ASME BPVC 2010 Section VIII Division 2 Alternative Rules

ASME BPVC 2010 Section VIII Division 2 Alternative Rules The ASME Boiler & Pressure Vessel Code (BPVC) is an American Society of Mechanical Engineers (ASME) standard that regulates the design and construction of boilers and pressure vessels.[1] The document is written and maintained by volunteers chosen for their technical expertise .[2] The American Society of Mechanical Engineers works as an Accreditation Body and entitles independent third parties such as verification, testing and certification agencies to inspect and ensure compliance to the BPVC.[3]

2010 ASME Boiler and Pressure Vessel Code AN INTERNATIONAL CODE VIII Division Alternative Rules Rules for Construction of Pressure Vessels ``,````,,,,````,`,`,```,`,``,,-`-`,,`,,`,`,,` - Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Tech Stds & Safety Auth./9991061001 Not for Resale, 07/20/2010 09:30:59 MDT ``,````,,,,````,`,`,```,`,``,,-`-`,,`,,`,`,,` - INTENTIONALLY LEFT BLANK Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Tech Stds & Safety Auth./9991061001 Not for Resale, 07/20/2010 09:30:59 MDT A N I N T E R N AT I O N A L CO D E 2010 ASME Boiler & Pressure Vessel Code 2010 Edition July 1, 2010 ``,````,,,,````,`,`,```,`,``,,-`-`,,`,,`,`,,` - VIII Division Alternative Rules RULES FOR CONSTRUCTION OF PRESSURE VESSELS ASME Boiler and Pressure Vessel Committee on Pressure Vessels Three Park Avenue • New York, NY • 10016 USA Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Tech Stds & Safety Auth./9991061001 Not for Resale, 07/20/2010 09:30:59 MDT Date of Issuance: July 1, 2010 (Includes all Addenda dated July 2009 and earlier) This international code or standard was developed under procedures accredited as meeting the criteria for American National Standards and it is an American National Standard The Standards Committee that approved the code or standard was balanced to assure that individuals from competent and concerned interests have had an opportunity to participate The proposed code or standard was made available for public review and comment that provides an opportunity for additional public input from industry, academia, regulatory agencies, and the public-at-large ASME does not “approve,” “rate,” or “endorse” any item, construction, proprietary device, or activity ASME does not take any position with respect to the validity of any patent rights asserted in connection with any items mentioned in this document, and does not undertake to insure anyone utilizing a standard against liability for infringement of any applicable letters patent, nor assume any such liability Users of a code or standard are expressly advised that determination of the validity of any such patent rights, and the risk of infringement of such rights, is entirely their own responsibility Participation by federal agency representative(s) or person(s) affiliated with industry is not to be interpreted as government or industry endorsement of this code or standard ASME accepts responsibility for only those interpretations of this document issued in accordance with the established ASME procedures and policies, which precludes the issuance of interpretations by individuals The footnotes in this document are part of this American National Standard The above ASME symbols are registered in the U.S Patent Office “ASME” is the trademark of the American Society of Mechanical Engineers No part of this document may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written permission of the publisher Library of Congress Catalog Card Number: 56-3934 Printed in the United States of America Adopted by the Council of the American Society of Mechanical Engineers, 1914 Revised 1940, 1941, 1943, 1946, 1949, 1952, 1953, 1956, 1959, 1962, 1965, 1968, 1971, 1974, 1977, 1980, 1983, 1986, 1989, 1992, 1995, 1998, 2001, 2004, 2007, 2010 The American Society of Mechanical Engineers Three Park Avenue, New York, NY 10016-5990 Copyright © 2010 by THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS All Rights Reserved Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Tech Stds & Safety Auth./9991061001 Not for Resale, 07/20/2010 09:30:59 MDT ``,````,,,,````,`,`,```,`,``,,-`-`,,`,,`,`,,` - ASME collective membership mark CONTENTS PART - GENERAL REQUIREMENTS 1.1 General 1-2 1.1.1 Introduction 1-2 1.1.2 Organization 1-2 1.1.3 Definitions 1-2 1.2 Scope 1-3 1.2.1 Overview .1-3 1.2.2 Additional Requirements for Very High Pressure Vessels 1-3 1.2.3 Geometric Scope of This Division .1-4 1.2.4 Classifications Outside the Scope of this Division 1-4 1.2.5 Combination Units .1-5 1.2.6 Field Assembly of Vessels 1-5 1.2.7 Pressure Relief Devices .1-6 1.3 Standards Referenced by This Division 1-6 1.4 Units of Measurement 1-6 1.5 Technical Inquires .1-7 1.6 Tables 1-8 Annex 1.A Submittal Of Technical Inquiries To The Boiler And Pressure Vessel Standards Committee 1.A.1 Introduction .1-10 1.A.2 Inquiry Format 1-11 1.A.3 Code Revisions or Additions .1-11 1.A.4 Code Cases 1-11 1.A.5 Code Interpretations 1-12 1.A.6 Submittals 1-12 Annex 1.B Definitions 1.B.1 Introduction .1-13 1.B.2 Definition of Terms 1-13 Annex 1.C 1.C.1 1.C.2 1.C.3 1.C.4 Guidance For The Use Of US Customary And SI Units In The ASME Boiler And Pressure Vessel Codes Use of Units in Equations 1-15 Guidelines Used to Develop SI Equivalents 1-15 Soft Conversion Factors 1-16 Tables 1-17 PART - RESPONSIBILITIES AND DUTIES 2.1 General 2-3 2.1.1 Introduction 2-3 2.1.2 Definitions 2-3 2.1.3 Code Reference 2-3 2.2 User Responsibilities 2-3 2.2.1 General .2-3 2.2.2 User’s Design Specification .2-3 2.3 Manufacturer’s Responsibilities 2-6 2.3.1 Code Compliance .2-6 2.3.2 Materials Selection 2-6 2.3.3 Manufacturer’s Design Report 2-6 Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS iii Licensee=Tech Stds & Safety Auth./9991061001 Not for Resale, 07/20/2010 09:30:59 MDT ``,````,,,,````,`,`,```,`,``,,-`-`,,`,,`,`,,` - Foreword xix Statements of Policy xxi Personnel xxii 2.3.4 2.3.5 2.3.6 2.3.7 2.3.8 2.3.9 2.4 2.4.1 2.4.2 2.4.3 Manufacturer’s Data Report 2-7 Manufacturer’s Construction Records 2-7 Quality Control System .2-7 Certification of Subcontracted Services .2-8 Inspection and Examination .2-8 Application of Code Stamp 2-8 The Inspector .2-8 Identification of Inspector 2-8 Inspector Qualification 2-8 Inspector’s Duties 2-9 Annex 2.A Guide For Certifying A User’s Design Specification 2.A.1 General 2-10 2.A.2 Certification of the User’s Design specification 2-10 2.A.3 Tables 2-12 Annex 2.B Guide For Certifying A Manufacturer’s Design Report 2.B.1 General 2-13 2.B.2 Certification of Manufacture’s Design Report 2-13 2.B.3 Tables 2-15 Annex 2.C Report Forms And Maintenance Of Records 2.C.1 Manufacturer’s Data Reports 2-16 2.C.2 Partial Data Reports 2-17 2.C.3 Maintenance of Records 2-17 Annex 2.D Guide For Preparing Manufacturer’s Data Reports 2.D.1 Introduction .2-19 2.D.2 Tables 2-20 Annex 2.E Quality Control System 2.E.1 General 2-29 2.E.2 Outline of Features Included in the Quality Control System .2-29 2.E.3 Authority and Responsibility .2-30 2.E.4 Organization 2-30 2.E.5 Drawings, Design Calculations, and Specification Control .2-30 2.E.6 Material Control 2-30 2.E.7 Examination and Inspection Program 2-30 2.E.8 Correction of Nonconformities 2-30 2.E.9 Welding .2-30 2.E.10 Nondestructive Examination .2-30 2.E.11 Heat Treatment 2-31 2.E.12 Calibration of Measurement and Test Equipment .2-31 2.E.13 Records Retention .2-31 2.E.14 Sample Forms 2-31 2.E.15 Inspection of Vessels and Vessel Parts 2-31 2.E.16 Inspection of Pressure Relief Valves 2-31 Annex 2.F Contents And Method Of Stamping 2.F.1 Required Marking for Vessels 2-33 2.F.2 Methods of Marking Vessels with Two or More Independent Chambers 2-33 2.F.3 Application of Stamp 2-34 2.F.4 Part Marking 2-34 2.F.5 Application of Markings 2-34 2.F.6 Duplicate Nameplate 2-35 2.F.7 Size and Arrangements of Characters for Nameplate and Direct Stamping of Vessels 2-36 2.F.8 Attachment of Nameplate or Tag 2-36 iv ``,````,,,,````,`,`,```,`,``,,-`-`,,`,,`,`,,` - Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Tech