Assessment of Allowable Flaw Sizes Based on Tensile Properties Evaluated by Instrumented Indentation Testing

Abstract When a flaw is detected in power plant piping and it is judged to be allowable by the code consensus, the plant operation can be continued without the need for repair or replacement. The benefit of instrumented indentation technique (IIT) for the analysis of allowable flaw sizes is critically assessed in this study based on experimental data and code calculations. Intrinsic standard deviations of yield and ultimate tensile strengths for Type 304 stainless steels are discussed in this paper. As a result, IIT method is capable to estimate the flow stress for Type 304 stainless steel within 5% deviation from the result of conventional tensile tests. Then, the allowable circumferential flaw sizes for pipes subjected to tensile loading are obtained based on strength properties assessed by IIT. In addition, the allowable flaw sizes are compared to the allowable flaw sizes derived from the flow stress tabulated in the ASME (American Society of Mechanical Engineers) code section II, Materials. The conclusion is drawn that IIT is a beneficial method for the Limit Load Criteria analysis.