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Welding Defects
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Meaning:
A welding defect is any type of flaw in
a welding job that compromises the use
and function of the object that received
the welding.
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Types of Welding defects
Lack of Fusion
Undercutting
Pinholes
Cracking
Misalignment
Gas Inclusions
Porosity
Craters
Overlap
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Types of Welding defects
Lamellar Tearing
Reheat cracking
Root and Toe Cracks
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Lack of Fusion
Lack of fusion is the poor adhesion of the weld
bead to the base metal. If the weld heat was not
high enough, the metals being welded together
may not have become molten during the welding
process and the two pieces did not join.
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Under Cutting
Welding along a line or using an arc voltage that is
too low can produce a groove or a slight ditch in
the metal right along the weld line. This is known
as undercutting.
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Pinholes
Welding defect caused by the high welding
temperatures is known as Pinholes. If the
temperature of arc making of the weld is very high,
then tiny holes resembling pin holes may appear
on the surface of the weld.
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Cracking
This defect typically occurs because the welder
was using the wrong type of wire electrode to make
the weld. A combination of poor design and
inappropriate procedure may result in high
residual stresses and cracking.
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Misalignment
This type defect is generally caused by a
setup/fit up problem, or trying to join plates
of different thickness.
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Gas Inclusions
Gas inclusions is also a defect that includes porosity,
blow holes, and pipes. The cause for gas inclusions is
the entrapment of gas within the solidified weld.
It can be from any of the following causes: high
sulphur content in the electrode, excessive moisture
from the electrode or wrong welding.
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Craters
Crater cracks occur when a crater is not filled
before the arc is broken. This causes the outer
edges of the crater to cool more quickly than the
crater, which creates sufficient stresses to form a
crack.
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Overlapping
The protrusion of weld metal beyond the weld toe
or weld root. It is caused by poor welding
techniques and can generally be overcome by an
improved weld procedure. The overlap can be
repaired by grinding off excess weld metal and
surface grinding smoothly to the base metal.
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Lamellar Tearing
Lamellar tearing is a type of defect that is most likely
to occur below a welded joint at points of high stress
concentration. Lamellar tearing is caused mainly by
sulphur inclusions in the material. Other causes
include an excess of hydrogen in the alloy.
This defect can be removed by keeping the amount of
sulfur in the steel alloy below 0.005%
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Root and Toe Cracks
A root crack is the crack formed by the short bead at the
root beginning of the welding, low current at the beginning
and due to improper filler material used for welding.
Major reason for happening of these types of cracks is
hydrogen embrittlement.
These types of defects can be eliminated using high current
at the starting and proper filler material.
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Reheat Cracking
Reheat cracking is a type of cracking that occurs in HSLA
steels, particularly chromium, molybdenum and vanadium
steels, during post heating.
It is caused by the poor creep ductility of the heat affected
zone.
It can be eliminated by heat treating first with a low
temperature soak and then with a rapid heating to high
temperatures, grinding or peening the weld toes