Stds & Safety Auth./9991061001 Not for Resale, 07/20/2010 09:30:59 MDT 2.F.9 Figures .2-37 Annex 2.G Obtaining And Using Code Stamps 2.G.1 Code Stamps Bearing Official Symbol 2-38 2.G.2 Application for Authorization 2-38 2.G.3 Issuance of Authorization 2-38 2.G.4 Inspection Agreement 2-39 2.G.5 Quality Control System .2-39 2.G.6 Evaluation for Authorization and Reauthorization 2-39 2.G.7 Code Construction Before Receipt of Certificate of Authorization 2-40 PART - MATERIALS REQUIREMENTS 3.1 General Requirements 3-4 3.2 Materials Permitted For Construction of Vessel Parts .3-4 3.2.1 Materials for Pressure Parts 3-4 3.2.2 Materials for Attachments to Pressure Parts 3-4 3.2.3 Welding Materials .3-5 3.2.4 Dissimilar Materials 3-5 3.2.5 Product Specifications 3-5 3.2.6 Certification 3-6 3.2.7 Product Identification and Traceability .3-6 3.2.8 Prefabricated or Preformed Pressure Parts 3-7 3.2.9 Definition of Product Form Thickness 3-8 3.2.10 Product Form Tolerances .3-9 3.2.11 Purchase Requirements 3-9 3.3 Supplemental Requirements for Ferrous Materials .3-9 3.3.1 General .3-9 3.3.2 Chemistry Requirements 3-9 3.3.3 Ultrasonic Examination of Plates .3-9 3.3.4 Ultrasonic Examination of Forgings 3-9 3.3.5 Magnetic Particle and Liquid Penetrant Examination of Forgings 3-10 3.3.6 Integral and Weld Metal Overlay Clad Base Metal 3-10 3.4 Supplemental Requirements for Cr–Mo Steels 3-11 3.4.1 General .3-11 3.4.2 Postweld Heat Treatment 3-11 3.4.3 Test Specimen Heat Treatment 3-11 3.4.4 Weld Procedure Qualifications and Weld Consumables Testing 3-11 3.4.5 Toughness Requirements 3-12 3.4.6 Ultrasonic Examination .3-12 3.5 Supplemental Requirements for Q&T Steels with Enhanced Tensile Properties 3-12 3.5.1 General .3-12 3.5.2 Parts for Which Q&T Steels May be Used 3-12 3.5.3 Structural Attachments 3-13 3.6 Supplemental Requirements for Nonferrous Materials .3-13 3.6.1 General .3-13 3.6.2 Ultrasonic Examination of Plates .3-13 3.6.3 Ultrasonic Examination of Forgings 3-13 3.6.4 Liquid Penetrant Examination of Forgings 3-14 3.6.5 Clad Plate and Products .3-14 3.7 Supplemental Requirements for Bolting 3-14 3.7.1 General .3-14 3.7.2 Examination of Bolts, Studs, and Nuts 3-14 Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS v Licensee=Tech Stds & Safety Auth./9991061001 Not for Resale, 07/20/2010 09:30:59 MDT ``,````,,,,````,`,`,```,`,``,,-`-`,,`,,`,`,,` - Annex 2.H Guide To Information Appearing On The Certificate Of Authorization 2.H.1 Introduction .2-41 2.H.2 Tables 2-42 2.H.3 Figure 2-43 Threading and Machining of Studs 3-15 Use of Washers 3-15 Ferrous Bolting 3-15 Nonferrous Bolting 3-16 Materials for Ferrous and Nonferrous Nuts of Special Design 3-16 Supplemental Requirements for Castings 3-16 General .3-16 Requirements for Ferrous Castings 3-17 Requirements for Nonferrous Castings 3-18 Supplemental Requirements for Hubs Machined From Plate 3-19 General .3-19 Material Requirements .3-19 Examination Requirements 3-19 Data Reports and Marking 3-20 Material Test Requirements 3-20 General .3-20 Requirements for Sample Test Coupons 3-20 Exemptions from Requirement of Sample Test Coupons 3-20 Procedure for Obtaining Test Specimens and Coupons .3-21 Procedure for Heat Treating Test Specimens from Ferrous Materials .3-22 Test Coupon Heat Treatment for Nonferrous Materials 3-23 Material Toughness Requirements 3-23 General .3-23 Carbon and Low Alloy Steels Except Bolting 3-23 Quenched and Tempered Steels 3-28 High Alloy Steels Except Bolting 3-29 Non-Ferrous Alloys 3-33 Bolting Materials .3-33 Toughness Testing Procedures 3-33 Impact Testing Of Welding Procedures and Test Plates of Ferrous Materials 3-35 Allowable Design Stresses 3-37 Strength Parameters 3-37 Physical Properties 3-37 Design Fatigue Curves 3-37 Nomenclature 3-37 Definitions 3-38 Tables 3-39 Figures .3-49 Annex 3.A Allowable Design Stresses 3.A.1 Allowable Stress Basis – All Materials Except Bolting 3-71 3.A.2 Allowable Stress Basis – Bolting Materials 3-71 3.A.3 Tables 3-73 Annex 3.B Requirements for Material Procurement (Currently Not Used) Annex 3.C Iso Material Group Numbers (Currently Not Used) Annex 3.D Strength Parameters 3.D.1 Yield Strength 3-100 3.D.2 Ultimate Tensile Strength 3-100 3.D.3 Stress Strain Curve 3-100 3.D.4 Cyclic Stress Strain Curve .3-101 3.D.5 Tangent Modulus .3-101 3.D.5.1 Tangent Modulus Based on the Stress-Strain Curve Model 3-101 3.D.5.2 Tangent Modulus Based on External Pressure Charts .3-102 3.D.6 Nomenclature 3-103 Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS vi Licensee=Tech Stds & Safety Auth./9991061001 Not for Resale, 07/20/2010 09:30:59 MDT ``,````,,,,````,`,`,```,`,``,,-`-`,,`,,`,`,,` - 3.7.3 3.7.4 3.7.5 3.7.6 3.7.7 3.8 3.8.1 3.8.2 3.8.3 3.9 3.9.1 3.9.2 3.9.3 3.9.4 3.10 3.10.1 3.10.2 3.10.3 3.10.4 3.10.5 3.10.6 3.11 3.11.1 3.11.2 3.11.3 3.11.4 3.11.5 3.11.6 3.11.7 3.11.8 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 3.D.7 Tables 3-104 Annex 3.E Physical Properties 3.E.1 Young’s Modulus 3-109 3.E.2 Thermal Expansion Coefficient .3-109 3.E.3 Thermal Conductivity 3-109 3.E.4 Thermal Diffusivity 3-109 PART - DESIGN BY RULE REQUIREMENTS 4.1 General Requirements 4-6 4.1.1 Scope 4-6 4.1.2 Minimum Thickness Requirements .4-6 4.1.3 Material Thickness Requirements 4-7 4.1.4 Corrosion Allowance in Design Equations 4-7 4.1.5 Design Basis 4-7 4.1.6 Design Allowable Stress 4-9 4.1.7 Materials in Combination 4-10 4.1.8 Combination Units .4-10 4.1.9 Cladding and Weld Overlay 4-10 4.1.10 Internal Linings 4-11 4.1.11 Flanges and Pipe Fittings 4-11 4.1.12 Nomenclature 4-11 4.1.13 Tables .4-13 4.2 Design Rules for Welded Joints 4-14 4.2.1 Scope 4-14 4.2.2 Weld Category 4-14 4.2.3 Weld Joint Type .4-14 4.2.4 Weld Joint Factor .4-14 4.2.5 Types of Joints Permitted 4-14 4.2.6 Nomenclature 4-21 4.2.7 Tables .4-22 4.2.8 Figures .4-43 4.3 Design Rules for Shells Under Pressure 4-47 4.3.1 Scope 4-47 4.3.2 Shell Tolerances .4-47 4.3.3 Cylindrical Shells .4-48 4.3.4 Conical Shells 4-48 4.3.5 Spherical Shells and Hemispherical Heads 4-48 4.3.6 Torispherical Heads 4-48 4.3.7 Ellipsoidal Heads .4-51 4.3.8 Local Thin Areas .4-51 4.3.9 Drilled Holes Not Penetrating Through the Vessel Wall 4-52 4.3.10 Combined Loadings and Allowable Stresses .4-53 4.3.11 Cylindrical-To-Conical Shell Transition Junctions Without a Knuckle 4-54 4.3.12 Cylindrical-To-Conical Shell Transition Junctions with a Knuckle 4-57 4.3.13 Nomenclature 4-59 4.3.14 Tables .4-64 4.3.15 Figures .4-74 4.4 Design Rules for Shells Under External Pressure and Allowable Compressive Stresses 4-81 4.4.1 Scope 4-81 4.4.2 Design Factors 4-81 Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS vii Licensee=Tech Stds & Safety Auth./9991061001 Not for Resale, 07/20/2010 09:30:59 MDT ``,````,,,,````,`,`,```,`,``,,-`-`,,`,,`,`,,` - Annex 3.F Design Fatigue Curves 3.F.1 Smooth Bar Design Fatigue Curves 3-110 3.F.2 Welded Joint Design Fatigue Curves 3-111 3.F.3 Nomenclature 3-112 3.F.4 Tables 3-113 4.4.3 4.4.4 4.4.5 4.4.6 4.4.7 4.4.8 4.4.9 4.4.10 4.4.11 4.4.12 4.4.13 4.4.14 4.4.15 4.4.16 4.4.17 4.5 4.5.1 4.5.2 4.5.3 4.5.4 4.5.5 4.5.6 4.5.7 4.5.8 4.5.9 4.5.10 4.5.11 4.5.12 4.5.13 4.5.14 4.5.15 4.5.16 4.5.17 4.5.18 4.5.19 4.5.20 4.6 4.6.1 4.6.2 4.6.3 4.6.4 4.6.5 4.6.6 4.6.7 Material Properties 4-82 Shell Tolerances .4-82 Cylindrical Shell 4-84 Conical Shell 4-88 Spherical Shell and Hemispherical Head 4-89 Torispherical Head 4-90 Ellipsoidal Head .4-90 Local Thin Areas .4-91 Drilled Holes Not Penetrating Through the Vessel Wall 4-91 Combined Loadings and Allowable Compressive Stresses .4-91 Cylindrical-To-Conical Shell Transition Junctions Without A Knuckle 4-98 Cylindrical-To-Conical Shell Transition Junctions With A Knuckle 4-99 Nomenclature 4-99 Tables .4-104 Figures .4-105 Design Rules for Shells Openings in Shells and Heads 4-112 Scope .4-112 Dimensions and Shape of Nozzles 4-112 Method of Nozzle Attachment 4-112 Nozzle Neck Minimum Thickness Requirements 4-113 Radial Nozzle in a Cylindrical Shell 4-113 Hillside Nozzle in a Cylindrical Shell .4-117 Nozzle in a Cylindrical