Document 3dRO1GwwO2qmEnM9jLLjDbjy

OCT-28-1397 08=41 CONDEA United States Environmental Protection Agency 281 588 3478 P.03/08 United States Occupational Safety and Health Administration EPA550-F-97-002F September 1997 &EPA cepNH OSHA^ EPA and OSHA SHAFT BLOW-OUT HAZARD OF CHECK AND BUTTERFLY VALVES The Environmental Protection Agency (EPA) and Occupational Safety and Health Administration (OSHA) are leading tills Ahrt ae part of their ongoing efforts to protect human health and the environment by preventing ohamloal accidents. Under CERCIA, section 104 ie), the Clean Air Act (CAA). and the Occupational Safety and Health Act (OSH Act). EPA and OSHA have euthortty to conduct ohamloal accident Investigations. Additionally, in January 1995. the Adndnlstratian esked EPA end OSHA to jointly undertake Investigations to determine the root eauaa(s) of chemical accidents and to issue pubRo reports containing recommendation* to prevent similar accidents. EPA and OSHA have created chemical aceidant investigation team to work Jointly tn these efforts. Prior to the release of a full report. EPA and OSHA Intend to publish Alert* as promptly as possible to increase awareness of possible hazards. Alerts may also bs issued whan EPA and OSHA become aware of a significant hazard. It Is Important that faciStias, SERCs. LEPCs, amergenoy rasPondera end othars review this information and take appropriate Steps to minimize risk. Problem torque from the drive shaft to the disk fell out of its keyway, disconnecting the drive shaft from the disk. System ertain types of check and butterfly pressure was high enough to eject .the Cvalves can undergo sh&ft-di$k unrestrained drive shaft from the valve, separation, and fail cata carrying with it the external strophically or "blow-out", causing ctooxuincterweight assembly, weighing over and/or flammable gas releases, fires, and 200 lbs., a distance of 43 feet away. vapor cloud explosions. Such valve failures can occur even when the valves The absence of the drive shaft left a bole are operated within their design limits in the valve body the diameter of the of pressure and temperature. shaft (3.7S inches) directly to atmosphere, and initiated a high- Accident History pressure light hydrocarbon leak. The leak continued for approximately 2 to 3 minutes, forming a large cloud of ICrlvogreieenaaxfltosspluevlnoosuewrlaeonucslfrt'su)scagssinitunetodavuwg1frdainoabrn9aelehlv-ei9lmalsrdaeiudw7cihnnrorhadiwsemeunafnthncficainteatoMcrsaseoni3ufudos.r0obsedlhaa0eiesfnenarpdqetljgpflu,niutqGsgetreihusiiphgbMeueeemtlsmvnfovZlreheatawaaalrmyycnppnta-hditodcomiledrrauowicamdglcktrlbaoy.eniaclmlrel(lierlkintaToboaeaegosuhongsdasrnedneesssi,stedccmirMrbfaveanleeaoarwafxssfqaouimmpepntaiuskjrdlocoyuompoeeier.trrmdslreinaennideobtccTegcednnllexeohoglatuyttssemhulemfaln,eeinodgspieaaslartshtocgxninvipontgfpeaddeoamehnlnaorrneyddnipastotdtalideleiuscaechormdl,octtcleenleoatc,yumaarmgapirrasncdrrerdiihoneenabupeudbodlptosiosontniutsrv-lerged`yaelotnvtthossniroysasntewdiesptun1grn(myoifg0umnnrasrsec.oeigtcmmon,etpafiulmsTaaaifritlrtibthnehnairyaslreyydeeysn,.,l The check valve was designed with a drive shaft that connects the internal valve disk to an external pneumatic cylinder (see diagram on next page). The valve failed when a dowel pin designed to fasten the drive shaft to the disk sheared and a key designed to transfer damage due to the blast wave). Nearby highways were closed for several hours. Damage cost to the facility alone is estimated at approximately 90 million dollars. Fortunately, no fatalities and only minor injuries to workers resulted from the accident. Printed on recycledpaper OCT-28-1997 08:42 CONDEft UISTPMP}QflQ33Q 281 588 3478 P.04/06 Shaft Blow-Out Hazard ofChecK and Butterfly Vbfve* September 1997 Previous malfunctions involving check valves of the same or similar design occurred at facilities In 1980, 1991, and 1994. In each case, the affected check valve was located in a large diameter (36-inch Or greater) pipe in a hydrocarbon gas compression system. Also in each previous case, a dowel pin fastening the valve's drive shaft to its disk sheared (in the 1980 case the pin was possibly never installed) and a rectangular key fell out of its keyway, disconnecting the drive shaft from the disk. Although shaft-disk separation occurred in each previous cose, it did not result in shaft