emergency isolation of chemical plants

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Process Safety Guide: GBHE-PSG-001

EMERGENCY ISOLATION OF CHEMICAL PLANTS

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Process Safety Guide: Emergency Isolation of Chemical Plants CONTENTS 1 Introduction 2 When should Emergency Isolation Valves be Installed 3 Emergency Isolation Valves and Associated Equipment 3.1 Installations on existing plant 3.2 Actuators 3.3 Power to close or power to open 3.4 The need for testing 3.5 Hand operated Emergency Valves 3.6 The need to stop pumps in an emergency 3.7 Location of Operating Buttons 3.8 Use of control valves for Isolation 4 Detection of Leaks and Fires 5 Precautions during Maintenance 6 Training Operators to use Emergency Isolation Valves 7 Emergency Isolation when no remotely operated valve is available References Glossary Appendix I Some Fires or Serious Escapes of Flammable Gases or Liquids that could have been controlled by Emergency Isolation Valves Appendix II Some typical Installations



Emergency Isolation of Chemical Plants 1 Introduction Many serious fires have occurred in the oil and chemical industries because leaks of highly flammable gases or liquids could not be contained. For example, the serious fire at Feyzin in France in 1966 started while water was being drained from a tank of liquefied petroleum gas. The drain valves could not be shut, LPG flowed out and was ignited by a car on a motorway 500 feet away. Many fires have occurred as a result of gland leaks on pumps handling very cold liquefied hydrocarbons. Appendix I describes some incidents that could have been prevented by the installation of emergency isolation valves. They were all the result of leaks of flammable gases or liquids. On other plants equipment failure or human failure has led to leaks of toxic gases or vapors or corrosive liquids, but these do not seem to be so well documented. As a result there is a need to provide means of isolating leaks before they fire or before serious damage or injury results. This guide is intended to help plant designers and operators decide when emergency isolation valves should be provided and it gives some details of types that have been used. It is suggested that new and existing plants handling toxic or flammable materials should be reviewed in the light of this guide. 2 When should Emergency Isolation Valves be Installed?

It is impracticable to install emergency isolation valves to isolate every piece of equipment which might leak. They should be installed only when the chance of a leak is significant or the consequences serious. The former usually occurs on equipment subject to extremes of temperature or pressure, particularly if it is also subject to thermal shock, or subject to vibration. In practice, the weakest points are usually pump glands, followed by stirrer glands and reciprocating compressor glands In addition, experience shows that water drain points are often left running unattended.



Prevention of the leak in the first place is, of course, far better than isolating it after it has occurred. It would be better to spend $2,000 on making sure a pump does not leak than on providing a valve to isolate the pump when it starts to leak. However, in many cases it is not possible to reduce the chance of a leak to an acceptable level and emergency isolation valves should then be installed. When deciding whether or not to Install emergency isolation valves, the size and consequences of a leak must be considered as well as the probability that it will occur. Three situations should be considered:- (a) The equipment is particularly liable to leak for example, very hot or cold pumps. (b) The equipment is less likely to leak but if it does leak a very large quantity of material will run out and there is no way of stopping it, for example, the bottom pump on a still containing more than, say, 50 tons, of flammable Liquid. (C) The equipment is less likely to leak but if It does so, the rate of leakage will be very large For example, a very large pump. In addition, if the inventory between the emergency isolation valve and the leak is large, or if the isolation valve is unlikely to give a good shut off, then an emergency blow-down valve may be needed as well as an emergency isolation valve. The following illustrates the kind of argument that may be used to decide whether or not emergency isolation is justified in a particular case:- Suppose the cost of installing an emergency isolation valve (or motorizing an existing valve) is $1,650. Suppose a leak on the equipment being protected could lead to damage and loss of profit worth $1,650,000. Then if the chance of a leak of this size is greater than 1 in 1,000 in the life of the plant (or in 10,000 per year) the expenditure is justified as an insurance policy, quite apart from any risk to life.



