Our client had several weld neck flanges of various sizes in storage intended for use in different projects for future maintenance and repair works. An assessment was required regarding their suitability for future use.
It was discovered that the Charpy values for the flanges were below the standard requirements. An Engineering Critical Assessment (ECA) was required to assess the criticality of the low Charpy values when subjected to the specified operational loading. The flange sizes range from 1-inch to 6-inch WNF with class rating from 150 to 1500.
A combination of three-dimensional finite element-based continuum and fracture mechanics models were used to evaluate the criticality of the low Charpy values.
The critical flaw locations were identified from the locations of high stress concentration from the stress analyses of continuum models. Subsequently, the Crack Driving Force (CDF) approach, involving local fracture model of the critical flaw locations, was used to identify the tolerability of the low Charpy values.
The assessments enabled the identification of flanges that are acceptable for the intended service conditions despite the Charpy values below specification.
For flanges identified as not tolerable, target acceptable Charpy value or Crack Tip Opening Displacement was presented to facilitate decision on re-verification.