Influence of Sustained and Expansion Loads on Lifetime Prediction of Piping Components Operating in the Creep Range
SMiRT-21, New-Delhi India, 6-11 November 2011, Paper-689
One of the most common failure modes for elevated temperature piping working in the creep conditions is initiation, growth of cracks in pipe bends that finally leads to the failure. Failure of bends is much more dangerous than appearance of cracks in the piping joint welds or tees due to size of affected areas.
It is known that for pipe bends, working in creep range, attention must be paid to imperfections of the cross-section, such as out-of-roundness and different wall-thickness, and their interaction with the internal pressure as well as bending and torsion moments.
FE analyses of different bend configuration have been performed to investigate effect of the above factors on the creep damage of this element. It was recognized that out-of-roundness and bending moments are significant contributors to the stress state of pipe bends and hence in the creep cumulative damage. Neglecting of these factors could lead to big uncertainties in the remaining life prediction.