An unfinished chapter
Philip A. Henry, E2G | The Equity Engineering Group, Inc., USA, examines ongoing efforts to update and improve the current industry codes and standards on pressure relief valve instability. he increased emphasis on safety in the ammonia and fertilizer industries has produced greater sophistication in the analysis of overpressure concerns. One area where this is particularly evident is in the study of the stability of pressure relief valves (PRVs) during activation. This affects all industries where PRVs are used to provide overpressure protection, including the ammonia and fertilizer industries. The current guidance published in industry codes and standards is not sufficient to ensure that any company is
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fully protected from PRV instability issues. Limiting the inlet pressure losses to 3% of set pressure is a requirement laid out in ASME Section VIII, Appendix M that relates to preventing valve instability during an overpressure event.1 This 3% rule also appears in other industry standards, such as API 520 Part II and ISO 4126-9.2,3 However, the former states that limiting the inlet pressure drop to a specific value may not be the primary factor that guarantees PRV stability. PRV stability is an evolving issue, and there are additional factors that impact whether the valve operates in a stable manner.
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