Effect of Thermal Gradient on Mechanical Properties of Pressure Vessel Welds

Abstract

Pressure vessel is a closed container required to accommodate fluids at a pressure considerably higher than the surrounding pressure. Pressure vessel is one of the most important components used extensively in various industries e.g. nuclear power industry, thermal power industry based on fossil fuels as well as liquid and gaseous fuels, cryogenics industry, oil refinery industry, etc. In most of the mentioned industries, fabricated pressure vessels are used. Pressure vessels used in various nuclear power industries are fabricated using suitable welding processes. Thermal damage in pressure vessel is caused by thermal shock (or stress). Thermal shock can lead to excessive thermal gradient, which in turn can lead to considerably high stresses. These stresses can be of the nature of tensile as well as compressive. Stresses arising due to cyclic thermal shock cause fatigue failure of the materials. Stresses arising due to thermal shock are a major concern in reactor pressure vessels because of the magnitude of stresses involved. During rapid heating (or cooling) of a thick-walled pressure vessel such as the reactor pressure vessel, one part of the wall may try to expand (or contract) while the adjacent part, which has not yet been exposed to the temperature change, tries to restrain it. Thus, both sections are under stresses.The scope of this work is to study the effect of thermal stresses on mechanical behaviour of welded structure, which isformed between one of the most extensively used carbon steel in the nuclear industry, subjected to thermal cycling. Temperature range, thermal cycling duration, pre-bending stress and number of cycles are variables involved.