Design Assessment of Austenitic Stainless Steel Components for Applications Covered by ASME III Class 1 Code Requirements

The UK Technical Advisory Group on the Structural Integrity of High Integrity Plant (TAGSI) has recently undertaken an assessment of a new method of classification of austenitic stainless steel components based on their safety function and the consequences of their failing to perform that function. The intent of the safety classification is to ensure that the probability of occurrence of any potential failure bears an inverse relation to the severity of its consequence, so that a low risk is incurred from failure of any type. Specifically, TAGSI was invited to: 1. consider circumstances under which Subsection NB of the ASME III Code for Class 1 components contributes adequate margins against gross failure of austenitic stainless steel components classified as High Integrity; and if necessary 2. define additional contributions that need to be met to provide assurance against gross failure of austenitic stainless steel components for the High Integrity severity level. In producing its response, TAGSI interpreted the Question as relating strictly to the austenitic stainless steel pipework and associated welds of the relevant class of PWR systems that have the safety classification of High Integrity. Dissimilar metal welds were excluded from consideration, and it was assumed that a robust EAC prevention strategy is in place. The generic response produced by TAGSI to the above Question is summarised within this framework.