1. Weld assessments and
Weld assessments and
weld properties
weld 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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2. Objectives
Objectives
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.
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3. 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
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4. Weld assessments
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Reliable products
Specifications
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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5. Destructive testing
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• 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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6. Destructive testing
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• 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.
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11. Destructive testing
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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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12. Non-destructive testing
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• 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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13. Visual inspection
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• 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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14. Weld size measurements
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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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15. Liquid-penetrant inspection
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• 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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16. 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
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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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17. Method and applications
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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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18. Magnetic particle inspection
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• 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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19. Method and applications
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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.
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20. Method and applications
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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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21. Radiographic examination
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• 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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22. Method and applications
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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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23. Method and applications
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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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24. Precautions
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• 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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25. Ultrasonic inspection
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• 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.
Ultrasonic inspection
www.instytutgamma.com
Ultrasonic inspection of aluminium
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26. Ultrasonic inspection
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There are two ways of using ultrasonic waves for welded joint inspection.
Transmission Reflection
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27. 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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28. Guide to weld quality control techniques
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29. Weld properties
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• 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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30. Mechanical properties of weldments
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Hardness profile
Hardness profile
Hardness test orientation in the weld joint of
AISI 1040 friction weld
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31. Mechanical properties of weldments
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Tensile properties
Crack initiated at the weld zone
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32. Mechanical properties of weldments
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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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33. Mechanical properties of weldments
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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 (o
C)
Im
p
act
En
erg
y
(J)
As Deposited
Reheated
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34. Mechanical properties of weldments
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Fatigue properties
Number of cycle
1e+3 1e+4 1e+5 1e+6 1e+7 1e+8
σ
σ
σ
σmax
,
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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35. Mechanical properties of weldments
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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 III
m = 2.02
BuRTi EBW01
m = 9.05
BuRTi EBW02
m = 2.35
Ti679-BuRTi-TI679 TIG01
m = 6.84
Ti679-BuRTi-Ti679 TIG02
m = 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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36. Corrosion of weldments
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Corrosion in
weld joint
PLUMBING - 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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37. References
References
•
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 mechanical
properties 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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