Accurate data on the frequency of gland failure is usually not available. However, it is not always necessary. Our experience may tell us that the chance of a fire is a lot less than 1 in 1,000, or our experience may tell us that the chance of a fire is a lot greater than 1 in 1,000. In either of these cases the problem is solved as we know what action to take; it is not worthwhile looking for data on the frequency of pump fires or trying to synthesize a figure from the reliability figures for seal components. If, however, our experience tells us that the chance of a fire is about 1 in 1,000 (say, between 1 in 100 and 1 in 10,0001 in the lifetime of the plant then it is worthwhile expending some effort in trying to obtain more accurate data on the frequency of pump fires. If experienced judgment has to be used to estimate the probability of a leak, why not use experienced judgment to decide whether or not an emergency valve is necessary? The answer is that it is easier to estimate a piece of missing data than to estimate the answer to a whole problem. In some cases, particularly where toxic or corrosive materials are concerned, the chance of damage to equipment is small but there is a significant risk of injury to people. The methods of hazard analysis can be used in these cases. It is necessary to estimate: (a) The chance that a leak will occur. (b) The chance that a man will be near enough to be injured at the time - this can be estimated by measuring the 'population density' in the area. For corrosive liquids, we also need to know the chance that the man will be In the line of fire, i.e. what is the solid angle of the leak. From these figures the probability that a man will be injured can be estimated and compared with the usual criteria (Refs. 1,2 and 3). Similar arguments can be used to decide whether or not emergency isolation valves should be fitted on process drain lines. The chance of an uncontrolled leak should be considered as well as the total quantity that can run out. As already stated, experience shows that operators are reluctant to spend long periods of time waiting whilst draining water from oil tanks. Despite instruction to the contrary, they leave the drain point unattended. If they forget to return in time, or the quantity of water is less than expected, a leak occurs. As a general rule, remotely operated isolation valves should be installed on all process drain lines on storage tanks or process vessels containing LPG. Drain points used only for maintenance should be blanked off. (Ref 4).



Occasionally a plant contains a number of possible points of leakage and fitting remotely operated isolation valves to all of them may be impracticable. In these cases it may be possible to minimize the extent of the leak and the consequences of any subsequent fire by dividing the plant into sections by a number of emergency isolation valves. Another method is to group points of leakage so that they are protected by a single valve. For example, on LPG storage vessels, there should be only one outlet below the liquid 'level, protected by a remotely operated isolation valve, and all pump suction lines, drain points, sample points, instrument connections etc. should come after this valve (Ref. 4). Finally; the need to isolate the feed to a plant in an emergency must not be overlooked. An emergency valve on the feed line may be desirable. Hoses or flexible arms used for loading liquefied flammable gases or liquefied toxic gases such as chlorine or ammonia into road or rail tank wagons or ships' tanks have broken on many occasions. Filling lines should, therefore, be fitted with remote isolation valves and the tankers fitted with a non-return valves (or remote isolation valves if the same line is used for filling and emptying). Remotely operated isolation valves are better than excess flow valves as the latter operate only when the leak rate is 50% or more above the normal flow; heavy leaks can occur without them operating. When pipelines are large, power operated emergency valves installed primarily for safety reasons have been used instead of ordinary isolation valves In order to avoid the effort involved in operating large hand valves.



3 Emergency Isolation Valves and Associated Equipment 3.1 Installations on Existing Plant. When emergency isolation valves are being installed on an existing plant, it is usually cheaper and more convenient to motorize an existing valve, than to install a new one, as this would involve cutting lines. For example to install a new valve at the point indicated below would be expensive and involve a shut down. It would be cheaper and more convenient to fit electric or pneumatic actuators on the two existing suction valves. This has the additional advantage that the quantity of material that can leak out, after the valves have been closed is much reduced. For liquids below their boiling points at atmospheric pressure, the difference is not great, but for flashing liquids the difference is considerable.

It is not usually considered necessary to fit emergency isolation valves on pump delivery lines, as non return valves are normally fitted and prevent back flow. 3.2 Actuators Emergency isolation valves may be operated either electrically or pneumatically (or hydraulically if a hydraulic oil supply is available on the plant). For new installations fire-safe pneumatically operated ball valves are preferred, for example, Wilmot-Breedon valves flitted With Truflo actuators.



The following types of actuator have been used: - Electrically operated Rotork, Limitorque (with pneumatic operation if power fails) Jones· Tate Pneumatically operated Taylair (for gate valves) Truflo (for ball vialves) Hatlersley Newman (for ball or gate valves) Typically, electrically operated valves take about one minute to operate, pneumatically operated ball valves rather less and pneumatically operated gate valves rather longer. No doubt other types are available and their absence from this list does not mean that they are unsatisfactory. 3.3 Power to Close or Power to Open? In most cases emergency isolation valves are held open by air pressure or electric power and they will close when the pressure falls or the current is isolated. If operators forget to operate these valves, and a fire occurs, then the impulse lines will be burnt through and the valves will close. (A fusible section in a mechanical linkage behaves similarly) There are however exceptions:- Power is needed to open and to close emergency isolation valves when the valves are very large and, in some cases, when existing valves have been motorized. Sometimes the valves are deliberately designed so that air pressure or electric power is required to close them. This is done when the consequences of a serious trip are serious, accidental closure of the valves being less likely when power is required to close them. In these exceptional cases, if we are dealing with flammable materials, then the air lines or cables to the valves must be provided with 15 minute fire protection.



