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.
For long sections of pipe, the thermal expansion of trapped liquid can be significant. It is often required that the increase in volume of the fluid be determined in order to select suitable thermal relief valves to protect the integrity of the pipework. This article details how to calculate the required relief flow rate to prevent over pressure due to thermal expansion.