Shell Oriented at an Angle from the Longitudinal Axis 4-117 Radial Nozzle in a Conical Shell .4-118 Nozzle in a Conical Shell .4-118 Radial Nozzle in a Spherical Shell or Formed Head 4-119 Hillside or Perpendicular Nozzle in a Formed Head .4-123 Circular Nozzles in a Flat Head .4-123 Spacing Requirements for Nozzles 4-124 Strength of Nozzle Attachment Welds 4-125 Local Stresses in Nozzles in Shells and Formed Heads from External Loads 4-128 Inspection Openings 4-129 Reinforcement of Openings Subject to Compressive Stress 4-130 Nomenclature 4-131 Tables .4-134 Figures .4-135 Design Rules for Flat Heads 4-142 Scope .4-142 Flat Unstayed Circular Heads 4-142 Flat Unstayed Non-Circular Heads 4-143 Integral Flat Head With A Centrally Located Opening 4-143 Nomenclature 4-145 Tables .4-147 Figures .4-153 4.7 4.7.1 4.7.2 4.7.3 4.7.4 4.7.5 4.7.6 4.7.7 4.7.8 4.8 4.8.1 4.8.2 4.8.3 Design Rules for Spherically Dished Bolted Covers .4-154 Scope .4-154 Type A Head Thickness Requirements 4-154 Type B Head Thickness Requirements 4-154 Type C Head Thickness Requirements 4-155 Type D Head Thickness Requirements 4-156 Nomenclature 4-160 Tables .4-162 Figures .4-163 Design Rules for Quick Actuating (Quick Opening) Closures 4-166 Scope .4-166 Definitions .4-166 General Design Requirements 4-166 ``,````,,,,````,`,`,```,`,``,,-`-`,,`,,`,`,,` - Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS viii Licensee=Tech Stds & Safety Auth./9991061001 Not for Resale, 07/20/2010 09:30:59 MDT 2010 SECTION VIII, DIVISION 2) 3) If the pressure due to closure of the valve cannot exceed the following: i) the documented test pressure, multiplied by the ratio of stress value at the design temperature to the stress value at the test temperature, or ii) if the test pressure is calculated per Part 8, paragraph 8.2.1.e , in addition to the stress ratio specified in paragraph 9.A.2.2.7.b.2.i, the test pressure shall also be multiplied by the ratio of the nominal thickness minus the corrosion allowance to the nominal thickness then, as a minimum, administrative controls and mechanical locking elements are required, or If the pressure due to closure of the valve could exceed the pressure in paragraph 9.A.2.2.7.b.2 , then the user shall either: i) eliminate the stop valve, or ii) apply administrative controls, mechanical locking elements, valve failure controls, and valve operation controls, or iii) provide a pressure relief device to protect the equipment that could be overpressured due to closure of the stop valve 9.A.2.2.8 Stop Valves Provided in the Relief Path of Equipment Where Fire is the Only Potential Source of Overpressure Full area stop valves located in the relief path of equipment where fire is the only potential source of overpressure not require mechanical locking elements, valve operation controls, or valve failure controls provided the user has documented operating procedures requiring the equipment isolated from its pressure relief path is depressured and free of all liquids 9.A.3 Inlet Piping Pressure Drop for Pressure Relief Valves For pressure relief valves, the flow characteristics of the upstream system shall be such that the cumulative total of all non-recoverable inlet losses shall not exceed 3% of the valve set pressure The inlet pressure losses shall be determined accounting for all fittings in the upstream system, including rupture disks installed in the pressure relief valve inlet piping, and shall be based on the valve nameplate capacity corrected for the characteristics of the flowing fluid 9.A.4 Discharge Lines from Pressure Relief Devices a) Where it is feasible, the use of a short discharge pipe or vertical riser, connected through long-radius elbows from each individual device, blowing directly to the atmosphere, is recommended For pressure relief valves, such discharge pipes shall be at least of the same size as the valve outlet Where the nature of the discharge permits, telescopic (sometimes called "broken") discharge lines, whereby condensed vapor in the discharge line, or rain, is collected in a drip pan and piped to a drain, are recommended This construction has the further advantage of not transmitting discharge pipe strains to the pressure relief device In these types of installations, the backpressure effect will be negligible, and no undue influence upon normal operation of the pressure relief device can result b) When discharge lines are long, or where outlets of two or more pressure relief devices are connected into a common line, the effect of the back pressure on pressure relief device operation and capacity shall be considered The sizing of any section of a common discharge header downstream from each of the two or more pressure relief devices that may reasonably be expected to discharge simultaneously shall be based on the total of their outlet areas, with due allowance for the pressure drop in all downstream sections Use of specially designed devices suitable for use on high or variable backpressure service should be considered c) The flow characteristics of the discharge system of high lift, top guided direct spring loaded pressure relief valves or pilot-operated pressure relief valves in compressible fluid service shall be such that the static pressure developed at the discharge flange of a conventional direct spring loaded pressure relief valve 9-8 ``,````,,,,````,`,`,```,`,``,,-`-`,,`,,`,`,,` - Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Tech Stds & Safety Auth./9991061001 Not for Resale, 07/20/2010 09:30:59 MDT 2010 SECTION VIII, DIVISION will not exceed 10% of the set pressure when flowing at rated capacity Other valve types exhibit various degrees of tolerance to back pressure and the Manufacturer's recommendation should be followed d) All discharge lines shall be run as directly as practicable to the point of final release for disposal For the longer lines, due consideration shall be given to the advantage of long-radius elbows, avoidance of close-up fittings, minimizing line strains and using well-known means of support to minimize line sway and vibration under operating conditions e) Provisions should be made in all cases for adequate drainage of discharge lines f) It is recognized that no simple rule can be applied generally to fit the many installation requirements Installations vary from simple short lines that discharge directly to the atmosphere to the extensive manifold discharge piping systems where the quantity and rate of the product to be disposed of requires piping to a distant safe place 9.A.5 Cautions Regarding Pressure Relief Device Discharge into a Common Header Because of the wide variety of types and kinds of pressure relief devices, it is not considered advisable to attempt a description of the effects produced by discharging them into a common header Several different types of pressure relief devices may conceivably be connected into the same discharge header and the effect of backpressure on each type may be radically different Data compiled by the Manufacturers of each type of pressure relief device used should be consulted for information relative to its performance under the conditions anticipated 9.A.6 9.A.6.1 Pressure Differentials (Operating Margin) for Pressure Relief Valves General a) Due to the variety of service conditions and the various designs of pressure relief valves, only general guidance can be given regarding the differential between the set pressure of the pressure relief valve and the operating pressure of the vessel b) Providing an adequate pressure differential for the application will minimize operating difficulty The following is general advisory information on the characteristics of the intended service and of the pressure relief valves that may bear on the proper pressure differential selection for a given application These considerations should be reviewed early in the system design since they may dictate the maximum allowable working pressure of the system 9.A.6.2 Considerations for Establishing the Operating Margin 9.A.6.2.1 Process Conditions a) To minimize