Download - Welding presentation

Welding Inspector

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Main Responsibilities 1.1

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Personal Attributes 1.1

Important qualities that good Inspectors are expected to haveare:

•Honesty

•Integrity

•Knowledge

•Good communicator

•Physical fitness

•Good eyesight

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Standard for Visual Inspection 1.1

Basic Requirements

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Welding Inspection 1.2

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Aids to Visual Inspection (to BS EN 970)

When access is restricted may use:• a mirrored boroscope• a fibre optic viewing system

• welding gauges (for checking bevel angles, weld profile, filletsizing, undercut depth)

• dedicated weld-gap gauges and linear misalignment (high-low)gauges

• straight edges and measuring tapes• magnifying lens (if magnification lens used it should have

magnification between X2 to X5)

1.3Welding Inspectors EquipmentMeasuring devices:

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flexible tape, steel rule

Temperature indicating crayons

Welding gauges

Voltmeter

Ammeter

Magnifying glass

Torch / flash light

Gas flow-meter

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HI-

LO

Sin

gle

Pu

rpos

e W

eld

ing

Gau

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Welding Inspectors Gauges 1.3

10mm

G.A.L.

S.T.D.16mm

L

10mm

G.A.L.

S.T.D.

16mm

0 1/4 1/2 3/4

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Welding Inspectors Equipment 1.3

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1.5

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Typical Duties of a Welding Inspector

1.5

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Typical Duties of a Welding Inspector 1.5

Before Welding

Equipment:

• all inspection equipment is in good condition & calibrated asnecessary

• all safety requirements are understood & necessary equipmentavailable

Materials:

• can be identified & related to test certificates, traceability !

• are of correct dimensions

• are in suitable condition (no damage/contamination)

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Before Welding

Consumables:

• in accordance with WPS’s

• are being controlled in accordance with Procedure

Weld Preparations:

• comply with WPS/drawing

• free from defects & contamination

Welding Equipment:

• in good order & calibrated as required by Procedure

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Before WeldingFit-up

• complies with WPS

• Number / size of tack welds to Code / goodworkmanship

Pre-heat

• if specified

• minimum temperature complies with WPS

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1.5

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1.6Typical Duties of a Welding InspectorDuring Welding

Welding consumables

• in accordance with WPS

• in suitable condition

• controlled issue and handling

Welding Parameters

• current, voltage & travel speed – as WPS

Root runs

• if possible, visually inspect root before single-sided welds arefilled up

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1.6Typical Duties of a Welding Inspector

During Welding

Inter-run cleaning

in accordance with an approved method (& back gouging) togood workmanship standard

Distortion control

• welding is balanced & over-welding is avoided

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1.6

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1.6Typical Duties of a Welding InspectorAfter Welding

Repairs

• monitor repairs to ensure compliance with Procedure, ensureNDT after repairs is completed

• PWHT

• monitor for compliance with Procedure

• check chart records confirm Procedure compliance

Pressure / Load Test

• ensure test equipment is suitably calibrated

• monitor to ensure compliance with Procedure

• ensure all records are available

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1.6Typical Duties of a Welding Inspector

After Welding

Documentation

• ensure any modifications are on ‘as-built’ drawings

• ensure all required documents are available

• Collate / file documents for manufacturing records

• Sign all documentation and forward it to QC department.

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ObserveTo observe all relevant actions related to weld quality throughoutproduction.

RecordTo record, or log all production inspection points relevant to quality,including a final report showing all identified imperfections

CompareTo compare all recorded information with the acceptance criteriaand any other relevant clauses in the applied application standard

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Summary of Duties

Welding Inspector

Terms & DefinitionsSection 2

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2.1

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Welding Terminology & Definitions

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Welding Terminology & Definitions 2.1

What is a Joint?

• The junction of members or the edges of members that areto be joined or have been joined (AWS)

• A configuration of members (BS499)

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Joint Terminology 2.2

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Welded Butt Joints 2.2

________

__ __________

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Welded Tee Joints 2.2

_________

_________

Weld Terminology 2.3

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Butt Preparations – Sizes 2.4

Partial Penetration Butt Weld

Design Throat

Thickness

Full Penetration Butt Weld

Design Throat

Thickness

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Actual Throat

Thickness

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Actual Throat

Thickness

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Weld Zone Terminology 2.5

C

B

WeldBoundary

D

A

Weldmetal

HeatAffectedZone

Face

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Excess RootPenetration

Weld Zone Terminology 2.5

Weld cap width

DesignThroatThickness

Actual ThroatThickness

Heat Affected Zone (HAZ) 2.5

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Joint Preparation Terminology 2.7

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Joint Preparation Terminology 2.8 & 2.9

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Angle of bevel Angle of bevel

Single Sided Butt Preparations 2.10

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Double Sided Butt Preparations2.11

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Weld Preparation

Butt Weld - Toe Blend

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Fillet Weld Features 2.13

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Fillet Weld Throat Thickness 2.13

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Deep Penetration Fillet Weld Features 2.13

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Fillet Weld Sizes 2.14

Calculating Throat Thickness from a known Leg Length:

Design Throat Thickness = Leg Length x 0.7

Question: The Leg length is 14mm.

What is the Design Throat?

Answer: 14mm x 0.7 = 10mm Throat Thickness

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Fillet Weld Sizes 2.14

Calculating Leg Length from a known Design ThroatThickness:

Leg Length = Design Throat Thickness x 1.4

Question: The Design Throat is 10mm.

What is the Leg length?

Answer: 10mm x 1.4 = 14mm Leg Length

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Features to Consider 2 2.14

Importance of Fillet Weld Leg Length Size

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2.15Fillet Weld Profiles

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“s” = Effective throat thickness

sa

“a” = Nominal throat thickness

Deep penetration fillet welds from high heatinput welding process MAG, FCAW & SAW etc

Fillet Features to Consider

EFFECTIVE THROAT THICKNESS

2.15

PA 1G/1F Flat/Downhand

PB 2F Horizontal-Vertical

PC 2G Horizontal

PD 4F Horizontal-Vertical(Overhead)

PE 4G Overhead

PF 3G/5G Vertical-Up

PG 3G/5G Vertical-Down

H-L045 6G InclinedPipe(Upwards)

J-L045 6G InclinedPipe(Downwards)

Welding Positions 2.17

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Welding Positions 2.17

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ISO

Welding position designation 2.17

Butt welds in plate (see ISO 6947)

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Overhead - PEFlat - PA

Verticalup - PF

Verticaldown - PG

Horizontal - PC


Butt welds in pipe (see ISO 6947)

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Flat - PAaxis: horizontalpipe: rotated

H-L045

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Horizontal - PC

pipe: fixed

pipe: fixed

Vertical up - PF Vertical down - PGaxis: horizontal axis: horizontal

pipe: fixed

J-L045axis: inclined at 45° axis: inclined at 45° axis: vertical

pipe: fixed


Fillet welds on plate (see ISO 6947)

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Flat - PA Overhead - PD

Vertical up - PF Vertical down - PG

Horizontal - PB


Fillet welds on pipe (see ISO 6947)

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Flat - PAaxis: inclined at 45°pipe: rotated

Overhead - PDaxis: verticalpipe: fixed

axis: horizontalpipe: fixed

axis: horizontalpipe: fixed

Horizontal - PBaxis: verticalpipe: fixed

Horizontal - PB Vertical up - PF Vertical down - PGaxis: horizontalpipe: rotated

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Plate/Fillet Weld Positions 2.17

