23368109-04-WIS5-MechanicalTesting-2006

Copyright © 2006, TWI LtdWorld Centre for Materials Joining Technology

CSWIP 3.1 Welding InspectionCSWIP 3.1 Welding Inspection

TWI Training & Examination TWI Training & Examination ServicesServices

Destructive TestingDestructive Testing

Course Reference WIS 5Course Reference WIS 5Course notes section reference 4Course notes section reference 4


The destruction of a welded The destruction of a welded unit or by cutting out selected unit or by cutting out selected specimens from the weld specimens from the weld is is carried out to check the carried out to check the mechanical properties of the mechanical properties of the joint materials. They can be joint materials. They can be produced to:produced to:

What is Destructive Testing ?What is Destructive Testing ?

Destructive Testing DefinitionsDestructive Testing Definitions

• Approve welding procedures (BS EN 288)Approve welding procedures (BS EN 288)

• Approve welders (BS EN 287)Approve welders (BS EN 287)

• Production quality controlProduction quality control


Qualitative and Quantitative TestsQualitative and Quantitative Tests

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

The following mechanical tests have no units and are termedThe following mechanical tests have no units and are termed

qualitativequalitative tests for tests for assessing joint qualityassessing joint quality• Macro testingMacro testing• Bend testingBend testing• Fillet weld fracture testingFillet weld fracture testing• Butt weld nick-break testingButt weld nick-break testing


• MalleabilityMalleability• DuctilityDuctility• ToughnessToughness• HardnessHardness• Tensile StrengthTensile Strength

Ability of a material to Ability of a material to withstand deformation under withstand deformation under static compressive loading static compressive loading without rupturewithout rupture

DefinitionsDefinitionsMechanical Properties of metalsMechanical Properties of metals are related to the amount of are related to the amount of deformation which metals can withstand under different deformation which metals can withstand under different circumstances of force application.circumstances of force application.



Ability of a material undergo Ability of a material undergo plastic deformation under plastic deformation under static tensile loading without static tensile loading without rupture. Measurable rupture. Measurable elongation and reduction in elongation and reduction in cross section areacross section area




Ability of a material to Ability of a material to withstand bending or the withstand bending or the application of shear stresses application of shear stresses by impact loading without by impact loading without fracture.fracture.




Measurement of a materials Measurement of a materials surface resistance to surface resistance to indentation indentation from another from another material by static loadmaterial by static load




Measurement Measurement of the of the maximum force required to maximum force required to fracture a materials bar of fracture a materials bar of unit cross-sectional area in unit cross-sectional area in tension tension



Tensile SpecimensTensile Specimens

Fracture Fillet Fracture Fillet SpecimenSpecimen

CTOD SpecimenCTOD Specimen

Charpy SpecimenCharpy Specimen

Bend Test Bend Test SpecimenSpecimen

Mechanical Test SamplesMechanical Test Samples


Destructive TestingDestructive Testing

Typical Positions for Test Typical Positions for Test PiecesPieces

Specimen Type PositionSpecimen Type Position

•Macro + HardnessMacro + Hardness 5 5

•Transverse TensileTransverse Tensile 2, 4 2, 4

•Bend TestsBend Tests 2, 4 2, 4

•Charpy Impact TestsCharpy Impact Tests 3 3

•Additional TestsAdditional Tests 3 3

WELDING PROCEDURE QUALIFICATION TESTINGWELDING PROCEDURE QUALIFICATION TESTING

22

33

44

55

top of fixed pipetop of fixed pipe


Mechanical TestingMechanical Testing

Hardness TestingHardness Testing



DefinitionDefinition

• Measurement of resistance of a material against Measurement of resistance of a material against penetration of an indenter under a constant loadpenetration of an indenter under a constant load

• There is a direct correlation between UTS and hardnessThere is a direct correlation between UTS and hardness

Hardness tests:Hardness tests:

• BrinellBrinell

• VickersVickers

• RockwellRockwell



Objectives:Objectives:

• measuring hardness in different areas of a welded jointmeasuring hardness in different areas of a welded joint

• assessing resistance toward brittle fracture, cold cracking assessing resistance toward brittle fracture, cold cracking and corrosion sensitivity in Hand corrosion sensitivity in H22SS

Information to be supplied on the test report:Information to be supplied on the test report:

• material typematerial type

• location of indentationlocation of indentation

• type of hardness test and load applied on the indentertype of hardness test and load applied on the indenter

• hardness valuehardness value



Hardness Test Methods Typical DesignationsHardness Test Methods Typical Designations

