wis5-imperfections-2006.ppt

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Copyright2006,TWILtdorld entre for Materials Joining Technology

CSWIP 3.1 Welding Inspection

TWI Training & ExaminationServices

Welding &Materials

Imperfect ions

Course Reference WIS 5

Course notes section reference 3, 6 & 16


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Welding Imperfect ions

All welds have imperfections

Imperfections are classed as defects when they are of a

type, or size, not allowed by the Acceptance Standard

A defect is an unacceptable imperfection

A weld imperfection may be allowed by one Acceptance

Standard but be classed as a defect by another Standard

and require removal/rectification


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Standards for Welding Imperfections

BSEN ISO 6520-1(1998) Welding and allied processesClassification of geometric

imperfections in metallic materials -

Part 1: Fusion welding

Imperfections are classified into 6 groups, namely:

1 Cracks

2 Cavities

3 Solid inclusions

4 Lack of fusion and penetration5 Imperfect shape and dimensions

6 Miscellaneous imperfections


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Standards for Welding Imperfections

EN ISO 5817 (2003) Welding - Fusion-welded joints in steel,nickel, titanium and their alloys (beam

welding excluded) - Quality levels for

imperfections

This main imperfections given in EN ISO 6520-1 are listed inEN ISO 5817 with acceptance criteria at 3 levels, namely

Level B (highest)

Level C (intermediate)

Level D (general)

This Standard is directly applicable to visual testing of welds

...(weld surfaces & m acro exam inat ion)


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Welding imperfect ions

classi f icat ion

Cracks


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Cracks

Cracks that may occur in welded materials arecaused generally by many factors and may beclassified by shape and position.

Note: Cracks are classed as Planar Defects.

Classified by Shape

Longitudinal

Transverse

Chevron

Lamellar Tear

Classified by Position

HAZ

Centerline

Crater

Fusion zone

Parent metal


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Longitudinal parent metal

Longitudinal weld metal

Lamellar tearing

Transverse weld metal

Cracks



Transverse crack Longitudinal crack

Cracks



Main Crack Types

Solidification Cracks

Hydrogen Induced Cracks Lamellar Tearing

Reheat cracks

Cracks



Solidification Cracking

Occurs during weld solidification process

Steels with high sulphur impurities content (low ductility at

elevated temperature)

Requires high tensile stress

Occur longitudinally down centre of weld

Cracks



Cracks

Hydrogen Induced Cold Cracking

Requires susceptible hard grain structure, stress, low

temperature and hydrogen

Hydrogen enters weld via welding arc mainly as result of

contaminated electrode or preparation

Hydrogen diffuses out into parent metal on cooling

Cracking developing most likely in HAZ


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orld entre for Materials Joining Technology

Cracks

Lamellar Tearing

Step like appearance

Occurs in parent material or HAZ

Only in rolled direction of the parent material

Associated with restrained joints subjected to through

thickness stresses on corners, tees and fillets

Requires high sulphur or non-metallic inclusions




Cracks

Re-Heat Cracking

Occurs mainly in HAZ of low alloy steels during post weld

heat treatment or service at elevated temperatures

Occurs in areas of high stress and existing defects

Prevented by toe grinding, elimination of poor profilematerial selection and controlled post weld heat treatment




Weld ing Imperfect ions Class i f icat ion

Cavities




Gas Cavit ies

Root piping

Cluster porosityGas pore

Blow holeHerringbone porosity

Gas pore 1.6mm

Causes:

Loss of gas shield

Damp electrodes

Contamination

Arc length too large

Damaged electrode flux

Moisture on parent material

Welding current too low




Root pip ing

Porosi ty

Gas Cavit ies




Cluster porosity Herringbone porosity

Gas Cavit ies


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Crater pipe

Weld crater

Crater Pipe


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Crater pipe is a shrinkage defect and not a gas defect, it has

the appearance of a gas pore in the weld crater

Causes:

