Geometric Shape Imperfections - Excess weld metal

Excess weld metal (also called cap height, overfill or reinforcement)

Fig.1. Excess weld metal

This is weld metal lying outside the plane joining the weld toes. Note that the term 'reinforcement', although used extensively in the ASME/AWS specifications is avoided in Europe as it implies it adds strength to the welded joint, which is rarely the case.

Common causes

This imperfection is formed when excessive weld metal is added to the joint, which is usually a result of poor welder technique for manual processes but may be due to poor parameter selection when the process is mechanised. That is, too much filler metal for the travel speed used. In multi-run welding a poor selection of individual bead sizes can result in a bead build-up pattern that overfills the joint. Different processes and parameters (eg voltage) can result in different excess weld metal shapes.

Acceptance

The acceptability of this imperfection is very dependent on the application in which the product will be used. Most standards have limit, related to material thickness (eg10%), but also have a maximum upper limits. Both the ratio and the maximum may be related to the severity of service that the component is expected to see. The following table gives examples taken from BS EN 25817.

Excess weld metal limits for quality levels:
Severity of service	Moderate, D	Stringent, B
Limit (up to maximum)	h = 1mm + 0.25 b	h = 1mm + 0.25 b
Maximum	10 mm	3 mm
Transition required	smooth	smooth
Where: h = height of excess & b = width of bead (see figure)

 An important reason for limiting the height of excess weld metal is that it represents a non-value added cost. However, it must be remembered that the height of the weld cap influences the resultant toe blend. A sharp transition causes a local stress concentration that can contribute to loss of strength, which is particularly important in fatigue situations. As a result most specifications state that 'smooth transition is required'.

Avoidance

If the imperfection is a result of welder technique then welder retraining is required. For mechanised techniques an increase in travel speed or voltage will help to reduce cap height.