Piping and fitting dynamic reliability program

There is a general concern about the over-conservatism in the treatment of infrequent dynamic loads in the design of nuclear power plant piping. To address this concern, in 1985 the Electric Power Research Institute (EPRI) in conjunction with the U. S. Nuclear Regulatory Commission (NRC) initiated the Piping and Fitting Dynamic Reliability (PFDR) Program with General Electric Company as the prime contractor and ANCO Engineers as the subcontractor for component testing. The ultimate objective of this program is to introduce new, improved, realistic and defensible ASME Code design rules which take advantage of the inherent dynamic margin in piping and which result in a more balanced piping design between infrequent dynamic loads and daily operating loads. The basis for the proposed changes in design criteria will be derived from an extensive testing program together with supporting analyses. The first of three testing programs is focusing on the behavior of typical piping components when subjected to dynamic loading introduced through hydraulically operated sleds. A second testing program is investigating the behavior of piping systems under dynamic loading and the third program is focusing on development of a laboratory type specimen which can be used to quantitatively evaluate low cycle fatigue in the presence of ratcheting. This paper represents a status report of results of the component tests to date. The tests have demonstrated that the mode of component failure is fatigue ratcheting and not plastic collapse. No appreciable loss of flow area has been observed even for inertia loads many times (15-27) the safe shutdown earthquake (SSE). System tests are expected to corroborate these findings.