operational problems, the user should consider not only normal operating conditions of fluids, pressures, and temperatures, but also start-up and shutdown conditions, process upsets, anticipated ambient conditions, instrument response times, pressure surges due to quick closing valves, etc b) When such conditions are not considered, the pressure relief valve may become, in effect, a pressure controller, a duty for which it is not designed c) Additional consideration should be given to hazard and pollution associated with the release of the fluid Larger differentials may be appropriate for fluids that are toxic, corrosive, or exceptionally valuable 9.A.6.2.2 Pressure Relief Valve Characteristics a) The blowdown characteristic and capability is the first consideration in selecting a compatible pressure relief valve and operating margin After a self-actuated release of pressure, the pressure relief valve must be capable of reclosing above the normal operating pressure For example, if the pressure relief valve is set at 690 kPa (100 psig) with a 7% blowdown, it will close at 641 kPa (93 psig) The operating ``,````,,,,````,`,`,```,`,``,,-`-`,,`,, Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS 9-9 Licensee=Tech Stds & Safety Auth./9991061001 Not for Resale, 07/20/2010 09:30:59 MDT 2010 SECTION VIII, DIVISION pressure must be maintained below 641 kPa (93 psig) in order to prevent leakage or flow from a partially open valve b) Users should exercise caution regarding the blowdown adjustment of large spring-loaded valves Test facilities, whether owned by Manufacturers, repair houses, or users, may not have sufficient capacity to accurately verify the blowdown setting The settings cannot be considered accurate unless made in the field on the actual installation c) Pilot-operated valves represent a special case from the standpoints of both blowdown and tightness The pilot portion of some pilot-operated valves can be set at blowdowns as short as 2% This characteristic is not, however, reflected in the operation of the main valve in all cases The main valve can vary considerably from the pilot depending on the location of the two components in the system If the pilot is installed remotely from the main valve, significant time and pressure lags can occur, but reseating of the pilot assures reseating of the main valve The pressure drop in the connecting piping between the pilot and the main valve must not be excessive; otherwise, the operation of the main valve will be adversely affected The tightness of the main valve portion of these combinations is considerably improved above that of conventional valves by pressure loading the main disk or by the use of soft seats or both Despite the apparent advantages of pilot-operated valves, users should be aware that they should not be employed in abrasive or dirty service, in applications where coking, polymerization, or corrosion of the wetted pilot parts can occur, or where freezing or condensation of the fluid at ambient temperatures is possible For all applications, the pressure relief valve Manufacturer should be consulted prior to selecting a valve of this type d) Tightness capability is another factor affecting valve selection, whether spring-loaded or pilot-operated It varies somewhat depending on whether metal or resilient seats are specified, and also on such factors as corrosion or temperature The required tightness and test method should be specified to comply at a pressure no lower than the normal operating pressure of the process A recommended procedure and acceptance standard is given in API Standard 527, Seat Tightness of Pressure Relief Valves It should also be noted that any degree of tightness obtained should not be considered permanent Service operation of a valve almost invariably reduces the degree of tightness e) Application of special designs such as O-rings or resilient seats should be reviewed with the pressure relief valve Manufacturer f) The anticipated behavior of the pressure relief valves includes allowance for a plus-or-minus tolerance on set pressure that varies with the pressure level Installation conditions, such as backpressure, variations, and vibrations influence selection of special designs and may require an increase in the differential pressure (operating margin) 9.A.6.2.3 General Recommendations for Pressure Differentials (Operating Margin) The following pressure differentials are recommended unless the pressure relief valve has been designed or tested in a specific or similar service, and a smaller differential has been recommended by the Manufacturer a) A minimum difference of 35 kPa (5 psi) is recommended for set pressures to 485 kPa (70 psi) In this category, the set pressure tolerance is + 13.8 kPa (+2 psi), and the differential to the leak test pressure is 10% or 35 kPa (5 psi), whichever is greater b) A minimum differential of 10% is recommended for set pressures from 490 to 6900 kPa (71 psi to 1000 psi) In this category, the set pressure tolerance is + 3% and the differential to the leak test pressure is 10% c) A minimum differential of 7% is recommended for set pressures above 6900 kPa (1000 psi) In this category, the set pressure tolerance is + 3% and the differential to the leak test pressure is 5% d) Pressure relief valves having small seat sizes will require additional maintenance when the pressure differential approaches these recommendations ``,````,,,,````,`,`,```,`,``,,-`-`,,`,,`,`,,` - Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS 9-10 Licensee=Tech Stds & Safety Auth./9991061001 Not for Resale, 07/20/2010 09:30:59 MDT 2010 SECTION VIII, DIVISION 9.A.7 Pressure Relief Valve Orientation Spring-loaded pressure relief valves normally should be installed in the upright position with the spindle vertical Where space or piping configuration preclude such an installation, the valve may be installed in other than the vertical position provided that: a) The pressure relief valve design is satisfactory for such position and is acceptable to the Manufacturer of the valve, b) The media is such that solid material will not accumulate at the inlet of the pressure relief valve, and c) Drainage of the discharge side of the pressure relief valve body and discharge piping prevents collection of liquid on the valve disk or in the discharge piping Reaction Forces and Externally Applied Piping Loads a) The discharge of a pressure relief device imposes reactive flow forces on the device and associated piping The design of the installation may require computation of the bending moments and stresses in the piping and vessel nozzle There are momentum effects and pressure effects at steady state flow as well as transient dynamic loads caused by opening b) Mechanical forces may be applied to the pressure relief device by discharge piping as a result of thermal expansion, movement away from anchors, and weight of any unsupported piping The resultant bending moments on a closed pressure relief device may cause leakage, device damage, and excessive stress in inlet piping The design of the installation should consider these possibilities 9.A.9 Sizing of Pressure Relief Devices for Fire Conditions a) Excessive pressure may develop in pressure vessels by vaporization of the liquid contents and/or expansion of vapor content due to heat influx from the surroundings, particularly from a fire b) Pressure relief systems for fire conditions are usually intended to release only the quantity of product necessary to lower the pressure to a predetermined safe level, without releasing an excessive quantity This control is especially important in situations where release of the contents generates a hazard because of flammability or toxicity c) Under fire conditions, consideration must also be given to the possibility that the safe pressure level for the vessel will be reduced due to heating of the vessel material, with a corresponding loss of strength d) Several equations have evolved over the years for calculating the pressure relief capacity required under fire conditions The