Mechanical Designs for Relief Valves for Cryogenic Apparatuses and Installations

<!--HTML-->Spring related pressure relief valves, mounted at ambient temperature, are state of the art to protect cryogenic apparatuses and installations against excessive pressure. However experiences shows limitations in applications on cryogenic pressure vessels: Set pressure varies in a wide range, unauthorized increase of set pressure, seat not tight etc. Alternatively, in some applications, spring related relief valves with cold seating, so called “Quench Relief Valves” (QRV) are used. Beside their relief function further functionalities like tight seating for system isolation as well as shut-off function for bypass precooling may be requested. So QRV’s shall be used in parallel to a cold or warm bursts disc at higher set pressure because of its rules non-conformity. There are also pressure relief valves with warm seat available on which the set pressure is based on an adjustment of forces by permanent magnets. Pressure vessel rules allows also the choice for an active triggered pressure relief valve (Controlled Safety Pressure Relief Systems, CSPRS) e. g. with a fast opening cryogenic shut-off valve. Valve and its switching and control components used for such a smart relief design should fulfil similar reliability requests to qualify for use in SIL 3 applications. For mechanical devices functional qualification tests at service conditions are to be considered. Mechanical design and function of such pressure relief valves will be shown and discussed considering its limitations regarding applications of pressure vessel rules.