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Design Codes - PlantThis Technical Measures Document covers the design codes for plant. Reference ismade to relevant codes of practice and standards.

The relevant Level 2 Criteria are:

5.2.1.5(35)a,b, c5.2.1.5(37)5.2.1.6(38)e, f, g5.2.1.75.2.1.85.2.1.10(55)5.2.1.125.2.2.1

This Technical Measures Document includes the following sections:

Introduction to Plant Design

General PrinciplesInherently Safer DesignDesign Assessments

General Considerations

Temperature and PressureMaterials of ConstructionCorrosion/Erosion

Specific Equipment - Mechanical Design

Pressure VesselsOther Vessels (including Storage Tanks)Reactor DesignHeat Exchange EquipmentFurnaces/BoilersRotating Equipment (including seals, vibration control)

Structural Design Considerations (including lightning)Special Cases

Chlorine StorageAmmonia StorageLPG StorageHydrocarbons Storage

Construction of PlantCommissioning/Verification of Manufacture and Construction Standards

Reference is made to relevant codes of practice and standards where applicable.

Related Technical Measures Documents are Corrosion / Selection of Materials,Design Codes - Pipework, Explosion Relief, Relief Systems / Vent Systems,Training, Plant Modification / Change Procedures, Reaction / Product Testing.

Introduction to Plant designGeneral principles

The design of a process plant is a complex activity that will usually involve many

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different disciplines over a considerable period of time. The design may also gothrough many stages from the original research and development phases, throughconceptual design, detailed process design and onto detailed engineering designand equipment selection. Many varied and complex factors including safety, health,the environment, economic and technical issues may have to be considered beforethe design is finalised - See Technical Measures Document - Training.

At each stage it is important that the personnel involved have the correct combinationof technical competencies and experience in order to ensure that all aspects of thedesign process are being adequately addressed. Evidence of the qualifications,experience and training of people involved in design activities should be presentedin the Safety Report to demonstrate that the complex issues associated with designhave been considered and a rigorous approach has been adopted.

The process design will often be an iterative process with many different optionsbeing investigated and tested before a process is selected. In many occasions anumber of different options may be available and final selection may depend upon arange of factors.

The process design should identify the various operational deviations that mayoccur and any impurities that may be present. In the mechanical design, thematerials of construction chosen need to be compatible with the process materialsat the standard operating conditions and under excursion conditions. The materialsof construction also need to be compatible with each other in terms of corrosionproperties. Impurities which may cause corrosion, and the possibility of erosion alsoneed to be considered so that the detailed mechanical design can ensure thatsufficient strength is available and suitable materials of construction are selected forfabrication - See Technical Measures Document - Corrosion / Selection of Materials.

Detailed mechanical, structural, civil and electrical design of equipment comes afterthe initial process design which covers the steps from the initial selection of theprocess to be used, through to the issuing of process flow sheets. Such flowsheetswill include the selection, specification and chemical engineering design of theequipment. These are then used as the basis for the further detailed design.

This Technical Measures Document primarily considers the latter stages of thedetailed design processes and identifies the detailed design issues, codes andapplicable standards for the mechanical design of equipment.

Design factors are an essential component in order to give a margin of safety in thedesign. Design factors may be appropriate in either the mechanical engineeringdesign or in the process design where factors are often added to allow someflexibility in process operation. For mechanical and structural design the magnitudeof design factors should allow for uncertainties in material properties, designmethods, fabrication and operating loads.

Plant design should take account of the relevant codes and standards. Conformitybetween projects can be achieved if standard designs are used wheneverpracticable.

Codes and Standards

Modern engineering codes and standards cover a wide range of areas including:

Materials, properties and compositions;Testing procedures; for example for performance, compositions and quality;Preferred sizes; for example for tubes, plates and standard sections;Design methods and inspection and fabrication;Codes of practice for plant operation and safety.