major differences involve heat flux rates There is no single equation yet developed which takes into account all of the many factors that could be considered in making this determination When fire conditions are a consideration in the design of a pressure vessel, the following references which provide recommendations for specific installations may be used: 1) API Recommended Practice 520, Sizing, Selection, and Installation of Pressure-Relieving Systems in Refineries, Part – Sizing and Selection, Seventh Edition, January 2000, American Petroleum Institute, Washington, DC 2) API Standard 521, Pressure-Relieving and Depressuring Systems, Fifth Edition, Jan 2007, American Petroleum Institute, Washington, DC 3) API Standard 2000, Venting Atmospheric and Low-Pressure Tanks (Nonrefrigerated and Refrigerated), Fifth edition, April 1998, American Petroleum Institute, Washington, DC 4) AAR Standard M-1002, Specifications for Tank Cars, 1978, Association of American Railroads, Washington, DC 9-11 Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Tech Stds & Safety Auth./9991061001 Not for Resale, 07/20/2010 09:30:59 MDT ``,````,,,,````,`,`,```,`,``,,-`-`,,`,,`,`,,` - 9.A.8 2010 SECTION VIII, DIVISION 5) Safety Relief Device Standards: S-l.l, Cylinders for Compressed Gases; S-1.2, Cargo and Portable Tanks; and S-1.3, Compressed Gas Storage Containers, Compressed Gas Association, Arlington, VA 6) NFPA Code Nos 30, 58, 59, and 59A, National Fire Protection Association, Batterymarch Park, Quincy, MA, 02169-7471 7) Pressure-Relieving Systems for Marine Cargo Bulk Liquid Containers, 1973, National Academy of Sciences, Washington, DC ``,````,,,,````,`,`,```,`,``,,-`-`,,`,,`,`,,` - 9.A.10 Use of Pressure Indicating Devices to Monitor Pressure Differential If a pressure indicating device is provided to monitor the vessel pressure at or near the set pressure of the pressure relief device, one should be selected that spans the set pressure of the pressure relief device and is graduated with an upper limit that is neither less than 1.25 times the set pressure of the pressure relief device nor more than twice the maximum allowable working pressure of the vessel Additional devices may be installed if desired 9-12 Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Tech Stds & Safety Auth./9991061001 Not for Resale, 07/20/2010 09:30:59 MDT 2010 SECTION VIII, DIVISION ANNEX 9.A BEST PRACTICES FOR THE INSTALLATION AND OPERATION OF PRESSURE RELIEF DEVICES (INFORMATIVE) 9.A.1 Introduction This Annex provides additional guidance for design of pressure relief device installations This Annex is a supplement to the installation requirements provided in Part Note that there may be jurisdictional requirements related to the installation of pressure relief devices 9.A.2 Provisions for the Installation of Stop Valves in the Relief Path 9.A.2.1 General The general provisions for the installation of pressure relieving devices are covered in paragraph 9.6 The following paragraphs contain requirements for system and stop valve design when stop valves are to be located within the relief path These stop valves are sometimes necessary for the continuous operation of processing equipment of such a complex nature that shutdown of any part of it is not feasible or not practical The requirements cover stop valves provided upstream and downstream of pressure relief valves, provided in the relief path where there is normally a process flow and in a relief path where fire is the only potential source of overpressure 9.A.2.2 Stop Valves Located in the Relief Path 9.A.2.2.1 General ``,````,,,,````,`,`,```,`,``,,-`-`,,`,,`,`,,` - a) A stop valve(s) located within the relief path is not allowed except as permitted by paragraphs 9.A.2.2.5, 9.A.2.2.6, 9.A.2.2.7 and 9.A.2.2.8 below, and only when specified by the user The responsibilites of the user are summarized in paragraph 9.A.2.2.3 The specific requirements of paragraphs 9.A.2.2.5, 9.A.2.2.6, 9.A.2.2.7 and 9.A.2.2.8 are not intended to allow for operation above the maximum allowable working pressure b) The pressure relief path shall be designed such that the pressure in the equipment being protected does not exceed the maximum allowable working pressure before the pressure at the pressure relief device reaches its set pressure and the pressure does not exceed the allowable overpressure limits of Section VIII, Division 9.A.2.2.2 Definitions a) b) Administrative Controls are procedures that, in combination with mechanical locking elements, are intended to ensure that personnel actions not compromise the overpressure protection of the equipment They include, as a minimum: 1) Documented Operation and Maintenance Procedures, 2) Operator and Maintenance Personnel Training in the above procedures The Pressure Relief Path consists of all equipment, pipe, fittings and valves in the flow path between any protected equipment item and its pressure relieving device and the pressure relieving device and the discharge point of the relieving stream Stop valves within a pressure relief path include, but are not limited to, those located directly upstream and downstream of the pressure relief device that may be provided exclusively for pressure relief device maintenance 9-5 Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Tech Stds & Safety Auth./9991061001 Not for Resale, 07/20/2010 09:30:59 MDT 2010 SECTION VIII, DIVISION c) Valve Operation Controls are devices used to ensure that stop valves within the pressure relief path are in their proper (open/closed) position They include the following: 1) Mechanical Interlocks which are designed to prevent valve operations which could result in the blocking of a pressure relief path before an alternative pressure relief path is put into service 2) Instrumented Interlocks which function similar to mechanical interlocks, except that instrument permissives and/or overrides are used instead of mechanical linkages/devices to prevent valve positions that block the pressure relief path 3) Three-way valves designed to prevent a flow path from being blocked without another flow path being simultaneously opened d) Valve Failure Controls are measures taken in valve design, configuration, and/or orientation of the stop valve with the purpose of preventing an internal failure of a stop valve from closing and blocking the pressure relief path An example of valve failure controls is the installation of gate valves with the stem oriented at or below the horizontal position e) A Full Area Stop Valve is a valve in which the flow area of the valve is equal to or larger than the inlet flow area of the pressure relief device f) Mechanical Locking Elements are elements that when installed on a stop valve, provide a physical barrier to the operation of the stop valve, such that the stop valve is not capable of being operated unless a deliberate action is taken to remove or disable the element Such elements when used in combination with administrative controls, ensure that the equipment overpressure protection is not compromised by personnel actions Examples of mechanical locking elements include locks (with or without chains) on the stop valve handwheels, levers, or actuators, and plastic or metal straps (car seals) that are secured to the valve in such a way that the strap must be broken to operate the stop valve g) A Management System is the collective application of administrative controls, valve operation controls, and valve failure controls, in accordance with the applicable requirements of this Division 9.A.2.2.3 Responsibilities The user has the responsibility to establish and maintain a management system that ensures that a vessel is not operated without overpressure protection These responsibilities include, but are not limited to, the following: a) Deciding and specifying if the overpressure protection system will allow the use of stop valves(s) located in the relief path Establishing the pressure relief philosophy and the administrative controls requirements c) Establishing the required level of reliability, redundance, and