Pressure relief valve size selection

Figure 7-7A. Pressure level relationship conditions for pressure relief valve installed on a pressure vessel (vapor phase). Single valves (or more) used for process or supplemental valves for external fire (see labeling on chart). Reprinted by permission, Sizing, Selection and Installation of Pressure Relieving Devices in Refineries, Part 1 Sizing and Selection, API RP-520, 5th Ed., July 1990, American Petroleum Institute.

Sizing, 451, 453, 455, 459, 462 Sonic flow, 461 Types, illustrations, 411-421 Rupture disk, liquids, 462, 466 Rupture disk/pressure-relief valves combination, 463 Safely relief valve, 400 See Relief valve Safety valve, 400, 434 Safety, vacuum, 343 Scale-up, mixing, 312, 314—316 Design procedure, 316-318 Schedules/summaries Equipment, 30, 31 Lines, 23, 24 Screen particle size, 225 Scrubber, spray, 269, 270 Impingement, 269, 272 Separator applications, liquid particles, 235 Liquid particles, 235 Separator selection, 224, 225 Comparison chart, 230 Efficiency, 231... 

American Petroleum Institute Washington www.api.org API Recommended Practice 520 Part 1 - Sizing and Selection API Recommended Practice 520 Part 2 - Installation API Recommended Practice 521 - Guide for Pressure Relief and Depressurizing Systems API Standard 526 - Flanged Steel Pressure Relief Valves API Standard 527 - Seat Tightness of Pressure Relief Valves API Recommended Practice 576- Inspection of Pressure Relieving Devices... 

Pressure-relief valves protect life and property. They are installed on pressurized systems in almost all types of industries such as refineries, oil and gas production facilities, pipelines, electric power generating plants, paper mills, chemical plants, and other industrial facilities worldwide. Pressure-relief designs are available for both compressible and noncompressible fluid applications in a wide range of sizes, material selections, pressure classes and temperature ranges. 

Sizing and selection of relief valves must comply with criteria specified in applicable codes and standards as well as the manufacturer s data concerning the flow characteristics for each design type. Pressure-relief valve manufacturers provide catalogs and computer sizing programs to aid in the sizing and selection of their specific products (Fig. 5.186). 

In this chapter, following topics will be discussed type of pressure relief devices, their characteristics, ASME code PRD set pressure, maximum operating pressure, contingency analysts, pressure reliefvalve and rupture disk sizing, pressure relief valve inlet/outlet piping sizing, Eind PRD selection. 

This section describes the various pressure relief devices that are commonly used, with their characteristics and criteria for selection. Basic calculation procedures for sizing PR valves are covered in subsequent discussions. 

When designing the inlet piping to a relief valve, what pressure losses are recommended See API 520, Sizing, Selection, and Installation (1994). 

From API Std. 526 we would select an H orifice relief valve with effective orifice area 0.785 in. A size 2H3 carbon steel relief valve will allow a set pressure up to 740 psig in the expected range of operation temperature. In practice, however, we would have to consider two-phase flow due to entrainment of boiling liquid with the vapor and might select a larger orifice size after more detailed design. 

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