VickersVickers 240 HV10240 HV10

RockwellRockwell Rc 22Rc 22

BrinellBrinell 200 BHN-W200 BHN-W

usually the hardest regionusually the hardest region

1.5 to 3mm1.5 to 3mm

HAZHAZ

fusion line fusion line or or fusion fusion

boundaryboundary


Vickers Hardness TestVickers Hardness Test

Typical location of the indentationsTypical location of the indentations

Butt weld from one side only

Butt weld from both side


Vickers hardness tests:Vickers hardness tests:

• indentation body is a square based diamond pyramid (136º indentation body is a square based diamond pyramid (136º included angle)included angle)

• the average diagonal (d) of the impression is converted to a the average diagonal (d) of the impression is converted to a hardness number from a tablehardness number from a table

• it is measured in HV5, HV10 or HV025it is measured in HV5, HV10 or HV025 Adjustable Adjustable shuttersshuttersIndentationIndentationDiamond Diamond

indentorindentor

Vickers Hardness TestVickers Hardness Test


Vickers Hardness Test MachineVickers Hardness Test Machine


• Hardened steel ball of given diameter is subjected for a Hardened steel ball of given diameter is subjected for a given time to a given loadgiven time to a given load

• Load divided by area of indentation gives Brinell hardness Load divided by area of indentation gives Brinell hardness in kg/mmin kg/mm22

• More suitable for on site hardness testingMore suitable for on site hardness testing

Brinell Hardness TestBrinell Hardness Test

30KN30KN

Ø=10mm steel ball


Rockwell Hardness TestRockwell Hardness Test

1KN1KN

Ø=1.6mm steel ball

Rockwell BRockwell B Rockwell CRockwell C

1.5KN1.5KN

120°Diamond Cone


Schlerescope Hardness TestSchlerescope Hardness Test

• dynamic and very portable hardness testdynamic and very portable hardness test

• accuracy depends on the the condition of the test/support accuracy depends on the the condition of the test/support surfaces and the support of the test piece during the testsurfaces and the support of the test piece during the test

• for more details, see ASTM E448for more details, see ASTM E448



Impact TestingImpact Testing


Charpy V-Notch Impact TestCharpy V-Notch Impact Test

Objectives:Objectives:• measuring impact strength in different weld joint areasmeasuring impact strength in different weld joint areas• assessing resistance toward brittle fractureassessing resistance toward brittle fracture

Information to be supplied on the test report:Information to be supplied on the test report:• Material typeMaterial type• Notch typeNotch type• Specimen sizeSpecimen size• Test temperatureTest temperature• Notch locationNotch location• Impact Strength ValueImpact Strength Value


Charpy V-Notch Impact Charpy V-Notch Impact TestTest

SpecimenSpecimen PendulumPendulum(striker)(striker)

Anvil (support)Anvil (support)


Charpy V-notch impact test specimenCharpy V-notch impact test specimen

Specimen dimensions according ASTM E23Specimen dimensions according ASTM E23

ASTM: American Society of Testing MaterialsASTM: American Society of Testing Materials


10 mm10 mm8

mm

8 m

m2

mm

2 m

m22.522.5oo

Machined Machined notchnotch

100% Ductile100% DuctileMachined Machined

notchnotch

Large reduction Large reduction in area, shear in area, shear lipslips

Fracture surface Fracture surface 100% bright 100% bright crystalline brittle crystalline brittle fracturefracture

Randomly torn, Randomly torn, dull gray fracture dull gray fracture surfacesurface

Charpy Impact TestCharpy Impact Test

100% Brittle100% Brittle


- 50- 50 00- 20- 20 - 10- 10- 40- 40 - 30- 30

Ductile fractureDuctile fracture

Ductile/BrittleDuctile/Brittletransition transition pointpoint

47 Joules47 Joules

28 Joules28 Joules

Testing temperatureTesting temperature - Degrees Degrees CentigradeCentigrade

Temperature rangeTemperature range

Transition rangeTransition range

Brittle fractureBrittle fracture

Ductile / Brittle Transition Ductile / Brittle Transition CurveCurve

Three specimens are normally tested at each temperatureThree specimens are normally tested at each temperature

Energy absorbedEnergy absorbed


- 50- 50 00- 20- 20 - 10- 10- 40- 40 - 30- 30

Ductile fractureDuctile fracture

Ductile/BrittleDuctile/Brittletransition transition pointpoint

47 Joules47 Joules

28 Joules28 Joules

Testing temperatureTesting temperature - Degrees Degrees CentigradeCentigrade

Temperature rangeTemperature range

Transition rangeTransition range


Ductile / Brittle Transition Ductile / Brittle Transition CurveCurve

Mn < 1.6 % increases Mn < 1.6 % increases toughness in steels*toughness in steels*