maintenance of instrumented interlocks, if used d) Establishing procedures to ensure that the equipment is adequately protected against overpressure e) Ensuring that authorization to operate indentified valves is clear and that personnel are adequately trained for the task f) Establishing management systems to ensure that administrative controls are effective g) Establishing the analysis procedures and basis to be used in determining the potential levels of pressure if the stop valve(s) is closed h) Ensuring that the analysis described in paragraph 9.A.2.2.3.g is conducted by personnel who are qualified and experienced with the analysis procedure i) Ensuring that the other system components are acceptable for the potential levels of pressure established in paragraph 9.A.2.2.3.g j) Ensuring that the results of the analysis described in paragraph 9.A.2.2.3.g are documented and reviewed and accepted in writing by the individual responsible for the operation of the vessel and valves ``,````,,,,````,`,`,```,`,``,,-`-`,,`,,`,`,,` - b) 9-6 Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Tech Stds & Safety Auth./9991061001 Not for Resale, 07/20/2010 09:30:59 MDT 2010 SECTION VIII, DIVISION k) Ensuring that the administrative controls are reviewed and accepted in writing by the individual responsible for operation of the vessel and valves 9.A.2.2.4 Requirements of Procedures/Management Systems a) Procedures shall specify that valves requiring mechanical locking elements and/or valve operation controls and/or valve failure controls shall be documented and clearly identified as such b) The Management System shall document the administrative controls (training and procedures), the valve controls, and the performance of the administrative controls in an auditable form for management review 9.A.2.2.5 Stop Valves Provided in Systems for Which the Pressure Originates Exclusively From an Outside Source A vessel or system for which the pressure originates from an outside source exclusively may have individual pressure relieving devices on each vessel, or connected to any point on the connecting piping, or on any one of the vessels to be protected Under such an arrangement, there may be stop valve(s) between any vessel and the pressure relieving devices, and these stop valve(s) need not have any administrative controls, valve operation controls, or valve failure controls, provided that the stop valves also isolate the vessel from the source of pressure 9.A.2.2.6 Stop Valves Provided Upstream or Downstream of the Pressure Relief Device Exclusively for Maintenance of That Device Full area stop valve(s) may be provided upstream and/or downstream of the pressure relieving device for the purpose of inspection, testing and repair of the pressure relief device or discharge header isolation, provided that, as a minimum, the following requirements are complied with: c) Administrative controls are provided to prevent unauthorized valve operation d) Valves are provided with mechanical locking elements e) Valve failure controls are provided to prevent accidental valve closure due to mechanical failure f) Procedures are in place to provide pressure relief protection during the time when the system is isolated from its pressure relief path These procedures shall ensure that when the system is isolated from its pressure relief path, an authorized person shall continuously monitor the pressure conditions of the vessel and shall be capable of responding promptly with documented, pre-defined actions, either stopping the source of overpressure or opening alternative means of pressure relief This authorized person shall be dedicated to this task and shall have no other duties when performing this task g) The system shall be isolated from its pressure relief path for only the time required to test, repair, and/or replace the pressure relief device 9.A.2.2.7 Stop Valves Provided in the Pressure Relief Path Where There is Normally Process Flow Stop valve(s), excluding remotely operated valves, may be provided in the relief path where there is normally process flow, provided the requirements in paragraphs 9.A.2.2.7.a and 9.A.2.2.7.b, as a minimum, are complied with These requirements are based on the overpressure scenarios involving accidental closure of a single stop valve within the relief path (see paragraph 9.A.2.2.3.g) The accidental closure of these stop valve(s) in the pressure relief system need not be considered in the determination of the specified design pressure in Part of this Division a) The flow resistance of the valve in the full open position does not reduce the relieving capacity below that required by paragraph 9.1.3 b) The closure of the valve will be readily apparent to the operators such that corrective action, in accordance with documented operating procedures, is required and: 1) If the pressure due to closure of the valve cannot exceed 116% of the maximum allowable working pressure, then no administrative controls, or valve failure controls are required, or 9-7 ``,````,,,,````,`,`,```,`,``,,-`-`,,`,,`,`,,` - Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Tech Stds & Safety Auth./9991061001 Not for Resale, 07/20/2010 09:30:59 MDT 2010 SECTION VIII, DIVISION 2) 3) If the pressure due to closure of the valve cannot exceed the following: i) the documented test pressure, multiplied by the ratio of stress value at the design temperature to the stress value at the test temperature, or ii) if the test pressure is calculated per Part 8, paragraph 8.2.1.e , in addition to the stress ratio specified in paragraph 9.A.2.2.7.b.2.i, the test pressure shall also be multiplied by the ratio of the nominal thickness minus the corrosion allowance to the nominal thickness then, as a minimum, administrative controls and mechanical locking elements are required, or If the pressure due to closure of the valve could exceed the pressure in paragraph 9.A.2.2.7.b.2 , then the user shall either: i) eliminate the stop valve, or ii) apply administrative controls, mechanical locking elements, valve failure controls, and valve operation controls, or iii) provide a pressure relief device to protect the equipment that could be overpressured due to closure of the stop valve 9.A.2.2.8 Stop Valves Provided in the Relief Path of Equipment Where Fire is the Only Potential Source of Overpressure Full area stop valves located in the relief path of equipment where fire is the only potential source of overpressure not require mechanical locking elements, valve operation controls, or valve failure controls provided the user has documented operating procedures requiring the equipment isolated from its pressure relief path is depressured and free of all liquids 9.A.3 Inlet Piping Pressure Drop for Pressure Relief Valves For pressure relief valves, the flow characteristics of the upstream system shall be such that the cumulative total of all non-recoverable inlet losses shall not exceed 3% of the valve set pressure The inlet pressure losses shall be determined accounting for all fittings in the upstream system, including rupture disks installed in the pressure relief valve inlet piping, and shall be based on the valve nameplate capacity corrected for the characteristics of the flowing fluid 9.A.4 Discharge Lines from Pressure Relief Devices a) Where it is feasible, the use of a short discharge pipe or vertical riser, connected through long-radius elbows from each individual device, blowing directly to the atmosphere, is recommended For pressure relief valves, such discharge pipes shall be at least of the same size as the valve outlet Where the nature of the discharge permits, telescopic (sometimes called "broken") discharge lines, whereby condensed vapor in the discharge line, or rain, is collected in a drip pan and piped to a drain, are recommended This construction has the further advantage of not transmitting discharge pipe strains to the pressure relief device In these types of installations, the backpressure effect will be negligible, and no undue influence upon normal