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Shape Defects
There are several common shape defects encountered when welding. These include:
- Overfill is described as the presence of weld metal which exceeds that required by the design.
- In addition to the higher than necessary cost of welding the problem may lead to stress intensification at the toe of the weld, slag entrapment, and unacceptable appearance or surface finish.
- Root convexity results from excessive penetration on the underside of a full penetration weld. As with excessive reinforcement it may give rise to stress intensification and in the case of circumferential welds in pipe, it may cause turbulent flow or corrosion problems.
- Root concavity or 'suck-back' may occur if the rear of the weld pool is too hot or large, and the combined effect of concentration and surface tension results in a root surface which is concave.
- Underfil, occurs if insufficient weld metal is deposited in the joint the parent material may remain unfused. Alternatively, the weld area may be melted but the combined effect of the arc force and the flow of molten metal may prevent complete joint filling producing a depression in the surface at the weld boundary.
- Partial penetration may be acceptable in some butt welding applications, but full penetration is often required when improved performance, particularly with respect to fatigue loading and corrosion resistance is required.
- Lack of fusion between successive runs or between the weld bead and the parent material can produce serious, crack-like defects. These defects reduce the load-carrying area of the joint and produce stress intensification, and are therefore considered unacceptable in welds, which are subjected to fatigue loading or moderate static loads.
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