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Welding Inspector

Welding ImperfectionsSection 3

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3.1

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Welding Imperfections

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Welding Imperfections 3.1

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3.1Welding imperfectionsclassification

Cracks

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Cracks 3.1

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

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Cracks 3.1

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Cracks 3.1

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Cracks 3.2

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Solidification CracksHydrogen Induced CracksLamellar TearingReheat cracks

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Cracks 3.2

Solidification Cracking

• Occurs during weld solidification process

• Steels with high sulphur impurities content (low ductilityat elevated temperature)

• Occur longitudinally down centre of weld

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Cracks 3.3

Hydrogen Induced Cold Cracking

• Hydrogen enters weld via welding arc mainly as result ofcontaminated electrode or preparation

• Hydrogen diffuses out into parent metal on cooling

• Cracking developing most likely in HAZ

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Lamellar Tearing 3.5

• Location: Parent metal

• Steel Type: Any steel type possible

• Susceptible Microstructure: Poor through thickness ductility

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Lamellar tearing has a step like appearance due to the solidinclusions in the parent material (e.g. sulphides andsilicates) linking up under the influence of welding stresses

Low ductile materials in the short transverse directioncontaining high levels of impurities are very susceptible tolamellar tearing

It forms when the welding stresses act in the shorttransverse direction of the material (through thicknessdirection)

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Gas Cavities 3.6

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Gas Cavities 3.7

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Root piping

Porosity

Gas Cavities 3.8

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Crater pipe

Weld crater

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Crater cracks

(Star cracks)

Crater pipe

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Solid Inclusions 3.10

Slag inclusions are defined as a non-metallic inclusion causedby some welding process

Solid Inclusions 3.11

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• 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 related – particularly dip-transfer GMAW

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

Lack of Fusion3.13

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Undercut 3.18

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Surface and Profile 3.19

Surface and Profile 3.19

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Overlap 3.21

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Overlap 3.21

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Set-Up Irregularities 3.22

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Weld Root Imperfections 3.24

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Weld Root Imperfections 3.25

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3.27

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Miscellaneous Imperfections

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Mechanical Damage 3.28

Mechanical damage can be defined as any surface materialdamage cause during the manufacturing process.

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3.28

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Mechanical Damage

Welding Inspector

Destructive TestingSection 4

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Qualitative and Quantitative Tests 4.1

The following mechanical tests have units and are termedquantitative tests to measure Mechanical Properties• Tensile tests (Transverse Welded Joint, All Weld Metal)• Toughness testing (Charpy, Izod, CTOD)• Hardness tests (Brinell, Rockwell, Vickers)

The following mechanical tests have no units and are termedqualitative tests for assessing joint quality• Macro testing• Bend testing• Fillet weld fracture testing• Butt weld nick-break testing

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Mechanical Test Samples 4.1

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Destructive Testing 4.1

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Definitions

Definitions

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Definitions

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Definitions

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Definitions

Transverse Joint Tensile Test 4.2

Weld on plate

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Multiple cross jointspecimensWeld on pipe

Tensile Test 4.3

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STRA (Short Transverse Reduction Area)For materials that may be subject to Lamellar Tearing

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UTS Tensile test 4.4

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Charpy V-Notch Impact Test 4.5

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Ductile / Brittle Transition Curve 4.6

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Comparison Charpy Impact Test Results 4.6

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Charpy V-notch impact test specimen 4.7

Charpy V-Notch Impact Test 4.8

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Charpy Impact Test 4.9

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Hardness Testing 4.10

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4.10

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Hardness Testing

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Vickers Hardness Test 4.11

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Vickers Hardness Test Machine4.11

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Brinell Hardness Test 4.11

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Ø=10mmsteel ball

Rockwell Hardness Test

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Ø=1.6mmsteel ball

120 DiamondCone

4.12

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Hardness Testing

Hardness specimens can also be used for CTOD samples

Fatigue Fracture 4.13

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Fatigue Fracture 4.13

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Toe grinding, profile grinding.

The elimination of poor profiles

The elimination of partial penetration welds and welddefects

Operating conditions under the materials endurance limits

The elimination of notch effects e.g. mechanical damagecap/root undercut

The selection of the correct material for the serviceconditions of the component

Fatigue FracturePrecautions against Fatigue Cracks

Fatigue FractureFatigue fracture occurs in structures subject to repeatedapplication of tensile stress.

Crack growth is slow (in same cases, crack may grow into anarea of low stress and stop without failure).

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Fatigue Fracture

• Crack growth is slow

• It initiate from stress concentration points

• load is considerably below the design or yield stress level

• The surface is smooth

• The surface is bounded by a curve

• Bands may sometimes be seen on the smooth surface –”beachmarks”.They show the progress of the crack front from the point of origin

• Final fracture will usually take the form of gross yielding (as themaximum stress in the remaining ligament increase!)

• Fatigue crack need initiation + propagation periods

Bend Tests 4.15

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Root bend Side bend

Side bend tests are normally carried out on welds over 12mm in thickness

Bending test 4.16

Types of bend test for welds (acc. BS EN 910):

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Fillet Weld Fracture Tests 4.17

Object of test:

• To break open the joint through the weld to permitexamination of the fracture surfaces

• Specimens are cut to the required length

• A saw cut approximately 2mm in depth is applied alongthe fillet welds length

• Fracture is usually made by striking the specimen with asingle hammer blow

• Visual inspection for defects

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4.17

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Fillet Weld Fracture Tests

Fillet Weld Fracture Tests 4.17

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Nick-Break Test 4.18

Object of test:

• To permit evaluation of any weld defects across thefracture surface of a butt weld.

•Specimens are cut transverse to the weld

•A saw cut approximately 2mm in depth is applied along thewelds root and cap

•Fracture is usually made by striking the specimen with asingle hammer blow

•Visual inspection for defects

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Nick-Break Test 4.18

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Nick Break Test 4.18

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Qualitative: (Have no units/numbers)

For assessing joint quality

Macro tests

Bend tests

Fillet weld fracture tests

Butt Nick break tests

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Quantitative: (Have units/numbers)

To measure mechanical properties

Hardness (VPN & BHN)

Toughness (Joules & ft.lbs)

Strength (N/mm2 & PSI, MPa)

Ductility / Elongation (E%)

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We test welds to establish minimum levels of mechanicalproperties, and soundness of the welded joint

We divide tests into Qualitative & Quantitative methods:

Welding Inspector

WPS – Welder QualificationsSection 5

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5.1

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Welding ProceduresProducing a welding procedure involves:

• Planning the tasks

• Collecting the data

• Writing a procedure for use of for trial

• Making a test welds

• Evaluating the results

• Approving the procedure

• Preparing the documentation

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Welding Procedures 5.2

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Production welding conditions must remain within the range ofqualification allowed by the WPQR

The welding engineer writes qualified Welding ProcedureSpecifications (WPS) for production welding

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5.3

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5.3

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Components of a welding procedureParent material

• Type (Grouping)• Thickness• Diameter (Pipes)• Surface condition)

Welding process• Type of process (MMA, MAG, TIG, SAW etc)• Equipment parameters• Amps, Volts, Travel speed

Welding Consumables• Type of consumable/diameter of consumable• Brand/classification• Heat treatments/ storage

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Components of a welding procedureJoint design

•Edge preparation•Root gap, root face•Jigging and tacking•Type of baking

Welding Position•Location, shop or site•Welding position e.g. 1G, 2G, 3G etc•Any weather precaution

Thermal heat treatments•Preheat, temps•Post weld heat treatments e.g. stress relieving

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Welding Procedures

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Example:

Welding

Procedure

Specification

(WPS)

Welder Qualification 5.4

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Welder Qualification 5.10

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Welders name and identification numberDate of test and expiry date of certificateStandard/code e.g. BS EN 287Test piece detailsWelding process.Welding parameters, amps, voltsConsumables, flux type and filler classification detailsSketch of run sequenceWelding positionsJoint configuration detailsMaterial type qualified, pipe diameter etcTest results, remarksTest location and witnessed byExtent (range) of approval

Welding Inspector

Materials InspectionSection 6

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Material InspectionOne of the most important items to consider is Traceability.

