect lying outside thevisible HAZ. What would this defect possibly signify?a. HAZ cracking.b. Toe cracking.c. Lamination.d. Lamellar tearing.

12. Which electrode deposits weld metal with the greatest ductility and resistance to cracking?a. Rutile.b. Cellulosic.c. Basic.d. Oxidising.

13. Which one of the following is not helpful in minimising angular distortion during welding?a. Use of double 'V' weld prep using balanced welding technique.b. Pre-setting of work piece.c. Applying post weld heat soak.d. Changing from a single 'V' prep for thick material.

14. Argon purging on the root side is necessary in the TIG welding of stainless steel to:a. Obtain full penetration.b. Obtain full fusion.c. Avoid porosity in the root.d. Obtain a satisfactory weld surface finish.

15. Which of the following can arise from copper inclusions in a mild steel weld?a. Weld metal cracks.b. HAZ cracks.c. Lack of fusion.d. Porosity.

16. Stress relief is not helpful in which of the following cases?a. In improving resistance to stress corrosion.b. In improving dimensional stability after machining.c. In lowering the peak residual stresses.

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d. In softening the metal.17. Stray arc strikes are undesirable since they:

a. Leave a poor surface finish.b. Cause weld metal cracking.c. Reduce corrosion resistance.d. Cause local hardening and cracking in the parent material.

18. Cold cracking is most likely to occur in a weldment if:a. The rate of cooling is too fast.b. The rate of cooling is too slow.c. It lacks ductility at high temperatures.d. Impurities are present at its grain boundaries.

19. Chromium, when added to steel as an alloying element, has the effect of making the alloymore:a. Ductile.b. Plastic.c. Hardenable.d. Malleable.

20. When depositing weld metal, fusion will take place at the sides of the joint resulting in anadmixture between weld metal and parent metal. This alloying effect is known as:a. Diffusion.b. Absorption.c. Dilution.d. Migration.

21. Percentage elongation of a metal undergoing a tensile test is a measure of:a. Elasticity.b. Plasticity.c. Ductility.d. Malleability.

22. When a longitudinal load is put on a lap joint, the stress set up is normally:a. Shear stress.b. Tensile stress.c. Compressive stress.d. Residual stress.

23. When a metal is subjected to a fluctuating load, a condition of cyclic stressing can be set up,which eventually can result in structural breakdown known as:a. Tensile failure.b. Fatigue failure.c. ):ield failure.d. Shear failure.

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13124. What happens to the mechanical properties of steel if the carbon content is increased to

0.5%?a. The material becomes softer.b. Malleability is increased.c. The tensile strength is increased.d. Ductility is increased.

25. Columnar growth takes place when a metal is:a. Cold.b. Losing heat.c. Being heated.d. Being rolled.

26. If a low carbon steel pipe has to carry a liquid, care must be taken when making the buttwelds to ensure penetration is not excessive because it:a. Reduces the flow rate of the liquid.b. May increase the rate of corrosion.c. Can contaminate the liquid.d. May cause excessive pipe wear.

27. When a steel suffers hot shortness, it is mostly due to the presence of:a. Sulphur.b. Phosphorous.c. Silicon.d. Manganese.

28. When a steel is heated to above its upper critical temperature, the structure produced is:a. Martensite.b. Austenite.c. Pearlite.d. Sorbite.

29. The type of crystal normally found in a single run arc weld in the as welded condition is:a. Equi-axed.b. Polycrystalline.c. Dendritic.d. Columnar.

30. The first sub-zone in the heat affected zone of the parent metal nearest the weld deposit willconsist of:a. Large crystal grains.b. Small crystal grains.c. Elongated crystal grains.d. Distorted crystal grains.

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MULTICHOICE PAPER SEVEN

1. Pipe welding codes are set up by:a. Welding operators.b. State governments.c. Associations, societies, insurance companies, manufacturers and the military.d. Construction unions.

2. The different grain structure between the weld deposit and the base metal can be determinedby:a. A face bend test.b. A root bend test.c. A hardness test.d. An etching test.

3. A root bend test is used to test the amount of weld:a. Ductility.b. Elongation.c. Hardness.d. Penetration.

4. What would be observed if a fillet weld were sectioned and macro-etched?a. The grain of the other beads is coarser than the [mal bead.b. The penetration and fusion into the root is very deep.c. Each bead appears to be distinctly separated from the adjoining beads.d. The grain structure remains the same in all passes.