blow-out or catastrophic failure. This may be because the valves m these instances were installed in lowerpressure service, or because the malfunctioning valves were identified before shaft blow-out occurred. In the 1991 incident, the malfunction was manifested by the erratic operation of the valve, which was observed to operate Independently from its external drive mechanism. System pressure was low enough (70 psig) that the failure was detected before the shaft was expelled out of the valve body. (At the time the malfunctioning valve was identified, the valve shaft was protruding about 0.75 inches out of the valve body.) In the 1980 and 1994 cases, the malfunction was identified when workers noted that thi external piston rod connecting the airassist cylinder to the drive shaft had broken due to axial movement of the drive shaft. Hazard Awareness systems containing chemicals leading to hydrogen embrittlement. heck and butterfly valves are used in Valves subject to this hazard may be designed Cmany industries, including refineries, with a two-piece valve stem (sometimes referred petrochemical plants, chemical plants, to as a 'stub-shaft" design). In each of the cases power generation facilities, and others. Mdeossctribed above, the malfunctioning component modem valve designs incorporate features that was a Clow stub-shaft Model CMZ reduce or eliminate die possibility of shaft blow pneumatically assisted swing check valve (see out. However, older design check and butterfly diagram below). In these check valves, one stem valves with external appendages such as piece functions as a drive shaft that connects the pneumatic-cylinders, counterweights, manual interns 1 valve disk to an external air-assist operators, or dashpocs may be subject to this cylinder and counterweight assembly. The drive hazard Shaft blow-out may be of particular shaft penetrates the pressure boundary through concern wherever these valves are installed in a stuffing box. The exterior portion of the drive Simplified cross-sectional view ofcheck valve (flow direction is into page) OCT-28-1'397 08 M2 CGNDEA VISTfi(UEJGft0B02W> 281 588 3478 P.05/06 Shtrfi Blow-Out Hazard of Check and Butterfly VWvw SeptemberJ997 shaft is connected to a pneumatic piston and counterweight, and the interior portion of the shaft is coupled directly to the valve disk using a cylindrical hardened steel dowel pin and a rectangular bar key. This arrangement provides a power-assist to close the valve during compressor shut down, preventing reverse flow of compressed gases. These particular valves have probably not been produced since 1985, but still exist in some process facilities constructed before that date. Similar valves currently or previously produced and sold by other valve manufacturers may also be subject to this hazard. Operational Factors The valve is subject to high cyclic loads. In all or the above incidents, the valve repeat edly slammed shut with great force during compressor trips and shutdowns. Such re peated high stresses may cause propagation of intergranular cracks in critical internal com ponents, such as dowel pins. The valve is subject to low or unsteady flow conditions, such that disk flutter or chatter occur, resulting in increased wear of keys, dowel pins, or other critical internal components. Factors in Valve Failure A number of design and operational factors may contribute to this hazard. These include the following: Design Factors The valve has a shaft or stem piece which penetrates the pressure boundary and ends inside the pressurized portion of the valve. This feature results in an unbalanced axial thrust on the shaft which tends to force it (if unconstrained) out of the valve. The valve contains potential internal failure points, such as shaft dowel-pins, keys, or bolts such that shaft-disk separation can occur inside the valve. The dimensions and manufacturing tolerances of critical internal parts (e.g., keys, keyways, pins, and pin holes) as designed or as fabricated cause these parts to carry abnormally high loads (e.g.. in the 1997 accident, the dowel pin rather than the key transmitted torque from die shaft to the disk). The valve stem or shaft is not blow-out resistant. Non blow-out resistant design features may include two-piece valve stems that penetrate the pressure boundary (resulting in a differential pressure