The materials are of little use if we can not, by use of an effective QAsystem trace them from specification and purchase order to finaldocumentation package handed over to the Client.

All materials arriving on site should be inspected for:

• Size / dimensions

• Condition

• Type / specification

In addition other elements may need to be considered depending onthe materials form or shape

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Pipe InspectionWe inspect the condition

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

Specification

Weldedseam

Size

LP5

Other checks may need to be made such as: distortion tolerance,number of plates and storage.

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Size5L

Plate InspectionWe inspect the condition

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

Specification

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

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Lapping

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Lamination

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Welding Inspector

Codes & StandardsSection 7

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Codes & StandardsThe 3 agencies generally identified in a code or standard:

The customer, or client

The manufacturer, or contractor

The 3rd party inspection, or clients representative

Codes often do not contain all relevant data, but mayrefer to other standards

Welding Inspector

Welding SymbolsSection 8

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Weld symbols on drawingsAdvantages of symbolic representation:• simple and quick plotting on the drawing

• does not over-burden the drawing

• no need for additional view

• gives all necessary indications regarding the specific joint tobe obtained

Disadvantages of symbolic representation:• used only for usual joints

• requires training for properly understanding of symbols

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Weld symbols on drawings

The symbolic representation includes:

• an arrow line

• a reference line

• an elementary symbol

The elementary symbol may be completed by:

• a supplementary symbol

• a means of showing dimensions

• some complementary indications

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Dimensions

a = Design throat thicknesss = Depth of Penetration, Throat thicknessz = Leg length (min material thickness)

•In a fillet weld, the size of the weld is the leg length•In a butt weld, the size of the weld is based on the depth of thejoint preparation

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Weld symbols on drawings

Elementary Welding Symbols(BS EN ISO 22553 & AWS A2.4)

Convention of the elementary symbols:Various categories of joints are characterised by an elementary symbol.

The vertical line in the symbols for a fillet weld, single/double bevel buttsand a J-butt welds must always be on the left side.

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Sketch

Elementary Welding Symbols

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Elementary Welding Symbols

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ISO 2553 / BS EN 22553

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Plug weld

Resistance spot weld

Resistance seam weld

Square Butt weld

Steep flankedSingle-V Butt

Surfacing

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ISO 2553 / BS EN 22553

ISO 2553 / BS EN 22553

ISO 2553 / BS EN 22553

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ISO 2553 / BS EN 22553

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ISO 2553 / BS EN 22553

az s

ISO 2553 / BS EN 22553

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ISO 2553 / BS EN 22553s6

s6

6mm fillet weld

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ISO 2553 / BS EN 22553

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80 80 80

909090

6

6

5

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ISO 2553 / BS EN 22553

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ISO 2553 / BS EN 22553

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680 80 80

909090

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ISO 2553 / BS EN 22553

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ISO 2553 / BS EN 22553

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ISO 2553 / BS EN 22553

az s

ISO 2553 / BS EN 22553Complimentary Symbols

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ISO 2553 / BS EN 22553

AWS A2.4 Welding Symbols

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AWS Welding Symbols

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AWS Welding Symbols

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AWS Welding Symbols

1/8

AWS Welding Symbols

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FCAW

Sequence ofOperations

1st Operation

1(1-1/8)

60o

3rd Operation

2nd Operation

AWS Welding Symbols

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1(1-1/8)1/860o

FCAW

Sequence ofOperations

RT

MT

MT

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AWS Welding SymbolsDimensions- Leg Length

6/86 leg on member A

Member A 6

8

Member B

Welding Inspector

Intro To Welding ProcessesSection 9

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Welding Processes

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Monitoring Heat Input

• Heat Input:The amount of heat generated in thewelding arc per unit length of weld.

Expressed in kilo Joules per millimetrelength of weld (kJ/mm).

Heat Input (kJ/mm)= Volts x AmpsTravel speed(mm/s) x 1000

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Weld and weld pool temperatures


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• Monitoring Heat Input As Required by• BS EN ISO 15614-1:2004• In accordance with EN 1011-1:1998When impact requirements and/or hardness requirements arespecified, impact test shall be taken from the weld in the highestheat input position and hardness tests shall be taken from theweld in the lowest heat input position in order to qualify for allpositions

Welding Inspector

MMA WeldingSection 10

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MMA - Principle of operation

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MMA welding

Main features:• Shielding provided by decomposition of flux covering• Electrode consumable• Manual process

Welder controls:•

•

•

•

Arc lengthAngle of electrodeSpeed of travelAmperage settings

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MMA Welding Variables

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MMA welding parametersTravel speed

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MMA welding parametersType of current:•

•

•

•

•

voltage drop in welding cables is lower with ACinductive looses can appear with AC if cables are coiledcheaper power source for ACno problems with arc blow with ACDC provides a more stable and easy to strike arc, especiallywith low current, better positional weld, thin sheet applications

• welding with a short arc length (low arc voltage) is easier withDC, better mechanical properties

• DC provides a smoother metal transfer, less spatter

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MMA welding parametersWelding current

MMA - Troubleshooting

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MMA Welding Consumables

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Manual Metal Arc Welding (MMA)

•••••

•••••

Welding Inspector

TIG WeldingSection 11

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Tungsten Inert Gas Welding

TIG - Principle of operation

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TIG Welding Variables

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ARC CHARACTERISTICS

TIG torch set-up

• Electrode extension

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Tungsten Electrodes

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Tungsten electrode types

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black

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white

Electrode tip for DCEN

Electrode tip for AC

DC -ve AC

TIG Welding Variables

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Choosing the proper electrode

Shielding gas requirements

• Preflow andpostflow

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TIG Welding ConsumablesWelding consumables for TIG:

•Filler wires, Shielding gases, tungsten electrodes (non-consumable).

•Filler wires of different materials composition and variablediameters available in standard lengths, with applicablecode stamped for identification

•Steel Filler wires of very high quality, with copper coating toresist corrosion.

•shielding gases mainly Argon and Helium, usually of highestpurity (99.9%).

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Tungsten Inclusion

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May be caused by Thermal Shock ofheating to fast and small fragments

break off and enter the weld pool, so a“slope up” device is normally fitted to

prevent this could be caused by touchdown also.