Many companies have their own in-house standards which are primarily based onthe published codes, such as BS5500, with added extras which cover eithertechnical or contractual matters. In the safety report the base document for the inhouse codes should be clearly stated and the key safety related deviations orenhancements demonstrated so that the assessor can determine their adequacy.

A Safety Report should demonstrate that consideration has been given to theappropriate standards and codes of practice developed by legislators, regulators,professional institutions and trade associations. It should also demonstrate that forany equipment that is installed, the operating procedures, testing regimes andmaintenance strategies that are in place meet or exceed these requirements interms of safety performance.

Inherently Safer design

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The principles of inherently safer design are particularly important for major hazardplants and should be considered during the design stage. The Safety Report shouldadequately demonstrate that consideration has been given to the concepts. Somecompanies now have design procedures that require a review of designs and seekto ensure that inherently safer concepts have been addressed.

Inherently safe design should be considered during the design stage in an effort toreduce the hazard potential of the plant. Protective equipment installed ontostandard equipment to control accidents and protect people from theirconsequences is often complex, expensive and requires regular testing andmaintenance. Attempts should be made to reduce the requirement for suchprotective equipment by designing simpler and safer processes in the first instance.A number of approaches can be considered but basically an inherently safer plantcan be achieved by minimising the inventories of hazardous substances in storageand in process and hence the risk of a major accident can be significantly reduced.

Some of the techniques that can be considered are:

Intensification - this technique involves reducing the inventory of hazardousmaterials to a level whereby it poses a reduced hazard. This often meanscarrying out the reaction or unit operation in a smaller volume. It can be appliedto a wide range of unit operations including reactors, distillation and heatexchange but it may involve different mechanisms and approaches having tobe employed to the reaction chemistry and control systems;Substitution - this technique involves replacing a hazardous material (orfeature) with a safer one. For example, flammable solvents, refrigerants andheat transfer media can often be replaced by non-flammable or lessflammable (high boiling) materials. Often hazardous processes can also bereplaced by inherently safer processes that do not involve the use of hazardoussubstances or which operate at lower temperatures and pressures;Attenuation - using a hazardous material under less hazardous conditions. Forexample, quantities of chlorine, ammonia and LPG can be stored asrefrigerated liquids under atmospheric pressure rather than under pressure atambient temperature. Materials likely to form explosive dusts can be used andstored as slurries to minimise hazards;Limitation - affected by equipment design or changes to reaction conditionsrather than by adding on protective equipment. For example, the selection ofsome types of gaskets can reduce leak rates from equipment in the event of aleak hence limiting the hazard. Many runaway reactions can be prevented,either by changing the order of addition, reducing the temperature or changingother parameters;Simplification - simpler plants are friendlier and safer than complex plants andtherefore less likely to have a major accident caused by operator error;Knock-on effects - plants should be designed to reduce the likelihood ofincidents producing knock-on effects or domino effects in other areas;Avoid incorrect assembly - for critical equipment plants can be designed sothat incorrect assembly is difficult or impossible. Consideration should begiven to installing different types of connections on inlet/outlet pipework toavoid the possibility of wrong connections being made.

Further guidance on inherently safer design can be found in ̀ Cheaper, Safer Plants'- Kletz, T.A., 1984, IChemE, ISBN 0 8529 5167 1.

Design Assessments

A design should be subject to a number of detailed assessments throughout itsdevelopment. Evidence that some system of assessment has taken place shouldbe provided in the Safety Report. A number of different features can be examinedand assessed. Examples are given below:

Value engineering assessment;Energy efficiency assessment;Reliability and availability assessment;Hazard identification and assessment;Occupational health assessment;Environmental assessment.

These assessments all have a specific individual focus but in the context of COMAHit needs to be demonstrated that major accident hazards are not introduced as aresult of the assessments that are undertaken. For example any decisions taken asa result of a value engineering assessment that result in standby equipment not beinstalled, or equipment of a lesser specification being chosen should also

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demonstrate that the major accident hazard implications of such decisions havealso been considered.

