Limit Load Analysis Method for a Pipe with an Axial Shallow Flaw

概要

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JSME Rules on Fitness-for-Service (FFS) for Nuclear Power Plants (2008 ed.) gives acceptance standards for detected flaws during in-service inspection. As for plastic collapse it regulates the maximum stress or allowable flaw size by the limit load method. However it is found that even smaller flaws than the allowable flaws without evaluation are not accepted according to the procedure of the JSME rule. This is caused by the combination of the rule-basis flow stress and safety factor in the JSME rule. The safety factor of the JSME rule was set by following the procedure of ASME Sec. XI in 1998, on the other hand the definition of rule-basis flow stress was original of the JSME rule and excessive conservativeness arises from their combination. It is known that plastic collapse stress is influenced by the flaw shape, especially in the case of a shallow flaw and it increases up to ultimate stress. In this paper a new parameter, fracture criterion stress σc at plastic collapse depending on flaw depth is introduced into the JSME rule in order to exclude excessive conservativeness and perform more rational evaluation..