What Are Welding Defects And Their Types?
- The defects in the weld can be defined as irregularities in the weld metal produced due to incorrect welding parameters or wrong welding procedures or wrong combination of filler metal and parent metal.
- Weld defect may be in the form of variations from the intended weld bead shape, size and desired quality. Defects may be on the surface or inside the weld metal. Certain defects such as cracks are never tolerated but other defects may be acceptable within permissible limits.
- Welding defects may result into the failure of components under service condition, leading to serious accidents and causing the loss of property and sometimes also life.
- Various welding defects can be classified into groups such as cracks, porosity, solid inclusions, lack of fusion and inadequate penetration, imperfect shape and miscellaneous defects.
Cracks
Cracks may be of micro or macro size and may appear in the weld metal or base metal or base metal and weld metal boundary. Cracks occur when localized stresses exceed the ultimate tensile strength of material. These stresses are developed due to shrinkage during solidification of weld metal.
Porosity
Porosity results when the gases are entrapped in the solidifying weld metal. These gases are generated from the flux or coating constituents of the electrode or shielding gases used during welding or from absorbed moisture in the coating. Rust, dust, oil and grease present on the surface of work pieces or on electrodes are also source of gases during welding. Porosity may be easily prevented if work pieces are properly cleaned from rust, dust, oil and grease.
Solid Inclusion
Solid inclusions may be in the form of slag or any other non-metallic material entrapped in the weld metal. Slag inclusion can be prevented if proper groove is selected, all the slag from the previously deposited bead is removed, too high or too low welding currents and long arcs are avoided.
Lack of Fusion
Lack of fusion is the failure to fuse together either the base metal and weld metal or subsequent beads in multi pass welding because of failure to raise the temperature of base metal or previously deposited weld layer to melting point during welding. It can be avoided by properly cleaning of surfaces to be welded, selecting proper current, proper welding technique and correct size of electrode.
Incomplete penetration
Incomplete penetration means that the weld depth is not up to the desired level or root faces have not reached to melting point in a groove joint. If either low currents or larger arc lengths or large root face or small root gap or too narrow groove angles are used then it results into poor penetration.