3.4 The Need for Testing? Emergency Isolation valves must be tested regularly, typically once/month, or they may not operate when required. Often a valve can be quickly closed and then opened without upsetting the process. If this is not the case, a stop should be used to prevent the valve closing fully. The stop must be removed after testing is complete. A complete test should be carried out when the plant is shut down. An advantage of motorizing existing pump suction valves, as shown on the diagram in Section 3.1, is that testing presents no problems: each valve is tested while the other is on line. Non-return valves used in conjunction with emergency isolation valves, as described above, must also be inspected (or tested) regularly. (Though as simple mechanical equipment they will need inspections or testing less often than pneumatic or electrical equipment). 3.5 Hand-operated Emergency Valves If the suction vessel is some distance from the likely point of leakage then a hand-operated emergency valve may be acceptable. It must be possible to reach it when a leak occurs, without exposing the operators to undue risk. A man should not be expected to go upstairs to operate an emergency valve. These hand-operated emergency valves must also be exercised regularly or they will be too stiff to operate when required In anger. Note that moving the emergency valve further away from the point of leakage increases the quantity of material that will continue to leak out after the valve is closed and may strengthen the case for a blow down valve, this is particularly Important if the liquid is above its atmospheric pressure boiling point so that a lot of it has to flash to reduce the pressure. In a few cases mechanical linkages have been used instead of electric or pneumatic means to operate valves from a distance. Sometimes, particularly on older plants, hand-operated valves are used for emergency isolations but the operators are protected from the point of leakage by walls. These are not recommended as the walls interfere with ventilation and prevent the dispersal of small leaks.



3.6 The Need to Stop Pumps In an Emergency When all emergency isolation valve is fitted on the suction of a pump or a compressor, the motor should be tripped automatically when the valve is operated otherwise the machine may overheat and set fire to the leak. 3.7 Location of Operating Buttons Care should be taken that the operating buttons for emergency isolation valves are not so close to the likely point of leakage that they cannot be reached when a leak or fire occurs. One serious fire occurred because this point had been overlooked. Motorized suction valves had been installed on a pump, primarily for process convenience, and the operating buttons placed close to the pump. The fact that the valves might be required in an emergency had been overlooked (Ref 5). Of course, the operating buttons should not be too far away or there will be delay before they can be operated. On many installations there is one button about 30 feet away and another in the control room. 3.8 Use of Control Valves for Isolation Control valves are sometimes used as emergency isolation valves. They do not give as good an isolation as a valve designed for the purpose but when a control valve exists, installation of an additional valve may not be justified. On other occasions a control valve is used to back up a special emergency valve. If a control valve is to be used as an emergency valve a special emergency button should be provided It should not be left to the operator to close the valve by altering the control setting.



Flowchart for selection of ALARP Isolation Methods



Examples of methods for securing isolations

4 Detection of Leaks and Fires Emergency isolation valves are of little value if we do not know when a leak or fire occurs so that the emergency valves can be actuated. Unless operators are present on the plant most of the time, it is usually necessary to install leak or fire detectors in conjunction with remote isolation valves. For flammable gases or liquids, combustible gas detectors are usually preferred to fire detectors as they detect leaks before they fire. Sieger flammable gas detectors are of proved reliability. For advice on fire detectors see Ref.6.



5 Precautions during Maintenance Several accidents have occurred (Ref 12) because motorized valves were used to isolate equipment which was under maintenance and power was accidentally isolated or restored. If power opens the valve, then the power must he disconnected before equipment is given to maintenance, i.e., on electrically operated valves the fuses must he withdrawn, on pneumatically or hydraulically operated valves the impulse lines must be vented and the vent valves locked open. If power keeps the valve closed then it must be held shut by a locked clamp strong enough to withstand the loss of power Simple clamps which give a little when power is removed, thus allowing the valve to open slightly, are not suitable 6 Training Operators to use Emergency Isolation Valves Operating emergency isolation valves usually results in the interruption of process flow and the shut-down of the plant. Operators are therefore often reluctant to use them. Not only do they wish to maintain production but the subsequent start-up of the plant may involve them in extra work. On a number of occasions experienced supervisors have entered the vapor cloud around a leak of flammable gas or liquid In order to shut down a leaking pump and start up the spare instead of using the emergency valve provided The need to avoid taking unnecessary risk should be emphasized during operator training In the diagram in Section 3.1, motorizing the two suction valves near the pumps, instead of installing a single notarized valve next to the suction vessel, will overcome the reluctance of operators to interrupt the process.



