The Purpose of Pressure Relief Systems

All process systems, from domestic water heaters to petroleum production facilities to high-pressure polymerization reactors to atmospheric storage tanks involve the containment of fluids. These fluids are contained in equipment and piping fabricated from materials that have limited mechanical yield strengths. Such equipment and piping are generally fabricated following the rules of one or more industry standards, rooted in engineering science and experience, that specify maximum allowable pressures at which these components are to be operated. These maximum pressures are specified with the intention of providing a sizable “safety margin” between the maximum pressure and the pressure at which the material yield strength would be reached. Stressing these materials beyond their yield strengths could lead to undesirable consequences, varying from an explosive rupture of a high-pressure vessel to a spill of flammable liquid to a release of toxic gases into the atmosphere. Pressure relief systems are installed to protect equipment from failure caused by overpressure.

As defined by American Petroleum Institute Recommended Practice 521, a “pressure relieving system is an arrangement of a pressure-relieving device, piping, and a means of disposal intended for the safe relief, conveyance, and disposal of fluids.” A relieving system, per this definition, “may consist of only one pressure relief device, either with or without discharge pipe, on a single vessel or line.” A more complex pressure relief system “may involve many pressure-relieving devices manifolded into common headers to terminal disposal equipment.”

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