Three specimens are normally tested at each temperatureThree specimens are normally tested at each temperature

Energy absorbedEnergy absorbed


Impact Energy JoulesImpact Energy Joules

Room TemperatureRoom Temperature -20-20ooC TemperatureC Temperature

1.1. 197 Joules197 Joules

2.2. 191 191 JoulesJoules





Average =Average = 191 191 JoulesJoules Average =Average = 51 51 JoulesJoules

The test results show the specimens carried out at room The test results show the specimens carried out at room temperature absorb more energy than the specimens carried temperature absorb more energy than the specimens carried out at -20out at -20ooCC

Comparison Charpy Impact Test Comparison Charpy Impact Test ResultsResults


Charpy Impact TestCharpy Impact Test

Reporting resultsReporting results

• Location and orientation of notch Location and orientation of notch

• Testing temperatureTesting temperature

• Energy absorbed in joulesEnergy absorbed in joules

• Description of fracture (brittle or ductile)Description of fracture (brittle or ductile)

• Location of any defects presentLocation of any defects present

• Dimensions of specimenDimensions of specimen



Tensile TestingTensile Testing


UTS Tensile testUTS Tensile test


Tensile TestsTensile Tests

Different tensile tests:Different tensile tests:

• Transverse tensile.Transverse tensile.

• All-weld metal tensile testAll-weld metal tensile test

• Cruciform tensile testCruciform tensile test

• Short tensile test (through thickness test)Short tensile test (through thickness test)


All-Weld Metal Tensile All-Weld Metal Tensile SpecimenSpecimen

Transverse Tensile Transverse Tensile SpecimenSpecimen

Tensile TestTensile Test


Transverse Joint Tensile TestTransverse Joint Tensile Test

Objective:Objective:

Measuring the overall strength of the weld jointMeasuring the overall strength of the weld joint

Information to be supplied on the test report:Information to be supplied on the test report:• material typematerial type• specimen typespecimen type• specimen size (see QW-462.1) specimen size (see QW-462.1) • UTSUTS• location of final rupturelocation of final rupture


Transverse Joint Tensile Test Transverse Joint Tensile Test

Weld on plateWeld on plate

Multiple cross joint Multiple cross joint specimensspecimensWeld on pipeWeld on pipe


Maximum load applied = 220 kN.Maximum load applied = 220 kN.

Least cross sectional area = 25 mm X 12 mmLeast cross sectional area = 25 mm X 12 mm

UTS = UTS = Maximum load appliedMaximum load applied Least c.s.a.Least c.s.a.

UTS = UTS = 220 000 220 000 25mm X 12mm25mm X 12mm

UTS = 733.33 N/mmUTS = 733.33 N/mm22

Transverse Tensile TestTransverse Tensile Test


Reporting results: Reporting results:

• Type of specimen e.g. reduced section Type of specimen e.g. reduced section

• Whether weld reinforcement is removedWhether weld reinforcement is removed

• Dimensions of test specimenDimensions of test specimen

• The ultimate tensile strength in N/mmThe ultimate tensile strength in N/mm22, p.s.i or Mpa, p.s.i or Mpa

• Location of fracture.Location of fracture.

• Location and type of any flaws present if anyLocation and type of any flaws present if any

Transverse Tensile TestTransverse Tensile Test


Tensile test piece cut along weld specimen.Tensile test piece cut along weld specimen.

Direction of the test *Direction of the test *

BS 709 / BS EN 10002BS 709 / BS EN 10002

All Weld Metal Tensile TestingAll Weld Metal Tensile Testing

All Weld Metal Tensile TestAll Weld Metal Tensile Test


Gauge lengthGauge length

Increased gauge length Increased gauge length

Object of test:Object of test:

Ultimate tensile strength.Ultimate tensile strength.

Yield strength.Yield strength.

Elongation %(ductility).Elongation %(ductility).

