Welding Present a Ion 1

8/3/2019 Welding Present a Ion 1

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Welding Inspection

Presenter

Steve CaveSenior P & EW Instructor


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WELDING PRESENTATIONBy

Steve Cave

The Certified Welding Inspector (CWI) plays an important roleduring any welded construction activities ensuring the requiredspecifications and standards are followed. Due to the numerousmaterials and processes associated with metal joining (welding)

THIS PRESENTATION SHALL SHOW ONLY THE BASICWELDING PROCESSES AND EXAMINATION METHODS (NDE).National and International Codes and Specifications along withmeasuring devices are the Inspectors tools. Hopefully the following

presentation shall give an insight into basic welding inspection.


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How To Prevent WeldFailure


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Weld Failures

Today welding is the most common method used for joining

steel fabrications largely because of the speed at which jointscan be made and the reliability of these joints in service.

However because most welding operations are now relatively

simple to perform it is all too easy to forget the complexity of

the chemical and metallurgical actions that are taking placewhen the weld is being deposited. Therefore not surprisingly

welds occasionally fail.


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Overload

Before applying the various design formulas, the problem itself

must be analyzed and clearly stated. This is not alwaysobvious, and trying to solve the wrong problem can quickly

lead to insufficient design stresses. When a load is placed on a

member, stress and strain result. Stress is the internal

resistance to the applied force. Strain is the amount of "give or

deformation caused by the stress, such as deflection inbending, elongation in tension, contraction in compression,

and angular twist in torsion.


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Overload

For example of this is a lifting lug on a pressure vessel. If thevessel is lifted by a spreader beam the loading condition on

the lug consists of a simple vertical force putting the

attachment welds either in tension or shear. However if the

vessel is lifted with a rope sling the loading condition

becomes more complex because there is now a horizontal

component of the force to consider as well a the vertical one,

which effectively increases the loading on the welds.


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Joint Design

A welded joint should be designed such that the welder can

easily manipulate the electrode to ensure good fusion,

particularly in the root of the joint. The profile of each run

should be roughly as wide as it is deep; wide shallow weld

beads and particularly deep narrow beads are both ideal

candidates for hot cracking.


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Hot CrackingA good example of this type of failure is on the weld used to

secure the small plug in the mandrill hole of a spun dished

head on a pressure vessel, a weld that many people do nottake seriously because of its size. As the weld cools it

contracts causing the plug to move , if the weld at the other

side of the plug is still solidifying it could easily fail. This is

because of the very high contraction stresses generated by

the plug as the weld starts to solidify.


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Bad Welding MethodsIt is very important when carrying out any welding to ensure

that it is done correctly. Consideration has to be given to all

aspects of the process and also the environment. Oftenwelding has to be carried out under site conditions, the

welding is often carried out in situation so that small general

purpose electrodes are used resulting in low weld heat input

which when combined with no preheat gives very rapid heat

dissipation Which can create a hard micro structureparticularly in the location of the heat affected zone.


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Bad Welding MethodsThis along with high levels of residual stress will create the

ideal condition for hydrogen induced cracking, which although

normally associated with high strength steels can occur in lowcarbon steels if the conditions are right. The resulting crack

may not occur immediately the weld cools down but some time

afterward, therefore if this type of failure is expected non

destructive examination should be delayed by at least 48

hours after welding.


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Metallurgical failureMaterials that are to be welded have to tolerate severe

thermal transients created by the welding process without

suffering deterioration of their mechanical properties oradverse phase changes. The metallurgical composition or

temper conditions of certain types of metal may make them

unsuitable to weld or may require special controls to be

imposed during the welding operation. For example some

steels that are easy to machine may contain high levels ofsulphur that may result in cracking of any attaching weld.

Therefore this type of material should not be used on load

bearing fabricated items such as the eye bolts that are often

found holding down man way covers on pressure vessels.


