The Stress Variation In High Temperature And High Pressure Pipe Elbows And Reasons Analysis

Supercritical and ultra supercritical units with the steam temperature and thesteam pressure up to 600℃ and 30MPa will become predominate one in the futuredecade. In such a situation it is necessary to ensure the safety and the reliability ofpower generation equipment during their operation, especially, for high temperaturepipelines connecting the boiler and the steam turbine. More attention must be paid topipe bends or elbows which have initial ovality and thickness asymmetry. At this area,it produces a complicated multiaxial stress and varies with time due to creep.In this paper, finite element analysis has been carried out for 90°steam pipeelbows made from 9Cr-1MoNbV(P91) steels. The stress distribution in the pipe elbowduring creep is discussed. The ovality and the different initial thickness asymmetry ofsteam pipe elbows are confirmed the effect on the stress distribution variation in pipeelbow. Finally, based on influence of ovality and thickness an analytical model tocalculate equivalent stress of elbow from straight pipe stress is presented.