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 |
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