Welding Presentation

What is welding : Welding is a material joining process in which a localized coalescence of metals or non metals produced either by heating the materials to suitable temperature with or without the application of pressure or by the application of pressure alone.

This can either with or without the addition of filler metal.SourceElectrode (-) Work (+)

Applicable codes and standards:

ASME code for Process Piping:ASME B31.3ASME code for NDT:ASME Sec.VASME code for Design and Constrn. of Pressure Vessels:ASME Sec.VIIIASME code for welding and brazing qualification:ASME Sec.IXASME code for material specification, welding rodselectrodes and filler metals: ASME Sec.II, Prt.CAPI code for Const. of welded oil storage tanks:API 650API code for Const. of large welded low pr. storage tanks:API 620

CLASSIFICATION OF WELDING PROCESSESBased on :Energy Transfer -

1. Electrical to heat Ex: Arc, Resistance2. Mechanical to heat Ex: Friction 3. Chemical to heat Ex: Gas, Explosion4. Light to Heat Ex: LASER- EBW5. Sound to heat Ex: Ultrasonic Type of welding -

1. Fusion welding Ex: Arc, Gas2. Solid state welding Ex: FrictionMode of welding -

1. Manual welding2. Semi Automatic welding3. Automatic weldingWelding Process -

1. Without addition of weldment Ex: Ultrasonic, ERW, Plasma2. With addition of weldment Ex: Arc- Normal polarity- Reverse polarity

Various welding processes : By GasGTAWMIGMAGPLASMABy FluxSMAW(MMAW)SAWShielded Metal Arc Welding

SMAW: Shielded metal arc welding SAW : Submerged arc welding GTAW: Gas Tungsten arc welding MIG : Metal inert gas welding MAG : Metal active gas welding ( also called CO2 welding )

Gas Tungsten arc welding (GTAW) :Description of the Process

GTAW is an arc welding process that uses an arc between a tungsten electrode and the work piece. A non reactive gas sustains the arc and protects the molten metal from atmospheric contamination. The non reactive gas is normally argon or nitrogen. Application

Widely used in the fabricating industries for the construction and repair almost all metals. It is especially used for aluminum and magnesium,, The process is flexible and safe to use. Good ventilation and protective clothing is essential.

Shielded metal arc welding (SMAW) :Description of the ProcessSMAW is an arc welding process that uses a arc between a electrode and the work piece. The arc melts the electrode and the work piece. The flux on the electrode mixes with the impurities in the molten pool and floats on the top of the weld in the form of slag, which protects the joint from atmospheric contamination. This is the most commonly used process

Application

Widely used in the fabricating industries for the construction and repair of plain carbon and low alloy steels. Stainless steel, inconel, nickel and cast iron electrodes are also commonly used, The equipment is of initial low cost, and the process is flexible and safe to use. Good ventilation and protective clothing is essential.

1- Flat(1G)Welding positions : 3 - Vertical - UP(3G)3A - Vertical - DOWN1A- Horizontal fillet2- Horizontal (2G)4- Over head(4G)5 Pipe- Fixed - down hill(5G)5 A Pipe- Fixed - Up hill 6G((ALL POSITION WELD)450+ 50

Type of JointButt JointFillet JointSquare ButtSingle VDouble VSingle JDouble JCorner EdgeTee

Type of Joints :Butt joint : Corner joint : Corner joint : Edge joint : Tee joint :

Different types of grooves : Square grooveSingle J grooveSingle Bevel grooveSingle Vee grooveDouble Bevel grooveSingle U grooveDouble Vee grooveDouble U groove

37.5019.1 mm2 mm100>22.2 mmEdge preparation for Butt welding:Nominal Thickness ( t ) Edge preparation

t = < 3.5 mm Straight or slightly beveled angle t = 3.5 to 22.2 mmSingle V beveled edge (figure 1) t = > 22.2 mm Compound V beveled edge (figure 2) (37.50 upto 19.1mm 100 balance)figure 2figure 1

All welded branch connections shall be joined to the header by full penetration welds.

Branch reinforcement pad or segments there of shall be provide with minimum 3 mm drilled and tapped holes prior to fitting to the main pipe for leak detection, venting and testing facility.

Whenever possible pad should be made in one piece.

BRANCH CONNECTIONS:Full penetrationPartial penetration

Material Composition Of Some Basic Materials.

