Weld defects, their Causes & Remedies

Two Major Aspects of Fusion Welding

Effects of welding	Defects of welding
Effects of welding are those which will always happen when we weld	Defects are those which can be theoretically eliminated, such as
Residual stresses	Cracks, Lack of Fusion, slag inclusions, porosity and undercuts
Distortion	Only when we understand the nature of these defects and why they occur, can we eliminate them
Formation of HAZ with metallurgical changes

Discontinuities & Defects

Discontinuity

An interruption of the typical structure of a material, such as a lack of homogeneity in its mechanical, metallurgical, or physical characteristics.

A discontinuity is not necessarily a defect but all defects are discontinuities.

Defect

A defect is a rejectable discontinuity, which occurs in an amount great enough to render a particular object or structure unsuitable for its intended service based on criteria in the applicable code.

Classification of Defects

Planar defects / Two dimensional defects	Geometric defects	Geometric defects
cracks, lack of fusion, lack of penetration, are critical in nature and are not tolerated to any extent	slag inclusion, cavities, porosity, etc are tolerated to a certain extent depending on the product class and applicable code.	excess reinforcement, under fill, root suck back, distortion are also permitted to a certain extent.

Types of Defects

External defects	Internal defects	Dimensional defects
Cracks Blowhole and porosity Slag Inclusions Lack of fusion Lack of Root penetration Tungsten inclusion Lamination	Cracks Blowhole and porosity Slag Inclusions Lack of fusion Lack of Root penetration Tungsten inclusion Lamination	Distortion Incorrect Joint Penetration Incorrect Weld Size Incorrect Weld Profile Misalignment