During work to divert a pipeline using a bypass stopple operation, an Operator performed NDE at locations where the diversion was to tie-in, to ensure that no defects were present.
The NDE (consisting of UT) showed a series of axially orientated indications embedded at various depths from the outer surface. In view of this the Operator commissioned AFAA to assess the significance of the defects found during NDE. AFAA provide the following robust approach to the assessment of planar defects:
Determine defect size andlocation (NDE)
Gather defect location data
Gather material data of pipe at defect location
Determine loadings and stresses at defect location
Determine where defect lies on FAD
Determine critical defect size
Determine fatigue crack growth (if applicable)
Determine defect size margin
The defect assessment software created by AFAA was used to assess the significance of the defects. It was found that the most onerous embedded defect was well within the FAD, hence showing that the pipeline was fit-for-purpose.