An Improvement in the Code Evaluation of Flawed Pipes
ASME Code Section XI Nonmandatory Appendix C [1] formalized evaluation of flaws in piping for justification of continued service of piping components with an identified crack-like flaw. The revision of this appendix in 2004 was a significant improvement in the evaluation methodology for both flawed austenitic stainless steel and ferritic steel pipe depending upon the failure mode governed by limit load (fully plastic), elastic-plastic fracture mechanics, or linear elastic fracture mechanics. The appendix also provides a screening procedure to determine failure mechanism and a procedure for flaw modeling based on the estimated flaw size at the end of a specified evaluation period. The purpose of this paper is to propose an improvement to the limit load method applicable to screened-in carbon steel, wrought stainless steel base material, stainless steel weld material with nonflux weld, and cast products in which the ferrite content is less than twenty percent. In addition, changes in the formulation are proposed to extend the methodology to non-crack-like flaws. Both crack-like and non-crack-like circumferential flaws in the piping are analyzed to simplify formulation for flaw evaluation. The paper concludes that the proposed formulation improves efficiency of the application of Appendix C methodology for crack-like flaw and non-crack-like flaw evaluations.