1、Sizing, Selection, and Installationof Pressure-relieving Devices Part ISizing and SelectionAPI STANDARD 520NINTH EDITION, JULY 2014Special NotesAPI publications necessarily address problems of a general nature. With respect to particular circumstances, local,state, and federal laws and regulations s
2、hould be reviewed.Neither API nor any of APIs employees, subcontractors, consultants, committees, or other assignees make anywarranty or representation, either express or implied, with respect to the accuracy, completeness, or usefulness of theinformation contained herein, or assume any liability or
3、 responsibility for any use, or the results of such use, of anyinformation or process disclosed in this publication. Neither API nor any of APIs employees, subcontractors,consultants, or other assignees represent that use of this publication would not infringe upon privately owned rights.Users of th
4、is standard should not rely exclusively on the information contained in this document. Sound business,scientific, engineering, and safety judgment should be used in employing the information contained herein.Work sites and equipment operations may differ. Users are solely responsible for assessing t
5、heir specific equipmentand premises in determining the appropriateness of applying the standard. At all times users should employ soundbusiness, scientific, engineering, and judgment safety when using this standard.API publications may be used by anyone desiring to do so. Every effort has been made
6、by the Institute to assure theaccuracy and reliability of the data contained in them; however, the Institute makes no representation, warranty, orguarantee in connection with this publication and hereby expressly disclaims any liability or responsibility for loss ordamage resulting from its use or f
7、or the violation of any authorities having jurisdiction with which this publication mayconflict.API publications are published to facilitate the broad availability of proven, sound engineering and operatingpractices. These publications are not intended to obviate the need for applying sound engineer
8、ing judgmentregarding when and where these publications should be utilized. The formulation and publication of API publicationsis not intended in any way to inhibit anyone from using any other practices.Any manufacturer marking equipment or materials in conformance with the marking requirements of a
9、n API standardis solely responsible for complying with all the applicable requirements of that standard. API does not represent,warrant, or guarantee that such products do in fact conform to the applicable API standard.All rights reserved. No part of this work may be reproduced, translated, stored i
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11、rewordAPI Standard 520, Sizing, Selection, and Installation of Pressure-relieving Devices, is the result of several years workby engineers in the petroleum industry. The information in this standard is intended to supplement the informationcontained in Section VIIIPressure Vessels, of the ASME Boile
12、r and Pressure Vessel Code. The recommendationspresented in this publication are not intended to supersede applicable laws and regulations.Users of this standard are reminded that no publication of this type can be complete, nor can any written document besubstituted for qualified engineering analys
13、is.Shall: As used in a standard, “shall” denotes a minimum requirement in order to conform to the specification.Should: As used in a standard, “should” denotes a recommendation or that which is advised but not required in orderto conform to the specification.The current edition of this standard, pub
14、lished in two parts, has been updated with respect to the practices generallyused in the installation of all devices covered in the previous editions; the current edition also contains additionalinformation based on revisions suggested by many individuals and several organizations.The First Edition
15、of this standard was initially released as a recommended practice in 1955. The Second Edition waspublished in two parts: Part I, Design, in 1960 and Part II, Installation, in 1963. The Third Edition of Part I was issuedin November 1967 and reaffirmed in 1973. The Fourth Edition was issued in Decembe
16、r 1976, the Fifth Edition wasissued in July 1990, the Sixth Edition was issued in March 1993, the Seventh Edition was issued in January 2000,and the Eighth Edition was issued in December 2008.Nothing contained in any API publication is to be construed as granting any right, by implication or otherwi
17、se, for themanufacture, sale, or use of any method, apparatus, or product covered by letters patent. Neither should anythingcontained in the publication be construed as insuring anyone against liability for infringement of letters patent.This document was produced under API standardization procedure
18、s that ensure appropriate notification andparticipation in the developmental process and is designated as an API standard. Questions concerning theinterpretation of the content of this publication or comments and questions concerning the procedures under whichthis publication was developed should be
19、 directed in writing to the Director of Standards, American PetroleumInstitute, 1220 L Street, NW, Washington, DC 20005. Requests for permission to reproduce or translate all or any partof the material published herein should also be addressed to the director.Generally, API standards are reviewed an
20、d revised, reaffirmed, or withdrawn at least every five years. A one-timeextension of up to two years may be added to this review cycle. Status of the publication can be ascertained from theAPI Standards Department, telephone (202) 682-8000. A catalog of API publications and materials is publishedan
21、nually by API, 1220 L Street, NW, Washington, DC 20005.Suggested revisions are invited and should be submitted to the Standards Department, API, 1220 L Street, NW,Washington, DC 20005, standardsapi.org.iiiContentsPage1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
22、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Normative References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Terms and Definitions. . . . . . . . . . . . .
