Defect Tolerance in Pipeline Girth Welds

摘要

The definition of tolerable levels for defects in automatically welded girth welds for offshore application is discussed. Laboratory tests on defective samples and confirmatory full size bend/pressure tests give a relationship between stress level for failure and defect size. For ductile failure, the tests and complementary finite element stress analyses show that plastic collapse criteria adopted in published recommendations can be unnecessarily conservative. This is particularly so for the high stress levels which can occur during laying of offshore pipelines. An alternative defect acceptance level was proposed for this application. The result is a standard which has considerable benefit in offshore girth welding in permitting embedded planar defects equivalent to one weld pass depth.