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  • 1. A P I PUBL*2028 91 0732270 OLOL370 1 Flame Arresters in Piping Systems API PUBLICATION 2028 SECOND EDITION, DECEMBER 1991 American Petroleum Institute 1220 L Street, Northwest Washington, D.C. 20005 1’ 1COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 2. A P I PUBL*ZO28 91 = 0732290 OLOL39L 3 Flame Arresters in Piping Systems Safety and Fire Protection Department API PUBLICATION 2028 SECOND EDITION, DECEMBER 1991 American Petroleum InstituteCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 3. A P I PUBL*2028 91 0 7 3 2 2 7 0 0101392 5 SPECIAL NOTES 1. API PUBLICATIONS NECESSARILY ADDRESS PROBLEMS OF A GENERAL NATURE. WITH RESPECT TO PARTICULAR CIRCUMSTANCES, LOCAL, STATE, AND FEDERAL LAWS AND REGULATIONS SHOULD BE REVIEWED. 2. API IS NOT UNDERTAKING TO MEET THE DUTIES OF EMPLOYERS, MANU- FACTURERS, OR SUPPLIERS TO WARN AND PROPERLY TRAIN AND EQUIP THEIR EMPLOYEES, AND OTHERS EXPOSED, CONCERNING HEALTH AND SAFETY RISKS AND PRECAUTIONS, NOR UNDERTAKINGTHEIR OBLIGATIONS UNDER LOCAL, STATE, ORFEDERAL LAWS. 3. INFORMATION CONCERNING SAFETY AND HEALTH RISKS AND PROPER PRECAUTIONS WITH RESPECT TO PARTICULAR MATERIALS AND CONDI- TIONS SHOULD BE OBTAINED FROMTHE EMPLOYER, THE MANUFACTURER OR SUPPLIEROF THAT MATERIAL, OR THE MATERIAL SAFETY DATA SHEET. 4. NOTHING CONTAINEDIN ANY API PUBLICATION IS BE CONSTRUED AS TO GRANTING ANY RIGHT, BY IMPLICATION OR OTHERWISE, FOR THE MANU- FACTURE, SALE, OR USE OF ANY METHOD, APPARATUS, ORPRODUCT COV- ERED BY LETTERS PATENT. NEITHER SHOULD ANYTHING CONTAINED IN THE PUBLICATIONBE CONSTRUED AS INSURZNG ANYONE AGAINST LIABIL- ITY FOR INFRINGEMENT OF LETTERS PATENT. 5. GENERALLY, API STANDARDS AREREVIEWED AND REVISED,REAF- FIRMED, OR WITHDRAWN AT LEAST EVERY FIVE YEARS. SOMETIMES A ONE- TIME EXTENSION OF UP TO TWO YEARS WILL BE ADDED TO THIS REVIEW CYCLE. THIS PUBLICATION WILL NO LONGERBE IN EFFECT FIVE YEARS AF- TER ITS PUBLICATION DATE AS AN OPERATIVE API STANDARDOR, WHERE AN EXTENSION HAS BEEN GRANTED, UPON REPUBLICATION. STATUS OF THE PUBLICATION CAN BE ASCERTAINED FROM THE API AUTHORING DEPART- MENT [TELEPHONE (202) 682-8000]. A CATALOG OF API PUBLICATIONS AND MATERIALS IS PUBLISHED ANNUALLY AND UPDATED QUARTERLY BY API, 1220 L STREET,N.W., WASHINGTON, D.C. 20005. Copyright 0 1991 American Petroleum InstituteCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 4. A P I PUBL*K2028 91 0 7 3 2 2 9 0 0101393 7 FOREWORD This publication is intended to alert industry to the limitations of flame arresters. Flame arresters are usually testedin configurations that produce low flame speeds only. highly The variable conditions surrounding arrester applications may result in high flame speeds that could render the arresters ineffective. A P I publications may be used by anyone desiring to do so. Every effort has been made of the by the Institute assure the accuracy and reliability data contained in them; however, to the Institute makes no representation, warranty, or guarantee in connection with this pub- lication and hereby expressly disclaims any liability or responsibility for loss ordamage re- sulting from its use or for the violation of any federal, state, or municipal regulation with which this publication may conflict. Suggested revisions are invited and should be submitted to the director of the Safety and Fire Protection Department, American Petroleum Institute, 1220 L Street, N.W., Washing- ton, D.C. 20005. iiiCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 5. ~ ~ _ _ _ _ _ A P I PUBL*2028 73 I0732290 0303394 9 CONTENTS Page SECTION 1 GENERAL ............................................................................. - 1 1.1 Purpose ............................................................................................................ 1 1.2 Referenced Publications .................................................................................. 1 SECTION 2--FL AME PROPAGATION ................................................. 1 SECTION 3 -LISTED FLAME ARRESTERS ..................................... 2 3.1 Problems in Piping Systems ............................................................................ 2 3.2 Design ............................................................................................................. 2 3.3 Limitations ...................................................................................................... 2 3.4 Test Procedures ............................................................................................... 2 3.5 Untested Arresters ........................................................................................... 2 3.6 Flame Arresters in Series ................................................................................ 2 SECTION 4--uNL ISTED ARRESTERS ................................................ 3 4.1 Description ...................................................................................................... 3 4.2Water Seals ...................................................................................................... 3 4.3 Packed Beds .................................................................................................... 3 4.4Velocity-Type Arresting Devices .................................................................... 3 4.5 Mechanical Interruption of Flame Path ........................................................... 