23、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Pressure-relief Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84.1 General . . . . . . .
24、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84.2 Pressure-relief Valves (PRVs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25、. . . . 84.3 Rupture Disk Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274.4 Pin-actuated Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
26、 . . . . . . . . . . . . . . . . 414.5 Open Flow Paths or Vents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444.6 Other Types of Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
27、. . . . . . . . . . . . . . . . . . . . . . . . . . . 445 Procedures for Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445.1 Determination of Relief Requirements . . . . . . . . . . . . . . . . . . . . .
28、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445.2 API Effective Area and Effective Coefficient of Discharge. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 455.3 Backpressure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
29、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 465.4 Relieving Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505.5 Development of Sizing Equations . . . . . . . . . . . .
30、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545.6 Sizing for Gas or Vapor Relief . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 555.7 Sizing for Steam Relief . . . . . . . . .
31、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 725.8 Sizing for Liquid Relief: PRVs Requiring Capacity Certification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 755.9 Sizing for Liquid Relief: PRVs Not Requiri
32、ng Capacity Certification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795.10 Sizing for Two-phase Liquid/Vapor Relief. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 805.11 Sizing for Rupture Disk Devices . . . . . . . . . . . . .
33、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815.12 Sizing for Open Flow Paths or Vents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82Annex A (informative) Rupture Disk Device Specificat
34、ion Sheet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83Annex B (informative) Review of Flow Equations Used in Sizing Pressure-relief Devices . . . . . . . . . . . . . . . . 88Annex C (informative) Sizing for Two-phase Liquid/Vapor Relief . . . . . . . . . . . . . . .
35、. . . . . . . . . . . . . . . . . . . . . 109Annex D (informative) Pressure-relief Valve Specification Sheets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129Annex E (informative) Capacity Evaluation of Rupture Disk and Piping System 100 % Vapor Flow andConstant Pipe Diamete
36、r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
37、. . . 143Figures1 Conventional PRV with a Single Adjusting Ring for Blowdown Control . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 Balanced-bellows PRV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
38、 Balanced-bellows PRV with an Auxiliary Balanced Piston . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 Conventional PRV with Threaded Connections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 PRV Operation-Vapor/Gas Se
39、rvice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 Typical Relationship Between Lift of Disk in a PRV and Vessel Pressure . . . . . . . . . . . . . . . . . . . . . . . . . 147 PRV Operation-Liquid Service . . . . . . . . . . .
40、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 Typical Effects of Superimposed Backpressure on the Opening Pressure of Conventional PRVs . . . . 17vContentsPage9 Typical Effects of Backpressure on the Set Pressure of Balanced PRVs . . . . . .
41、. . . . . . . . . . . . . . . . . . . 1810 Pop-action Pilot-operated Valve (Flowing Type) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1911 Pop-action Pilot-operated Valve (Nonflowing Type) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
42、 . . . . . . . . . . . 2012 Modulating Pilot-operated Valve (Flowing Type) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2113 Pilot-operated Relief Valve with a Nonflowing Modulating Pilot Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321
43、4 Low-pressure Pilot-operated Valve (Diaphragm Type) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2315 Pressure Level Relationships for PRVs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2416 Typical Rel
44、ationship Between Lift of Disk or Piston and Vessel Pressure in a Pop-action Pilot-operated PRV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2517 Typical Relationship Between Lift of Disk or Piston and Ves
45、sel Pressure in a Modulating-action Pilot-operated PRV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2518 Pressure Level Relationships for Rupture Disk Devices . . . . . . . . . . . . . . . . . . . . . . .
46、. . . . . . . . . . . . . . . . 2919 Rupture Disk Device in Combination with a PRV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3020 Forward-acting Solid Metal Rupture Disk. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
47、 . . . . . . . . . . 3221 Forward-acting Scored Rupture Disk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3322 Forward-acting Composite Rupture Disk. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
48、 . . . . . . . . 3423 Reverse-acting Rupture Disk with Knife Blades . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3524 Reverse-acting Scored Rupture Disk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
49、. . . . . 3625 Graphite Rupture Disk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3726 Rupture Disk Application Parameters Assuming No Superimposed Backpressure . . . . . . . . . . . . . . . . 3927 Common Types of Manufacturing Ranges and Corresponding Burst Pressure Marking . . . . . . . . . . . . 4028 Rupture Disk Application Parameters with Superimposed Backpressure. . . . . . . . . . . . . . . . . . . . . . . . . 4229 Buckling Pin Valve. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