Most TIG sets these days have slope-up devices that brings the current tothe set level over a short period of

time so the tungsten is heated moreslowly and gently

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Tungsten Inert Gas Welding

Advantages

• High quality

• Good control

• All positions

• Lowest H2 process

• Minimal cleaning

• Autogenous welding

(No filler material)

• Can be automated4/23/2007

Disadvantages

• High skill factor required

• Low deposition rate

• Small consumable range

• High protection required

• Complex equipment

• Low productivity

• High ozone levels +HF

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Welding Inspector

MIG/MAG WeldingSection 12

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Gas Metal Arc Welding

MIG/MAG - Principle of operation

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MIG/MAG process variables

• Welding current

• Polarity

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•Increasing welding current

•Increase in depth and width

•Increase in deposition rate

MIG/MAG process variables

• Arc voltage

• Travel speed

4/23/2007

•Increasing arc voltage

•Reduced penetration, increased width

•Excessive voltage can cause porosity,spatter and undercut

•Increasing travel speed

•Reduced penetration and width, undercut287 of 691

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MIG/MAG – shielding gases

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MIG/MAG shielding gases

Argon (Ar):higher density than air; low thermal conductivity the archas a high energy inner cone; good wetting at the toes; lowionisation potential

Helium (He):lower density than air; high thermal conductivity uniformlydistributed arc energy; parabolic profile; high ionisationpotential

Carbon Dioxide (CO2):cheap; deep penetration profile; cannot support spraytransfer; poor wetting; high spatter

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Ar Ar-He He CO2

MIG/MAG Gas Metal Arc Welding

Electrodeorientation

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MIG/MAG - metal transfer modes

Set-up for dip transfer

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Set-up for spray transfer

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MIG/MAG welding gun assembly

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WELDING PROCESS

Flux Core Arc Welding

(Not In The Training Manual)

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Flux cored arc welding

“Outershield” - principle of operation

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“Innershield” - principle of operation

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ARC CHARACTERISTICS

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Flux cored arc welding

FCAW - differences from MIG/MAG

• usually operates in DCEPbut some “Innershield”wires operates in DCEN

• power sources need to bemore powerful due to thehigher currents

• doesn't work in deeptransfer mode

• require knurled feed rolls

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Backhand (“drag”) techniqueAdvantages

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Forehand (“push”) technique

Advantages

•

•

•

•

•

•

•

FCAW advantages

less sensitive to lack of fusionrequires smaller included angle compared to MMAhigh productivityall positionalsmooth bead surface, less danger of undercutbasic types produce excellent toughness propertiesgood control of the weld pool in positional welding especiallywith rutile wires

• seamless wires have no torsional strain, twist free• ease of varying the alloying constituents• no need for shielding gas

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FCAW disadvantages• limited to steels and Ni-base alloys• slag covering must be removed• FCAW wire is more expensive on a weight basis than solid

wires (exception: some high alloy steels)• for gas shielded process, the gaseous shield may be

affected by winds and drafts• more smoke and fumes are generated compared with

MIG/MAG• in case of Innershield wires, it might be necessary to

break the wire for restart (due to the high amount ofinsulating slag formed at the tip of the wire)

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Welding Inspector

Submerged Arc WeldingSection 13

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• Submerged arc welding was developed in the Soviet Unionduring the 2nd world war for the welding of thick section steel.

• The process is normally mechanized.

• The process uses amps in the range of 100 to over2000, whichgives a very high current density in the wire producing deeppenetration and high dilution welds.

• A flux is supplied separately via a flux hopper in the form of eitherfused or agglomerated.

• The arc is not visible as it is submerged beneath the flux layerand no eye protection is required.

SAW Principle of operation

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Principles of operation

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- +

Submerged Arc Welding

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SAW process variables

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SAW process variables

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SAW operating variables

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SAW Consumables(Covered in detail in Section 14)

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SAW Consumables

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SAW equipment

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Amps

ARC CHARACTERISTICSConstant Voltage Characteristic

Small change in voltage =large change in amperage

The selfadjusting arc.

OCV

Large arc gap

Small arc gap

Volts

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SAW equipment

•

•

•

•

Courtesy of ESAB AB

Courtesy of ESAB AB

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•

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SAW technological variables


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+Earth position

Direction oftravel

-

•welding towards earth produces backward arc blow

•deep penetration

•convex weld profile


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+

Weld backing

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Starting/finishing the weld

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SAW variants

SAW variants

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SAW variants

SAW variants

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SAW variants

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SAW variants

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SAW variants

SAW variants

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Advantages of SAW

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Welding Inspector

Welding ConsumablesSection 14

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BS EN 499 MMA Covered Electrodes

Covered Electrode

Yield Strength N/mm2

Toughness

Chemical composition

Flux Covering

Weld Metal Recoveryand Current Type

Welding Position

Hydrogen Content

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•

•

•

•

MMA (SMAW)

• BS EN 499: Steel electrodes

• AWS A5.1 Non-alloyed steel

electrodes

• AWS A5.4 Chromium

electrodes

• AWS A5.5 Alloyed steel

electrodes

Welding Consumable StandardsMIG/MAG (GMAW) TIG (GTAW)

• BS 2901: Filler wires

• BS EN 440: Wire electrodes

• AWS A5.9: Filler wires

• BS EN 439: Shielding gases

SAW

• BS 4165: Wire and fluxes

• BS EN 756: Wire electrodes

• BS EN 760: Fluxes

• AWS A5.17: Wires and fluxes

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Welding Consumable Gases

4/23/2007

Welding ConsumablesEach consumable is critical in respect to:

• Size, (diameter and length)

• Classification / Supplier

• Condition

• Treatments e.g. baking / drying

• Handling and storage is critical for consumable control

• Handling and storage of gases is critical for safety

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Welding consumables for MMA:

• Consist of a core wire typically between 350-450mm in lengthand from 2.5mm - 6mm in diameter

• The wire is covered with an extruded flux coating

• The core wire is generally of a low quality rimming steel

• The weld quality is refined by the addition of alloying andrefining agents in the flux coating

• The flux coating contains many elements and compoundsthat all have a variety of functions during welding

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EN 499-E 51 3 B

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MMA Welding ConsumablesCellulosic electrodes:• covering contains cellulose (organic material).

• produce a gas shield high in hydrogen raising the arcvoltage.

• Deep penetration / fusion characteristics enables weldingat high speed without risk of lack of fusion.

• generates high level of fumes and H2 cold cracking.

• Forms a thin slag layer with coarse weld profile.

• not require baking or drying (excessive heat will damageelectrode covering!).

• Mainly used for stove pipe welding

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Advantages:

• Deep penetration/fusion

• Suitable for welding in allpositions

• Fast travel speeds

• Large volumes of shielding gas

• Low control

4/23/2007

Disadvantages:

• High in hydrogen

• High crack tendency

• Rough weld appearance

• High spatter contents

• Low deposition rates

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Advantages:

• Easy to use

• Low cost / control

• Smooth weld profiles

• Slag easily detachable

• High deposition possiblewith the addition of ironpowder

Disadvantages:

• High in hydrogen

• High crack tendency

• Low strength

• Low toughness values

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MMA Welding ConsumablesRutile Variants

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Advantages

• High toughness values

• Low hydrogen contents

• Low crack tendency

Disadvantages

• High cost

• High control

• High welder skillrequired

• Convex weld profiles

• Poor stop / startproperties

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BS EN 499 MMA Covered Electrodes

BS EN 499 MMA Covered ElectrodesElectrodes classified as follows:• E 35 - Minimum yield strength 350 N/mm2

Tensile strength 440 - 570 N/mm2

• E 38 - Minimum yield strength 380 N/mm2







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AWS A5.1 Alloyed Electrodes

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AWS A5.5 Alloyed Electrodes

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75-90% for usual electrodes

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Electrode efficiency

Covered electrode treatment

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Covered electrode treatment

TIG Consumables

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TIG Welding ConsumablesWelding consumables for TIG:

•Filler wires, Shielding gases, tungsten electrodes (non-consumable).