3 SECTION 5-SU"ARY ........................................................................... 3 SECTION 6 -REFERENCES ..................................................................... 4COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 6. A P I PUBL*K2028 71 W 0732290 OLO1395 0 M Flame Arresters in Piping Systems SECTION I-GENERAL 1.I Purpose This publication is intended to alert industry to the limita- tions of flame arresters. The highly variable conditions sur- The availability of commercial flame arresters listed by rounding applications of arresters may result in high flame nationally recognized testing laboratories has frequently led speeds that could render the arresters ineffective. to the installation of these arresters in piping systems; how- ever, the actual conditions under which these arresters will operate may be far different from the conditionsunder which the arresters were tested and listed by the testing laborato- 1.2 Referenced Publications ries. Listed arresters are normally tested under nonflowing The most recent editions of the following standards, conditions and with ignition at the open ends of pipes at- codes, and specifications are cited in this publication. tached to the arresters. The testing is conducted with limited lengths of the attached pipes. Flames propagating through API piping systems continuously accelerate and can reach veloc- Pub1 2210 Flame Arresters for Vents of Tanks Storing ities that are much higher than those at which the arresters Petroleum Products were tested. As a result, flame arresters, whether listed or not, may not be effective when they are incorrectly applied u L 1 in piping systems. Listed arresters should not be installed in UL 525 Flame Arresters for Use on Vents ofstorage piping systems unless they been tested under conditions have Tanksfor Petroleum Oil and Gasoline equivalent to those expected in the specific applications. Gas and Oil Equipment SECTION 2-FLAME PROPAGATION Flames propagating through piping systems are capable of ber of ways in which even higher pressures can begener- reaching extremely high speeds. Initially, the flames travel at ated: of a burning velocity characteristic the mixture; this velocity, sometimes tabulated in handbooks, is usually a few feet per a. At closed ends and elbows, the pressure is increased by second. Then the flames begin to accelerate. This accelera- reflection of the detonation wave. tion process is assisted by turbulence, which can be induced b. At the point where the deflagration transforms into a det- in the unburnedmixture by the flames themselves or can re- onation, even higher pressures can occur during a phase of sult from such factors as flow, pipe wall roughness, or turbu- the detonation known as the overdriven phase [3]. lence-producing fittings [l]. c. When flames are propagating toward a closed system, pressures higher than 20 times the initial absolute pressure Note: The flame velocity at a given point a functionof the lengthof pipe is and sue of pipe through which the flames have traveled, the intensity tur- of can occur under certain circumstances because of a process bulence, the properties the particular fiammable mixture, and other factors. of known as pressure piling. In pressure piling, the deflagration causes precompression of the gas before the transition to det- Flames can accelerate to a velocity that permits their onation. travel upstream as well as downstream of the original direc- tion of the flow They can readily reach a velocity of sev- [2]. Flame propagation makes the installation of flame ar- eral hundred feet per second. If the flamesare propagating in resters in piping systems fundamentally different from the the unburned medium at a velocity less than the speedof installation of arresters on tank vents. T n vents have little ak sound, it is known as a deflagration, but if the pipe is long or nopipe length present between the arrester and an exter- enough, flame propagation under detonation conditions can nal ignition source at the open end (see Underwriters Labo- occur. In detonations, flames can travelseveral thousand feet ratories Gas and Oil Equipment and API Publication per second and are accompanied by pressure pulses; the 2210). magnitude of the pressure pulses may exceed 20 times the initial absolute pressure [ 13. Although the magnitude of the pressure pulses may ex- Underwriters Laboratories, 333 Pfingsten Road, Northbrook, Illinois ceed 20 times the initial absolute pressure, there are a num- 60062-2096. 1COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 7. A P I PUBL*2028 9 3 E 0 7 3 2 2 9 0 0 3 0 3 3 9 6 2 2 API PUBLICATION 2028 SECTION 3-LISTED FLAME ARRESTERS 3.1 Problems in PipingSystems section of pipe that isthe same size as the arrester. To be ef- fective, listed arresters must be installed in accordance with Installing flame arresters in piping systems with extended their listed installation parameters. or continuous pipe lengths presents a complex design prob- lem. The criteria for the design of flame arresters for contin- 3.4 Procedures Test uous piping systems have not even been established yet. Systems with extended or continuous pipe lengths mayhave The test procedure for listed arresters which is provided pipe lengths that would permit flames to attain enough veloc- UL 525 defines ignition as occurring at the open end of in ity to pass through an arrester. Alternatively,the high pres- the discharge pipe and under nonflowing conditions, so this