Too fast a cooling

rate

Deoxidization

reactions and liquid

to solid volume

change

Contamination

Crater cracks

(Star cracks)

Crater pipe

Crater Pipe


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Solid Inclusions


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Sol id Inc lusions

Slag inclusions are defined as a non-metallic inclusion caused

by some welding processCauses:

Slag originates from

welding flux

MAG and TIG welding

process produce silicainclusions

Slag is caused by

inadequate cleaning

Other inclusions include

tungsten and copper

inclusions from the TIG

and MAG welding process

Slag inclusions

Parallel slag lines

Lack of sidewallfusion withassociated slag

Lack of interun

fusion + slag


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Elongated slag linesInterpass slag inclusions

Sol id Inc lus ions


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Lack of Fusion


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Typical Causes of Lack of Fusion:

welding current too low

bevel angle too steep

root face too large (single-sided weld)

root gap too small (single-sided weld)

incorrect electrode angle

linear misalignment

welding speed too high

welding process relatedparticularly dip-transfer GMAW

flooding the joint with too much weld metal (blocking Out)


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Lack o f Fus ion

Incomplete filled groove +

Lack of sidewall fusion

1

2

1. Lack of sidewall fusion

2. Lack of inter-run fusion

Causes:

Poor welder skill

Incorrect electrode

manipulation

Arc blow

Incorrect welding

current/voltage

Incorrect travel speedIncorrect inter-run cleaning


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Lack of sidewall fusion + incomplete filled groove

Lack o f Fus ion


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Overlap


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Overlap

An imperfection at the toe or root of a weld caused by metal

flowing on to the surface of the parent metal without fusing to it

Causes:

Contamination

Slow travel speed

Incorrect welding

technique

Current too low


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Overlap

Toe Overlap

Toe Overlap


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Weld Root Imperfections


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Weld Root Imperfec t ions

Incomplete root fusion

Incomplete root penetration

Causes:

Low Amps/volts

Large Root face

Small Root Gap

Fast Travel Speed

Incorrect Electrode

Angle

Contamination

Arc blow


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Lack of root penetration Lack of root fusion

Weld Roo t Imperfect ions


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Weld Root Imperfect ions

Lack of Root FusionLack of Root Penetration


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Concave Root

Causes:

Excessive back purge pressure

during TIG welding

Excessive root bead grindingbefore the application of the

second pass

welding current too high for 2nd

pass overhead welding

root gap too large - excessive

weaving

A shallow groove, which may occur in the root of a butt weld



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Concave Root



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Excessive root penetration

Causes:

Root faces too small

Root gap too large

Excessive amps/volts

Slow travel speed

Root penetration bead in excess in accordance with the

relevant specification being used



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Excessive rootpenetration



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Concave root Excess root penetration



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Causes:

High Amps/volts

Small Root face

Large Root Gap

Slow Travel Speed

Burn through

A localized collapse of the weld pool due to excessive

penetration resulting in a hole in the root run



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Burn Through



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Causes:

Loss or insufficient back

purging gas

Most commonly occurs

when welding stainlesssteels

Purging gases include

argon, helium and

occasionally nitrogen

Oxid ized Roo t (Roo t Cok ing )


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Imperfect Shape and Dimensions


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Surface and Profi le

Incomplete filled groove Poor cap profile

Excessive cap height

Poor cap profiles and

excessive cap reinforcements

may lead to stress

concentration points at the

weld toes and will also

contribute to overall poor toe

blend


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Incomplete filled grooveExcess cap reinforcement



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Poor Cap Profile & Poor Toe Blend


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Poor

Stop / Starts


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Cap and Root Undercu t

An irregular groove at the toe of a weld run in the parent metal

Causes:

Excessive amps/volts

Excessive travel speed

Incorrect electrode angle

Excessive weaving

Incorrect welding

technique

Electrode too large

Arc length too high

C


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Cap Undercu t

Intermittent Cap Undercut


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Cap undercutRoot undercut

Undercut

W ld i I f t i Cl i f i t i


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Miscellaneous Imperfections


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Welding Imperfect ionsMiscellaneous Imperfections