ALLOY

CARBON

MANGANESE

CHROMIUM

NICKEL

MOLYBDENUM

OTHERS

SA515

0.28-0.33

0.98

0.13-0.45 Si

**

SA516

0.24-0.29

0.79-1.3

0.13-0.45 Si

**

SA106

0.25

0.27-0.93

0.4

0.4

0.15

**

SA333 Gr 1

0.3

0.4-1.06

**

SA333 Gr 3

0.19

.31-.64

3.18-3.82

0.18-0.37 Si

**

SA335 P1

0.1-0.2

0.3-0.8

0.44-0.65

**

SA335 P11

0.05-0.15

0.3-0.6

1.0-1.5

0.44-0.65

**

SA335 P22

0.05-0.15

0.3-0.6

1.9-2.6

0.87-1.13

**

SS304

0.08

2.0

18-20

8-11

**

SS304L

0.04

2.0

18.0-20.0

8.0-11.0

**

SS316

0.08

2.0

16-18

11-14

2.0-3.0

**

SS316L

0.035

2.0

16-18

11-14

2.0-3.0

**

SS321

0.08

18

10

Ti

**

SS347

0.08

2.0

17.0-20.0

9.0-13.0

Cb

**.

Incoloy600

0.15

1.0

14.0-17.0

72.0

0.5 Si. , 0.5 Cu.

0.015 S.

Incoloy800

0.1

1.5

19-23

30-35

1.0 Si. ,0.75 Cu.

0.15-0.60 Al

0.15-0.60 Ti

0.015 S

Manurite 36XM

0.4-0.6

2.0

23-27

32-35

1.5 Si. ,1.0Nb.

Addl. Ti.

2 RE 69

0.020

25.0

22.0

2.1

Nitrogen

HK-40

0.35-0.45

1.5

23-27

19-22

2.0 Si

SS316L MOD.

0.030

2.0

17.0min.

13.0min.

2.0-3.0

P : 0.040

S : 0.030

** RESIDUAL MATERIALS

SULFUR

:0.035 MAX.

PHOSPHOROUS :0.035 MAX.

Welding Machines:WELDING TRANSFORMERS: (AC)It operates with AC power supply and has no rotating parts.No rotating parts.Low machine cost.Non ferrous can not be welded.Arc blow problem does not arise.Arc is never stable.

WELDING GENERATOR: (DC)It gives DC for welding and it is run by AC.It has rotating parts.Non ferrous can be welded.Arc blow is severe Arc is more stable

Electrode - ve -Straight Polarity ( 2/3rd of heat at electrode )Electrode + ve-Reverse Polarity ( 2/3rd of heat at work piece)

yTypical AC welding circuit

Welding consumables - selectionThe term welding consumable refers to the filler metals employed in different forms in various welding processes.Metallurgical :

Base materialsMechanical propertiesChemical compositionCorrosion requirementsPhysical propertiesSoundness & Structural stabilityHeat treatmentMechanical :

Thickness of materialDimension & No of componentsProcess :

Available forms of consumablesAdaptability for the jobWelding process selectedThe selection of welding electrode is to be done taking following factors in to consideration.