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Weld DefectsThey can usually be attributed to the welders inability to set up

and manipulate the welding equipment; although bad joint

design and faulty welding equipment can also be responsible.The most significant defects are cracks and those that

resemble cracks such as lack of fusion, cold overlap etc. This

is because of the risk that the crack may become unstable and

propagate when loaded causing a dramatic failure often by

brittle fracture


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Weld Defects

Porosity seldom causes weld failure in multi-run welds

however it is a sign that something has gone wrong withwelding operation and can often be caused by other defects

that may not have been detected such as lack of side wall

fusion. Weld profile can also cause failure, if the weld size is

too small because the joint is underfilled with weld then its

load carrying capability will be reduced, if the joint containsexcessive weld metal this can create a notch effect which

can lead to failure by fatigue if the loading condition

fluctuates.


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ConclusionTo minimize these problems the following points should be

considered

1. Design of the weld based on the loading condition(s) the joint will carry

2

. Accessibility to enable ease of welding

3

. Control of distortion

4

. Careful consideration of the welding environment

5

. Matching welding process with materials

6

.

A factor of safety applied to the design stress of the weld which should be based on

the consequence of weld failure and the level of non destructive testing that is to be carried

out.


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Welding Inspection

Duties of a Welding Inspector


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Duties Prior to Welding

Obtain all relevant documentation Relevant specifications.

Relevant procedures.

Copies of welders test test certificates. Copies of drawings.


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Duties Prior to Welding Obtain all relevant documentation

Ensure welder qualification. Correct material type condition etc.

Correct equipment with certificates.

Correct consumables type condition,size.

Correct pre heat.


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Duties Prior to Welding

Assess / measure fit up

Root face. Bevel angle.

Root gap.

Alignment. Joint cleanliness.

Ensure no undue stress is applied to the

joint.


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Duties During welding Check root internally.

Ch

eck all back gouged welds.


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Duties After welding Ensure welds are post cleaned.

Visual inspection of welds for defects.

Visually check for arc strikes.

Check weld contour and weld width.

Ensure joint is covered to retard cooling

rate. Ensure monitor post weld heat

treatment.


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Duties After welding Report on weld.

Ch

eck NDT

reports wh

ere needed.


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Welding Processes


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Shielded Metal Arc Welding


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Gas Metal Arc Welding


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Tungsten Arc Welding


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Submerged Arc Welding


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Problems Associated WithIncorrect Weld Joint Fit Up


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Root Problems

b) burnthrough

Gap size too large:

a) excess penetration

c) shrinkage grooves d) gas entrapment


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Root ProblemsGap size too small:

1) incomplete penetration

2) incomplete root fusion 3) incomplete side wall fusion

4) slag inclusions 5) root concavity


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Root ProblemsRoot face too large:

a) incomplete root penetrationb

) incomplete root fusion


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Root ProblemsRoot face too small:

1) excessive penetration 2) burnthrough

3) root concavity 4) root undercut


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Included Angle Too large

a) excess penetration b) incomplete filled groove


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Fillet WeldsGap size too large:

1) reduced root penetration 2) slag inclusions

3) gas inclusions

4) reduced verticalleg length size

5) cracking


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Included Angle Too Small1) incomplete root penetration 2) incomplete interun fusion

3) incomplete root fusion 4) incomplete sidewall fusion

5) excessive cap6) poor toe blend

7) slag inclusions


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Visual Inspection of Welds


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Butt Weld Sizea) excess weld metal height

b) root penetration

c) weld width

d) root bead width


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Fillet welds (size)Consider:

a) z minimum (and maximum) leg lengthsize

b) a minimum design throatthickness


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Shape (Butt Welds)

Ideally, (a) is the most desirable butvery often it may be difficult toachieve. Because of this, one shouldassess the excess weld height inconjunction with the weld profile andperhaps the toe blending.

Consider:


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Shape (Fillet Welds)

In normal practice, (a) is the most desirablebut, again, in many instances it is difficult toachieve. Acceptance levels, therefore, allow

tolerances on weld shape.

Consider:


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Toe Blend (Butt Welds)

Depending on the service conditions

of the product, the toe blend may beof greater importance than the sizeand shape of the weld. A poor toeblend may reduce service life by aconsiderable margin if the product isunder a cyclic load.

For butt welds, consider:

In normal practice, (a) is the mostdesirable but, again, in manyinstances it is difficult to achieve.

Acceptance levels, therefore, allowtolerances on weld shape.


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Toe Blend (Fillet Welds)For fillet welds, consider:

In normal practice, (a) is the mostdesirable but, again, in manyinstances it is difficult to achieve.

