Effects of External Loads on the Reliability of Welded Pipe with Circumferential Crack

Abstract

The reliability of welded pressure pipe with circumferential surface crack was calculated by using 3-D stochastic finite element method. This method has overcome the shortcomings of conservative results in safety assessment with deterministic fracture mechanics method. The calculation of reliability was based on 3-D elastic-plastic stochastic finite element program which was developed by ourselves. The effects of variables such as bending moment, the inner pressure on the structure reliability were discussed. The calculation results indicate that the bending moment has great effect on the reliability of the welded pipe, and the inner pressure has little effect on the reliability of the welded pipe if the inner pressure is less than 10MPa. If the mean value of the inner pressure changed from 0.5MPa to 30MPa, the failure probability will changes from 10-6 to 10-2. The bending moment also has great effect on the reliability. When the mean value of moment is changed from10000 Nm to 15000 Nm, the failure probability of the welded pipe increases dramatically for the same inner pressure. Irrespective of the changing of moment, the pipe has higher reliability if the inner pressure is less than 6 MPa. The method has put forward a new way for safety assessment of welded pipe with circumferential surface crack.