weld assessments and weld propertieseng.sut.ac.th/metal/images/stories/pdf/07_ weld porperties...

Weld assessments and Weld assessments and

weld propertiesweld properties

Subjects of Interest

Part I Weld assessment

Part II Weld properties

Suranaree University of Technology Sep-Dec 2007

• Mechanical properties

• Corrosion in weldment

• Destructive testing

• Non destructive testing

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ObjectivesObjectives

This chapter aims to:

• This chapter provides information on weld mechanical

assessments: Destructive testing and non destructive testing

(NDT).

• Students are required to analyse mechanical properties

and corrosion of weldments, such that information can be

used for the selection of the weldments in service.

Suranaree University of Technology Sep-Dec 2007Tapany Udomphol

Weld assessments

•Weldments normally contain defects.

However we need to keep weld defects

at a minimum level to maintain reliable

products.

Pressure vessel weld joint heat treatment

Swing arm

Longitudinal crack

Crater cracking


Weld assessments


Reliable productsSpecifications

Quality control method

Appropriate

welding method

• Destructive testing • Non destructive testing

• Mechanical testing, i.e., tensile,

fracture toughness, impact,

fatigue tests.

• Expensive, require specimen

preparation under standard specifications.

• Weldments are not destroyed.

• Many NDT techniques are

expensive and have their own

limitations.

• Inspection should be carefully

planned to make sure the

technique used is capable of

detecting the concerned defects.

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Destructive testing


• Mechanical tests are destructive testing, which are expensive since it requires

specimen preparation and then destroying it.

• The orientation of the weld in the testpiece must be recorded.

• Requires standard specimen dimension for each specification used.

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Destructive testing


• Mechanical tests are

destructive testing, which are

expensive since it requires

specimen preparation and

destroying it.

• The orientation of the weld in

the testpiece must be recorded.

• Requires standard specimen

dimensions for each

specification used.

Method of cutting test-pieces from

procedure approval plate.Tapany Udomphol

Destructive testing


AWS all-weld metal testTensile test specimen

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Destructive testing


Three types of bend test

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Destructive testing


AWS fillet break test.

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Destructive testing


Impact Charpy V notch specimens

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Destructive testing


N = Normal to the weld direction

P = Parallel to the weld direction

Q = Weld thickness direction

First letter : the direction normal to the crack plane

Second letter: the expected direction of crack propagation

Specimen orientations NP and PN are referred to as through-thickness notched

Specimen orientations NQ and PQ are referred to as surface notched

P

Q

N

NP

NQ

PQ

PN

(c) EB and TIG welds

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Non-destructive testing


•We must remember that NDT result itself cannot guarantee whether the weld

is acceptable, but can only report what types of defects we discover.

There are a range of NDT techniques available;

• Visual inspection

• Liquid penetrant inspection

• Magnetic-particle inspection

• Radiography

• Ultrasonic inspection

Note: At least one of the NDT methods should be taken for

weld inspections.

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Visual inspection


• Weld defects can often be

discovered by naked eyes and

can be repaired at this stage:

•Weld dimensions

• Joint penetration

• Surface defects

Simple fillet-weld gauges

Check on defects

• Surface cracks

• Crater cracks

• Incomplete root penetration

• Undercut

• Underfill on face, groove, or fillet

(concave)

• Underfill of root (suck back)

• Excessive face reinforcement,

groove, or fillet (convex)

• Excessive root reinforcement

• Overlap

• Misalignment

• Arc strikes

• Excessive spatter

•Warpage (distortion)

• Base metal defects

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Weld size measurements


Fillet weld size and method of checking

• It is important to measure weld size.

• Size of fillet welds can be easily

measured by using weld gauges (different

standard gauges used:

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Liquid-penetrant inspection


• Low surface tension

• Low viscosity

• Can be dye or fluorescenceProperties

• Used to detect minute discontinuities such as

cracks, pores, which are open to the surface.

• Can be applied to ferrous & non ferrous metals,

glass and plastics.

• The surface must be clean.

