The behaviour of dynamically loaded pipes with circumferential flaws under internal pressure and external bending loads

Abstract

For the determination of the load bearing capacity, the deformation, leak-before break- and fracture behaviour, bending tests on vessels out of ferritic and austenitic materials containing a circumferential defect were performed. The vessels were loaded over a temperature range extending from 20°C to 580°C by internal pressure and additionally by an externally applied quasi-static or dynamic bending moment. For the test a 4-point bending test rig providing a bending moment up to 3 MNm was used. Parallel to the tests the failure curves as well as the leak-before-break curves were calculated with the aid of engineering type calculational methods. No significant difference as far as load bearing capacity is concerned, can be established between quasi-static and dynamic loading. In most cases fracture occurred after considerable plastic deformation in the test cross section. The engineering type methods applied to the theoretical calculation of the leak-before-break curve on the corresponding defect curve proved to be conservative with respect to safety.