All-Weld Metal Tensile TestAll-Weld Metal Tensile Test


2 marks are made2 marks are made

During the test, Yield & Tensile strength are recordedDuring the test, Yield & Tensile strength are recorded

The specimen is joined and the marks are re-measuredThe specimen is joined and the marks are re-measured

A measurement of 75mm will give Elongation of 50 %A measurement of 75mm will give Elongation of 50 %


Gauge length 50mmGauge length 50mm

Increased gauge length 75mm Increased gauge length 75mm


Original gauge length = 50mmOriginal gauge length = 50mm

Increased gauge length = 64Increased gauge length = 64

Elongation % = Elongation % = Increase of gauge lengthIncrease of gauge length X 100 X 100 Original gauge lengthOriginal gauge length

Elongation % = Elongation % = 64 X 10064 X 100 5050

Elongation = 28%Elongation = 28%



All-Weld Metal Tensile TestAll-Weld Metal Tensile TestReporting results:Reporting results:

• Type of specimen e.g. reduced section Type of specimen e.g. reduced section

• Dimensions of test specimenDimensions of test specimen

• The u.t.s, yield strength in N/mmThe u.t.s, yield strength in N/mm22, p.s.i or Mpa, p.s.i or Mpa

• Elongation %Elongation %

• Location and type of any flaws present if anyLocation and type of any flaws present if any


STRA (Short Transverse Reduction Area)STRA (Short Transverse Reduction Area)


STRA testSTRA test

Original CSA

Reduced CSA


STRA testSTRA test

20

15

10

STRA % Reduction of CSA



Macro / Micro ExaminationMacro / Micro Examination


Macro / Micro ExaminationMacro / Micro ExaminationObject:Object:

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

• Carried out on full thickness specimensCarried out on full thickness specimens

• The width of the specimen should include HAZ, weld and The width of the specimen should include HAZ, weld and parent plateparent plate

• They maybe cut from a stop/start area on a welders They maybe cut from a stop/start area on a welders approval testapproval test


Macro / Micro ExaminationMacro / Micro ExaminationWillWill Reveal:Reveal:

• Weld soundnessWeld soundness

• Distribution of inclusionsDistribution of inclusions

• Number of weld passesNumber of weld passes

• Metallurgical structure of weld, fusion zone and HAZMetallurgical structure of weld, fusion zone and HAZ

• Location and depth of penetration of weldLocation and depth of penetration of weld

• Fillet weld leg and throat dimensionsFillet weld leg and throat dimensions


• Visual examination for Visual examination for defectsdefects

• Cut transverse from the Cut transverse from the weldweld

• Ground & polished P400 Ground & polished P400 grit papergrit paper

• Acid etch using 5-10% Acid etch using 5-10% nitric acid solutionnitric acid solution

• Wash and dryWash and dry

• Visual evaluation under 5x Visual evaluation under 5x magnificationmagnification

• Report on resultsReport on results

• Visual examination for Visual examination for defects & grain structuredefects & grain structure

• Cut transverse from a Cut transverse from a weldweld

• Ground & polished P1200 Ground & polished P1200 grit paper, 1µm pastegrit paper, 1µm paste

• Acid etch using 1-5% Acid etch using 1-5% nitric acid solutionnitric acid solution

• Wash and dryWash and dry

• Visual evaluation under Visual evaluation under 100-1000x magnification100-1000x magnification

• Report on resultsReport on results

MacroMacro MicroMicro


Metallographic ExaminationMetallographic Examination

Macro examinationMacro examination Micro examinationMicro examination


Metallographic Metallographic examinationexamination

Objectives:Objectives:

• detecting weld defects (macro)detecting weld defects (macro)

• measuring grain size (micro)measuring grain size (micro)

• detecting brittle structures, precipitates, etcdetecting brittle structures, precipitates, etc

• assessing resistance toward brittle fracture, cold cracking assessing resistance toward brittle fracture, cold cracking and corrosion sensitivityand corrosion sensitivity

Information to be supplied on the test report:Information to be supplied on the test report:

• material typematerial type

• etching solutionetching solution

• magnificationmagnification

• grain sizegrain size

• location of examined arealocation of examined area

• weld imperfections (macro)weld imperfections (macro)

• phase, constituents, precipitates (micro)phase, constituents, precipitates (micro)



Bend TestingBend Testing



• To determine the soundness of the weld zone. Bend testing can To determine the soundness of the weld zone. Bend testing can also be used to give an assessment of weld zone ductility.also be used to give an assessment of weld zone ductility.

