An Alternative Approach to Assess the Integrity of Corroded Line Pipe - Part II: Alternative Criterion

Part II of this paper builds on the review of the experimental database and the analysis of the related trends that defined the approach to develop an alternative criterion in Part I based on an upper limit on failure pressure for very small defects and a lower limit that reflects large areal defects. Results are developed for specific combinations of defect size and profile through parametric analyses. These results are used to:

1. compare this alternative approach with other criteria for metal-loss defects, and

2. derive the mathematical form of the alternative criterion.

Results from these analyses are used to illustrate the effects of defect profile, size, and spacing, to define the transition between the two noted limits on failure pressure. This parametric analysis has been done using a special purpose numerical finite element model in conjunction with the failure criterion outlined in Part I. Trends in these data are used to identify the preliminary form of the function needed to modify the reference stress for defect-free pipe to account for the size, shape, and spacing of the defects. The results of this parametric analysis are cast into a mathematical format that is then used to predict the failure pressure response of the defect set that underlies the development of the ASME B31G criterion. These same data are used to infer defect sizes where the upper limit on failure pressure can be expected as well as defect sizes where the lower limit involving large areal defects will control failure.