7 Emergency Isolation when No Remotely Operated Valve is Available However many remotely operated isolation valves are installed, it is always possible that a leak will occur on equipment which is not fitted with one. The men on the job then have to decide whether they should take a chance and enter a vapor cloud to close a valve or whether they should allow the leak to continue. In these cases it is often possible to push back the vapor with water sprays and approach the valve behind the water. This technique can be used leaks that are on fire and with leaks that have not fired.



References 1 'Hazard Analysis - A Quantitative Approach to Safety' I Chem E Symposium Series No. 34, 'Major Loss Prevention in the Process Industries', p. 75. 2 'Specifying and Designing Protective Systems', Loss Prevention, Volume 6,1972, p 15. 3 F ire Detection Newsletters, obtainable from Central Safety Department. 4 'Case Study of a Reactor Fire', RM Zielinski, Chm. Eng. Progr., August, 1967, 63, No.8, P. 50. 5 Verbal report by EW Langley of HM Factory Inspectorate, Chemical Branch, 1966, Chemical Age, 8 March 1970. 6 NFPA Quarterly, July 1951 (Reprint No. Q45-3) 7 NFPA quarterly, October 1961 (Reprint No. 055-5) 8 Report No. 0.21, 100/B, 'Report on a Fire on No.2 Crude Oil Distillation Plant', TA Kletz, 7.7.69. 9 Safety Newsletters No. 42, Item 2 and No. 57, Item 5. 10 Report No. 0.21,186/B, 'Safety in Design of Plants Handling Liquefied Light Hydrocarbon - Review of Work Camed out Mid-1966 to Mid-1970', Appendix 1. by HG Simpson, 22.12.70. 11 Management of health and safety at work. Management of Health and Safety at Work Regulations 1999. Approved Code of Practice and guidance L21 (Second edition) HSE Books 2000 ISBN 0 7176 2488 9 12 The tolerability of risk from nuclear power stations HSE Books 1992 ISBN 0 11 886368 1 13 Successful health and safety management HSG65 (Second edition) HSE Books 1997 ISBN 0 7176 1276 7



14 Internal control: guidance for directors on the combined code and Implementing Turnbull: a boardroom briefing, both published by the Institute of Chartered Accountants in England and Wales in 1999, are available at www.icaew.co.uk 15 Safety signs and signals. The Health and Safety (Safety Signs and Signals) Regulations 1996. Guidance on Regulations L64 HSE Books 1996 ISBN 0 7176 0870 0 16 Safe use of work equipment. Provision and Use of Work Equipment Regulations 1998. Approved Code of Practice and guidance L22 (Second edition) HSE Books 1998 ISBN 0 7176 1626 6 17 Guidelines for the Management, Design, Installation and Maintenance of Small Bore Tubing Systems EHS16 Institute of Petroleum 2000 ISBN 0 85293 275 8 18 BS EN 764-7: 2002 Pressure equipment. Safety systems for unfired pressure vessels British Standards Institution ISBN 0 580 39863 3 19 Reducing error and influencing behavior HSG48 (Second edition) HSE Books 1999 ISBN 0 7176 2452 8 20 Guidance on permit-to-work systems: A guide for the petroleum, chemical and allied industries HSG250 HSE Books 2005 ISBN 0 7176 2943 0 21 Manual handling. Manual Handling Operations Regulations 1992 (as amended). Guidance on Regulations L23 (Third edition) HSE Books 2004 ISBN 0 7176 2823 X 22 Control of substances hazardous to health (Fifth edition). The Control of Substances Hazardous to Health Regulations 2002 (as amended). Approved Code of Practice and guidance L5 (Fifth edition) HSE Books 2005 ISBN 0 7176 2981 3 23 Safe work in confined spaces. Confined Spaces Regulations 1997. Approved Code of Practice, Regulations and guidance L101 HSE Books 1997 ISBN 0 7176 1405 0 24 Safe maintenance, repair and cleaning procedures. Dangerous Substances and Explosive Atmospheres Regulations 2002. Approved Code of Practice and guidance L137 HSE Books 2003 ISBN 0 7176 2202 9