There are three ways to perform a bend test:There are three ways to perform a bend test:

Root bendRoot bend

Face bendFace bend

Side bendSide bend

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

Bend TestsBend Tests


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

Thickness of material - “t”Thickness of material - “t”

““t” up to 12 mmt” up to 12 mm

““t” over 12 mmt” over 12 mm

Root / face Root / face bendbend

Side bendSide bend


Bending test methodsBending test methods

Guided bend testGuided bend test Wraparound bend testWraparound bend test


Defect Defect indicationindicationGenerally this Generally this specimen specimen would be would be unacceptable unacceptable

Face bendFace bendSide bendSide bend

Root bendRoot bend

Acceptance forAcceptance forminor ruptures on minor ruptures on tension surfacetension surfacedepends upon code depends upon code requirements requirements

Bend TestingBend Testing


Bend TestsBend Tests

Reporting results: Reporting results:

• Thickness and dimensions of specimenThickness and dimensions of specimen

• Direction of bend (root, face or side)Direction of bend (root, face or side)

• Angle of bend (90Angle of bend (90oo, 120, 120oo, 180, 180oo))

• Diameter of former. (typical 4T)Diameter of former. (typical 4T)

• Appearance of joint after bending e.g. type and location of Appearance of joint after bending e.g. type and location of any flaws.any flaws.



Fillet Weld Fracture TestingFillet Weld Fracture Testing


Fillet Weld Fracture TestsFillet Weld Fracture TestsObject of test:Object of test:

• To break open the joint through the weld to permit To break open the joint through the weld to permit examination of the fracture surfacesexamination of the fracture surfaces

• Specimens are cut to the required lengthSpecimens are cut to the required length

• A saw cut approximately 2mm in depth is A saw cut approximately 2mm in depth is applied along applied along the fillet welds lengththe fillet welds length

• Fracture is usually made by striking the specimen with a Fracture is usually made by striking the specimen with a single hammer blowsingle hammer blow

• Visual inspection for defectsVisual inspection for defects


Fracture should break weld saw cut to root Fracture should break weld saw cut to root

2mm 2mm NotchNotch

HammerHammer

Fillet Weld Fracture TestsFillet Weld Fracture Tests


This fracture indicates This fracture indicates lack of fusion lack of fusion

This fracture has This fracture has occurred saw cut to root occurred saw cut to root

Fillet Weld Fracture TestsFillet Weld Fracture Tests

Lack of PenetrationLack of Penetration


Fillet Weld Fracture TestsFillet Weld Fracture TestsReporting results:Reporting results:

• Thickness of parent material Thickness of parent material

• Throat thickness and leg lengthsThroat thickness and leg lengths

• Location of fractureLocation of fracture

• Appearance of joint after fractureAppearance of joint after fracture

• Depth of penetrationDepth of penetration

• Defects present on fracture surfacesDefects present on fracture surfaces



Nick-Break TestingNick-Break Testing


Nick-Break TestNick-Break Test


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

• Specimens are cut transverse to the weldSpecimens are cut transverse to the weld

• A saw cut approximately 2mm in depth is applied along the A saw cut approximately 2mm in depth is applied along the welds root and capwelds root and cap

• Fracture is usually made by striking the specimen with a Fracture is usually made by striking the specimen with a single hammer blowsingle hammer blow

• Visual inspection for defectsVisual inspection for defects


Approximately 230 mmApproximately 230 mm

19 mm19 mm

3 mm3 mm

3 mm3 mm

Notch cut by hacksawNotch cut by hacksaw

Weld reinforcement Weld reinforcement may or may not be may or may not be removedremoved

Nick-Break TestNick-Break Test


Nick Break TestNick Break Test

Inclusions on fracture Inclusions on fracture lineline

Lack of root penetration Lack of root penetration or fusionor fusion

Alternative nick-break test Alternative nick-break test specimen, notch applied all specimen, notch applied all way around the specimen way around the specimen


Nick-Break TestNick-Break TestReporting results: Reporting results:

• Thickness of parent material Thickness of parent material

• Width of specimenWidth of specimen

• Location of fractureLocation of fracture

• Appearance of joint after fractureAppearance of joint after fracture

• Depth of penetrationDepth of penetration

• Defects present on fracture surfacesDefects present on fracture surfaces


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

We divide tests into Qualitative & Quantitative methods:

Qualitative: (Have no units)

Macro tests

Bend tests

Fillet weld fracture tests

Butt Nick break tests

Quantitative: (Have units)

Hardness (VPN & BHN)

Toughness (Joules & ft.lbs)

Strength (N/mm2 & PSI, MPa)

Ductility / Elongation (E%)

Summary of Mechanical TestingSummary of Mechanical Testing


Hydrostatic testHydrostatic test

Is an under pressureIs an under pressure leakage proof test leakage proof test

Vessel configuration:Vessel configuration:

• the test should be done after any stress reliefthe test should be done after any stress relief

• components that will not stand the pressure test (e.g. components that will not stand the pressure test (e.g. flexible pipes, diaphragms) must be removedflexible pipes, diaphragms) must be removed

• the ambient temperature MUST be above 0°C (preferably the ambient temperature MUST be above 0°C (preferably 15÷20°C)15÷20°C)


Hydrostatic TestHydrostatic Test

Test procedure:Test procedure: • blank off all openings with solid flangesblank off all openings with solid flanges• use correct nuts and bolts, NOT “G” clampsuse correct nuts and bolts, NOT “G” clamps• two pressure gauges on independent tapping points two pressure gauges on independent tapping points

should be usedshould be used• for safety purposes bleed all the air outfor safety purposes bleed all the air out• pumping should be done slowly (no dynamic pressure pumping should be done slowly (no dynamic pressure

stresses)stresses)• test pressure - see relevant standards (PD 5500, ASME VIII). test pressure - see relevant standards (PD 5500, ASME VIII).

