Abstract: The reliability of welded pressure pipe with circumferential surface crack was calculated by using 3D 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 3D elasticplastic stochastic finite element program which was developed by ourselves. The effects of variables such as fracture toughness, bending moment and depth of the circumferential surface crack on the structure reliability were also discussed. The calculation results indicate that the crack opening angle has certain effect on the reliability of the welded pipe. When the mean value of bending moment is 10 kN·m, with the crack opening angle increasing from 30° to 180°, the failure probability of the welded pipe changes from 3.837 9×10-8 to 3.694 3×10-6. When the mean value of bending moment is 15 kN·m, with the crack opening angle increasing from 30° to 180°, the failure probability of the welded pipe changes from 3.986 5×10-6 to 1.936 7×10 -3. The bending moment has great effect on the reliability of the welded pipe. When the mean value of moment is changed from 10 to 15 kN·m, the failure probability of the welded pipe increases dramatically for the same circumferential crack opening angle. Regardless of changing of moment, the pipe has higher reliability if the crack opening angle is less than 60?. The method has put forward a new way for safety assessment of welded pipe with circumferential surface crack. © Shanghai Jiaotong University and Springer-Verlag Berlin Heidelberg 2011.

Key words: Circumferential surface crack; Reliability; Safety assessment; Stochastic finite element method; Welded pipe