USE OF THE REFERENCE STRESS METHOD IN ESTIMATING THE LIFE OF PIPE BENDS UNDER CREEP CONDITIONS

The effect that the change of ovality of pipe bends, due to creep unde r internal pressure, has on the stationary-state stress state has been investigated using a reference stress approach. Attention has been fo cused on practical pipe bend geometries and loading conditions in powe r plant applications. Prediction of failure times based on stationary- state stresses, for cases in which ovality changes are neglected and i n which ovality is included, indicate that the change of ovality can b e very significant in some practical situations. Failure times obtaine d using a creep continuum damage mechanics approach have also been com pared with those obtained using the stationary-state predictions with ovality changes included. These results indicate that even sophisticat ed damage mechanics analyses are inadequate unless the effects of the changing ovality which occurs are taken into account. (C) 1998 Elsevie r Science Ltd. All rights reserved.