Usually 150% design pressureUsually 150% design pressure• hold the pressure for minimum 30 minuteshold the pressure for minimum 30 minutes


Hydrostatic test Hydrostatic test What to look for:What to look for:

• leaks (check particularly around seams and nozzle welds!)leaks (check particularly around seams and nozzle welds!)

• dry off any condensation with a compressed air-linedry off any condensation with a compressed air-line

• watch the gauges for pressure dropwatch the gauges for pressure drop

• check for distortion of flange faces, etccheck for distortion of flange faces, etc


Any QuestionsAny Questions

??Mechanical TestingMechanical Testing


WELDING TECHNOLOGYWELDING TECHNOLOGY

QuestionQuestionHow are the mechanical properties of Carbon & Carbon-How are the mechanical properties of Carbon & Carbon-Manganese steel weld joints influenced by the welding parameters Manganese steel weld joints influenced by the welding parameters used - current, voltage & travel speed ?used - current, voltage & travel speed ?

(assuming that sound welds are produced)(assuming that sound welds are produced)

AnswerAnswerStrength Strength - does not change very much over a wide - does not change very much over a wide

range of welding conditions range of welding conditions

Toughness Toughness - high heat input tends to reduce toughness in - high heat input tends to reduce toughness in weld & HAZ weld & HAZ

Hardness Hardness - low heat input tends to increase HAZ hardness- low heat input tends to increase HAZ hardness


Welding TechnologyWelding Technology

ARC WELDING - HEAT INPUT CONTROLARC WELDING - HEAT INPUT CONTROL

Heat InputHeat Input == Volts x AmpsVolts x Amps J/mmJ/mm

Travel Speed (mm/sec)Travel Speed (mm/sec)

(Usual practice is to divide by 1000 to give units as kJ/mm)(Usual practice is to divide by 1000 to give units as kJ/mm)

Heat InputHeat Input == Volts x Amps Volts x Amps kJ/mm kJ/mm

Travel Speed (mm/sec)Travel Speed (mm/sec) x 1000x 1000


Welding Positions Welding Positions (to EN Standards)(to EN Standards)

PA (flat)PA (flat)

PB (horiz.- vert.)PB (horiz.- vert.)

PE (overhead)PE (overhead)

PCPC

PDPDPF (vert.-up)PF (vert.-up)

PG (vert.- down)PG (vert.- down)


Welding Positions Welding Positions (to EN Standards)(to EN Standards)

45°45°

H-L045H-L045 vertical-up progressionvertical-up progression

J-L045J-L045 vertical-down progressionvertical-down progression


Welding PositionsWelding Positions

Question:Question:

How does welding position influence heat input ?How does welding position influence heat input ?

Answer:Answer:

• Highest heat input usually associated with vertical-up Highest heat input usually associated with vertical-up welding (PF or 3G with uphill progression) because of welding (PF or 3G with uphill progression) because of relatively low travel speedrelatively low travel speed

• Lowest heat input usually associated with vertical-down Lowest heat input usually associated with vertical-down welding (PG or 3G or 5G with downhill progression) because welding (PG or 3G or 5G with downhill progression) because of relatively high-speed travelof relatively high-speed travel



THE HEAT AFFECTED ZONE (HAZ)THE HEAT AFFECTED ZONE (HAZ)

tempered zonetempered zone

grain growth zonegrain growth zone

recrystallised zonerecrystallised zone

partially transformed zonepartially transformed zone

Max

imu

m

Tem

per

atu

resolid-liquid transitionsolid-liquid transition zonezonesolid solid

weld weld metalmetal

unaffected basematerial



High & Low Heat Input WeldingHigh & Low Heat Input Welding

High heat input - small number of large weld beadsHigh heat input - small number of large weld beads

large % of ‘as-cast’ large % of ‘as-cast’ microstructure in microstructure in

weld metalweld metal

wide HAZwide HAZ

Low heat input - large number of small weld beadsLow heat input - large number of small weld beads

large % of ‘refined’ large % of ‘refined’ microstructure in microstructure in

weld metalweld metal

narrow HAZnarrow HAZ



design temperatureImpact Test TemperatureImpact Test Temperature

good toughnessgood toughnessin steel atin steel at

design temp.design temp.