5. What is the most common cause of failure in root bend tests?a. Too high a current setting.b. Too long a pause in the down cycle of the weave.c. Lack of fusion and penetration.d. Too high a travel speed.

6. The purpose of a nick break specimen is to provide a test for:a. Tensile strength an9 fracture appearance.b. Ductility and fracture appearance.c. Elongation and fracture appearance.d. Soundness and fracture appearance.

7. Which organisation publishes the most commonly used code for boiler and pressure vesselwelding?a. American Welding Society.b. American Society ofMechanical Engineers.c. American Petroleum Institute.d. American National Standards Institute.

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8. A low hydrogen electrode, according to BS 639, would contain:a. No hydrogen.b. Less than 15 ml of hydrogen per 100 grams of deposited weld metal.c. Between 15 ml and 25 ml of hydrogen per 100 grams of deposited weld metal.d. Less than 25 ml of hydrogen per 100 grams of deposited weld metal.

9. The second run in a three run butt weld using the stovepipe technique is known as the:a. Filling run.b. Hot pass.c. Intermediate run.d. Sealing run.

10. You could determine that an electrode is cellulosic by its:a. BS 639 coding.b. Colour.c. Trade name.d. BS 499 coding.

11. Which type of electrode coating gives the most voluminous gas shield?a. Rutile.b. Basic.c. Oxidising.d. Cellulosic.

12. Which of the following steels is likely to be more susceptible to hydrogen cracking?a. Carbon equivalent of less than 0.25 %.b. Carbon equivalent of 0.35%.c. Carbon equivalent of 0.38%.d. Carbon equivalent of 0.43%.

13. Preheating and interpass heating are used primarily for:a. Aiding fusion.b. Reducing hydrogen content of weld preparation prior to welding.c. Ensure a fine grain size.d. Slow down the cooling rate after welding.

14. Submerged arc welds made with re-cycled flux are liable to:a. Porosity.b. Course grain size.c. Undercut.d. Incomplete penetration.

15. Incomplete penetration in a single 'V' butt joint could be caused by:a. Too large a root gap.b. Too small a root gap.c. Too high a heat input.d. Too small a root face.

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16. In submerged arc welding, which of the following width to depth ratios would be likely toresult in solidification cracking?a. 1 : 3.b. 3 : 1.c. 2: 1.d. 1 : 1.

17. You are responsible for controlling welding on site. A large incidence ofporosity has beenreported in recent welding. Would you investigate?a. The electrode type.b. Power source.c. Electrode storage.d. Day temperature.

18. The main reason why all adhering scale should be removed when the pipe end preparation ismade by oxy-gas cutting is?a. Oxidisation of the weld metal is minimised.b. The speed ofwelding is increased.c. Pipe bore alignment is made easier.d. Reduction of the weld deposit is prevented.

19. When manual metal arc welding low carbon steel, which electrode covering will give thegreatest degree of penetration?a. Iron powder.b. Rutile.c. Cellulosic.d. Low hydrogen.

20. When tungsten arc gas shielded welding stainless steel, which one of the following shouldbe used?a. Alternator.b. A. C. transformer.c. D. C. generator.d. Constant potential rectifier.

21. Which gas shroud should be used when tungsten arc gas shielded welding aluminium alloys?a. Nitrogen.b. Carbon dioxide.c. Argon/carbon dioxide mixture.d. Argon.

22. The most common type of defect found in a structure when it is undergoing service is:a. Fatigue cracking.b. Crystallisation.c. Weld decay.d. Stress fracture.

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23. In the examination of a welded aluminium joint, macro etching may reveal:a. Lack of inter-run penetration.b. Carbon pick-up.c. Weld decay.d. Micro cracks.

24. MMA welds made with damaged electrode coatings are subject to:a. Porosity.b. Undercut.c. Excessive penetration.d. Excessive bead height.

25. Which physical test is more likely to reveal HAZ embrittlement?a. Transverse tensile.b. All weld tensile.c. Root bend.d. Charpy impact.

26. Which of the following destructive tests is not normally required for welder approval?a. Bend tests.b. Macro examination.c. Impact tests.d. Fracture tests.

27. Too large a diameter offiller rod should not be used to make a welded joint because:a. Excess reinforcement profile will be difficult to obtain.b. The included bevel angle will have to be reduced.c. Root fusion may be difficult to obtain.d. The gap setting will have to be changed.

28. Ifpipe bores are not matched correctly it can result in:a. Lack of root penetration.b. Incorrect gap setting.c. Excessive root faces.d. Overheating during welding.