A number of companies have developed detailed procedures for design studies thatincorporate many of these assessments into a formalised structure.

Evidence that Hazard identification and/or HAZOP studies have been carried outshould be provided as evidence that a design has been evaluated and carefullyconsidered before being installed on the plant. See Technical Measures Document -Plant Modification / Change Procedures.

General considerationsThere are several general topics that are common to the detailed mechanicaldesign of many types of equipment and these are discussed in greater detail below:

Temperature and Pressure;Materials of Construction;Corrosion/Erosion.

A number of potential hazards can be introduced if these are not given adequateconsideration. Loss of containment may occur due to leaks, equipment failure, fireor explosion and result in a major accident.

Temperature and pressureTemperature and pressure are two basic design parameters. Any equipment that isto be installed should be designed to withstand the foreseeable temperature andpressure over the whole life of the plant. The combination of temperature andpressure should be considered since this affects the mechanical integrity of anyequipment that is installed.

Temperature

In determining design temperatures a number of factors should be consideredincluding:

the temperature of the fluids to be handled;Joule-Thomson effect (The Joule-Thomson effect is the change in temperaturethat accompanies expansion of a gas without production of work or transfer ofheat. At ordinary temperatures and pressures, all real gases except hydrogenand helium cool upon expansion and this phenomenon is often utilised inliquefying gases);ambient temperatures;solar radiation; andheating and cooling medium temperatures.

Consideration needs to be given to the temperature of the fluids that are to behandled and any excursions in temperature that could occur as a result of the failureof temperature control systems. Account should be taken of foreseeable reactionsthat may occur that are likely to increase or reduce the heat input to the system.

The extremes of ambient temperature should be taken into account for plant situatedoutside buildings. Solar radiation on the exposed surface area of large storagetanks can significantly increase surface temperatures for storage vessels leading tosignificant thermal expansion of vessel contents. Likewise the low temperatures thatcan be achieved under conditions of snow, ice and wind, which can causesolidification of contents in vessels and pipelines, should also be considered.External facilities should be designed to accommodate the cycling of temperaturesbetween extreme weather conditions.

If secondary heating and cooling systems are employed then the maximum andminimum temperatures that can be achieved by these secondary systems shouldbe assessed assuming failure of any control systems associated with thesesystems. Care should be taken to ensure that the maximum temperature that can beachieved by heating oil systems or the minimum temperature that can be achievedby cryogenic cooling systems does not compromise the design of the equipment. Itshould not adversely affect the mechanical strength and hence integrity, or result inadditional process hazards as a result of overheating, decomposition or runawayreactions.

The strength of materials decreases with increasing temperature and therefore themaximum design temperature should take into account the strength of materialused for fabrication.

Evidence should be provided in the safety report that the process conditions and

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environment in which the equipment is to be utilised have been assessed and thatan appropriate design temperature has been selected.

Pressure

A vessel should be designed to withstand the maximum pressure to which it is likelyto be subjected in operation.

For vessels under internal pressure the design pressure is usually taken at thatwhich the relief valve is set. This is normally 5-10% above the normal workingpressure to avoid inadvertent operation during minor process upsets. Vesselssubjected to external pressure should be designed to resist the maximumdifferential pressure that is likely to occur. Vessels likely to be subjected to vacuumshould be designed for full negative pressure of 1 bar unless fitted with an effectiveand reliable vacuum breaker device.

Account should also be taken of foreseeable reactions which may occur that arelikely to increase the heat input to a system, or gas evolution and hence result inincreased or decreased temperatures and pressures. Where strongly exothermicreactions or runaway reactions are possible it may not be possible to adequatelydesign the equipment to withstand the maximum predicted temperature andpressure. Under such circumstances some form of pressure relief system may beappropriate in order to protect the equipment and prevent catastrophic failure of theequipment from occurring. See Technical Measures Document - Reaction / ProductTesting.