25 Remotely operated shutoff valves (ROSOVs) for emergency isolation of hazardous substances: Guidance on good practice HSG244 HSE Books 2004 ISBN 0 7176 2803 5 26 Guidelines for the Management of Integrity of Bolted Pipe Joints EHS15 UKOOA 2002 27 Memorandum of guidance on the Electricity at Work Regulations 1989 HSR25 HSE Books 1989 ISBN 0 11 883963 2 28 Electricity at work: Safe working practices HSG85 (Second edition) HSE Books 2003 ISBN 0 7176 2164 2 29 BS EN 60947: 1998 Specification for low-voltage switchgear and control gear British Standards Institution ISBN 0 580 29155 3 30 Work with ionizing radiation. Ionizing Radiations Regulations 1999. Approved Code of Practice and guidance L121 HSE Books 2000 ISBN 0 7176 1746 7 31 Electrostatics. Code of practice for the avoidance of hazards due to static electricity PD CLC/TR 50404: 2003 ISBN 0 580 42225 9 32 Petroleum and natural gas industries – pipeline transportation systems – pipeline valves ISO 14313: 1999 International Organization for Standardization 33 Institute of Gas Engineers IGE/TD/3 Edition 4 (1677) Steel and PPE pipelines for gas Distribution 2003 34 BS 6990: 1989 Code of practice for welding on steel pipes containing process fluids or their residuals British Standards Institution ISBN 0 580 16672 4 35 Institute of Gas Engineers IGE/TD/1 Edition 4 (1670) Steel pipelines for high pressure gas transmission 2001 36 Approved Supply List. Information approved for the classification and labeling of substances and preparations dangerous for supply. Chemicals (Hazard Information and Packaging for Supply) Regulations 2005. Approved List L42 (Eighth edition) HSE Books 2002 ISBN 0 7176 6138 5



37 Pipelines Safety Regulations 1996 SI 1996/825 The Stationery Office 1996 ISBN 0 11 054374 4 38 Institute of Gas Engineers IGE/SR/22 (1625) Purging operations for fuel gases in transmission, distribution and storage 1999 39 BS 6739: 1986 Code of practice for instrumentation in process control systems: installation, design and practice British Standards Institution ISBN 0 580 15295 2 Glossary baseline isolation standard the minimum acceptable standard of final isolation applied under normal circumstances. This standard is based on risk assessment. It can be determined using the methodology in Appendix 6 or by other means. blank flange (blind) a component for closing an open end of pipe work, which is suitably rated to maintain the pressure rating of the pipe and of an appropriate material to withstand the contents of the line. bleed or vent valve a valve for draining liquids or venting gas from a pressurized system. block valve a valve which provides a tight shut-off for isolation purposes. double block and bleed (DBB) an isolation method consisting of an arrangement of two block valves with a bleed valve located in between. double-seated valve a valve which has two separate pressure seals within a single valve body. It is designed to hold pressure from either direction (as opposed to a single seated valve). It may include a body vent between seals to provide a block and bleed facility. extended isolation: isolation which is to remain in place for more than three months. fluid freely moving substance. Includes liquids and gases.



hazardous substance a substance which is able to cause harm or damage if loss of containment occurs. In some cases (e.g. water) the specific situation determines whether the substance belongs within this category. intolerable risk: risk at an unacceptably high level. Until the risk has been reduced, activity should not be started (or continued). If the risk cannot be reduced, even with unlimited resources, the proposed activity should not go ahead. isolating authority person authorized to approve proposed isolations. isolation the separation of plant and equipment from every source of energy (pressure, electrical and mechanical) in such a way that the separation is secure. isolation envelope that part of the pipe work system which is within the isolation points forming the boundary within which intrusive work can be performed. Where a valved isolation allows a physical isolation to be effected, it is the physical isolation point that forms the boundary of the isolation envelope. isolation envelope that part of the pipe work system which is within the isolation points forming the boundary within which intrusive work can be performed. Where a valved isolation allows a physical isolation to be effected, it is the physical isolation point that forms the boundary of the isolation envelope. isolation scheme a system incorporating three key components – management arrangements, risk control procedures and working-level practices, to ensure hazardous substances are not released nor people exposed to risks to their health and safety during the maintenance or repair of process plant or pipelines. own isolation: isolation where the same person both installs the isolation and carries out the intrusive work. Such isolations may be carried out under PTW or procedural control. permit-to-work (PTW) a formal written system used to control certain types of work which are hazardous. pig a device that can be driven through a pipeline by means of fluid pressure for purposes such as cleaning, dewatering, inspecting, measuring, etc.