operation of the pressure relief device can result b) When discharge lines are long, or where outlets of two or more pressure relief devices are connected into a common line, the effect of the back pressure on pressure relief device operation and capacity shall be considered The sizing of any section of a common discharge header downstream from each of the two or more pressure relief devices that may reasonably be expected to discharge simultaneously shall be based on the total of their outlet areas, with due allowance for the pressure drop in all downstream sections Use of specially designed devices suitable for use on high or variable backpressure service should be considered c) The flow characteristics of the discharge system of high lift, top guided direct spring loaded pressure relief valves or pilot-operated pressure relief valves in compressible fluid service shall be such that the static pressure developed at the discharge flange of a conventional direct spring loaded pressure relief valve 9-8 ``,````,,,,````,`,`,```,`,``,,-`-`,,`,,`,`,,` - Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Tech Stds & Safety Auth./9991061001 Not for Resale, 07/20/2010 09:30:59 MDT 2010 SECTION VIII, DIVISION will not exceed 10% of the set pressure when flowing at rated capacity Other valve types exhibit various degrees of tolerance to back pressure and the Manufacturer's recommendation should be followed d) All discharge lines shall be run as directly as practicable to the point of final release for disposal For the longer lines, due consideration shall be given to the advantage of long-radius elbows, avoidance of close-up fittings, minimizing line strains and using well-known means of support to minimize line sway and vibration under operating conditions e) Provisions should be made in all cases for adequate drainage of discharge lines f) It is recognized that no simple rule can be applied generally to fit the many installation requirements Installations vary from simple short lines that discharge directly to the atmosphere to the extensive manifold discharge piping systems where the quantity and rate of the product to be disposed of requires piping to a distant safe place 9.A.5 Cautions Regarding Pressure Relief Device Discharge into a Common Header Because of the wide variety of types and kinds of pressure relief devices, it is not considered advisable to attempt a description of the effects produced by discharging them into a common header Several different types of pressure relief devices may conceivably be connected into the same discharge header and the effect of backpressure on each type may be radically different Data compiled by the Manufacturers of each type of pressure relief device used should be consulted for information relative to its performance under the conditions anticipated 9.A.6 9.A.6.1 Pressure Differentials (Operating Margin) for Pressure Relief Valves General a) Due to the variety of service conditions and the various designs of pressure relief valves, only general guidance can be given regarding the differential between the set pressure of the pressure relief valve and the operating pressure of the vessel b) Providing an adequate pressure differential for the application will minimize operating difficulty The following is general advisory information on the characteristics of the intended service and of the pressure relief valves that may bear on the proper pressure differential selection for a given application These considerations should be reviewed early in the system design since they may dictate the maximum allowable working pressure of the system 9.A.6.2 Considerations for Establishing the Operating Margin 9.A.6.2.1 Process Conditions ``,````,,,,````,`,`,```,`,``,,-`-`,,`,,`,`,,` - a) To minimize operational problems, the user should consider not only normal operating conditions of fluids, pressures, and temperatures, but also start-up and shutdown conditions, process upsets, anticipated ambient conditions, instrument response times, pressure surges due to quick closing valves, etc b) When such conditions are not considered, the pressure relief valve may become, in effect, a pressure controller, a duty for which it is not designed c) Additional consideration should be given to hazard and pollution associated with the release of the fluid Larger differentials may be appropriate for fluids that are toxic, corrosive, or exceptionally valuable 9.A.6.2.2 Pressure Relief Valve Characteristics a) The blowdown characteristic and capability is the first consideration in selecting a compatible pressure relief valve and operating margin After a self-actuated release of pressure, the pressure relief valve must be capable of reclosing above the normal operating pressure For example, if the pressure relief valve is set at 690 kPa (100 psig) with a 7% blowdown, it will close at 641 kPa (93 psig) The operating 9-9 Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Tech Stds & Safety Auth./9991061001 Not for Resale, 07/20/2010 09:30:59 MDT 2010 SECTION VIII, DIVISION b) Users should exercise caution regarding the blowdown adjustment of large spring-loaded valves Test facilities, whether owned by Manufacturers, repair houses, or users, may not have sufficient capacity to accurately verify the blowdown setting The settings cannot be considered accurate unless made in the field on the actual installation c) Pilot-operated valves represent a special case from the standpoints of both blowdown and tightness The pilot portion of some pilot-operated valves can be set at blowdowns as short as 2% This characteristic is not, however, reflected in the operation of the main valve in all cases The main valve can vary considerably from the pilot depending on the location of the two components in the system If the pilot is installed remotely from the main valve, significant time and pressure lags can occur, but reseating of the pilot assures reseating of the main valve The pressure drop in the connecting piping between the pilot and the main valve must not be excessive; otherwise, the operation of the main valve will be adversely affected The tightness of the main valve portion of these combinations is considerably improved above that of conventional valves by pressure loading the main disk or by the use of soft seats or both Despite the apparent advantages of pilot-operated valves, users should be aware that they should not be employed in abrasive or dirty service, in applications where coking, polymerization, or corrosion of the wetted pilot parts can occur, or where freezing or condensation of the fluid at ambient temperatures is possible For all applications, the pressure relief valve Manufacturer should be consulted prior to selecting a valve of this type d) Tightness capability is another factor affecting valve selection, whether spring-loaded or pilot-operated It varies somewhat depending on whether metal or resilient seats are specified, and also on such factors as corrosion or temperature The required tightness and test method should be specified to comply at a pressure no lower than the normal operating pressure of the process A recommended procedure and acceptance standard is given in API Standard 527, Seat Tightness of Pressure Relief Valves It should also be noted that any degree of tightness obtained should not be considered permanent Service operation of a valve almost invariably reduces the degree of tightness e) Application of special designs such as O-rings or resilient seats should be reviewed with the pressure relief valve Manufacturer f) The anticipated behavior of the pressure relief valves includes allowance for a plus-or-minus tolerance on set pressure that varies with the pressure level Installation conditions, such as backpressure, variations, and vibrations influence selection of special designs and may require an increase in the differential pressure (operating margin) 9.A.6.2.3 General Recommendations for Pressure Differentials (Operating Margin) The following pressure differentials are recommended unless the pressure