Thermal Expansion Relief Requirements for Liquids, Vapors, and Supercritical Fluids

Vessels and pipes filled with fluids require pressure relief in order to protect from loss of containment caused by fluid thermal expansion. Thermal expansion of fluids occurs when the fluid is heated as a result of steam tracing, solar radiation, external fire, etc.

In addition to establishing the required thermal relief requirements, it is also useful to establish the maximum pressure that can be reached during limited heating for either non-vented or partially vented fluid filled systems. In order to obtain better estimates of the maximum pressure reached, the elasticity of the piping/vessel should be considered. For partially vented systems, the excess volumetric expansion (fluid expansion - vessel/piping expansion) rate will govern the relief requirements.

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