•Filler wires of different materials composition and variablediameters available in standard lengths, with applicablecode stamped for identification

•Steel Filler wires of very high quality, with copper coating toresist corrosion.

•shielding gases mainly Argon and Helium, usually of highestpurity (99.9%).

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TIG Welding Consumables

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Fusible Inserts

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Fusible Inserts

Shielding gases for TIG welding

Argon

• low cost and greater availability

• heavier than air - lower flow rates than Helium

• low thermal conductivity - wide top bead profile

• low ionisation potential - easier arc starting, better arcstability with AC, cleaning effect

• for the same arc current produce less heat than helium -reduced penetration, wider HAZ

• to obtain the same arc arc power, argon requires a highercurrent - increased undercut

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Helium

• costly and lower availability than Argon

• lighter than air - requires a higher flow rate compared withargon (2-3 times)

• higher ionisation potential - poor arc stability with AC, lessforgiving for manual welding

• for the same arc current produce more heat than argon -increased penetration, welding of metals with high meltingpoint or thermal conductivity

• to obtain the same arc arc power, helium requires a lowercurrent - no undercut

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Hydrogen

• not an inert gas - not used as a primary shielding gas

• increase the heat input - faster travel speed and increasedpenetration

• better wetting action - improved bead profile

• produce a cleaner weld bead surface

• added to argon (up to 5%) - only for austenitic stainlesssteels and nickel alloys

• flammable and explosive

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Nitrogen

• not an inert gas

• high availability - cheap

• added to argon (up to 5%) - only for back purge for duplexstainless, austenitic stainless steels and copper alloys

• not used for mild steels (age embritlement)

• strictly prohibited in case of Ni and Ni alloys (porosity)

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MIG / MAG Consumables(Gases Covered previously)

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MIG/MAG Welding ConsumablesWelding consumables for MIG/MAG

• Spools of Continuous electrode wires and shielding gases

• variable spool size (1-15Kg) and Wire diameter (0.6-1.6mm) supplied in random or orderly layers

• Basic Selection of different materials and their alloys aselectrode wires.

• Some Steel Electrode wires copper coating purpose iscorrosion resistance and electrical pick-up

• Gases can be pure CO2, CO2+Argon mixes and Argon+2%O2mixes (stainless steels).

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MIG/MAG Welding Consumables

Flux Core Wire Consumables(Not in training manual)

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Flux Core Wire Consumables

Functions of metallic sheath:provide form stabilityto the wireserves as currenttransfer duringwelding

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Function of the filling powder:stabilise the arcadd alloy elementsproduce gaseousshieldproduce slagadd iron powder

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Types of cored wire

• not sensitive to moisturepick-up

• can be copper coated, bettercurrent transfer

• thick sheath, good formstability, 2 roll drive feedingpossible

• difficult to manufacture

4/23/2007

• good resistance tomoisture pick-up

• can be copper coated• thick sheath• difficult to seal the

sheath

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Core elements and their function

Aluminium - deoxidize & denitrify

Calcium - provide shielding & form slag

Carbon - increase hardness & strength

Manganese - deoxidize & increase strength and toughness

Molybdenum - increase hardness & strength

Nickel - improve hardness, strength, toughness & corrosionresistance

Potassium - stabilize the arc & form slag

Silicon - deoxidize & form slag

Sodium - stabilize arc & form slag

Titanium - deoxidize, denitrify & form slag4/23/2007

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SAW Consumables

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SAW Consumables

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SAW Consumables

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SAW Consumables

Baked at high temperature, glossy, hard and black in colour,cannot add ferro-manganese, non moisture absorbent andtends to be of the acidic type

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SAW Consumables

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SAW Consumables

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SAW Consumables

Agglomerated Flux:

Baked at a lower temperature, dull, irregularly shaped, friable,(easily crushed) can easily add alloying elements, moistureabsorbent and tend to be of the basic type

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SAW Consumables

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SAW Consumables

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SAW Consumables

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SAW filler material

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SAW filler material

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SAW filler material

Welding Inspector

Non Destructive TestingSection 15

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Non-Destructive TestingA welding inspector should have a working knowledge of NDTmethods and their applications, advantages anddisadvantages.

Four basic NDT methods

• Radiographic inspection (RT)

• Ultrasonic inspection (UT)

• Magnetic particle inspection (MT)

• Dye penetrant inspection (PT)

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•

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Radiographic Testing

•

•

•

•

•


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Densitometer

Radiographic Sensitivity

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Radiographic Sensitivity

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Radiographic Techniques

Single Wall Single Image (SWSI)

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Single Wall Single Image Panoramic

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Double Wall Single Image (DWSI)

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EN W10


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Double Wall Double Image (DWDI)

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4/23/2007

EN W10

ID MR12

4

1

3

2


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1 2

4 3

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Radiographic TestingComparison with Ultrasonic Examination

DISADVANTAGES

• health & safety hazard

• not good for thick sections

• high capital and relatively high running costs

• not good for planar defects

• X-ray sets not very portable

• requires access to both sides of weld

• frequent replacement of gamma source needed (half life)

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Ultrasonic Testing

Ultrasonic Testing

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0 10 20 30 40 50

Ultrasonic Testing

Ultrasonic Testing

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0 10 20 30 40 50

CRT Display

initial pulse

defect echo

0 10 20 30 40 50

CRT Display

Ultrasonic Testing

initial pulse

defect echodefect

½ Skip

defect

Full Skip

Ultrasonic Testing

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Ultrasonic TestingComparison with Radiography

DISADVANTAGES

• no permanent record (with standard equipment)

• not suitable for very thin joints <8mm

• reliant on operator interpretation

• not good for sizing Porosity

• good/smooth surface profile needed

• not suitable for coarse grain materials (e.g., castings)

• Ferritic Materials (with standard equipment)4/23/2007

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Magnetic Particle TestingMain features:•

•

•

•

•

Surface and slight sub-surface detectionRelies on magnetization of component being testedOnly Ferro-magnetic materials can be testedA magnetic field is introduced into a specimen being testedMethods of applying a magnetic field, yoke, permanentmagnet, prods and flexible cables.

• Fine particles of iron powder are applied to the test area• Any defect which interrupts the magnetic field, will create a

leakage field, which attracts the particles• Any defect will show up as either a dark indication or in the

case of fluorescent particles under UV-A light a green/yellowindication

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Electro-magnet (yoke) DC or AC

Prods DC or AC

Magnetic Particle Testing


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Penetrant TestingMain features:

• Detection of surface breaking defects only.

• This test method uses the forces of capillary action

• Applicable on any material type, as long they are non porous.

