Interaction and Assessment of Multiple Local Wall Thinning Defects

The safety assessment of pipes with multiple local wall thinning defects (LWTs) is systematically investigated by finite element analyses (FEA) with special attention to the interaction of multiple LWTs. It is interesting that the arrangement of LWTs (axial arrangement and circumferential arrangement), the load condition (pure pressure, pure bending and complicated load) and the relative depth play important roles in the interaction of multiple LWTs. The effective stress area and critical stress can be used to explain their influences. Moreover, existing assessment methods of multiple LWTs in some defect assessment standards such as API 579/ASME FFS, ASME B31G, BS 7910 and GB 19624 are reviewed. It’s noticed that the influences of arrangement, load condition and relative depth are ignored in existing standard methods, but they can influence the assessment results significantly. In order to consider these issues, an improved assessment of multiple LWTs based on API 579/ASME FFS is proposed. This improved assessment method has considered the influences of arrangement, load condition and relative depth, and can give better results.