Charpy V-Charpy V-notch notch

Toughness Toughness (Joules)(Joules)

unweldedfine grained

steel



design temperatureImpact Test TemperatureImpact Test Temperature

good toughnessgood toughnessin steel atin steel at


Charpy V-Charpy V-notch notch

Toughness Toughness (Joules)(Joules)

low toughnesslow toughnessin HAZ atin HAZ at


‘degraded’ HAZassociated with high heat input

welding

steelsteel HAZHAZ



HAZ HARDNESSHAZ HARDNESS

Cooling Rate of HAZ (°C / h)Cooling Rate of HAZ (°C / h)

HAZ HAZ HardnessHardness

Carbon-Manganese SteelsCarbon-Manganese Steels

high heat-input - high heat-input - lower hardnesslower hardness

low heat-input low heat-input higher hardnesshigher hardness

moderate heat input - moderate heat input - moderate hardnessmoderate hardness



Low Alloy SteelsLow Alloy Steels(higher Cr-Mo (higher Cr-Mo types)types)

HAZ HARDNESSHAZ HARDNESS

Cooling Rate of HAZ (°C / h)Cooling Rate of HAZ (°C / h)

HAZ HAZ HardnessHardness

HAZ will harden even when HAZ will harden even when heat input is relatively highheat input is relatively high


Fracture MechanismsFracture Mechanisms


•Ductile Fracture Ductile Fracture

•Brittle FractureBrittle Fracture

•Fatigue Fracture Fatigue Fracture

In-Service FractureIn-Service Fracture



Ductile FractureDuctile Fracture



Ductile (overload) fracture appears when yielding and Ductile (overload) fracture appears when yielding and deformation precedes failuredeformation precedes failure


• it is the result of overloadingit is the result of overloading

• evidence of gross yielding or plastic deformationevidence of gross yielding or plastic deformation

• the fracture surface is rough and tornthe fracture surface is rough and torn

• the surface shows 45° shear lips or have surfaces inclined the surface shows 45° shear lips or have surfaces inclined at 45° to the load direction (because maximum shear plane at 45° to the load direction (because maximum shear plane is at 45° to the load!)is at 45° to the load!)


Ductile fracture distinguish features:Ductile fracture distinguish features:



Brittle FractureBrittle Fracture


It is a fast, unstable type of fracture.It is a fast, unstable type of fracture.




Effect of a notch on tensile ductilityEffect of a notch on tensile ductility

d d

A notch also adversely affect fatigue strength!

Courtesy of Douglas E. Williams, P.E., Welding Handbook, Vol.1,Courtesy of Douglas E. Williams, P.E., Welding Handbook, Vol.1,

Ninth Edition,reprinted by permission of the American Welding SocietyNinth Edition,reprinted by permission of the American Welding Society



Brittle fracture distinguish features:Brittle fracture distinguish features:

• There is little or no plastic deformation before failureThere is little or no plastic deformation before failure

• The crack surface may show chevron marks pointing back The crack surface may show chevron marks pointing back to the initiation pointto the initiation point

• In case of impact fracture, the surface is rough but not torn In case of impact fracture, the surface is rough but not torn and will usually have a crystalline appearanceand will usually have a crystalline appearance

• The surface is normally perpendicular to the loadThe surface is normally perpendicular to the load



Brittle FractureBrittle FractureFactors affecting brittle fracture:Factors affecting brittle fracture:

• Temperature (transition curve, convergence of YS and UTS as Temperature (transition curve, convergence of YS and UTS as the temperature is reduced)the temperature is reduced)

• Crystalline structure (b.c.c. vs. f.c.c.)Crystalline structure (b.c.c. vs. f.c.c.)

• Material toughnessMaterial toughness

• Residual stressResidual stress

• Strain rate (YS increase but UTS remain constant)Strain rate (YS increase but UTS remain constant)

• Material thickness (restrain due to surrounding material)Material thickness (restrain due to surrounding material)

• Stress concentrations/weld defectsStress concentrations/weld defects



Causes for brittle fracture:Causes for brittle fracture:

• Presence of weld defects (poor quality)Presence of weld defects (poor quality)

• Poor toughness in parent material (wrong choice)Poor toughness in parent material (wrong choice)

• Poor toughness in HAZ (to high heat input)Poor toughness in HAZ (to high heat input)

• High level of residual stress (no PWHT, wrong design)High level of residual stress (no PWHT, wrong design)



Fatigue FractureFatigue Fracture


Fatigue FractureFatigue FractureIf a material is subjected to a static load, final If a material is subjected to a static load, final rupture is preceded by very large strains.rupture is preceded by very large strains.