physical disconnection a method of positive isolation where an air gap between the energy source and the plant/equipment is provided. pipeline cross-country, offshore and pipelines within sites, for example, storage sites, and petrochemical plant. This guidance uses the definition of ‘pipeline’ given in BS EN 14161 i.e. ‘the facilities through which fluids are conveyed, including pipe, pig traps, components and appurtenances, up to, and including the isolation valves’. However, pipeline installations such as compressor stations and pressure- regulating installations are not included in this definition – these are considered separately. Note that this differs from the legal definition of ‘pipeline’ within the Pipelines Safety Regulations 1996 (PSR) which includes certain pipeline installations, e.g. for gas pressure regulation. The relevant gas industry code for high pressure steel transmission pipelines is IGE/TD/1 and for distribution mains it is IGE/TD/3. pipeline installation installations such as pressure regulating installations, compressor stations which, together with the pipeline itself, comprise a pipeline system (as defined in BS EN 14161). The relevant gas industry code for pressure regulating installations is IGE/TD/13. pipe work piping interconnecting items of process plant. piping and instrumentation diagram (P&ID) schematic drawing defining the extent of equipment, piping and piping components and instrumentation. positive isolation complete separation of the plant/ equipment to be worked on from other parts of the system. pressurized plant facilities containing liquid or gases under pressure for treatment, processing or storage. proved isolation valved isolation where effectiveness of the isolation can be confirmed via vent/bleed points before breaking into system. short-duration work: work which does not extend beyond one operating shift. slip-ring a spacer ring installed in pipe work to facilitate the insertion of a spade.



spade (slip-plate) a solid plate for insertion in pipe work to secure an isolation. The spade must be of an appropriate material to withstand the line contents. spared equipment: equipment which is available to replace on-line equipment, e.g. during maintenance or in the event of breakdown. spectacle plate a combined spade and slip-ring. tagging temporary means of identifying a valve or other piece of plant. variation a situation where circumstances require the use of an isolation of a standard lower than the baseline isolation standard (or where relevant, the established company standard). Use of a variation is acceptable only when it is supported by a situation-specific risk assessment. Variations must be appropriately authorized and fully recorded.



APPENDIX I Some Fires or serious escapes of Flammable Gases or Liquids that could have been controlled by Emergency Isolation Valves Except where stated, the following accidents are taken from reference 10. 1 Leakages from Pump Glands or Seals Leakage from the seals of cold duty pumps on European Olefin Plants has been a not uncommon occurrence. One of the leaks which fired was on a Olefin Plant and it was a fortunate circumstance on this occasion that other plant above the pump was screened from the fire by a solid concrete floor. On another Olefin Plant there has been severe leakage from the seals of the C2 splitter reflux pumps on a number of occasions, giving rise to a cloud of vapor which, prior to the installations of the firewall and steam curtain in 1968, created a hazard on a Works road on 35 ft away. The vapor cloud from a major seal failure on one of the pumps in 1969 was contained and dispersed by means of the steam curtain. Another Company reported three major leaks from seals of cold ethylene pumps which occurred on different plants in 1968. The first resulted from the failure due to stress corrosion of one of two bolts which held the seal in position, allowing a large outflow of liquid which vaporized immediately and generated a large volume of Vapor. The vapor cloud was fortunately carried clear of adjacent flares and heaters by the wind blowing at the time, and did not ignite. It was estimated that 90,000 ft3 of vapor (3 tons) escaped in 20 minutes. The other two leaks both ignited near the pumps, apparently due to discharge of static electricity, the escape occurring in each case as a jet of vapor containing entrained droplets of liquid. Pumps handling C3 and C4 hydrocarbons at ambient temperature and moderate pressures have given little trouble with seal leaks on any Petrochemical plant, but there have been a number of gland failures of high pressure propylene injectors In 1956 there was an extensive fire, which caused serious injury to personnel as well as damage to plant. when gland studs failed and the cloud of vapor, escaping was ignited it the furnaces of a plant some 200 ft away. Following this fire the Injectors were resisted within a fire wall with steam ejectors, and were provided with remote isolation valves.



