1995:70 Crack Characterisation for In-service

During in-service inspection by non destructive testing the reliability is highly dependent on how the equipment is adjusted to the specific object and to the anticipated crack features. The crack feature and morphology vary widely between different cracking mechanisms and between material types, in which the cracks appear. The major objective of this study was to characterise a number of morphology parameters for common crack mechanism/ structure material combinations. Critical morphology parameters are crack orientation, shape, width, surface roughness and branching. The crack parameters were evaluated from failure analyses reported from the nuclear and non-nuclear industry. In addition, a literature review was carried out on crack parameter reports and on failure analysis reports, which were further evaluated.

The evaluated crack parameters were plotted and statistically processed in data groups with respect to crack mechanism and material type. The fatigue crack mechanisms were classified as mechanical, thermal or corrosion fatigue and the stress corrosion crack mechanisms as intergranular, transgranular or interdendritic stress corrosion cracking. Furthermore, some common weld defects were characterised for comparison. The materials were divided into three broad groups, namely, ferritic low alloy steels, stainless steels and nickel base alloys.

The results indicate significant differences between crack parameters when comparing data from different crack mechanism/material type combinations. Typical parameter values and scatter were derived for several crack mechanism/material data groups, where the amount of compiled data was sufficient for statistical significance.