5. mechanical testing

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Copyright 2004, TWI Ltd World Centre for Materials Joining Technology

TWICSWIP 3.1

WIS 5WELDING INSPECTION

DESTRUCTIVE TESTS


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Destructive tests

Involve the destruction of a welded unit or

selected specimens cut out from the weld

Destructive tests include:tensile test

bend test

impact test

hardness test

metallographic examination

creep test, etc.


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Tensile test

Objective:

measuring the overall strength of the weld jointInformations to be supplied on the test report:material type

specimen type

specimen size

(see QW-462.1)

UTS

location of finalrupture


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Bending test

Objectives:check if lack of fusion type of defects are present

assessing ductility of the weld jointInformations to be supplied on the test report:

material type

specimen type and

orientation (see QW-462.2;3)

bend radius/angle

test result (pass/fail)


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Bending test


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Charpy V-notch impact test

Objectives:measuring impact strength in differentweld joint area

assessing resistance toward brittle fractureInformations to be supplied on the test report:material type

notch type

specimen size

test temperature

notch location

impact strength value


7/20Copyright 2004, TWI Ltd World Centre for Materials Joining Technology

Charpy V-notch impact test specimen

55 mm

==

2 mm

10 mm

10 mm

45

R 0,25 mm

Specimen dimensions acc. ASTM E23



Charpy impact test Pendulum (striker)

Specimen

Anvil (support)




h2

h1




To define the type of failure, we can alsomeasure:

amount of crystalinity


lateral expansion




Testing temperature

Joulesabsorbed

DuctileFracture

47 Joules

28 Joules

TransitionZone

Transition Temperature Range

Mn < 1.6 % increases

toughness in steels*

BrittleFracture

Three specimens are normallytested at each temperature.

-40 -30 -20 -10 0 +10 +20 +30 + 40



Hardness

Definition - is the resistance of amaterial against penetration

Hardness tests: Brinell

Vickers

Rockwell

It is measured by indentation by apenetrator under a constant load

Between UTS and hardness is a directcorrelation



Hardness test

Objectives:measuring hardness in different areas of aweld joint

assessing resistance toward brittle fracture,

cold cracking and corrosion sensitivity in H2S

Informations to be supplied on the test report:material type

location of indentation

type of hardness test and load applied on theindenter

hardness value



Weld joint hardness test

Vickers hardness tests:

d = (d1+ d2)/2d2

d1

indentation body is a square based diamondpyramid (136 included angle)

the average diagonal (d) of the impression

is converted to a hardness number from atable

it is measured in HV5, HV10 or HV025



Vickers hardness test



Metallographic examination

Macro examination Micro examination



Metallographic examination

Objectives:detecting weld defects (macro)

measuring grain size (micro)

detecting brittle structures, precipitates, etc

assessing resistance toward brittle fracture,cold cracking and corrosion sensitivity

Informations to be supplied on the test report:material type

etching solution

magnification

grain size

location of examined area

weld imperfections(macro)

phase, constituents,

precipitates (micro)



Hydrostatic test

Is a test for leakage under pressureVessel configuration:

the test should be done after any stress

relief components that will not stand the pressure

test (e.g. flexible pipes, diaphragms) mustbe removed

the ambient temperature MUST be above0C (preferably 1520C)



Hydrostatic test procedure

blank off all openings with solid flanges use correct nuts and bolts, NOT G clamps

two pressure gauges on independenttapping points should be used

for safety purposes bleed all the air out

pumping should be done slowly (nodynamic pressure stresses)

test pressure - see relevant standards (PD5500, ASME VIII). Usually 150% designpressure

hold the pressure for minimum 30 minutes


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Copyright 2004 TWI Ltd World Centre for Materials Joining Technology

Hydrostatic test - what to look for

leaks (check particularly around seamsand nozzle welds!)

dry off any condensation with a

compressed air-line watch the gauges for pressure drop

check for distortion of flange faces, etc

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