ELECTRODE SELECTION

PRIVATEBASE METAL

CS

P1

P11

P22

304

304L

310

316

316L

321

347

CS

FILLER.WIRE

70S2

70SD2

80S2

90S2

309

309L

309

309Mo

309Mo

310

310

ELECTRODE

7018

7018-A1

8018

9018

309

309L

309

309Mo

309L

310

310

P1

FILLER.WIRE

70SD2

70SD2

80S2

90S2

309

309L

309

309Mo

309Mo

310

310

ELECTRODE

7018-A1

7018-A1

8018

9018

309

309L

309

309Mo

309L

310

310

P11

FILLER.WIRE

80S2

80S2

80S2

90S2

309

309L

309

309Mo

309Mo

310

310

ELECTRODE

8018

8018

8018

9018

309

309L

309

309Mo

309L

310

310

P22

FILLER.WIRE

90S2

90S2

90S2

90S2

309

309L

309

309Mo

309Mo

310

310

ELECTRODE

9018

9018

9018

9018

309

309L

309

309Mo

309L

310

310

304

FILLER.WIRE

309

309

309

309

308

308L

310

316

316L

347

347

ELECTRODE

309

309

309

309

308

308L

310

309Mo

316L

347

347

304L

FILLER.WIRE

309L

309L

309L

309L

308L

308L

310

316

316L

347

347

ELECTRODE

309L

309L

309L

309L

308L

308L

310

316

316L

347

347

316

FILLER.WIRE

309Mo

309Mo

309Mo

309Mo

316

316L

310

316

316L

347

347

ELECTRODE

309Mo

309Mo

309Mo

309Mo

316

316L

310

316

316L

347

347

316L

FILLER.WIRE

309Mo

309Mo

309Mo

309Mo

316L

316L

310

316L

316L

347

347

ELECTRODE

309Mo

309Mo

309Mo

309Mo

316L

316L

310

316L

316L

347

347

321

FILLER.WIRE

309

309

309

309

347

347

310

347

347

347

347

ELECTRODE

309

309

309

309

347

347

310

347

347

347

347

347

FILLER.WIRE

309

309

309

309

347

347

310

347

347

347

347

ELECTRODE

309

309

309

309

347

347

310

347

347

347

347

Electrode Classification - Mild steel & Low Alloy Steel

Ist - 2 or (3) digits - Tensile Strength in Psi3rd - Position - 1- All Position 2- Flat and horizontal fillet.Last digit - Usability / Coating

E XX10-DCEP , Deep penetration, cellulose - Sodium 0-10 % Fe powderE XXX1-AC/DCEP Deep penetration, cellulose - Potassium0 Fe E XX02-AC/DCEN Medium penetration, Rutile - Sodium 0-10 % Fe powderE XXX3-AC/DC Light penetration, Rutile- Pot 0-10 % Fe powderE XXX4 -AC/DC Light penetration, Rutile- Fe powder 25-40% Fe powderE XXX5 -DCEP Medium penetration Low Hydrogen- Sodium 0 Fe E XXX6 -AC/DCEP Medium penetration, Low Hydrogen-Potassium0 Fe E XXX8 -AC/DC Medium penetration, Low Hydrogen-Fe Powder 25-40% Fe powderE XX20 -AC/DC Light penetration Rutile Fe powder50 % Fe powderE XX27 -AC/DC Medium penetration, Low Hydrogen-Fe Powder 50% Fe powderE XX28 -AC/DCEP Medium penetration, Low Hydrogen-Fe Powder 50% Fe powder

When the 4th or 5th digit is 0 the type of coating and current are determined by the 3rd digit.

Eg: E - 6010 - Cellulose - Na Coating and DCEP E - 7018 - Low Hydrogen - Fe Powder coating AC/DC

FUNCTIONS OF FLUX

-Provides a protective atmosphere-Provides slag to protect molten metal.-Stabilizes the arc-Adds alloying elements to the weld metal-Reduces spatter of weld metal-Increases deposition efficiency-Removes oxides and impurities-Influences the shape of the bead-Influences the depth of arc penetration-Slows down the cooling rate of the weld

REQUIREMENTS OF GOOD FLUX

A flux should easily melt and should have a MP lower than parent and filler metal.

A flux should readily react with metallic oxides and form a fusible slag, and the blanket of slag should protect the metal from atmospheric oxidation and should be easy to remove upon completion of welding.

A flux should cause no corrosion action on the finished weld and its specific gravity should be lower than that of metal to enable the slag to float on the surface of the molten pool.

Electrode Classification - Stainless Steel

AWS ClassificationShort arc & Stringer bead for SS & Ni alloysSS Electrodes

Whether an electrode will operate on AC or DC or both depends on the characteristics of the coating.Eg: 308 - 15 (18 Cr 8 Ni ) 15 indicates that the electrode coating is suitable for DC only 410-16 (12Cr) 16 Indicates that the electrode is suitable for use with AC or DCEP.

1st 3 digits indicate the composition of the electrode and the last 2 digits indicates the type of welding current to be used.

Alloying elements in SS electrode.Cr - Improves corrosion resistanceNi - Adds on to corrosion resistance, prevents hardening of weld and base material during cooling.Mn- Adds strength and reduces crackingMo- Increases corrosion resistance and high temperature resistance.DC Vs AC - DC is more satisfactory than AC Welding.

When welding with 50 Hz AC, half the time the current flows from electrode to the work, The other half from the work to the electrode. Each second, there are 100 moments when the current changes direction. When there is no flow of current. this stop and go nature of AC results in an unstable arc, more spatter and poor penetration. When the current is made to flow in one direction- from the work to the electrode - as in reverse polarity there are 4 advantages. The arc is more stable, less spatter, faster welding, and bead appearance is better.

Tungsten Arc welding electrodes:

AWS Classification Type Tip Colour1EWP Pure Tungsten Green

2EW Th - 1 1% Thorium addedYellow

3EW Th - 2 2% Thorium addedRed

4EW Zr 0.5% Zirconium addedBrown

Diameter - 0.5 to 6.4 mmLength - 76 to 610 mm

Addition of Zirconium or Thorium to Tungsten electrode produces arc that startsmore easily and is more stable. By this electrode life increases and the arc has a tendency to concentrate in the weld pool.