Liquid panetrant

Principle of penetrant examination

• Liquid penetrant inspection is portable

and very easy to use on site.

• Required appropriate protections

because the liquid used might be toxic.

• Limited on surface inspection and

should be used in combination of other

NDT techniques.

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Note: Ultraviolet or black light source are

used for the inspection of fluorescence liquid

penetrant. Sound areas appear deep violet

while the defects will glow a brilliant

yellowish green.

Method and applications


Principle of liquid-penetrate inspection

• The liquid penetrant (normally red) is

applied on the surface containing cracks.

• Waiting for the liquid penetrates into the

cracks.

• Clean off the excess liquid from the surface,

but some liquid still remains in the cracks.

• Developer (chalk emulsion) is applied to

enhance the visible indication of cracks.

Liquid penetrant indication

www.instytutgamma.com

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• Used to detect defects in aluminium, magnesium, and stainless

steel weldments, when magnetic particle inspection cannot be used.

• Locating the cracks, leaks in all types of welds, weld in pressure,

storage vessels, piping for petroleum industry.

www.bbrail.com

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Magnetic particle inspection


• Magnetic particle inspection is used to detect cracks porosity, seams,

inclusions lack of fusion and other discontinuities in ferromagnetic materials.

• Used on the surface and shallow subsurface.

Magnetic fields around bar

magnet and a crack

Accumulation of magnetic

particles on defects

• The lines of force within the magnet run smoothly from S to N.

• When a crack is present, N and S poles are set up at the edges of the crack.

• The magnetic particles will be attracted to the crack (poles).

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Applying magnetic particles

Accumulation of magnetic powder indicating

the location of the cracks or defects.

Cracks

• Establishing a magnetic field in the test object.

• Applying magnetic particles to the surface of

the test object.

• Examining the surface by detecting

accumulation of magnetic particles � where

the defects are.

• Iron particles can be applied dry or wet.

• Detecting fluid is normally particles of

magnetic iron oxide suspended in

kerosene and may be coated with

fluorescence compound for viewing

under ultraviolet light.Tapany Udomphol



Magnetic particle inspection using alternating current

• Magnetic particle inspection

can be applied to any kinds of

welds.

• Can be used to detect defects

on each pass in multi-pass

welding after it has been

deposited.

• Parts may have to

demagnetized after inspection.

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Radiographic examination


• Interior defects (porosity, cracks, voids) can be examined by using X-ray or

gamma ray, which can penetrate through materials and its intensity depends

on materials thickness and density.

• Provide a permanent film record which is easy to interpret.

• Slow and expensive, however this method is positive to determine defect size.

• X-ray is generated by electron

bombardment on tungsten.

• Gamma ray is emitted by

radioactive elements.

Principal of radiography

• X-ray or gamma ray is absorbed during

transmission through the materials.

• Pores or defects absorb less energy

than uniform areas� giving a variation

of intensity of the beam generated on

the film placed underneath the

materials.

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Setting up to take radiograph

Examination of radiograph

• Exposure time: X-ray � 10 s to 10 mins,

gamma ray � 1 min to 24 hours

• After exposure, the cassette is developed and

fixed in the dark room.

• The film is then view against the bright light.

Radiogram

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• Radiography detection also

depends on orientation of the flaw

with respect to the beam.

• Used to detect defects in all types

of weldments and materials such as

aluminium, steel, magnesium.

• Used in pipeline industry.

Typical radiograph

Orientation of flaw with respect to X-rays

• Different intensity of the beam due

to discontinuities or defects in

the weld shown on the film.

Sound area

Defect

Light

Dark

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Precautions


• Require concrete, steel, lead-

lined bricks to house the X-ray to

protect the operator from

exposure.

• On site operation is carried out

in distance.

• X-ray is more manageable than

gamma ray. The area is safe when

switching off the X-ray source

while a radioactive isotope emits

radiation continuously and must be

kept in a shield container.

www.arrowheadproducts.net

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Ultrasonic inspection


• A beam of ultrasonic vibration produced by

quartz crystal is directed into the specimen to

detect defects or discontinuities.