• Penetrants are available in many different types:

• Water washable contrast

• Solvent removable contrast

• Water washable fluorescent

• Solvent removable fluorescent

• Post-emulsifiable fluorescent

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Penetrant Testing

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Penetrant Testing

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Penetrant Testing

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Penetrant Testing

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Penetrant Testing

Penetrant Testing

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Penetrant Testing

Advantages• Simple to use• Inexpensive• Quick results• Can be used on any non-

porous material• Portability• Low operator skill required

Disadvantages• Surface breaking defect only• little indication of depths• Penetrant may contaminate

component• Surface preparation critical• Post cleaning required• Potentially hazardous

chemicals• Can not test unlimited times• Temperature dependant

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Welding Inspector

Weld RepairsSection 16

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Weld RepairsWeld repairs can be divided into 2 specific areas:

•Production repairs

•In service repairs

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Weld RepairsA weld repair can be a relatively straight forward activity, butin many instances it is quite complex, and variousengineering disciplines may need to be involved to ensure asuccessful outcome.

•Analysis of the defect types may be carried out by theQ/C department to discover the likely reason for theiroccurrence, (Material/Process or Skill related).

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Weld RepairsA weld repair may be used to improve weld profiles orextensive metal removal:

•Repairs to fabrication defects are generally easier thanrepairs to service failures because the repair proceduremay be followed

•The main problem with repairing a weld is themaintenance of mechanical properties

•During the inspection of the removed area prior towelding the inspector must ensure that the defects havebeen totally removed and the original joint profile hasbeen maintained as close as possible

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Weld RepairsIn the event of repair, it is required:

• Authorization and procedure for repair

• Removal of material and preparation for repair

• Monitoring of repair Weld

• Testing of repair - visual and NDT

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Weld RepairsThere are a number of key factors that need to be considered

before undertaking any repair:

• The most important - is it financially worthwhile?

• Can structural integrity be achieved if the item is repaired?

• Are there any alternatives to welding?

• What caused the defect and is it likely to happen again?

• How is the defect to be removed and what welding process is tobe used?

• What NDE is required to ensure complete removal of the defect?

• Will the welding procedures require approval/re-approval?

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Weld Repairs• Cleaning the repair area, (removal of paint, grease, etc)

• A detailed assessment to find out the extremity of the defect.This may involve the use of a surface or sub surface NDE method.

• Once established the excavation site must be clearly identifiedand marked out.

• An excavation procedure may be required (method used i.e.grinding, arc-air gouging, preheat requirements etc).

• NDE should be used to locate the defect and confirm its removal.

• A welding repair procedure/method statement with theappropriate welding process, consumable, technique, controlledheat input and interpass temperatures etc will need to beapproved.

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Weld Repairs• Use of approved welders.

• Dressing the weld and final visual.

• A NDT procedure/technique prepared and carried out to ensurethat the defect has been successfully removed and repaired.

• Any post repair heat treatment requirements.

• Final NDT procedure/technique prepared and carried out afterheat treatment requirements.

• Applying protective treatments (painting etc as required).

• (*Appropriate’ means suitable for the alloys being repaired andmay not apply in specific situations)

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Weld Repairs• What will be the effect of welding distortion and residual

stress?

• Will heat treatment be required?

• What NDE is required and how can acceptability of therepair be demonstrated?

• Will approval of the repair be required – if yes, how and bywhom?

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Production Weld Repairs

Weld RepairsThe specification or procedure will govern how the defectiveareas are to be removed. The method of removal may be:

•Grinding

•Chipping

•Machining

•Filing

•Oxy-Gas gouging

•Arc air gouging

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Defect Excavation

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Arc-air gouging features

Production Weld RepairsProduction Repairs

•are usually identified during production inspection

•evaluation of the reports is usually carried out bythe Welding Inspector, or NDT operator

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Production Weld Repairs

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Plan View of defect

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Production Weld RepairsSide View of defect excavation

W

D

Side View of repair welding

In Service Weld RepairsIn service repairs

• Can be of a very complex nature, as the component is verylikely to be in a different welding position and conditionthan it was during production

• It may also have been in contact with toxic, or combustiblefluids hence a permit to work will need to be sought priorto any work being carried out

• The repair welding procedure may look very different to theoriginal production procedure due to changes in theseelements.

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In Service Weld RepairsOther factors to be taken into consideration:

Effect of heat on any surrounding areas of the componenti.e. electrical components, or materials that may becomedamaged by the repair procedure.

This may also include difficulty in carrying out any requiredpre or post welding heat treatments and a possiblerestriction of access to the area to be repaired.

For large fabrications it is likely that the repair must alsotake place on site and without a shut down of operations,which may bring other elements that need to beconsidered.

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Weld Repairs• Is welding the best method of repair?

• Is the repair really like earlier repairs?

• What is the composition and weldability of the base metal?

• What strength is required from the repair?

• Can preheat be tolerated?

• Can softening or hardening of the HAZ be tolerated?

• Is PWHT necessary and practicable?

• Will the fatigue resistance of the repair be adequate?

• Will the repair resist its environment?

• Can the repair be inspected and tested?4/23/2007

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Weld repair related problems• heat from welding may affect dimensional stability and/or

mechanical properties of repaired assembly

• due to heat from welding, YS goes down, danger ofcollapse

• filler materials used on dissimilar welds may lead togalvanic corrosion

• local preheat may induce residual stresses

• cost of weld metal deposited during a weld joint repaircan reach up to 10 times the original weld metal cost!

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Welding Inspector

Residual Stress & DistortionSection 17

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Residual stress

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Residual Stresses

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Stresses

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Stresses

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Stresses

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Residual Stresses

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Residual stress

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Residual stress

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Summary

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Summary

Types of distortionAngular distortion

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Distortion

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Distortion

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Distortion

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Distortion

Factors affecting distortion:

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Factors affecting distortionParent material properties:

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Factors affecting distortionJoint design:

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Factors affecting distortionWelding sequence:

Distortion prevention

Distortion prevention by pre-setting

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Distortion


Distortion prevention by pre-bending usingstrongbacks and wedges

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Distortion

Distortion preventionDistortion prevention by restraint techniques

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Distortion preventionDistortion prevention by restraint techniques

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Distortion preventionDistortion prevention by design

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Distortion preventionDistortion prevention by design

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Distortion preventionDistortion prevention by fabrication techniques


Distortion prevention by welding procedure

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Distortion preventionDistortion - Best practice for fabrication corrective techniques

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Distortion corrective techniques

Distortion - mechanical corrective techniques

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Distortion corrective techniquesDistortion - Best practice for mechanical corrective techniques

- clear

Distortion corrective techniquesDistortion - thermal corrective techniques

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General guidelines:

•Length of wedge = two-thirds of the plate width

•Width of wedge (base) = one sixth of its length (base to apex)

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•use spot heating to remove buckling in thin sheet structures

•other than in spot heating of thin panels, use a wedge-shapedheating technique

•use line heating to correct angular distortion in plate

•restrict the area of heating to avoid over-shrinking the component

•limit the temperature to 60° to 650°C (dull red heat) in steels toprevent metallurgical damage

•in wedge heating, heat from the base to the apex of the wedge,penetrate evenly through the plate thickness and maintain an eventemperature

Welding Inspector

Heat TreatmentSection 18

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Heat Treatment

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Heat TreatmentsMany metals must be given heat treatment before and afterwelding.

The inspector’s function is to ensure that the treatment isgiven correctly in accordance with the specification or as perthe details supplied.

