Estimation Method of Failure Bending Stress of Flawed Pipe Considering Internal Pressure on Flaw Surface and Change of Average Radius

Flaw may be initiated in the piping systems of nuclear power plants due to the age-related degradations such as fatigue or stress corrosion cracking. The estimation method of failure bending stress was provided in international codes such as ASME BPV Code Section XI. The failure bending stress was proposed based on the net-section stress approach and thin pipe theory in the current code. However, the internal pressure on flaw surface and the change of the average radius of the pipe due to the occurrence of flaw were not considered in current estimation method of failure bending stress. In fact, these influences may become more significant with the increasing flaw size. In this paper, the formulas of failure bending stress considered these factors are proposed, and some numerical investigations were performed to check the effects the internal pressure on flaw surface and the change of the average radius of the pipe. The proposed method is very simple and easy to apply.