Welding defects

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.



Types of Welding defectsLack of Fusion

Undercutting

Pinholes

Cracking

Misalignment

Gas Inclusions

Porosity

Craters

Overlap



Types of Welding defectsLamellar Tearing

Reheat cracking

Root and Toe Cracks



Lack of FusionLack 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.



Under CuttingWelding 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.



PinholesWelding 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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CrackingThis 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.



MisalignmentThis type defect is generally caused by a setup/fit up problem, or trying to join plates of different thickness.



Gas InclusionsGas 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.



CratersCrater 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.



OverlappingThe 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 TearingLamellar 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%



Root and Toe CracksA 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.



Reheat CrackingReheat 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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