Research on the Application of FEN for EAF Evaluation of the Austenitic SS Pipe Under Combined Transient Loads

Accumulative test data indicates that the effects of the light water reactor (LWR) environment could cause the fatigue resistance of materials used in the reactor coolant pressure boundary components to significantly reduce. EAF is used as the abbreviation of the environmentally assisted fatigue in the nuclear field. In 2007, NRC issued RG. 1.207. It was updated in 2014. And it requires that the effects of the light-water environment on the fatigue life reduction of metal components should be considered for new plants. And it suggests to use environmental correction factor (Fen) to account for EAF. Fen = Nair/Nwater (N is occurrences). NUREG/CR-6909 [1] presents the detail Fen calculation formula which includes the complicated influence of combined multi-parameters. Fen is a function of temperature, strain amplitude & rate, dissolved oxygen level in water, and sulfur content of the steel. Accordingly, Fen calculation will present a comparatively conservative result. Depends on the experience of the primary pressure boundary piping transient operation, Fen vary during each transient. More uncertainty and confusion are raised during the application of the Fen method. In the research work involved in this article, first, the typical character of piping thermal transient is derived based on the existing experience. Second, small specimen EAF tests are conducted depend on the above derived combined loading characters. Then effort is taken to improve the application of the Fen method for the combined multi-transient loading conditions. And the result is compared with that of the lowest instantaneous Fen method and equalization of the weighted Fen method. Finally, a designed test matrix is needed to prove its practicability furthermore.