Types of heat treatment available:•Preheat

•Annealing

•Normalising

•Quench Hardening

•Temper

•Stress Relief4/23/2007

Heat TreatmentsPre-heat treatments

• are used to increase weldability, by reducing suddenreduction of temperature, and control expansion andcontraction forces during welding

Post weld heat treatments

• are used to change the properties of the weld metal,controlling the formation of crystalline structures

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A

C

Post Weld Heat TreatmentsB

(A) Normalised

(B) Fully Annealed

(C) Water-quenched

(D) Water-quenched & tempered

D

Post Weld Heat TreatmentsThe inspector, in general, should ensure that:

• Equipment is as specified

• Temperature control equipment is in good condition

• Procedures as specified, is being used e.g.

o Method of application

o Rate of heating and cooling

o Maximum temperature

o Soak time

o Temperature measurement (and calibration)

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Time

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Post Weld Heat Treatment Cycle

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Heat TreatmentRecommendations

• Provide adequate support (low YS at high temperature!)

• Control heating rate to avoid uneven thermal expansions

• Control soak time to equalise temperatures

• Control temperature gradients - NO direct flame impingement!

• Control furnace atmosphere to reduce scaling

• Control cooling rate to avoid brittle structure formation

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Gas furnace heat treatment

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Post Weld Heat Treatment Methods

HF (Induction) local heat treatment

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Local heat treatment usingelectric heating blankets

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Welding Inspector

Cutting ProcessesSection 19

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Use of gas flame

Welding GougingBrazing

Heating4/23/2007

Straightening

Cutting

Blasting Spraying582 of 691

Regulators

583

valve

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Flashbackflamequenchedat theflashbackbarrier

Built-incheckFlamebarrier

Normalflow

Reverseflow

Flashback

Built-incheckvalvestopsreverseflow

Flashback arrestorsFlashback - recession of the flame into or back of the mixing chamber

SAFETY SAFETY SAFETY

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Oxyfuel gas cutting related terms

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Oxyfuel gas cutting quality• Good cut - sharp top edge, fine and even drag lines, little

oxide and a sharp bottom edge

Oxyfuel gas cutting quality

• Good cut - sharp top edge, fine and even drag lines, littleoxide and a sharp bottom edge

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Oxyfuel gas cutting quality• Good cut - sharp top edge, fine and even drag lines, little

oxide and a sharp bottom edge

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Special oxyfuel operations• Gouging

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Special oxyfuel operations

• Thin sheet cutting

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Cutting Processes

Plasma arc cutting• Uses high velocity jet of ionised gas through a

constricted nozzle to remove the moltenmetal

• Uses a tungsten electrode and water coolednozzle

• High quality cutting• High intensity and UV radiation

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Cutting ProcessesAir-arc for cutting or gouging

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Air-arc gouging features

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Welding Inspector

Arc Welding SafetyPlease discuss

Section 20

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Safety

• Electrical safety• Heat & Light

– Visible light– UV radiation - effects on skin

and eyes••••••

Fumes & Explosive GassesNoise levelsFire HazardsScaffolding & StagingSlips, trips and fallsProtection of others fromexposure

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Welding Inspector

Weldability Of SteelsSection 21

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Weldability of SteelsDefinition

It relates to the ability of the metal (or alloy) to be welded withmechanical soundness by most of the common welding processes,and the resulting welded joint retain the properties for which ithas been designed.

is a function of many inter-related factors but these may besummarised as:

•Composition of parent material

•Joint design and size

•Process and technique

•Access

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Weldability of SteelsThe weldability of steel is mainly dependant on carbon & other alloyingelements content.

If a material has limited weldability, we need to take special measures toensure the maintenance of the properties required

Poor weldability normally results in the occurrence of cracking

A steel is considered to have poor weldability when:

• an acceptable joint can only be made by using very narrow range ofwelding conditions

• great precautions to avoid cracking are essential (e.g., high pre-heat etc)

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The Effect of Alloying on SteelsElements may be added to steels to produce the propertiesrequired to make it useful for an application.

Most elements can have many effects on the properties ofsteels.

Other factors which affect material properties are:

•The temperature reached before and during welding

•Heat input

•The cooling rate after welding and or PWHT

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Steel Alloying Elements

Steel Alloying Elements

Phosphorus (P): Residual element from steel-making minerals. difficult to reducebelow < ~ 0.015% brittleness

Sulphur (S): Residual element from steel-making minerals

< ~ 0.015% in modern steels

< ~ 0.003% in very clean steels

Aluminium (Al): De-oxidant and grain size control

•typically ~ 0.02 to ~ 0.05%

Chromium (Cr): For creep resistance & oxidation (scaling) resistance for elevatedtemperature service. Widely used in stainless steels for corrosion resistance,increases hardness and strength but reduces ductility.

•typically ~ 1 to 9% in low alloy steels

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Nickel (Ni)Used in stainless steels, high resistance to corrosion from acids,increases strength and toughness

Molybdenum (Mo): Affects hardenability. Steels containing molybdenumare less susceptible to temper brittleness than other alloy steels.Increases the high temperature tensile and creep strengths of steel.typically ~ 0.5 to 1.0%

Niobium (Nb): a grain refiner, typically~ 0.05%

Vanadium (V): a grain refiner, typically ~ 0.05%

Titanium (Ti): a grain refiner, typically ~ 0.05%

Copper (Cu): present as a residual, (typically < ~ 0.30%)added to ‘weathering steels’ (~ 0.6%) to give better resistance toatmospheric corrosion

Classification of SteelsMild steel (CE < 0.4)•

•

Readily weldable, preheat generally not required if low hydrogenprocesses or electrodes are usedPreheat may be required when welding thick section material, highrestraint and with higher levels of hydrogen being generated

C-Mn, medium carbon, low alloy steels (CE 0.4 to 0.5)• Thin sections can be welded without preheat but thicker sections will

require low preheat levels and low hydrogen processes or electrodesshould be used

Higher carbon and alloyed steels (CE > 0.5)• Preheat, low hydrogen processes or electrodes, post weld heating and

slow cooling may be required

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Process Cracks

• Hydrogen Induced HAZ Cracking (C/Mn steels)

• Hydrogen Induced Weld Metal Cracking (HSLA steels).

• Solidification or Hot Cracking (All steels)

• Lamellar Tearing (All steels)

• Re-heat Cracking (All steels, very susceptible Cr/Mo/V steels)

• Inter-Crystalline Corrosion or Weld Decay (stainless steels)

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CrackingWhen considering any type of cracking mechanism, threeelements must always be present:

•

•

•

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StressResidual stress is always present in a weldment, throughunbalanced local expansion and contraction

RestraintRestraint may be a local restriction, or through platesbeing welded to each other

Susceptible microstructureThe microstructure may be made susceptible tocracking by the process of welding

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Cracks


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May occur:

• up to 48 hrs after completion

• In weld metal, HAZ, parentmetal.

• At weld toes

• Under weld beads

• At stress raisers.

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Also know as:

Cold Cracking, happens whenthe welds cool down.

HAZ cracking, normally occursin the HAZ.

