For systems where liquid product may be trapped in a pipe section of an extended period of time thermal expansion can become a problem. Heating of the fluid in the pipe results in a rapid pressure rise as the fluid expands which can quickly exceed the design pressure of the pipeline. The damaging effects of the thermal expansion can be mitigated through the use of thermal relief valves and where there is several potential pipe blockages in series, it is often necessary to ‘cascade’ thermal relief valves back to a tank. This article describes how to design a cascading thermal relief system.
This article lists the standard effective orifice areas for the orifice designations found in API RP 526 5th edition. These orifice designations set the minimum effective orifice area which a relief valve must have to meet the API 526 requirements and must be used with the sizing equations in API RP 520 Part I.