TWI Industrial Member Report Summary 749/2002
J B Wintle, R M Sanderson, and P H M Hart
Most engineers recognise the possibility of flaws in welds occurring during fabrication. Welding flaws may be characterised by type, frequency and distribution. This information can be useful for assessing the integrity of fabrications, planning which welds to inspect, and selection of the most suitable method of inspection.
Experienced welding engineers and metallurgists understand the factors that influence the occurrence of fabrication flaws and have characterised the underlying mechanisms giving rise to different types and sizes. Data about actual flaw occurrence is available from non-destructive testing (NDT) and destructive examination of specific welds, but the transferability and extrapolation of this data is sometimes questionable. The problem is to find a method for estimating the occurrence of flaws in welds of a given specification.
Three methods used to estimate the occurrence of fabrication flaws in welds are:
- Applying an assumed frequency distribution fitted to actual flaw data obtained from NDT or destructive examination of welds.
- Probabilistic modelling of the mechanisms of flaw formation.
- Using expert judgement to weight the influencing factors within a simple model that is calibrated against actual flaw data.
It is believed that knowledge of these methods and the available data is limited and that a review of the current knowledge and where advances can be made would be beneficial.
- Review the available methods for estimating the frequency and size distribution of fabrication flaws in welds of interest to TWI industrial members.