PLANT MATERIAL PROBLEMS
The important information in this chapter is summarized below.
Plant Material Problems Summary
Thermal fatigue is the fatigue type of most concern. Thermal fatigue
results from thermal stresses produced by cyclic changes in temperature.
Fundamental requirements during design and manufacturing are used to
avoid fatigue failure.
Plant operations are performed in a controlled manner to mitigate cyclic
stress. Heatup and cooldown limitations, pressure limitations, and pump
operating curves are also used to minimize cyclic stress.
Work hardening has the effect of reducing ductility, which increases the
chances of brittle fracture.
Prior work hardening causes the treated material to have an apparently
higher yield stress; therefore, the metal is strengthened.
Creep is the result of materials deforming when undergoing elevated
temperatures and constant stress. Creep becomes a problem when the
stress intensity is approaching the fracture failure strength. If the creep
rate increases rapidly, the strain becomes so large that it could result in
failure. The creep rate is controlled by minimizing the stress and
temperature of a material.