Arc strike or stray arc:

accidental striking of an arc on to base material

loss of welding cable insulation

poor connection of current return cable

Spatter:

excessive current or voltage

Grinding mark / mechanical damage:

Torn surface

f


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Miscel laneous Imperfec t ions

Causes: Excessive current

Damp electrodes

Contamination

Incorrect wire feed speed

when welding with the

MAG welding process

Arc blow

Spatter


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Miscel laneous Imperfec t ions

Arc strike

Causes:

Accidental striking of the

arc onto the parent

material

Faulty electrode holder

Poor cable insulation

Poor return lead

clamping

W ld i I f t i Cl i f i t i


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Mechanical Damage

M h i l D


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Mechan ical Damage

Mechanical damage can be defined as any surface material

damage cause during the manufacturing process.

Grinding

Hammering

Chiselling

Chipping

Breaking off welded attachments

(torn surfaces)

Using needle guns to compress

weld capping runs

M h i l D


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Mechan ical Damage

Mechanical Damage/Grinding Mark

Chipping Marks



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Set-Up Irregularities

Unequal Leg Lengths


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A variation of leg lengths on a fillet weld

Note:Unequal leg lengths on a fillet weld may be specified as

part of the design, in which case it will not be

considered as a defect.

Unequal Leg Lengths

Set Up Irregu larit ies


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Set-Up Irregu larit ies

Plate/pipe Linear Misalignment

(Hi-Lo)

Angular Misalignment

Linear misalignmentismeasured from the lowest

plate to the highest point.

Angular misalignmentis

measured in degrees

S t U I l i t i


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Linear Misalignment

Set Up Irregu larit ies


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Linear Misalignment



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Material Inspec tion


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Material Inspec tion

Parent Material Imperfections

Material Inspec t ion


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Material Inspec t ion

All materials arriving on site should be inspected for:

Size / dimensions

Condition

Type / specification

In addition other elements may need to be considered

depending on the materials form or shape

Pipe Inspect ion


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Condition

(Corrosion, Damage, Wall thickness Ovality, Laminations & Seam)

Specification

Weldedseam

Size

LP5

Pipe Inspect ion

Other checks may need to be made such as: distortiontolerance, number of plates and storage*

Plate Inspec tion


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Size

Condition

(Corrosion, Mechanical damage, Laps, Bands &Laminations)

5L

Specification

Other checks may need to be made such as: distortiontolerance, number of plates and storage*

Plate Inspec tion

Rol ling Imperfect ions


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Laminations

Segregation

Cold Laps*

Direction of rolling

Rol ling Imperfect ions

Paren t Material Imperfect ions


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Paren t Material Imperfect ions

Lamination

Mechanical damage Lap

Segregation line

Laminations are caused in the parent plate by the steel making

process, originating from ingot casting defects.

Segregation bandsoccur in the centre of the plate and are low

melting point impurities such as sulphur and phosphorous.

Laps are caused during rolling when overlapping metal does not

fuse to the base material.


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apping

Lapping


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Lapping


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apping


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amination

Laminat ions


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Laminat ions

Plate Lamination

Mater ial imperfec t ions


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Any Questions

Mater ial imperfec t ions

Elements


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Elements

Iron Fe

Carbon C is for Strength

Manganese Mn is for Toughness

Silicon Si < 0.3% Deoxidiser

Aluminium Al Grain refiner,


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Elements

Vanadium V Strength

Nickel Ni Low temperature applications

Copper Cu Used for weathering steels (Corten)

Sulphur S Residual element (can cause hot

shortness)

Phosphorous P Residual element

Titanium Ti Grain refiner, Used a a micro alloying

element (S&T)

Niobium Nb Grain refiner, Used a a micro alloying

element (S&T)

(S&T) = Strength & Toughness


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Stainless Steel

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