A fire occurred In another European Petrochemical plant in 1972 when the bearing and gland of a large hydrocarbon pump collapsed. The fire burnt for 6 hours until it was found possible to drain the vessel feeding the fire, but was successfully contained end did not spread to the rest of the plant. The pump which leaked was provided With remotely operated isolation valves, but as these were installed primarily for process use, the operating buttons were placed near the pumps and could not be reached. By the time a supervisor took a chance and dashed In to operate the buttons, the electric cables to the actuators had been burnt through and the valves did not operate (Ref. 5). 2 Leakage from Equipment Joints and Valves The gasket of a level connection on the base of a reactor of a North American Polypropylene Plant, ruptured suddenly in 1964, (Ref 71, releasing "large cloud of propylene vapor. Immediate steps were taken to reduce the pressure in the reactor by isolation of flows in, blow-down and increased cooling of the Jacket, while a deluge system was activated covering the area with a water spray to reduce the chance of electrostatic ignition of the vapor and additional water, giving a total of 4000- 5000 gpm, was applied by fire hoses, to help disperse the vapor cloud. The fire spread to neighboring units causing considerable material damage, but fortunately only minor injuries to personnel. 3 Leakage from Equipment Fittings Another company have reported a fire on the ethylene feed gas compressor of a polyethylene plant which occurred when an escape of gas from the vicinity of the discharge pressure gauge ignited. No one was injured and the fire was extinguished after 40 minutes by shutting off the feed to the compressor.



4 Spillages from Drain Valves Two dangerous incidents have occurred on a European Petrochemicals plant, both associated with blockage of drain valves by ice or hydrate formation, In the first of these the drain valve on a butadiene storage sphere stuck open after draining water, causing butadiene to spill in the compound. The valve was closed after heating with a steam lance and the spillage, which was not large, was dispersed with steam. The compound wall was provided with a steam curtain which was actuated, and tests with a combustible gas detector on the roadway beyond the wall gave negative results In the second incident an amount of butadiene estimated at several tons was found in the bund round a stock tank. This had come from the drain of a torque tube, which had most probably been blocked open by a piece of ice or hydrate which subsequently melted. The disaster at the Rhone Alpes refinery at Feyzin in January 1966 (Ref 8) started with a blockage in the drain line from a propane storage sphere, which was almost certainly due to ice or hydrate. The drain line had two valves, and the open end pointed straight down to the ground below the sphere. The standing Instruction on the draining operation was to open the valve next to the tank fully, and control the draining with the second valve, so leaving the opportunity to isolate the lank by the fist valve in the event of any trouble with the second. On this occasion the operator, from another refinery, controlled the draining on the first valve with the second one wide open. When the first valve blocked he opened It wider, until the obstruction gave way, and a jet of propane issued full bore through the 2 in line, striking the ground below and rebounding into the operators f, and also so knocking the handle off the valve. Subsequent attempts to replace the handle of the first valve, and to shut the second valve failed. The resultant cloud of vapor was ignited at a point some 500 ft. away, and the flame flashed back to the sphere and continued to burn under it until the stock, originally 348 tons, was almost exhausted. Because of lack of experience of the fire brigade combined with shortage of firewater, the sphere was left without any cooling water in the belief that the relief valves would prevent over pressuring. In the event the metal of the sphere failed due to overheating, and the vessel ruptured, spreading the fire to neighboring storage spheres. In all, 18 people were killed and 81 injured.



A fire on an ethylene plant at Varennes, Quebec, in April, 1968, was caused in a similar way to the Feyzin disaster. A choke occurred during draining, of an intermediate stage catchpot on the process gas compressor, the operator opened both valves in the drain fully and the choke cleared suddenly, releasing a cloud of hydrocarbon vapor. The operator could not get to either of the valves to shut them and the cloud ignited. Another company has reported incidents on two different refineries in which mal-operation of the water drain on a debutanizer reflux drum allowed the escape of a large quantity of butane which was ignited some distance way. In one incident the oil/water interface in the separator vessel was lost, and an intermediate collecting pot provided was not used. The butane escaping spread through the drainage system, and was ignited in the vicinity of hot oil pumps. In the other incident the draining was done through a closed system, relying on feeling the cooling of the pipe by expansion of the butane when the interface was reached, and on this occasion sufficient butane was released into the drainage system to blow the water seals, giving a large escape of vapor over the ground which again was ignited In the vicinity of hot oil pumps. A fire occurred on a butadiene plant at Kobuta, Pennsylvania (Ref. 9) when a 1/2 in. valve on a still bottoms pump was left open at the start up of the pump, allowing the escape of a cloud of C4 hydrocarbon vapor which was ignited at a frnace185 ft away. Two people were injured, and the still was severely damaged. 5 Tank Wagon Hose Connections Numerous failures of hose connections to liquefied hydrocarbon tank wagons, followed by ignition of the escaping vapor have been reported by the NFPA. Out of a total of 12 incidents, which occurred in the USA over the period 1954- 1963, there were 5 hose bursts during loading or offloading, 5 hoses were broken by driving the tank wagon off before disconnecting, 1 hose was cut by being run over when the tank wagon was moved slightly during offloading and 1 hose was burnt through by a fire which started on a pump. People were killed in 4 of the Incidents, and injured in 2 more. Sources of ignition where these were identified were variously the tank wagon engine, an office heater, a boiler house, a domestic cooker and a private car.



