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Welding Defects
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Meaning: ď‚— 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 ď‚— 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 ď‚— 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 ď‚— 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 ď‚— 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 ď‚— 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 ď‚— 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.
ď‚— 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 ď‚— 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 ď‚— 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 ď‚— 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.
ď‚— 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
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