As part of the xLPR (Extremely Low Probability of Rupture) project, validation efforts were conducted to assess the predictive capability of axial surface crack (Ax-SC) and axial through-wall crack (Ax-TWC) stability modules employed for making the crack stability assessment. For the Ax-SC, the plastic collapse solution/criteria from the Ductile Fracture Handbook (DFH) was selected and employed after making detailed comparisons between the solutions obtained from the DFH and API-579/ASME FFS-1 solution methods. Experiments from past tests conducted for the Atomic Energy Commission (AEC) and by MPA-Stuttgart were used to validate the performance of the implemented axial SC stability module.
Similarly, for the axial TWC stability assessment, a Limit Load solution, and a numerical analysis procedure for an elastic-plastic fracture mechanics (EPFM) based method employing a J-integral fracture mechanics parameter approach using a GE/EPRI type J-estimation equation, and tabulated plastic influence functions based on pipe dimension and Ramberg-Osgood material parameters, were used. Experimental results from past pipe tests conducted for the AEC, others conducted for the PRCI, and by Tokyo Gas involving larger diameter pipes were used to validate the performance of the implemented axial TWC stability module.
In this paper, the selection of stability criteria/solutions, their performance and implications for the xLPR 2.0 code are discussed. The impact of using different flow stresses (function of yield and ultimate stresses), and stress magnification factor (Folias bulging factor) expressions, on the predictions is highlighted. Further, a conservative basis for the assessment of axial crack stability in welds is proposed. In closing, additional empirical corrections that can be incorporated without overly biasing the deterministic solutions/criteria that feed into a probabilistic analysis are highlighted.