Plant MaterialsDOE-HDBK-1017/2-93PLANT MATERIAL PROBLEMSSummaryThe important information in this chapter is summarized below.Plant Material Problems SummaryFatigue FailureThermal fatigue is the fatigue type of most concern. Thermal fatigueresults from thermal stresses produced by cyclic changes in temperature.Fundamental requirements during design and manufacturing are used toavoid fatigue failure.Plant operations are performed in a controlled manner to mitigate cyclicstress. Heatup and cooldown limitations, pressure limitations, and pumpoperating curves are also used to minimize cyclic stress.Work HardeningWork hardening has the effect of reducing ductility, which increases thechances of brittle fracture.Prior work hardening causes the treated material to have an apparentlyhigher yield stress; therefore, the metal is strengthened.CreepCreep is the result of materials deforming when undergoing elevatedtemperatures and constant stress. Creep becomes a problem when thestress intensity is approaching the fracture failure strength. If the creeprate increases rapidly, the strain becomes so large that it could result infailure. The creep rate is controlled by minimizing the stress andtemperature of a material.Rev. 0Page 31MS-05
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