Excess flow valves prevented serious damage in one incident, but failed in two other incidents, in one case because the rate of escape was too low to operate them. In another incident the excess flow valves were found to be wired open (Ref. 101. 6 Spillages when Opening up Plant for Maintenance Work Emergency Isolation valves cannot as a rule, be Installed to isolate these spillages as they are liable to occur almost anywhere on a plant. However, they would have prevented a serious leak and fire which occurred in 1967. A fitter opened up a pump for maintenance; hot oil carne out and caught fire as the suction valve had not been isolated The oil was above its autoignition temperature and caught fire. The fire resulted in the death of three men and the destruction of the unit. As the pump glands were liable to leak, the leaking oil was above its autoignition temperature and the inventory was large, the case for an emergency Isolation valve was good and one was fitted on the rebuilt plant. (Ref. 11).



Characteristics of common valve types. The isolation circumstances should always determine the valve selection



Appendix II - Some Typical Installations 1 LPG Storage Figure (1), adapted from Ref 4, shows the arrangement recommended in Ref. 4. There is only one connection to the vessel below the liquid level. There is no flange, valve, instrument or drain under the shadow of the vessel, but a remotely controlled fire-safe isolation valve is located on the far side of a separation wall. All branches to pump suction lines, drain lines, sample points, instruments, etc, come after this valve. 2 An Olefin Plant The attached table lists all the likely sources of leakage on a European Olefin Plant, the nature of the material, its temperature and pressure and the inventory which will leak out if a leak occurs and it cannot be isolated. It also shows whether or not an emergency isolation valve has been fitted. The column headed 'A or B' refers to page 2 of the main report. 'A' indicates that the equipment is particularly liable to leak, for example very hot or cold pumps. In assigning this classification experience in the industry as a whole is taken into account, and not just experience on this plant. 'B' indicates that the equipment is less likely to leak, but if it does leak, a very large quantity of material will run out, and unless there is an emergency isolation valve, there will be no way of stopping it. Unless otherwise stated, emergency isolation valves are fitted only on the suction lines of pumps and other items of equipment. Delivery lines are normally protected by non-return valves.



Fig 1 General Arrangement of Piping to an LPG Storage Vessel



Remote Isolation Valves -European Olefin Plant



3 An Aromatics Plant The attached table lists all the likely sources of leakage on a European Aromatics Plant, the nature of the material, its temperature and pressure and the inventory which will leak out if a leak occurs and it cannot be isolated. A and B have the same meaning as in (2) above. All the points where emergency isolation valves are fitted, have been listed. In addition, a number of points where they are not fitted, and there is no intention to fit them, are noted for comparison.



Remote Isolation Valves - European Aromatics Plant



Isolation methods 1 Physical isolation of pressurized systems is primarily achieved using various combinations of valves, spades and blank flanges. 2 Pipelines often have long sections of pipe between valves. You may need to use techniques such as pipe plugs or pipe freezing to enable the isolation of intermediate sections of pipe for maintenance purposes, when it is not reasonably practicable to use primary devices (see Table below). Such techniques are not appropriate for standard use on process plant and should be subject to task-specific risk assessment and senior- level authorization. 3 A summary of isolation techniques is given in Table below. This indicates the key features and applications of each device.



Checklists for monitoring and review Compliance monitoring checklist – do we do what we say we do? The model list below should be tailored to suit your own isolation systems. It should not be assumed to be a comprehensive model. Forms should allow the checker to assign relative importance of non-conformances, record the passing of the findings up the management chain to agree/implement actions, etc.



Checklist for company review of adequacy of SMS for isolations This checklist provides a basis (structured around the HSG653 model) for reviewing the adequacy of your safety management system (SMS) for isolation activities. Select the questions appropriate to your site and its hazards. You should also assess whether any additional questions will be appropriate for your operation.

emergency isolation of chemical plants

Technology

process safety guide

hand operated emergency

situ exsitu sulfiding

use of control valves

particular purpose

operated valve

implied warranty

gbh enterprises