Applicability of Existing Fracture Initiation Models to High-Strength Steel Line Pipe

The original fracture criteria developed by Maxey/Kiefner for axial through-wall and surface-cracked pipes have worked well for many industries for a large variety of low strength and low toughness materials. However, newer line-pipe steels have some unusual characteristics that differ from these older materials. One example is a single test that has demonstrated that X100 line-pipe with an axial through-wall-crack can fail at pressures about 30 percent lower than predicted with commonly used analysis methods for older steels. Thus, it is essential to review the currently available models and investigate the applicability of these models to newer high-strength line pipe materials. In this paper, the available models for predicting the failure behavior of axial-cracked pipes (through-wall-cracked and external surface-cracked pipes) were reviewed. The applicability of these models to high-strength steel pipes was investigated by analyzing limited full-scale pipe fracture initiation test results and the shortcomings were identified. For both through-wall and surface cracks, the major shortcomings were related to the characterization of the material toughness, which generally leads to non-conservative predictions in the J-T analyses. The findings in this paper may be limited to the test data that was consider for this study. The requisite characteristics of a potential model were also identified.