Pressure vessels should be fitted with some form of pressure relief device set at thedesign pressure of the equipment to relieve over-pressure in a controlled manner -see Technical Measures Documents - Relief Systems / Vent Systems, andExplosion Relief. The set pressure of a relief valve should be such that the valveopens when the pressure rise threatens the integrity of the vessel but not whennormal minor operating pressure deviations occur. It is necessary to balance anumber of factors in the selection of relief valve set pressures since if the potentialcause of pressure rise is runaway reaction then setting the relief pressure at a highlevel above the normal operating pressure may allow the reaction to reach a highertemperature and to proceed more rapidly before venting starts.

During the operation of the relief valve the pressure at the inlet to the relief valve (theoverpressure - this is usually taken to be no more than 10% for design purposes)can be expected to increase above the set point for the relief device. Theaccumulation in the vessel is the permitted increase in the system pressure abovethe design pressure in an emergency overpressure situation. The maximumallowable accumulated pressure (MAAP) is specified within the various codes andthis should be taken into account when the relief valve set point is selected.Normally the relief valve set point is set below or up to the maximum designpressure which allowing for the overpressure during a relief event ensures that theoverall pressure is below the MAPP. Specific guidance on the recommendations forpressure relief protective devices is given in Appendix J of BS 5500 : 1997. Othercodes permit higher MAAPs in certain circumstances.

Discharge of hazardous substances from relief systems under emergencyconditions should be routed to secondary containment vessels or to safe locationsso that additional hazards to personnel or equipment and the possible escalation ofan incident does not occur. This should be considered as part of the mechanicaldesign of the equipment if such systems are to be employed.

Evidence should be provided in the safety report that the process conditions andenvironment in which the equipment is to be utilised have been assessed and thatan appropriate design pressure has been selected.

Evidence should be provided in the Safety Report that the relief systems have beensuitably designed and consideration has been given to the discharge locations.Secondary containment facilities may be appropriate for discharge of relief streams.Documentation for relief streams should be available for inspection.

Consideration should be given to the possibility of pressure cycling in equipmentand subsequent failure of the equipment due to metal fatigue

Materials of constructionAnother important consideration in mechanical design is the selection of thematerial of construction.

In some cases the available materials of construction may constrain the designtemperatures and pressures that can be achieved and limit the design of the

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equipment.

The most important characteristics that should be considered when selecting amaterial of construction are summarised below:

Mechanical Properties;

Tensile strength;Stiffness;Toughness;Hardness;Fatigue resistance;Creep resistance;

The effect of low and high temperatures on the mechanical properties;Corrosion resistance;Ease of fabrication;Special properties - electrical resistance, magnetic properties, thermalconductivity;Availability in standard sizes;Cost.

The selection of a suitable material of construction is often carried out by disciplinessuch as process engineers. The advice of specialist materials engineers should besought in the event of difficult applications being identified.

The Safety report should contain evidence that the materials of construction thathave been selected are compatible with the process fluids to be handled and thedesign conditions that have been chosen.

Corrosion/erosionIf materials to be used in the process are corrosive then this should be taken intoaccount in the plant design and layout. Materials of construction should be carefullyselected, protected where possible and regularly inspected if the presence ofcorrosive materials or a corrosive environment is anticipated.

The layout of plant and equipment for corrosive materials is discussed in ̀ Safetyand Management - A Guide for the Chemical Industry' - the Association of BritishChemical Manufacturers, 1964. Printed by W.Heffer & Sons.

This topic is covered fully in the Technical Measures Document - Corrosion /Selection of Materials. See also Causes of Plant Failure.

General guidance on corrosion allowances for pressure vessels is given in BS5500. The standard recommends that all possible forms of corrosion such aschemical attack, rusting, erosion and high temperature oxidation are reviewed, thatparticular attention be paid to impurities and to fluid velocities, and that where doubtexists corrosion tests should be carried out.