• Sound area gives small loss of signal, except

when the ultrasonic is intercepted and reflected

by defects.


www.instytutgamma.com

Ultrasonic inspection of aluminium

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There are two ways of using ultrasonic waves for welded joint inspection.

Transmission Reflection

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Moving the probe to scan the thickness of

the weld with an angle probe.

• The location of the defect in the weld can be calculated.

• Can be used to test all kinds of metals and materials, complex

weldments. � widely used.

www.olympusndt.com

Ultrasonic inspection in pipeline

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Guide to weld quality control techniques


Weld properties


• Weldments normally possess a degradation of weld properties due to

changes in microstructures and defects.

• Weld properties should be assessed in order to correctly select the

weldment, which can satisfy the condition in service.

• Tensile properties

• Hardness

• Toughness

• Fatigue

• Corrosion

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Mechanical properties of weldments


Hardness profile

Hardness profile

Hardness test orientation in the weld joint of

AISI 1040 friction weld

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Tensile properties

Crack initiated at the weld zoneTapany Udomphol



Impact properties

Fractography of

weldments tested at (a)

Room temperature (b)

700oC

Fractography of base

metal at (a) Room

temperature (b) 700oC

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Impact properties

Charpy Impact Energy vTemperature

0

20

40

60

80

100

120

140

160

-200 -150 -100 -50 0 50 100

Temperature (oC)

Impact Energy (J)

As Deposited

Reheated

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Fatigue properties

Number of cycle

1e+3 1e+4 1e+5 1e+6 1e+7 1e+8

σσ σσmax, MPa

200

400

600

800

1000

TIMET bar III, AR

Autogenous BuRTi TIG weld, HT

Ti679-BuRTi-Ti679 TIG weld, AR

R = Pmin/Pmax = 0.1

Frequency ~ 70 Hz

• Lower fatigue limit

was observed in

autogenous TIG weld

of titanium alloys in

comparison to the

base metal.

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Fatigue properties

∆∆∆∆K, MPa.m1/2

1 10 100

da/dN, mm/cycle

1e-6

1e-5

1e-4

1e-3

1e-2

1e-1

TIMET bar IIIm = 2.02

BuRTi EBW01m = 9.05

BuRTi EBW02m = 2.35

Ti679-BuRTi-TI679 TIG01m = 6.84

Ti679-BuRTi-Ti679 TIG02m = 10.18

R = Pmin/Pmax = 0.1

Frequency = 0.25 Hz• Fatigue crack growth is

faster in the weld joint than

in the base metal.

• Factors affecting the FCG

results are coarsening

microstructure,

embrittlement, precipitation

hardening, etc.

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Corrosion of weldments


Corrosion in

weld jointPLUMBING - PIPING

•Corrosion failure of underground propane pipe•Broken stainless steel air injection pipes in a sewage treatment plant•Cracking of brass inserts in fire sprinkler head adaptors•Freeze failure of copper plumbing and air conditioner fittings

•Dry solder joints in copper plumbing fittings

•Pitting corrosion of copper pipes using well water•Pitting of air conditioner copper heat exchanger chillier water tubing•Corrosion of steam boilers•Rust clogging of high rise building steam heating systems

•Leakage of propane from a connector fitting with a worn rubber seal•Corrosion failures of underground fuel tanks

www.forensicmetallurgy.com

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ReferencesReferences

•


• Gourd, L.M., Principles of welding technology, 3rd edition, 1995,

Edward Arnold, ISBN 0 340 61399 8.

• Cary, H.B., Modern welding technology, 4th edition, 1998, Prentice

Hall, ISBN 0-13-241803-7.

• Sahin, M., Akata, H.E., Gulmez, T., Characterization of mechanicalproperties in AISI 1040 parts welded by friction welding. 2006.

• K.S. Guana, X.D. Xub, Y.Y. Zhangb and Z.W. Wang, Cracks and

precipitate phases in 321 stainless steel weld of flue gas pipe,

2005, Vol.12, Issue 4, p 623-633.

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