Fatigue failure analysis of copper pressure conduit

摘要

The analysis of initiation and propagation of a fatigue crack in a copper pressure conduit is presented. The pipe, made of high-purity copper in soft temper, was a part of the pneumatic-hydraulic drive system of a circuit breaker used in a power plant control system. Failure analysis was performed on the grounds of metallographic examination using light microscopy, SEM and evaluation of service loads that resulted in damage during the pipe service life. It was found that the crack initiated at the flange root of one pipe end, along a deep groove embossed by the sharp edge of the flanging device as a result of bending stresses, caused by repeated straightening of the pipe in each pressure-rise cycle. In this paper, beside the detailed fracture and material analysis to explain the reason for the failure, discussion of the ways to avoid such failures is also presented.