Abstract
The dynamic cracking arrest capability is very important for pipeline in failure control. DWTT (Drop-Weight Tear Test) is widely applied as a standard test for evaluating crack arrest characteristics of pipelines. But for high performance pipeline steel, the abnormal fracture appearance is frequently observed on fracture surface of DWTT specimens and it make DWTT technique difficult to evaluate the dynamic toughness by the current test standard. In this study, various types of DWTT specimens of a commercial API-X70 pipeline steel were conducted at different temperature. The fracture appearances of specimens are observed. The intrinsic causes of abnormal fracture appearance are analyzed basing on the three-dimensional fracture theory. It is found that the dynamic propagation speed of crack in high performance pipeline steel is largely scattered. The propagation speed of fracture can change the three-dimensional stress constraint and lead to difference in the fracture appearance of specimen. Compress deformation, local thickness increase, toughness decrease and stress increase can make the crack dynamic propagation manner change from ductile to brittle and produce abnormal fracture appearance. The approaches to prevent or reduce the occurrence of abnormal fracture appearance for high performance pipeline steel are discussed in this paper.
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