sures developed may damage the arresting element or test procedure is notappropriate for listed arresters in closed rupture the housing, enabling a flame to pass through de- the piping systems or with flowing flammable materials. Before vice. Pressures resulting from within a pipe may exceed the arresters are installed in piping systems, the arresters should strength of an attached vessel. be tested with a procedure that adequately represents the service conditions under which they will be used. The pa- 3.2 Design rameters of the test procedure must be equivalent to the op- erating conditions, which include fuel mixture composition, Listed flame arresters usually cellular arresters and in- are temperature, pressure, flow rate, and potential ignition loca- clude the following types: perforated-plate arresters, parallel- tions relative to the arresters. In some cases, testing under plate arresters, crimped-metal-ribbon arresters, and overdriven conditions or with pressure piling effects consid- sintered-metal arresters [4]. These devices are barriers that ered may be appropriate. In other cases, testing detonation arrest the flames by quenching is, the heatof the flames (that arresters at deflagration conditions should be considered be- is transferred to the walls an array of small passageways of cause arresters suitable for detonations have failed deflagra- in the arrester). critical parameters that govern the effec- tion tests [3]. The tiveness of cellular arresters are the diameter or width and the length of the flame passages. 3.5 Untested Arresters Cellular arresters (discussed inA P I Publication 2210) are listed by nationally recognized testing laboratories as in- Some improper installations of listed arresters have been tended for installation on atmospheric pressure tank vents in service for years without an accident, but this should not storing petroleum products and vents from the tanksof oil on be considered as proof that such installations are safe. In tankers (see Gas and Oil Equipment) [I]. The listings are most of these cases, the arresters have never been subjected usually based on tests made with mixtures of gasoline vapor to flame fronts. The spitistical risk is low because the re- and air and may not cover other mixtures. Arresters tested quired mixture and an ignition source have not occurred si- with gasoline vapor are probably suitable for use with most multaneously. common paraffin or aromatic hydrocarbons; however, they In facilities that terminate at continuous ignition sources, should not be used with burning gases and vapors, such fast such as furnaces, flare pits, or pilot lights, the probability of as hydrogen, acetylene, or olefinic hydrocarbons, without ad- a simultaneous occurrence of the propermixture and an igni- ditional tests. tion source is greater.Where arresters have been installed in piping between the and ignition sources, there have been gas 3.3 Limitations many instances of flames occurring within the piping, mi- grating through the arresters, and resulting in an explosion. While listed arresters are tested by laboratories, the test conditions may not beequivalent to or representative of the 3.6 FlameArrestersinSeries actual service conditions particular piping system designs. of The listings indicate whether the test conditions included ig- In many cases, placing two or more flame arresters in se- nition at the open end a pipe attachedto the device.I they of f ries provides only slight additional protection when com- indicate that ignition at the open end a pipe was included, of pared to a single arrester, If flame propagation conditions the listings would also indicate the maximum permissible cause the first arrester fail, there is a significant probability to length of the pipe.This limitation of pipe length means that that an identical second arrester will also fail. In any case, the stated length is the greatest for which the arrester was there is little if any test work to verify the benefits of ar- successfully tested; this presumes that the pipe is a straight resters in series.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 8. A P I PUBL*K202& 93 0732290- 0303397 4 ARRESTERS PIPING SYSTEMS FLAME IN 3 SECTION 4-UNLISTED ARRESTERS Description 4.1 4.4Velocity-TypeArrestingDevices Where the flow ofa gas mixture is limited to a single di- Besides listed arresters, there are other arresting devices rection, it is possible to ensure, by design, that the flow ve- and techniques in use within the hydrocarbon processing in- locity will never be less than the velocity corresponding to dustry, including water seals, packed beds, velocity-type ar- the maximum rate of propagation of flames in the mixture resting devices, and mechanical interruption of the flame path. These arresting devices and techniques also have lim- under consideration [l].For a small diameter pipe discharg- ing gasoline vapors into the open air, an efflux velocity of 10 itations and should be tested at full scale to determine their feet per second is considered adequate [2,6]; however, the effectiveness under actual service conditions. appropriate velocity must be determined for each case. The appropriate velocity can be determined from the gas mixture 4.2 Water Seals and pipe diameter [11. Controlling flow velocity through a velocity-type arresting Water seals are often designed and installed to prevent re- device should be regarded as an effective technique for