29. A correctly made tack weld should slope from the middle to the ends in order to:a. Aid better penetration at the join-up.b. Prevent porosity at the join-up.c. Reduce the electrode size required.d. Reduce the overall consumable consumption.

30. Two low carbon steel pipes, 150mm diameter and 6mm wall thickness, are to be butt weldedusing the TIG process. To ensure a full strength joint, which of the following preps is mostsuitable?a. Open single bevel.b. Open single Vee.c. Open square preparation.d. Closed square preparation.

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PROPERTIES OF MATERIALS

1. The ability of a material to withstand a load pulling it apart is called its _ __

2. The ability of a material to be stretched out without breaking is called _

3. An Izod impact machine is used to give indication of the of a material.

4. The ability to withstand indentation is called _

5. Lack of ductility is called _

6. The property of a metal to return to its original shape is called _

7. Increase in carbon content causes an in strength and hardness.

8. When carbon percentage increases, there is a decrease in _

9. Low carbon steel contains less than carbon.---

10. Low ductility in a weld metal could result in _

11. Alloying is used to mechanical and physical properties of a steel.

12. Sulphur and phosphorus are not alloying elements; they are _

13. Alloying allows designers to use sections and still have the same strength.

14. An alloy that contains a high percentage of chromium and nickel would have resistanceto _

15. Quenching a carbon or low alloy steel will result in an in hardness and a--- ---in ductility.

16. The hard constituent that results when steel is quenched is called _

17. The tough laminated structure that is formed on slow cooling of ferrite and iron carbide(cementite) is called---

18. The amount of martensite formed depends on the speed of and the percentageof---

19. After quenching, the structure may be improved by reheating to 200-300°C. This is called

20. Small percentages of chromium will increase the strength and "while a smallpercentage of nickel will increase _

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137ANSWERS

PAPER ONE1. d 2. d 3. b 4. c 5. c 6. b 7. c8. a 9. c 10. a 11. d 12. a 13. b 14. b15. c 16. a 17. a 18. b 19. a 20. d 21. c22. a 23. d 24. c 25. d 26. d 27. c 28. b29. b 30. b

PAPER TWO1. b 2. a 3. b 4. d 5. c 6. c 7. d8. d 9. d 10. d 11. b 12. b 13. c 14. b15. c 16. b 17. b 18. c 19. b 20. c 21. b22. d 23. c 24. b 25. c 26. c 27. b 28. b29. d 30. b

PAPER THREE1. d 2. a 3. d 4. d 5. d 6. c 7. b8. d 9. d 10. d 11. d 12. d 13. b 14. d15. d 16. d 17. b 18. d 19. a 20. d 21. d22. d 23. d 24. c 25. d 26. d 27. d 28. b29. c 30. b

PAPER FOUR1. c 2. b 3. c 4. b 5. a 6. a 7. b8. b 9. a 10. a 11. b 12. d 13. d 14. c15. c 16. b 17. c 18. a 19. c 20. a 21. c22. c 23. d 24. b 25. c 26. c 27. a 28. d29. a 30. b

PAPERFNE1. a 2. b 3. c 4. d 5. b 6. d 7. b8. c 9. d 10. d 11. d 12. d 13. d 14. d15. a 16. a 17. d 18. d 19. d 20. c 21. b22. a 23. b 24. b 25. a 26. b 27. b28. a 29. b 30. b

PAPER SIX1. b 2. c 3. b 4. d 5. c 6. b 7. d8. c 9. b 10. d 11. d 12. c 13. c 14. c15. a 16. b 17. d 18. a 19. c 20. c 21. c22. a 23. b 24. c 25. b 26. a 27. a 28.' b29. d 30. aPAPER SEVEN

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1. c 2. d 3. a 4. c 5. c 6. d 7. b8. b 9. b 10. a 11. d 12. d 13. b 14. a15. b 16. a 17. c 18. a 19. c 20. c 21. d22. a 23. a 24. a 25. d 26. c 27. c 28. a29. a 30. b

PROPERTIES OF MATERIALS

1. Tensile Strength.5.Brittleness.9.0.2%13. Smaller/Thinner.16.Martensite.19.Tempering.

2. Ductility. 3. Toughness.6. Elasticity. 7. Increase.10. Cracking. 11. Increase.14. Corrosion. 15.Increase Decrease17.Pearlite. 18. Cooling Carbon.20. Hardness....Toughness.

4. Hardness.8. Ductility.12. Impurities.

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