Classification of weld joint discontinuities :Welding process or Procedure related :

1. Misalignment2. Undercut3. Concavity or Convexity. 4. Burn-through5. Incomplete penetration6. Lack of fusion7. Shrinkage8. Arc strikes9. Slag inclusions10.Tungsten inclusions11.Spatter12. Porosity13. Excess penetration / OverlapMetallurgical related :

1. Cracks or fissuresa. Hot cracksb. Cold or delayed cracksc. Reheat, Stress-relief crackingd. Lamellar tearinge. Hydrogen induced cracking

Porosity is the presence of gas pockets or voids caused by the entrapment of gases evolved during weld solidification. They are usually in spherical shape, elongated tubular gas pockets are termed as worm holes or piping. Large isolated gas pockets are referred as blowholes and they are partially filled with slag.

Lack of penetration involves incomplete penetration of the weld through the thickness of the joint, it applies to the initial weld pass or passes made from one or both sides of a joint. In single weld joints such as butt joints in pipe lack of penetration is below the root weld representing a severe surface defect and it acts as surface notch, which acts as stress raiser resulting failure causing mechanical or thermal fatigue or stress corrosion. In double welded joints it may occur within the wall thickness as a buried defect.

LACK OF PENETRATIONPOROSITY

LACK OF PENETRATION

LACK OF PENETRATION

Incomplete fusion involves lack of complete melting and coalescence (fusion) of some portion of metal in a weld joint. It occurs in between the weld beads or between weld and base metal. Under cut represents an intermittent or continuos groove or channel melted into the base metal adjacent to the toe or surface of a weld and left unfilled by weld metal.Under cut significantly reduces the fatigue strength. In service conditions which involves mechanical and thermal fatigue, undercut represents a sharp notch and results failure of the joint. LACK OF FUSIONUNDER CUT

UNDER CUT

TUNGSTEN INCLUSIONS

The particles that are deposited in the weld metal from a tungsten electrode used in the process of inert gas- tungsten-arc welding (GTAW).Tungsten inclusions are not considered to be harmful unless their size and number becomes excessive, service and test results does not shown any fatigue cracks due to the presence of tungsten inclusions.MISALIGNMENT : It represents mismatch of both the surfaces of the joint across the weld root.

CAUSES : Improper weld fit-up, Ovality, Difference in ID.

BURN THROUGH

It refers to a coalescence of weld metal beyond the root. The droplets formed due to burn through are called icicles.CAUSES: Non uniform root gap, high current.

SPATTERS

The fine droplets of a metal, which are ejected from the weld are called spatters.CAUSE:When globules of metal from electrode transferred from electrode to pool bridge, the air gap create a short circuiting condition and will result in globule explosion.EXCESS PENETRATION / OVERLAP :

An excess of weld metal which extends beyond the limits of fusion is called excess penetration. CAUSES : Improper welding technique and welding current.

ARC STRIKE :

A scratch on the base metal where a careless welder has momentarily touched the base metal with the welding electrode to start the arc is called an arc strike.

SLAG INCLUSION:

Oxides and other non metallic solids entrapped in the weld metal or between the weld metal and base metal are refereed to as slag inclusions.

CAUSE: Contamination of weld with slag. Improper cleaning of beads in between passes.SHRINKAGE / DESTORTION:

While welding, the adjacent surface are heated to a liquid state. During cooling, the liquefied area shrinks and move towards the direction of original heat application. This leads to distortion.

CAUSE: Improper welding sequence , non uniform heating of two members of the joint during welding.

WELDING OF STAINLESS STEELSFERRITIC GRADE: ( Eg. SS405, SS409, SS429):

These grades are very difficult to weld.

Subjected to grain growth when heated to 750 deg. C. leading to HAZ with large grains.

Welding in these grades of SS leads to increase in brittleness and deterioration of mechanical properties.

These can be avoided by low welding current and preheating the base metal to 200 deg.c and marinating inter-pass temp. through out the welding.

After each bead the base metal is allowed to cool to preheat temp.

After welding post heating also shall be carried out.

WELDING OF STAINLESS STEELSMARTENSITIC GRADE: ( Eg. SS403, SS410, SS414):

These grades are slightly better weldability than ferritic grades.

Hardens on air cooling from high temperature and develop shrinkage cracks.

Can be avoided by pre heating to 200 deg. C and marinating through the welding and annealing the weldment just after the welding before the weld cools.

