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Flame Arresters in Piping SystemsAPI RECOMMENDED PRACTICE 2028THIRD EDITION, FEBRUARY 2002

Flame Arresters in Piping SystemsSafety & Fire ProtectionAPI RECOMMENDED PRACTICE 2028THIRD EDITION, FEBRUARY 2002

SPECIAL NOTESAPI publications necessarily address problems of a general nature. With respect to particular circumstances, local, state, and federal laws and regulations should be reviewed.API is not undertaking to meet the duties of employers, manufacturers, or suppliers towarn and properly train and equip their employees, and others exposed, concerning healthand safety risks and precautions, nor undertaking their obligations under local, state, or federal laws.Information concerning safety and health risks and proper precautions with respect to particular materials and conditions should be obtained from the employer, the manufacturer orsupplier of that material, or the material safety data sheet.Nothing contained in any API publication is to be construed as granting any right, byimplication or otherwise, for the manufacture, sale, or use of any method, apparatus, or product covered by letters patent. Neither should anything contained in the publication be construed as insuring anyone against liability for infringement of letters patent.Generally, API standards are reviewed and revised, reafÞrmed, or withdrawn at least everyÞve years. Sometimes a one-time extension of up to two years will be added to this reviewcycle. This publication will no longer be in effect Þve years after its publication date as anoperative API standard or, where an extension has been granted, upon republication. Statusof the publication can be ascertained from the API Standards Department [telephone (202)682-8000]. A catalog of API publications and materials is published annually and updatedquarterly by API, 1220 L Street, N.W., Washington, D.C. 20005.This document was produced under API standardization procedures that ensure appropriate notiÞcation and participation in the developmental process and is designated as an APIstandard. Questions concerning the interpretation of the content of this standard or comments and questions concerning the procedures under which this standard was developedshould be directed in writing to the API Standards Department, American Petroleum Institute, 1220 L Street, N.W., Washington, D.C. 20005. Requests for permission to reproduce ortranslate all or any part of the material published herein should also be addressed to the general manager.API standards are published to facilitate the broad availability of proven, sound engineering and operating practices. These standards are not intended to obviate the need for applying sound engineering judgment regarding when and where these standards should beutilized. The formulation and publication of API standards is not intended in any way toinhibit anyone from using any other practices.Any manufacturer marking equipment or materials in conformance with the markingrequirements of an API standard is solely responsible for complying with all the applicablerequirements 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, stored in a retrieval system, ortransmitted by any means, electronic, mechanical, photocopying, recording, or otherwise,without prior written permission from the publisher. Contact the Publisher,API Publishing Services, 1220 L Street, N.W., Washington, D.C. 20005.Copyright 2002 American Petroleum Institute

FOREWORDThis recommended practice was prepared under the direction of the API Safety and FireProtection Subcommittee. This third edition of API 2028 Flame Arresters in Piping Systemshas been extensively rewritten and updated from the previous edition. Appendices to the document are intended to provide additional supplementary information.This guide was prepared to help provide a basic understanding of ßame arresters used inpiping systems. The information presented is based primarily upon experience in the petroleum industry. It is not intended to exclude or limit the use of other approaches of comparable merit. Because of the special nature of ßame arresters, especially those used fordetonation protection, this recommended practice strongly encourages dialogue with theequipment supplier and the use of sound engineering judgement in ßame arrester selectionand application.iii

