Pressure Relief Valve Sizing Concerns for Valves in Ethylene, Propylene, and Ethane Service

Sizing pressure relief valves is a complex process for any chemical or petrochemical; however, relief devices in Ethylene, Propylene, and Ethane service can raise some unique concerns.  One concern is how the chemicals’ physical properties affect the operating conditions.  Chemical processes of Ethane, Ethylene, and Propylene are frequently operating in thermodynamic supercritical conditions because the chemicals’ temperatures and critical pressures are low.  Operating in thermodynamic supercritical conditions makes it even more imperative that the engineer ensures accurate physical properties are used in the analysis.  Another unique concern is the cryogenic processing conditions of these chemicals, which makes it challenging to meet material and brittle fracture hazards.  The last unique concern is the decomposition of these chemicals when at elevated pressure.  All three chemicals, but especially Ethylene, can decompose upon rapid depressurization from pressure greater than 4000 psig.

This paper is a brief analysis of these special considerations and how they could potentially affect a relief systems design.