Accurate estimates of fluid flow reaction forces are especially necessary for pressure relief systems. Substantial fluid flow reaction forces can be developed when relief systems actuate for both reactive and non-reactive systems. Specific relief systems scenarios where dynamic loads may be important include but are not limited to pressure relief caused by runaway reactions, loss of high-pressure/low-pressure interface, control valve failure, heat exchanger tube failure, etc. Even if the relief requirements or required vent size are properly calculated, without adequate relief piping supports, the relief system will most likely fail when a demand is placed on it. The likelihood of failure of poorly supported relief systems increases as the systems are actuated more than once, i.e. reaction forces damage to supports can be cumulative. Relief systems engineers are often challenged when developing reaction forces, especially for high pressure and/or emergency relief where dynamic loading becomes important. The recently published 2nd Edition of the CCPS Guidelines for Pressure Relief and Effluent Handling Systems includes a detailed chapter on how to calculate reaction forces for different types of relief devices and relief configurations. This paper provides a quick reference/primer on how to properly calculate fluid flow reaction forces.
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