CONTENTSPage1INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.1 Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.2 Scope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.3 Concept of Hazard vs. Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.4 Retroactivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .111112REFERENCED PUBLICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13DEFINITIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24COMBUSTION AND FLAME PROPAGATION . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.2 Combustion Rates and MESG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.3 Deßagration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.4 Detonation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .333445FLAME ARRESTER FUNCTION AND CONCERNS FOR USEIN PIPING SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.1 Flame Arrester Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.2 Pressure Concerns and Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.3 Potential Effects of Installation Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.4 Flame Arresters Not Using Metal Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.5 Pyrophoric Iron SulÞde Concerns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5.6 Unilateral and Bilateral Flame Arresters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44455666LIMITATIONS OF FLAME ARRESTERS ON TANK VENTS. . . . . . . . . . . . . . . . . 67FLAME ARRESTER TESTING AND CERTIFICATION . . . . . . . . . . . . . . . . . . . . .7.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7.2 Deßagration and Detonation Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7.3 Flame Retention Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7.4 SigniÞcance of MESG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7.5 Use of Established Test Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8SUMMARY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7APPENDIX AAPPENDIX B777777BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9GASES OR VAPORS WITH A MAXIMUM EXPERIMENTALSAFE GAP (MESG) 0.90 MM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11v

Flame Arresters in Piping SystemsSECTION 1—INTRODUCTION1.1 PURPOSEoverview of ßame arresters currently in use and some potential concerns or limitations. Applicable combustion and ßamepropagation parameters are discussed including the distinction between arresting ßames versus arresting detonations.This recommended practice is neither a design manual nora regulatory compliance document. It does provide referenceto more detailed technical discussions of ßame arresters andcombustion. Various standards, codes, and regulations arenoted in the Section 2 references and in the Appendix A Bibliography.This recommended practice is intended to inform industryabout limitations of ßame arresters installed in piping systems.Concerns about potential environmental effects of hydrocarbon and chemical vapor emissions have led to regulationsrequiring the installation of vapor control systems. In theUnited States, for marine transfer of oil or hazardous materials, United States Coast Guard regulations require installationof ßame arresters (suitable to interrupt a detonation) in vaporcontrol piping. These USCG regulations speciÞcally direct (indetail) where to install these ßame detonation arresters in thevapor control systems. An independent laboratory must testdetonation arresters installed to meet these regulations.The diversity of commercial ßame arresters can lead to theinstallation of these arresters in piping systems where the conditions within the piping may be signiÞcantly different fromthe conditions for which they were designed, or tested andlisted by testing laboratories. Under certain conditions, ßamespropagating through piping systems can reach velocities andpressures at which detonation can occur. Unless a ßamearrester has been designed and tested for a detonation, it maynot stop the progression of a combustion wave in the piping.Guidance is provided concerning the important factorsinvolved in the selection, installation and maintenance ofappropriate ßame arresters. The intent is to assist the user ofthis recommended practice in developing the awareness ofreview needs, and to encourage discussions with ßame arrestermanufacturers regarding speciÞc applications and test results.1.3 CONCEPT OF HAZARD VS. RISKHazards are properties of materials with the inherent abilityto cause harm. Flammability, toxicity, corrosivity, stored chemical or mechanical energy all are hazards associated with various industrial materials.Risk requires exposure. Theßammability of a material transported in piping is an inherenthazard, but becomes a risk only when having access to an oxidizer and being exposed to an ignition mechanism. There is norisk of ignition when there is no potential for those exposures.Determining the level of risk involves estimating the probability and severity of exposure conditions that could lead to harm.1.4 RETROACTIVITYAny provisions in this recommended practice related todesign are intended for reference when designing new facilities or when considering major revisions or expansions. It isnot intended that any recommendations in this recommendedpractice be applied retroactively to existing facilities unlessdeemed appropriate based on facility review. Each facilitymust make their own determination regarding how to complywith any applicable regulations.1.2 SCOPEThe scope of this recommended practice is the use and limitations of ßame arresters installed in piping systems in thepetroleum and petrochemical industries. It provides a generalSECTION 2—REFERENCED PUBLICATIONSThe most recent edition or revision of each of the followingstandards, codes, and regulations are cited in this recommended practice. Additional references not speciÞcally citedin this document are listed in the Bibliography, Appendix A.API1Std 2000RP 2210ASTM2F 1273Venting Atmospheric and Low-PressureStorage TanksFlame Arresters for Vents of Tanks StoringPetroleum ProductsStandard SpeciÞcation for Tank VentFlame Arresters2American Society for Testing and Materials, 100 Barr HarborDrive, West Conshohocken, Pennsylvania, USA 19428.www.astm.org1www.api.org1