Acceptance levels, therefore,allow tolerances on weld shape.


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Root Defects

Incomplete root penetration

Failure of weld metal to extend into the root of a joint

Lack of root fusionLack of union at the root of a joint

Excess penetration beadExcess weld metal protruding through the root ofa fusion weld made from one side only


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Root DefectsRoot concavity(suck-back; underwashing - non-standard terms)

A shallow groove which may occur in the root of a

butt weld, but full fusion is evident

Shrinkage grooveA shallow groove caused by contraction in the metalalong each side of a penetration bead or along theweld centreline

Burnthrough(melt through)

A localised collapse of the molten pool due toexcessive penetration, resulting in a hole in theweld run


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Contour Defects

Incompletely filled grooveA continuous or intermittent channelin the surface of a weld, runningalong its length, due to insufficientweld metal. The channel may bealong the centre or along one or

both edges of the weld


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Bulbous Contour

Bulbous contourA non-standard term used todescribe poor appearance


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Unequal Legs

Unequal legs

(non standard term)Variation of leg length on a fillet weldNote: Unequal leg lengths may bespecified as part of the design - in whichcase they are not imperfections


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Undercut

UndercutAn irregular groove at a toe of a run in theparent metal or in previously depositedweld metalThe inspector must determine if theundercut is continuous or intermittent, or

sharp or smooth


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Overlap

OverlapAn imperfection at the toe or root of aweld caused by metal flowing on to thesurface of the parent metal without fusingto it


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Crater Pipe

Crater pipeA depression due to shrinkage at the end of arun where the source ofheat was removed.Crater pipes may also lead to micro-cracking


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Surface CracksCrackA linear discontinuity produced by fractureCracks may be ...

a) ... longitudinal, in the weld metal, i.e. centreline

b) ... longitudinal, in the parent metal or heat affected zone

c) ... transverse

d) Crater crack(star cracking)


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Arc Strike

Stray flash/arc burn/arc strike(stray arcing)1. The damage on the parent materialresulting from the accidental striking of anarc away from the weld2. The accidental striking of an arc away

from the weldNote that the same term is used for both

the action and the result


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Weld Width

For butt welds and fillet welds,consider:

Weld width and consistency of weld width


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Weld Defects


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Lack of Side Wall Fusion


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Lack of Inter Run Fusion


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Porosity


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Slag Inclusions


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Incomplete Root Fusion

/Penetration


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Overlap


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Excess Weld Metal


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Excess Penetration


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Root Concavity


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Slag Inclusion


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Surface Breaking Porosity


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Cracking


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Arc Strikes


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Using Welding Inspection Tools


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Weld Profile Gauge

Measuring

Fillet Welds

MeasuringBevel Angle

Measuring CapReinforcement/Misalignment

Scale ininches or mm


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Hi Lo Gage

Measures Hi LoPipe ThicknessBevel Angle


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Using the tools


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ThroatThickness (WPG)Fillet Weld


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Cap Reinforcement (WPG)

Measuringthe height

of the cap


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Bevel Angle (WPG)

Measuringthe pipebevelangle

Readout


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Misalignment (WPG)Shownon scale


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Non Destructive Testing


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Visual Inspection

Visual inspection is the one NDT method

used extensively to evaluate the condition orthe quality of a weld or component. It is

easily carried out, inexpensive and Visualinspection is the one NDT method usedextensively to evaluate the condition or the

quality of a weld or component. It is easilycarried out, inexpensive and usually doesn'trequire special equipment.


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Radiography

X-rays are produced by high voltage x raymachines whereas gamma rays areproduced from radioactive isotopes such asIridium 192 The x-ray or gamma rays areplaced close to the material to bc inspectedand they pass through the material and are

then captured on film This film is thenprocessed and the image is obtained as aseries of gray shades between black andwhite.


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PenetrantTesting InspectionLiquid penetration inspection is a method that is usedto reveal surface breaking flaws by bleed out of a

colored or fluorescent dye from the flaw.


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Ultrasonic TestingUltrasonic inspection uses sound waves of shortwavelength and high frequency to detect flaws or

measure material thickness. It is used on aircraft,the power stations generating plant, or welds in

pressure vessels at an oil refinery or paper mill.

Welding Present a Ion 1

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