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8/6/2019 07_ Weld Por Per Ties and Assessment
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Weld assessments andWeld 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 mechanicalassessments: Destructive testing and non destructive testing(NDT).
Students are required to analyse mechanical properties
and corrosion of weldments, such that information can beused for the selection of the weldments in service.
Suranaree University of Technology Sep-Dec 2007Tapany Udomphol
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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
Suranaree University of Technology Sep-Dec 2007Tapany Udomphol
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Weld assessments
Suranaree University of Technology Sep-Dec 2007
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 standardspecifications.
Weldments are not destroyed.
Many NDT techniques areexpensive 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
Suranaree University of Technology Sep-Dec 2007
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
Suranaree University of Technology Sep-Dec 2007
Mechanical tests are
destructive testing, which areexpensive 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 fromprocedure approval plate.
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Destructive testing
Suranaree University of Technology Sep-Dec 2007
AWS all-weld metal testTensile test specimen
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Destructive testing
Suranaree University of Technology Sep-Dec 2007
Three types of bend test
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Destructive testing
Suranaree University of Technology Sep-Dec 2007
AWS fillet break test.
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Destructive testing
Suranaree University of Technology Sep-Dec 2007
Impact Charpy V notch specimens
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Destructive testing
Suranaree University of Technology Sep-Dec 2007
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
Suranaree University of Technology Sep-Dec 2007
We must remember thatNDT resultitself cannot guarantee whether the weld
is acceptable, but can only report whattypes 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
Suranaree University of Technology Sep-Dec 2007
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 defectsTapany Udomphol
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Weld size measurements
Suranaree University of Technology Sep-Dec 2007
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
Suranaree University of Technology Sep-Dec 2007
Low surface tension
Low viscosity
Can be dye or fluorescence
Properties
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
Suranaree University of Technology Sep-Dec 2007
Principle of liquid-penetrate inspection
The liquid penetrant(normally red) is
applied on the surface containing cracks.
Waiting for the liquidpenetrates into the
cracks.
Clean offthe 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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Method and applications
Suranaree University of Technology Sep-Dec 2007
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
Suranaree University of Technology Sep-Dec 2007
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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Method and applications
Suranaree University of Technology Sep-Dec 2007
Applying magnetic particles
Accumulation of magnetic powder indicating
the location of the cracks or defects.
Cracks
Establishing a magnetic fieldin 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 normallyparticles of
magnetic iron oxide suspended in
kerosene and may be coated with
fluorescence compoundfor viewingunder ultraviolet light.Tapany Udomphol
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Method and applications
Suranaree University of Technology Sep-Dec 2007
Magnetic particle inspection using alternating current
Magnetic particle inspection
can be applied to any kinds of
welds.
Can be used to detect defectson each pass in multi-pass
weldingafter it has been
deposited.
Parts may have to
demagnetizedafter inspection.
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Radiographic examination
Suranaree University of Technology Sep-Dec 2007
Interior defects (porosity, cracks, voids) can be examined by usingX-ray or
gamma ray, which can penetrate through materials and its intensity depends
on materials thickness and density.
Provide apermanent film recordwhich is easy to interpret. Slow and expensive, however this method is positive to determine defect size.
X-rayis generated by electron
bombardment on tungsten.
Gamma rayis emitted byradioactive elements.
Principal of radiography
X-ray or gamma rayis 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.Tapany Udomphol
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Method and applications
Suranaree University of Technology Sep-Dec 2007
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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Method and applications
Suranaree University of Technology Sep-Dec 2007
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 asaluminium, 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
Suranaree University of Technology Sep-Dec 2007
Require concrete, steel, lead-
lined bricks to house the X-rayto
protect the operator fromexposure.
On site operation is carried out
in distance.
X-ray is more manageable thangamma 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
Suranaree University of Technology Sep-Dec 2007
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, exceptwhen the ultrasonic is intercepted and reflected
by defects.
Ultrasonic inspection
www.instytutgamma.com
Ultrasonic inspection of aluminium
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Ultrasonic inspection
Suranaree University of Technology Sep-Dec 2007
There are two ways of using ultrasonic waves for welded joint inspection.
Transmission Reflection
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Suranaree University of Technology Sep-Dec 2007
Method and applications
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
Suranaree University of Technology Sep-Dec 2007Tapany Udomphol
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Weld properties
Suranaree University of Technology Sep-Dec 2007
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
Suranaree University of Technology Sep-Dec 2007
Hardness profile
Hardness profile
Hardness test orientation in the weld joint of
AISI 1040 friction weld
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Mechanical properties of weldments
Suranaree University of Technology Sep-Dec 2007
Tensile properties
Crack initiated at the weld zoneTapany Udomphol
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Mechanical properties of weldments
Suranaree University of Technology Sep-Dec 2007
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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Mechanical properties of weldments
Suranaree University of Technology Sep-Dec 2007
Impact properties
Charpy Impact Energy vTemperature
0
20
40
60
80
100
120
140
160
-200 -150 -100 -50 0 50 100
Temperature (oC)
Im
pactEnergy(J)
As Deposited
Reheated
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Mechanical properties of weldments
Suranaree University of Technology Sep-Dec 2007
Fatigue properties
Number of cycle
1e+3 1e+4 1e+5 1e+6 1e+7 1e+8
max,
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 incomparison to the
base metal.
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Mechanical properties of weldments
Suranaree University of Technology Sep-Dec 2007
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 EBW02
m = 2.35Ti679-BuRTi-TI679 TIG01m = 6.84
Ti679-BuRTi-Ti679 TIG02m = 10.18
R = Pmin/Pmax = 0.1Frequency = 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
Suranaree University of Technology Sep-Dec 2007
Corrosion in
weld jointPLUMBING - PIPING
Corrosion failure of underground propane pipeBroken stainless steel air injection pipes in a sewage treatment plantCracking of brass inserts in fire sprinkler head adaptorsFreeze failure of copper plumbing and air conditioner fittings
Dry solder joints in copper plumbing fittings
Pitting corrosion of copper pipes using well waterPitting of air conditioner copper heat exchanger chillier water tubingCorrosion of steam boilers
Rust clogging of high rise building steam heating systems
Leakage of propane from a connector fitting with a worn rubber sealCorrosion failures of underground fuel tanks
www.forensicmetallurgy.com
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ReferencesReferences
Suranaree University of Technology Sep-Dec 2007
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 AISI1040parts 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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