2CEN3EN 12874CGA4G-1.2API RECOMMENDED PRACTICE 2028Flame Arresters, Performance Requirements, Test Methods and Limits for oval Guide, A Guide to Equipment,Materials & Services Approved by FactoryMutual Research for Property Conservation ÒFlame Arresters for Gas Piping SystemsÓ ÒFlame Arresters, Dry TypeÓ ÒFlame Arresters, Hydraulic TypeÓ ÒDetonation Flame Arresters for Flammable Vapor Piping SystemsÓ ÒFlame Arresters for Storage Tank VentPipesÓIEC6IEC 79-1AFirst Supplement to Publication 79-1, Electrical apparatus for explosive gasatmospheres, Part 1: Construction and testof ßameproof enclosures of electricalapparatus3European Committee for Standardization, rue de Stassart 36, B1050 Brussels, Belgium. www.cenorm.be4Compressed Gas Association, Inc., Fifth Floor, 4221 Walney Road,Chantilly, Virginia 20151-2923. www.cganet.com5Factory Mutual Insurance Company, 22055 Network Place, Chicago, Illinois 60673-1220. www.fmglobal.com6International Electrotechnical Commission, 3 rue de VarembŽ, Casepostale 131, 1211 Geneva 20, Switzerland. www.iec.chAppendix D: Method of test for ascertainment of maximum experimental safe gapNFPA73069Flammable & Combustible Liquids CodeStandard on Explosion Prevention SystemsOSHA81910.106Subpart HÑHazardous MaterialsUL9UL 525USCG1033 CFR 154Standard for Safety for Flame ArrestersUL Gas and Oil Equipment DirectoryFacilities Transferring Oil or HazardousMaterial in Bulk Subpart E, Vapor Control Systems Appendix A to Part 154ÑGuidelines forDetonation Flame Arresters Appendix B to Part 154ÑStandard SpeciÞcation for Tank Vent Flame Arresters7NationalFire Protection Association, Batterymarch Park, Quincy,Massachusetts 02269. www.nfpa.org8U.S. Department of Labor, Occupational Safety and Health Administration, 200 Constitution Avenue, N.W., Washington, D.C. 20210.OSHA regulations are posted on, and can be downloaded from, theOSHA web site. www.osha.gov9Underwriters Laboratories, Inc., 333 PÞngsten Road, Northbrook,Illinois 60062. www.ul.com10United States Coast Guard, U.S. Department of Transportation.www.uscg.mil. The Code of Federal Regulations is available fromthe U.S. Government Printing OfÞce, Washington, D.C. 20402.SECTION 3—DEFINITIONS3.1 autoignition temperature: The minimum temperature at which a material will ignite with self-sustained combustion without an external source of ignition (such as a spark orßame).3.2 deflagration: A combustion wave that propagatessubsonically (as measured at the pressure and temperature ofthe ßame front) by the transfer of heat and active chemicalspecies to the unburned gas ahead of the ßame front.3.3 detonation: A reaction in a combustion wave propagating at sonic or supersonic velocity (as measured at the pressure and temperature of the ßame front). A detonation is stablewhen it has a velocity equal to the speed of sound in the burntgas or may be unstable (overdriven) with a higher velocity andpressure.3.4 explosion: A rapid release of energy (such as burning) which produces a pressure wave.3.5 hazard: An inherent chemical or physical propertywith the potential to do harm (ßammability, toxicity, corrosivity, stored chemical or mechanical energy).3.6 inerted: (For vessels under U.S. Coast Guard regulations.) Means the oxygen content of the vapor space in a tankvesselÕs cargo tank is reduced to 8% by volume or less, inaccordance with the inert gas requirements of 46 CFR 32.53or 46 CFR 153.500.3.7 maximum experimental safe gap (MESG): TheMESG is the maximum clearance between two parallel metalsurfaces that has been found, under speciÞed test conditions,to prevent an explosion in a test chamber from being propagated to a secondary chamber containing the same gas or