Austenitic filler rods may be used where ducility and corrosion resistance are required.

WELDING OF STAINLESS STEELSAUSTENITIC GRADES: ( Eg. SS304, SS316, SS310, SS347):

These grades have better weldability.

Susceptible to Inter Granular Carbide precipitation.

Can be prevented by:

Heat treatment

Stabilized grades

Extra low carbon grades

INSPECTION OF WELDS - NDT

TESTING METHODS :

The method that can be used for non-destructive testing depends on the physical properties of the material. A thorough knowledge of each NDT method is required to ensure the correct selection of the appropriate method for each application. NDT is used typically for the following reasons:

accident prevention to reduce costs to improve product reliability to determine acceptance to give information on repair criteria.

In order to gain the information and obtain valid results, the following is required:

trained and qualified personnel a procedure for conducting the test a system for reporting results a standard to interpret the results.

The objective of good and effective testing programme is to detect defects as specified by the design based on fitness for purpose

The commonly used NDT methods are:

Visual Inspection Liquid Penetration Inspection Magnetic Particle Inspection Eddy Current Inspection Ultrasonic Inspection Radiography Acoustic Emission Thermography Metallography

WELDING PROCEDURE SPECIFICATION (WPS):

Purpose :

The purpose of welding procedure specification and procedure qualificationrecord is to determine that the weldment proposed for construction is capableof having the required properties for its intended application.

The welding procedure qualification is therefore, strictly to establish the metallurgical compatibility of the weldment through mechanical tests and not the skill of the welder or the welding operator.The WPS is a list of the following welding variables with the proper values of these entered accordingly.

Welding process, Base metal, Joint design, Filler metal, Position, Preheat/inter pass/post heat, electrical characteristics, post weld heat treatment, Shielding gas, and Techniques.

PROCEDURE QUALIFICATION RECORD (PQR):A procedure qualification record (PQR) is a record of welding data used to weld a test coupon. It also contains the test results of the tested specimens.

The purpose of WQT is to establish the ability of the welder to deposit sound metal.The welder qualification can be done according to the following codes :

1. Indian Boiler Regulations - IBR chapter VIII2. ASME Boiler and Pressure Vessel Code - Section IX3. DIN 85604. BS 4872WELDER QUALIFICATION TEST:

WELDING SAFETY

The risks involved in the various welding processes can be broadly classified under the following headings:- Electric shock Burns Fumes Radiations from the arc Slag removal

Leather aprons, welding helmets, overalls, boots, welding screens are available to prevent burns from welding and cutting to the operator. Slag Removal Chipping hammers, and safety goggles approved in accordance with the requirements of BS 1524; BS 2092, must always be used in the removal of welding slag. Slag should be allowed to cool before removal, as this will not only improve the mechanical properties of the weld but will decrease the chance of hot slag burning any clothing or materials.

PLASTIC PIPINGTypes of Plastics:Thermoplastic & Thermosetting

Thermoplastics: Can be repeatedly reformed by application of heat.

PVC: Poly vinyl chlorideCPVC:Chlorinated PVCPP; Poly propylenePVDF:Vinylidene fluoride

The thermoplastic piping systems are manufactured by extrusionor moulding operation. These usually do not contain reinforcing material.

Thermosetting resins:

Once cured cannot be changed again in shape.

Epoxy resinsPolyester resinsPhenolic resin

Thermosetting piping systems are manufactured in a laminate construction and employ reinforcing material such as woven fibreglass cloth, fibreglass strand, asbestos etc.

The ratio of resin to the reinforcing material is extremely important.

WELDING OF PLASTIC PIPING: Only same base material can be welded together. Can be carried out by two methods Heating element welding - Parallel faces Hot gas welding - Apperture angle of 60 deg.

Welding with heating element: Wedge shaped electric heating element is used. The welding temp. is dependent on material and wall thickness. Before each weld, temp. shall be checked with cryon. The surfaces of the pipes to be welded shall be heated to welding temp. by the element and when the temp. is reached, the heating element shall be removed and pipes shall be welded by pressing together. The final contact pressure shall be maintained until the weld seam has become cold. Sudden cooling is not permitted.

HEATING ELEMENT BUTT FUSIN WELDING

Hot Gas Welding: Electrically heated or gas heated welding equipment shall be used.The welding gases shall be free from oil and water.The gas pressure shall be 0.5 Bar(g).The welding rods shall be of 3 to 5 mm dia.The filler material shall be of same quality as base metal.Neither the base nor the filler be over heated.