American Petroleum Institute

Sizing, Selection, and Installation of Pressure-Relieving Devices in Refineries; Part I - Sizing and Selection - Seventh Edition
 N RP 520 PT I

Annotation

1.1 SCOPE

This recommended practice applies to the sizing and selection of pressure relief devices used in refineries and related industries for equipment that has a maximum allowable working pressure of 15 psig [103 kPag] or greater. The pressure relief devices covered in this recommended practice are intended to protect unfired pressure vessels and related equipment against overpressure from operating and fire contingencies.

This recommended practice includes basic definitions and information about the operational characteristics and applications of various pressure relief devices. It also includes sizing procedures and methods based on steady state flow of Newtonian fluids.

Pressure relief devices protect a vessel against overpressure only; they do not protect against structural failure when the vessel is exposed to extremely high temperatures such as during a fire. See API Recommended Practice 521 for information about appropriate ways of reducing pressure and restricting heat input.

Atmospheric and low pressure storage tanks covered in API Standard 2000 and pressure vessels used for the transportation of products in bulk or shipping containers are not within the scope of this recommended practice.

The rules for overpressure protection of fired vessels are provided in Section I of the ASME Boiler and Pressure Vessel Code and ASME B31.1, and are not within the scope of this recommended practice.

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