Failure Analysis of an Elbow Pipe and Crack Propagation Behavior in a Nuclear Power Plant

The elbow pipe in domestic NPP (nuclear power plant) had the leakage, thereby Chinese national nuclear bureau manage it as class 1 events according to the classify criterion for international nuclear events by IAEA (international atomic energy associate). Then the failure components were tested with items of chemical compositions analysis, mechanic property tests, SEM (scan electronic microscopy) observation of fracture morphology, energy spectrum and micro-structure analysis, the results show that there are plenty of cold-worked slip band in micro-structures, hardness is 390 HV0 P yield strength is 581 MPa, the crack is embrittled and grow along grain boundary, the fracture present crystal characteristics. The tests were finished in the simulated water in micro-dynamic loop, and the technique of DCPD were used to measure the crack propagation rate, the results show that the crack propagation rate of such failure components is 6 × l0^-7 ∼ 7 × l0^-7 mm/s in 325 °C with 2 ppm dissolved oxygen. After the comprehensive analysis, the failure mode of the pipe is inter-granular stress corrosion crack (IGSCC ), the reason for such failure is the cold worked condition. (authors)