FLAME ARRESTERS IN PIPING SYSTEMSvapor at the same concentration. The MESG factor wasdeveloped for designing electrical equipment for use in hazardous atmospheres.3.8 pyrophoric: Iron sulÞde or carbonaceous materialswhich, when exposed to air, can oxidize and heat, providing asource of ignition if a ßammable vapor/air mixture is present.3.9 risk: The probability of exposure to a hazard whichcould result in harm to personnel, property, the environmentor the general public.33.10 risk assessment: The identiÞcation and analysis,either qualitative or quantitative, of the likelihood and outcome of speciÞc events or scenarios with judgements of probability and consequences.3.11 risk-based analysis: A review of potential needsbased on a risk assessment3.12 self-ignition temperature: See autoignition temperature.SECTION 4—COMBUSTION AND FLAME PROPAGATION4.1 GENERALThis discussion of the combustion of gases or vaporsemphasizes combustion phenomena in piping. This background focuses on understanding the functioning and potential problems when ßame arresters are used in piping systems.A ßame arrester may not function or provide the desired protection if it has not been designed for (or tested at) conditionsappropriate for the process in which it is to be installed (pressure, temperature, and fuel type).For combustion to occur, the gas or vapor must be mixedwith an oxidizer and must be within the ßammable limits forthe mixture. Typically, the oxidizer is the oxygen contained inair. Combustion within piping can occur even if the amount ofoxygen within the piping is signiÞcantly below the normal20.8% concentration of oxygen in air. It is a typical reÞneryand chemical plant safe operating practice to maintain processpiping at or below an oxygen concentration of 5%. The UnitedStates Coast Guard (USCG) regulations for marine transfervapor collection systems specify that when analyzers arerequired to be used, the process shall be shut down if the oxygen concentration increases to 8% or greater. As pressuresincrease, the level of oxygen required to have a combustiblemixture decreases. And, as the temperature of a ßammable gaseous mixture is increased, the ßammable limits increase orwiden. So, at elevated temperatures and pressures, a combustion reaction will be initiated more easily, and the reaction willproceed faster.Combustion reactions involving hydrocarbons or othercombustible gases or vapors in an 100% oxygen environmentare rapidly (explosively) accelerated. The presence of oxidizing agents, such as chlorine, ßuorine, nitrate salts, perchloratesalts, or peroxides, in a process stream can allow combustionto occur in the absence of oxygen or air. Unless conÞrmed bymanufacturerÕs tests, a ßame arrester may not have beendesigned for or tested for use in these special circumstances.Industry studies have documented many accidents where asigniÞcant contributing cause of the accident was the failureto maintain a piping system free of oxygen. This should berecognized during the process design, start-up, operation,shutdown and during maintenance activities requiring theopening of process piping or equipment. Flame arrestersshould not be used as a substitute for proper process designand operation.4.2 COMBUSTION RATES AND MESGThe combustion reaction rate for some particular gases orvapors, such as acetylene, hydrogen, or oleÞnic hydrocarbons, is signiÞcantly accelerated over rates for normal hydrocarbons. Specialty ßame arresters offered to quench ßamesfor such sensitive materials should be conÞrmed by manufacturerÕs tests for the speciÞc type of service, material, temperature, pressure and piping conÞguration.The Maximum Experimental Safe Gap (MESG) conceptwas developed for designing electrical equipment for use inhazardous atmospheres. MESG is deÞned as the maximumclearance between two parallel metal surfaces that has beenfound, under speciÞed test conditions, to prevent an explosionin a test chamber from being propagated to a secondarychamber containing the same gas or vapor at the same concentration. Some standards-making organizations and regulatory authorities have utilized a MESG threshold of 0.90 mmbelow which special testing of a ßame arrester is required. Alist of hydrocarbon and chemical gases or vapors which havebeen ide