Defects in Casting

Defects in Welding

The performance of welded structure in service depends on presence or absence of defects in weld joints. Weld defects impair the strength of welded joints and may results in the failure of a complete assembly / structure in service. In a general sense, the term weld defect refers to any departure in welded structure or welded joints from the specified requirements. According to the International Institute of Welding, the weld defects are classified into six groups as follows: (a) Cracks, (b) Cavities (blowholes, porosity, shrinkage, etc.), (c) Solid Inclusion, (d)
Incomplete fusion, (e) Imperfect Shape, (f) Miscellaneous defects(g)Under Cuts.
Cracks
Cracks are the most dangerous amongst all types of defects as it reduce the performance of a welded joint drastically and can also cause catastrophic failure. Depending on the position, location and orientation these can be categorised as longitudinal cracks, transverse cracks, crater cracks, under-bead cracks, and toe cracks. These cracks are usually visible and hence, referred to surface defects in weld joints. In general, the cracks in weld joints occur due to high concentration stresses during solidification of weld, poor fit-up and incorrect welding procedures, and poor edge quality. Formation of cracks can be controlled by preheating the joints, reducing the cooling rate, taking proper precautions during post weld heat treatment. Figure below. schematically shows some of the
. significant weld cracks