Flaw Tolerance of Pipelines Containing Circumferential Flaws Subjected to Axial Straining and Internal

A number of codified assessment procedures can be applied to assess the significance of circumferential flaws in pipes but these are generally stressed based. Efforts have been made to extend these so that they are applicable when the pipe is subject to axial plastic straining with and without internal pressure. In this paper results are presented for two full-scale tests which were axially loaded beyond yield. They were conducted on parent pipe to API 5L PSL 2 Grade X65, 273mm OD x 18.4mm WT and contained circumferential surface notches. In the first test the pipe was axially strained until failure and in the second test the pipe was first internally pressurised and then axially strained until a failure condition was reached. In both tests failure was ductile. The full-scale tests were accompanied by small-scale tests which included SENT tests to derive fracture toughness resistance curves. For the materials investigated, the SENT specimens with EDM notches produced almost identical resistance cures as those with fatigue pre-cracks. The behaviour of the pipes in terms of CTOD versus applied strain was compared with finite element analyses and failure analysis diagram (FAD) methods described in BS 7910. It is shown that a modification of the material specific FAD enables it to be extended up to 3% strain.