Delayed cracking, as it takestime for the hydrogen tomigrate. 48 Hours normally butup to 72,

Under-bead cracking, normallyhappens in the HAZ under aweld bead

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There is a risk of hydrogen cracking when all of the 4 factorsoccur together:

•Hydrogen

•Stress

More than 15ml/100g of weld metal

More than ½ the yield stress

•Temperature Below 300oC

•Hardness Greater than 400HV Vickers

•Susceptible Microstructure (Martensite)

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Precautions for controlling hydrogen cracking

• Pre heat, removes moisture from the joint preparations, andslows down the cooling rate

• Ensure joint preparations are clean and free fromcontamination

• The use of a low hydrogen welding process and correct arclength

• Ensure all welding is carried out is carried out under controlledenvironmental conditions

• Ensure good fit-up as to reduced stress

• The use of a PWHT• Avoid poor weld profiles

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Hydrogen absorbedin a long, orunstable arc

H2

H2 diffuses to γ in HAZ616 of 691

Cellulosic electrodesproduce hydrogen as ashielding gas

Hydrogen introduced inweld from consumable,oils, or paint on plate

H2

Martensite forms from γ

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Susceptible Microstructure:

Hard brittle structure – MARTENSITE Promoted by:

A) High Carbon Content, Carbon Equivalent (CE)


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Hydrogen Scales

List of hydrogen scales from BS EN 1011:part 2.

Hydrogen content related to 100 grams of weld metaldeposited.

• Scale A

• Scale B

• Scale C

• Scale D

• Scale E

High: >15 ml

Medium: 10 ml - 15 ml

Low: 5 ml - 10 ml

Very low: 3 ml - 5 ml

Ultra-low: < 3 ml

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Potential Hydrogen Level Processeslist of welding processes in order of potential lowest hydrogencontent with regards to 100g of deposited weld metal.

•TIG

•MIG

< 3 ml

< 5 ml

•ESW < 5 ml

•MMA (Basic Electrodes) < 5 ml

•SAW

•FCAW

< 10ml

< 15 ml

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Solidification CrackingAlso referred as

Hot Cracking: Occurring at high temperatures while the weld is hot

Centerline cracking: cracks appear down the centre line of the bead.

Crater cracking: Small cracks in weld centers are solidification cracks

Crack type:

Location:

Steel types:

Solidification cracking

Weld centreline (longitudinal)

High sulphur & phosphor concentration in steels.

Susceptible Microstructure: Columnar grains In directionof solidification

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•

•

•

•

•

•

•


Sulphur in the parent material may dilute in the weldmetal to form iron sulphides (low strength, low meltingpoint compounds)

During weld metal solidification, columnar crystals pushstill liquid iron sulphides in front to the last place ofsolidification, weld centerline.

The bonding between the grains which are themselvesunder great stress and may now be very poor to maintaincohesion and a crack will result, weld centerline.

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Solidification CrackingAvoidance

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Solidification CrackingPrecautions for controlling solidification cracking

• The use of high manganese and low carbon content fillers

• Minimise the amount of stress / restraint acting on the jointduring welding

• The use of high quality parent materials, low levels ofimpurities (Phosphor & sulphur)

• Clean joint preparations contaminants (oil, grease, paints andany other sulphur containing product)

• Joint design selection depth to width ratios

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Solidification cracking in Austenitic Stainless Steel

• particularly prone to solidification cracking

• large grain size gives rise to a reduction in grain boundary area withhigh concentration of impurities

• Austenitic structure very intolerant to contaminants (sulphur,phosphorous and other impurities).

• High coefficient of thermal expansion /Low coefficient of thermalconductivity, with high resultant residual stress

• same precautions against cracking as for plain carbon steels with extraemphasis on thorough cleaning and high dilution controls.

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Cracks

Lamellar Tearing

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Lamellar TearingFactors for lamellar tearing to occur

Cracks only occur in the rolled plate !

Close to or just outside the HAZ !

Cracks lay parallel to the plate surface and the fusion boundaryof the weld and has a stepped aspect.

• Low quality parent materials, high levels of impurities

• Joint design, direction of stress

• The amount of stress acting across the joint during welding

• Note: very susceptible joints may form lamellar tearing undervery low levels of stress

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Lamellar Tearing

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Lamellar Tearing

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Lamellar Tearing

Susceptible Non-Susceptible

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Lamellar Tearing

•

•

•

•

•

•

Crack type:

Location:

Steel types:

Microstructure:

Lamellar TearingLamellar tearing

Below weld HAZ

High sulphur & phosphorous steels

Lamination & Segregation

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Short Tensile (Through Thickness) Test

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High contractionalstrains

Lamellar tear

Restraint

Welding Inspector

Practical Visual InspectionSection 22

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S.T.D.L

HI-

LO

Sin

gle

Pu

rpos

e W

eld

ing

Gau

ge

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1

2

3

4

5

6

Plate / Pipe Inspection

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Welding Inspector

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Welding TemperaturesDefinitions

Preheat temperature

• is the temperature of the workpiece in the weld zone immediately beforeany welding operation (including tack welding!)

• normally expressed as a minimum Interpass temperature

– is the temperature in a multi-run weld and adjacent parent metalimmediately prior to the application of the next run

– normally expressed as a maximum

Pre heat maintenance temperature = the minimum temperature in theweld zone which shall be maintained if welding is interrupted and shall bemonitored during the interruption.

Pre-heat ApplicationFurnace - Heating entire component - best

Electrical elements -Controllable; Portable; Site use; Clean; Componentcannot be moved.

Gas burners - direct flame impingement; Possible local overheating; Lesscontrollable;Portable; Manual operation possible; Componentcan be moved.

Radiant gas heaters - capable of automatic control; No flameimpingement; No contact with component; Portable.

Induction heating - controllable; Rapid heating (mins not hours); Largepower supply; Expensive equipment

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Parameters to be measured:

Measuring pre heat in Welding

Pre-heat Application

Application Of Preheat

• Heat either side of joint

• Measure temp 2 mins after heat removal

• Always best to heat complete component rather than local ifpossible to avoid distortion

• Preheat always higher for fillet than butt welds due todifferent combined thicknesses and chill effect factors.

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Pre-Heat Application

Manual Gas Operation

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Welding Temperatures

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Combined ThicknessThe Chilling Effect of the Joint

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Combined Thickness

Combined Thickness

Combined chilling effect of joint type andthickness.

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The Chill Effect of the Material

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Heating Temperature Control

• TEMPILSTICKS - crayons, melt at set temps. Will not measuremax temp.

• Pyrometers - contact or remote, measure actual temp.

• Thermocouples - contact or attached, very accurate, measureactual temp.

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Temperature Test Equipment

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Temperature test equipment

Welding Inspector

CalibrationSection 24

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Calibration, validation and monitoringDefinitions:

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Calibration and validationFrequency - When it is required?

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Welding parameter calibration/validation

Which parameters need calibration/validation?

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PAMS (Portable Arc Monitor System)

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PAMS (Portable Arc Monitor System)

Use of PAMS

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Use of PAMS

Summary• a welding power source can only be calibrated if it has

meters fitted

• the inspector should check for calibration stickers, datesetc.

• a welding power source without meters can only bevalidated that the control knobs provide repeatability

• the main role is to carryout “in process monitoring” toensure that the welding requirements are met duringproduction

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Welding Inspector

Macro/Micro ExaminationSection 25

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Macro / Micro ExaminationObject:

• Macro / microscopic examinations are used to give a visualevaluation of a cross-section of a welded joint

• Carried out on full thickness specimens

• The width of the specimen should include HAZ, weld andparent plate

• They maybe cut from a stop/start area on a weldersapproval test

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Macro / Micro ExaminationWill Reveal:

• Weld soundness

• Distribution of inclusions

• Number of weld passes

• Metallurgical structure of weld, fusion zone and HAZ

• Location and depth of penetration of weld

• Fillet weld leg and throat dimensions

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Metallographic Examination

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