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Welding Defects

When we start talking about welding defects, first of all we should know about what is welding? So welding is a fabrication process that joins materials usually metals and thermoplastics,  by causing fusion which is different from the lower temperature metal joining techniques such as brazing and soldering, which do not melt the base metal.

In simple words, welding is a process of joining the two metals by applying heat, sometimes with pressure and sometimes with an intermediate or filler metal having a high melting point.

What are Welding Defects?

A welding defect is any flaw or imperfection that compromises the usefulness of weldments. In other words, 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.  Following are most common types of welding defects:

Types of Welding Defects:

  • —  Lack of Fusion
  • —  Undercutting
  • —  Pinholes
  • —  Cracking
  • —  Misalignment
  • —  Gas Inclusions
  • —  Porosity
  • —  Craters
  • —  Overlap
  • —  Lamellar Tearing
  • —  Reheat cracking
  • —  Root and Toe Cracks

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.

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.

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. 

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.

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

Gas Inclusions: Gas inclusion 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.
Porosity: Porosity is weld metal contamination in the form of a trapped gas. Shielding gases or gases released as a result of the torch being applied to treated metal are absorbed into the molten metal and released as solidification takes place.

Porosity: Porosity is weld metal contamination in the form of a trapped gas. Shielding gases or gases released as a result of the torch being applied to treated metal are absorbed into the molten metal and released as solidification takes place.

Crater: 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. 

Overlap: 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.

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.

Reheat Cracking: Reheat cracking is a type of cracking that occurs in HSLA (high strength low alloy) steels, particularly chromium, molybdenum and vanadium steels, during post heating.

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.

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