and unbalanced axial thrust as described above), single-diameter valve shafts (i.e.. a shaft not having an internal diameter larger than the diameter of its packing gland) or shafts without thrust retaining devices, such as splitring annular thrust retainers. Valves in high-pressure service lines may be more Ukely to undergo shaft blow-out (in the 1997 accident, system pressure at the failure point was approximately 300 psig). Valves used in hydrogen-rich or hydrogen sulfide-containing environments may be more susceptible to blow-out due to hydrogen embrittlement of critical internal components, particularly if these are made from hardened steel (as was the dowel pin in (he 1997 accident). Hazard Abatement acilities should review their process Fsystems to determine if they have valves installed that may be subject to this hazard If so, facilities should conduct a detailed hazard analysis to determine the risk of valve failure. Check valves or butterfly valves which are subject to several or all of tjte above design and operational factors are high risk for shaft blow-out. Detailed internal inspections may be necessary in order to identify high-risk valves. Facilities should consider replacing.high-risk valves_at_the earliest opportunity with a blow-out resistant design. Several blow-out resistant designs of check and butterfly valves are available. If immediate valve replacement is impossible or impractical, facilities should consider immediately modifying the valves to prevent shaft blow-out. Valve manufacturers should be consulted in order to ensure that any modifications made are safe. OCT-28-1337 08 M3 CONDEfi u I stABOi(M1292&2j 281 588 3478 P.06/06 4 Shaft Blow-Out Hazard of Check and Butteifly Valves September 1997 Information Resources on Valve Safety American Petroleum Institute 1220 L Street NW Washington. DC 20005 Phone: (202) 682-8000 Web site; http://www.api.org Some sources of information on valve safety are listed below. Relevant API standards include: API 598-1996 -- Valve Inspection and Testing General References API 570-1993 -- Piping Inspection Code: Information on cases of valve failure can be found Inspection. Repair. Alteration, and Rerating of In T. Kletz, What Went Wrong?, 3rd Edition, Gulf In-Service Piping Systems Publishing Co., Houston (1994). This reference contains general information related to cheek valve failure (pp 127, 129. and 175) and cites one specific case of check valve failure (page 124) similar to API 941-1991 -- Steels for Hydrogen Service at Elevated Temperatures and Pressure in Petroleum Refineries and Petrochemical Plants those described in this Alert. RelevantAPIRecommended Practices include: Information on hydrogen embrittlement can be found in F.P. Lees, Loss Prevention in the Process Industries: Hazard Identification. Ajjewmertf, and Control, 2nd edition, Butterworth-Heinemann Publishing, Oxford (1996), pp 12/82-83. RP 574-1992 -- Inspection of Piping. Tubing. Valves and Fittings RP 591-1993 -- User Acceptance of Refinery Valves Codes, Standards, and Regulations The American Society ofMechanical Engineers (ASME) has a standardfor valves. American Society of Mechanical Engineers 345 East 47th Sheet New York, NY 10017 or 22 Law Drive Fairfield, NJ 07007-2900 Phone: (800) 843-2763 Web site: http://www.asme.org Relevant ASME standards include: ASME B 16.34-1996 -- Valves,- Flanged. Threaded, and Welding End, an American National Standard. The American Petroleum Institute (API) has several relevant standards and Recommended Practices. Applicable regulations Include: 29 CFR 1910.119 Process Safety Management pf_HUhly_JBazardous Chemicals: Explosives Contact EPA's Emergency Planning and Community Riqht-to-Know Hotline (800 424-9346 or (703) 412-9810 TDD (800) 553-7672 Monday-Fwday, 9 AM to 6 PM, eastern time * Visit the EPA CEPPO Home Page on the Woruj Wide Web at: http://www.epa.gov/swercepp/ Visit OSHA's Home Page on the World Wide Web at: http://www.osha.gov/ NOTICE The etatemems In this document are intended solely ei guidance. ThU document does net eubetltute for EPA'a. OSHA's. or ether agency regulation*, nor la K a regulation haalf. fifts-apecWlc application of the guidance may very depending on process activities, end may not apply te e given situation. EPA or OSHA may revoke, modify, or suspend this guidance in tha future, a appropriate. TOTAL P.06