relief valve has been designed or tested in a specific or similar service, and a smaller differential has been recommended by the Manufacturer a) A minimum difference of 35 kPa (5 psi) is recommended for set pressures to 485 kPa (70 psi) In this category, the set pressure tolerance is + 13.8 kPa (+2 psi), and the differential to the leak test pressure is 10% or 35 kPa (5 psi), whichever is greater b) A minimum differential of 10% is recommended for set pressures from 490 to 6900 kPa (71 psi to 1000 psi) In this category, the set pressure tolerance is + 3% and the differential to the leak test pressure is 10% c) A minimum differential of 7% is recommended for set pressures above 6900 kPa (1000 psi) In this category, the set pressure tolerance is + 3% and the differential to the leak test pressure is 5% d) Pressure relief valves having small seat sizes will require additional maintenance when the pressure differential approaches these recommendations 9-10 Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Tech Stds & Safety Auth./9991061001 Not for Resale, 07/20/2010 09:30:59 MDT ``,````,,,,````,`,`,```,`,``,,-`-`,,`,,`,`,,` - pressure must be maintained below 641 kPa (93 psig) in order to prevent leakage or flow from a partially open valve 2010 SECTION VIII, DIVISION 9.A.7 Pressure Relief Valve Orientation Spring-loaded pressure relief valves normally should be installed in the upright position with the spindle vertical Where space or piping configuration preclude such an installation, the valve may be installed in other than the vertical position provided that: a) The pressure relief valve design is satisfactory for such position and is acceptable to the Manufacturer of the valve, b) The media is such that solid material will not accumulate at the inlet of the pressure relief valve, and c) Drainage of the discharge side of the pressure relief valve body and discharge piping prevents collection of liquid on the valve disk or in the discharge piping 9.A.8 Reaction Forces and Externally Applied Piping Loads a) The discharge of a pressure relief device imposes reactive flow forces on the device and associated piping The design of the installation may require computation of the bending moments and stresses in the piping and vessel nozzle There are momentum effects and pressure effects at steady state flow as well as transient dynamic loads caused by opening b) Mechanical forces may be applied to the pressure relief device by discharge piping as a result of thermal expansion, movement away from anchors, and weight of any unsupported piping The resultant bending moments on a closed pressure relief device may cause leakage, device damage, and excessive stress in inlet piping The design of the installation should consider these possibilities 9.A.9 Sizing of Pressure Relief Devices for Fire Conditions a) Excessive pressure may develop in pressure vessels by vaporization of the liquid contents and/or expansion of vapor content due to heat influx from the surroundings, particularly from a fire b) Pressure relief systems for fire conditions are usually intended to release only the quantity of product necessary to lower the pressure to a predetermined safe level, without releasing an excessive quantity This control is especially important in situations where release of the contents generates a hazard because of flammability or toxicity c) Under fire conditions, consideration must also be given to the possibility that the safe pressure level for the vessel will be reduced due to heating of the vessel material, with a corresponding loss of strength d) Several equations have evolved over the years for calculating the pressure relief capacity required under fire conditions The major differences involve heat flux rates There is no single equation yet developed which takes into account all of the many factors that could be considered in making this determination When fire conditions are a consideration in the design of a pressure vessel, the following references which provide recommendations for specific installations may be used: 1) API Recommended Practice 520, Sizing, Selection, and Installation of Pressure-Relieving Systems in Refineries, Part – Sizing and Selection, Seventh Edition, January 2000, American Petroleum Institute, Washington, DC 2) API Standard 521, Pressure-Relieving and Depressuring Systems, Fifth Edition, Jan 2007, American Petroleum Institute, Washington, DC 3) API Standard 2000, Venting Atmospheric and Low-Pressure Tanks (Nonrefrigerated and Refrigerated), Fifth edition, April 1998, American Petroleum Institute, Washington, DC 4) AAR Standard M-1002, Specifications for Tank Cars, 1978, Association of American Railroads, Washington, DC 9-11 ``,````,,,,````,`,`,```,`,``,,-`-`,,`,,`,`,,` - Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Tech Stds & Safety Auth./9991061001 Not for Resale, 07/20/2010 09:30:59 MDT 2010 SECTION VIII, DIVISION 5) Safety Relief Device Standards: S-l.l, Cylinders for Compressed Gases; S-1.2, Cargo and Portable Tanks; and S-1.3, Compressed Gas Storage Containers, Compressed Gas Association, Arlington, VA 6) NFPA Code Nos 30, 58, 59, and 59A, National Fire Protection Association, Batterymarch Park, Quincy, MA, 02169-7471 7) Pressure-Relieving Systems for Marine Cargo Bulk Liquid Containers, 1973, National Academy of Sciences, Washington, DC 9.A.10 Use of Pressure Indicating Devices to Monitor Pressure Differential If a pressure indicating device is provided to monitor the vessel pressure at or near the set pressure of the pressure relief device, one should be selected that spans the set pressure of the pressure relief device and is graduated with an upper limit that is neither less than 1.25 times the set pressure of the pressure relief device nor more than twice the maximum allowable working pressure of the vessel Additional devices may be installed if desired 9-12 ``,````,,,,````,`,`,```,`,``,,-`-`,,`,,`,`,,` - Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Tech Stds & Safety Auth./9991061001 Not for Resale, 07/20/2010 09:30:59 MDT ``,````,,,,````,`,`,```,`,``,,-`-`,,`,,`,`,,` - INTENTIONALLY LEFT BLANK Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Tech Stds & Safety Auth./9991061001 Not for Resale, 07/20/2010 09:30:59 MDT Boiler and 2010 ASME Pressure Vessel Code AN INTERNATIONAL CODE The ASME Boiler and Pressure Vessel Code (BPVC) is “An International Historic Mechanical Engineering Landmark,” widely recognized as a model for codes and standards worldwide Its development process remains open and transparent throughout, yielding “living documents” that have improved public safety and facilitated trade across global markets and jurisdictions for nearly a century ASME also provides BPVC users with integrated suites of related offerings: • referenced standards • training courses • related standards and guidelines • ASME press books and journals • conformity assessment programs • conferences and proceedings You gain unrivalled insight direct from the BPVC source, along with the professional quality and real-world solutions you have come to expect from ASME For additional information and to order: Phone: 1.800.843.2763 Email: infocentral@asme.org Website: go.asme.org/bpvc10 ``,````,,,,````,`,`,```,`,``,,-`-`,,`,,`,`,,` - X00082 Copyright ASME International Provided by IHS under license with ASME No reproduction or networking permitted without license from IHS Licensee=Tech Stds & Safety Auth./9991061001 Not for Resale, 07/20/2010 09:30:59 MDT ... 4.11.1 4.11 .2 4.11.3 4.11.4 4.11.5 4.11.6 4.11.7 4.11.8 4.11.9 4. 12 4. 12. 1 4. 12. 2 4. 12. 3 4. 12. 4 4. 12. 5 4. 12. 6 4. 12. 7 4. 12. 8 4. 12. 9 4. 12. 10 4. 12. 11 4. 12. 12 4. 12. 13 4.13 4.13.1 4.13 .2 4.13.3 4.13.4... 2- 3 2. 2.1 General .2- 3 2. 2 .2 User’s Design Specification .2- 3 2. 3 Manufacturer’s Responsibilities 2- 6 2. 3.1 Code Compliance .2- 6 2. 3 .2. .. 2. 3.5 2. 3.6 2. 3.7 2. 3.8 2. 3.9 2. 4 2. 4.1 2. 4 .2 2.4.3 Manufacturer’s Data Report 2- 7 Manufacturer’s Construction Records 2- 7 Quality Control System .2- 7 Certification