Validated sizing rule against chatter of relief valves during gas service

Spring loaded relief valves are commonly used for protecting pressure loade d vessels, piping, etc, against overpressure. If the relief valve is instal led improperly it may chatter while discharging. This behaviour is defined as an extremely rapid full opening and closing of the valve. The associated mechanical loads can damage the piping, equipment and the relief valve wit h the result of loss of pressure relief protection, undirected process flui d release, danger of fire and/or explosion, etc. In the technical guidelines and in the literature, sizing rules for the pro per installation of relief valves are recommended. Most commonly applied is the 3% pressure loss rule for the allowable inlet pipe pressure drop as re commended in the API RP 520 (API RP 520. Sizing, selection and installation of pressure-relieving systems in refineries, 1993) or AD A2 (AD-Merkblatt A2: Sicherheitseinrichtungen gegen Druckuberschreitung-Sicherheitsventile. 1993). Another recommendation is based on the transmission time and the amp litude of the pressure waves generated by the abrupt safety valve opening a nd closing. In addition to these elementary rules, sophisticated computer c odes for numerical simulation of the valve behaviour during the discharge p rocess need to include the interrelationship between the flow in the pipe a nd that in the safety valve. Experiments have been performed with the objective of checking the validity of the rules. Based also on results taken from the literature a modified p ressure surge sizing method is recommended. The usefulness of supplementary measures to establish in industrial installations a posteriore valve stabi lity, e.g., by increasing the inlet pipe diameter, reducing the safety valv e lift or installation of an oscillation damper are also evaluated. (C) 200 1 Elsevier Science Ltd. All rights reserved.