Recent development in low-constraint fracture toughness testing for structural integrity assessment of pipelines

Abstract

Fracture toughness measurement is an integral part of structural integrity assessment of pipelines. Traditionally, a single-edge-notched bend (SE(B)) specimen with a deep crack is recommended in many existing pipeline structural integrity assessment procedures. Such a test provides high constraint and therefore conservative fracture toughness results. However, for girth welds in service, defects are usually subjected to primarily tensile loading where the constraint is usually much lower than in the three-point bend case. Moreover, there is increasing use of strain-based design of pipelines that allows applied strains above yield. Low-constraint toughness tests represent more realistic loading conditions for girth weld defects, and the corresponding increased toughness can minimize unnecessary conservatism in assessments. In this review, we present recent developments in low-constraint fracture toughness testing, specifically using single-edge-notched tension specimens, SENT or SE(T). We focus our review on the test procedure development and automation, round-robin test results and some common concerns such as the effect of crack tip, crack size monitoring techniques, and testing at low temperatures. Examples are also given of the integration of fracture toughness data from SE(T) tests into structural integrity assessment.

Keywords

fracture toughness / constraint effect / single-edge-notched tension test / pipeline / structural integrity assessment

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Acknowledgements

We are grateful for the valuable discussions with staff of CanmetMATERIALS on a variety of aspects of SE(T) testing. This review was completed as part of the Welding and Strain Based Design project with funding provided by the Federal Program for Energy Research and Development (PERD) and Natural Resources Canada.

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