pre- verse gas flow, andtheir design is potentially capable of pre- venting flashbacks only when the ignition sourceis at the In venting flame propagation [4,5,1]. each water seal, the gas open end of the pipe. In the design of a velocity-type arrest- mixture is bubbled through a reservoir of water, a process ing device, some means must be provided either to maintain that mayprevent the passage of flames. The flames are inter- a minimum velocity under all operating conditions or to in- rupted because each gas bubble is isolated from the next. terrupt the gas supply if the flow velocity becomes too low. No standard design or listing is available for water seals. The design must also provide some means either to interrupt Each installation presents a specific problem involving the the gas supply or to extinguish burning within the velocity rate of the gas flow, the depth of the seal, and the size and the section of the arrester. This prevents the flames from heating configuration of the vessel that contains the water. Some im- the arrester enough to permit them to pass through it, which portant design considerations for the water seal are as fol- can occur within a few minutes. lows: a. It should prevent rupturing under flame-produced pres- 4.5 MechanicalInterruption of sure. Flame Path b. It should reliably maintain the required water level for A closed pipe valve can prevent flame passage as long as normal as well as flame-produced conditions. the valve can be closed quickly enough. Using a valve as a c. It should protect against freezing. flame arrester appears to be a limited option, though, Achieving the rapid response time for closure is difficult; however, because flames are accompanied by vibration, 4.3 Packed Beds pressure rise, temperature, and ultraviolet emissions, sensing For many years, gravel, raschig rings, small pebbles, and devices positioned some distance from the valve can be used other bulk materials have been used as flame arresters in to close it, precluding the passage of flames. Mechanical in- packed towers or columns. There are no established design terruption is probably more useful in combination with the criteria for using packed beds as flame arresters. other approaches discussed in this publication. SECTION 5-SUMMARY For cellular and other tested arresting devices, the follow- ditions should be conducted. Actual service conditions in- ing guidelines are recommended: clude mixture composition, temperature, pressure, flow rate, a. only a listed or tested arresting device that is within the and ignition location relative to the arrester. If detonatio-n range of its listed or tested parameters should be used. conditions can occur at the arrester, thedevice must be tested b. For applications that uselisted arresters outside the range under detonation as well as deflagration conditions. of their test parameters and for all unlisted devices, a full- c. The arresting device must be installed and maintained in scale test under conditions equivalent to actual service con- the exact mechanical form in which it was tested; this in-COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 9. A P I PUBLX2028 93 = 0732290 0303398 b 4 API PUBLICATION 2028 -_ cludes maintaining the exact form of the element, its hous- e. If the arresting device is not designed to withstand sus- ing, and gaskets. tained burning on the face, a provision must be made to de- d. For piping system applications where both flammable the tect and suppress or prevent burning. mixture andan ignition sourceare likely to be presentsimul- f. When an arrester is installed in a piping system, it should taneously, flame arresters should not be considered as the be checked periodically to ensure that it has not been dam- sole means of protection but shouldbe used as a supplement aged, has not clogged,or has not corroded. Therefore, the in- to other systems or operational controls. line arrester must be installed in a location that facilitates inspection and required maintenance. SECTION 6-REFERENCES 1. Howard, Walter B., “Flame Arresters and Flashback Committee on Safety and Fire Protection Spring Meeting, Arresters,” PlantlOperations Progress, American Institute Tulsa, Oklahoma, April 13,1989. of Chemical Engineers, New York, October 1982, Vol. 1, 4. Watson, P.B., “Flame Arresters,” Paper presented at the No. 4. Conference on Instrumentation and Safety in the Oil and 2. Broshchka, G.L., Ginsburgh, I., Mancini, R.A., and Will, Natural Gas Industries, Glasgow College of Technology, R.G., “A Study of Flame Arresters in Piping Systems,’’ Glasgow, Scotland, March 9-10, 1977. PlantlOperations Progress, American Institute of Chemical 5. Bartknecht, W., “Mechanical Flame Barriers,” Explo- Engineers, New York, January 1983, Vol. 2, No. 1. sions, Springer-Verlag,New York, 1981, pp. 155-158. 3. Roussakis, N., and Lapp, K., “A Comprehensive Test 6 . Wilson, R.P., and Crowley, D.P., Performance of Com- Method for Inline Flame Arresters,” Paper presented at API mercially Available Flame Arrestersfor ButanelAir and GasolinelAir Mixtures, NTIS No. AD 063002, 1978.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 10. ~~ A P I PUBLM2028 9 3 W 0732290 0303399 B I Order No. 855-20280 1-141&-12191-2.5C (9C)COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 11. A P I PUBL*202B 9 1 = 0732290 0101400 0 = American Petroleum Institute 1220 L Street, NorthwestCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services