If the same material is subjected to cyclic loads, If the same material is subjected to cyclic loads, failure may occur:failure may occur:

• At stress well below elastic limitAt stress well below elastic limit

• With little or no plastic deformationWith little or no plastic deformation


Fatigue cracking at the Fatigue cracking at the weld toeweld toe



Products liable to Fatigue Products liable to Fatigue FailureFailure

AerospaceAerospacePressure VesselsPressure Vessels

Piping systemsPiping systems Oil/Gas platformsOil/Gas platforms


Products liable to Fatigue Products liable to Fatigue FailureFailure

Lifting equipmentLifting equipment

Engineering plantEngineering plant

Overhead CranesOverhead Cranes

Rotating equipmentRotating equipment


Location: Location: Any stress concentration areaAny stress concentration area

Steel Type: Steel Type: All steel typesAll steel types

Susceptible Microstructure: Susceptible Microstructure: All grain structuresAll grain structures



• Fatigue cracks occur under cyclic stress conditionsFatigue cracks occur under cyclic stress conditions

• Fracture normally occurs at a change in section, notch and Fracture normally occurs at a change in section, notch and weld defects i.e stress concentration area weld defects i.e stress concentration area

• All materials are susceptible to fatigue crackingAll materials are susceptible to fatigue cracking

• Fatigue cracking starts at a specific point referred to as a Fatigue cracking starts at a specific point referred to as a initiation pointinitiation point

• The fracture surface is smooth in appearance sometimes The fracture surface is smooth in appearance sometimes displaying beach markingsdisplaying beach markings

• The final mode of failure may be brittle or ductile or a The final mode of failure may be brittle or ductile or a combination of bothcombination of both



• Toe grinding, profile grinding.

• The elimination of poor profiles

• The elimination of partial penetration welds and weld defects

• Operating conditions under the materials endurance limits

• The elimination of notch effects e.g. mechanical damage cap/root undercut

• The selection of the correct material for the service conditions of the component

Precautions against Fatigue Cracks



Fatigue fracture occurs in structures subject to repeated Fatigue fracture occurs in structures subject to repeated application of tensile stress. application of tensile stress.

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



Initiation points / weld defectsInitiation points / weld defects

Fatigue fracture surface Fatigue fracture surface

smooth in appearancesmooth in appearanceSecondary mode of failure Secondary mode of failure ductile fracture rough fibrous ductile fracture rough fibrous appearance appearance



• crack growth is slowcrack growth is slow

• it initiate from stress concentration pointsit initiate from stress concentration points

• load is considerably below the design or yield stress level load is considerably below the design or yield stress level

• the surface is smooththe surface is smooth

• the surface is bounded by a curvethe surface is bounded by a curve

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

• the surface is 90° to the loadthe surface is 90° to the load

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

• fatigue crack need initiation + propagation periodsfatigue crack need initiation + propagation periods


Fatigue fracture distinguish features:Fatigue fracture distinguish features:



Creep PhenomenonCreep Phenomenon


Creep is defined as a slow deformation under constant load at Creep is defined as a slow deformation under constant load at elevated temperatures.elevated temperatures.

Can occur in materials which are operated for extensive periods at Can occur in materials which are operated for extensive periods at high temperatures.high temperatures.

The reason for creep fracture is the flow (or plastic deformation) of The reason for creep fracture is the flow (or plastic deformation) of metals when held for long periods of time at stresses well bellow metals when held for long periods of time at stresses well bellow their normal yield strength.their normal yield strength.

Creep FailureCreep Failure

Creep fractureCreep fracture


Creep FailureCreep Failure

• Creep is a time-temperature dependant phenomenonCreep is a time-temperature dependant phenomenon

• Section under stress continue to deform even if the load is Section under stress continue to deform even if the load is maintained constantmaintained constant

• Creep is most likely when operating near the recrystallization Creep is most likely when operating near the recrystallization temperature of that materialtemperature of that material

• Usually appear in case of process plant equipment, due to Usually appear in case of process plant equipment, due to heating and cooling cyclesheating and cooling cycles

Creep failure distinguish features:Creep failure distinguish features:


Any QuestionsAny Questions

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23368109-04-WIS5-MechanicalTesting-2006

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