Introduction to Discontinuity Stress
Discontinuity takes places in a region or point of a system where a sudden change in load, geometry or material exists. The points in vicinity of a discontinuity area tend to have a different displacement due to a loading, whereas because of jointing to each other they reach to a common place. So a force which causes some stresses named “discontinuity stress” is developed at the joint. For instance pressure vessel knuckle area where the head connects to shell is prone to discontinuity stress because the geometry changes abruptly. Stresses developed at welded joints between core and jacket pipes are laid in this category. The loads at supporting points of a pipe cause discontinuity stresses which affect a small area of pipe named as discontinuity area. Comparing to whole system, these stresses exist in a small portion of a system and should be studied regarding their types and nature of loadings. Discontinuity stresses are categorized as local stresses and must be checked based on stress categories and proper allowable stresses mentioned in ASME BPVC section VIII div 2 respectively. The purpose of this paper is introduction to some models and methods which have been developed for calculation of discontinuity stresses at pipe supports.