The life of equipment subjected to corrosive environments can be increased byproper consideration of design details. Equipment should be allowed to drain freelyand completely and the internal surfaces should be smooth and free from locationswhere corrosion products can accumulate. Fluid velocities should be high enough toprevent deposition but not so high as to cause erosion.

The corrosion allowance is the additional thickness of metal added to allow formaterial lost by corrosion and erosion or scaling. For carbon and low-alloy steelswhere severe corrosion is not expected a minimum allowance of 2 mm is oftenused, where more severe corrosion is anticipated an allowance of 4 mm is oftenused. Most design codes and standards specify a minimum allowance of 1 mm.

A large proportion of failures in process plant and vessels are due to corrosion. It isoften the prime cause of deterioration and may occur on any part of a vessel. Theseverity of the deterioration is strongly influenced by the concentration, temperature,and nature of the corrosive agents in the fluids and the corrosion resistance of theconstruction materials. Corrosion may be of a general nature with fairly uniformdeterioration, or may be very localised with severe local attack. Erosion is oftenlocalised especially at areas of high velocity or impact.. Occasionally corrosion anderosion combine to increase rates of deterioration.

Erosion is a particular problem for solids handling in pipework, ducts and dryers. Itoccurs primarily at sites where there is a flow restriction or change in directionincluding valves, elbows, tees and baffles. Erosion is promoted by the presence ofsolid particles, by drops in vapours, bubbles in liquids or two-phase flow. Conditions

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that can cause severe erosion include pneumatic conveying, wet steam flow,flashing flow and pump cavitation. If erosion is likely to occur then more resistantmaterials should be specified or the material surface protected in some way. Forexample plastic inserts can be used to protect erosion-corrosion at the inlet to heatexchanger tubes.

See also BS 5493: 1977 - Code of Practice for protective coating of iron and steelstructures against corrosion.

Specific equipment - Mechanical designDesign issues, codes and standards applicable to several general categories ofequipment have been identified and are discussed below in further detail:

Pressure Vessels;Other Vessels (including Storage Tanks);Reactor Design;Heat Exchange Equipment;Furnaces and Boilers;Rotating Equipment.

Pressure vesselsIntroduction

There are numerous texts available on the details of pressure vessel designhowever the basis of the design of pressure vessels is the use of appropriateformulae for vessel dimensions in conjunction with suitable values of designstrength.

Pressure vessels can be divided into ̀ simple vessels' and those that have morecomplex features. The relevant standards and codes provide comprehensiveinformation about the design and manufacture of vessels and vessel design andfabrication is an area well covered by standards and codes. In general termsoutright failure of a properly designed, constructed, operated and maintainedpressure vessel is rare.

Design and manufacture is normally carried out to meet the requirements ofnational and international standards with one of the earliest being the AOTC1939/48/58 ̀ Rules for the construction, testing and scantlings of metal arc weldedsteel boilers and other pressure vessels'. The other principal standards in the UKwere BS 1500 and BS 1515, both of which are now withdrawn and superseded byBS 5500. The other most commonly used design code is ASME VIII. However it isunusual, though not unknown, for companies and operators to employ their owndesign codes.

Generally pressure vessel design codes covers equipment such as reactors,distillation columns, storage drums, heaters, reboilers, vaporisers, condensers,heat exchangers, bullets, spheres etc. Basically any equipment with a "shell" thatmay experience some internal pressure is covered. This section does not coverpiping systems (see separate Technical Measures Document on Design CodesPipework), atmospheric storage tanks and rotary machines. These are consideredin further detail later.

Simple vessels

A simple pressure vessel does not have any complicated supports or sections andthe ends are dished. The main code for simple vessels is BS EN 286-1:1991.`Simple unfired pressure vessels designed to contain air or nitrogen'. All aspects ofdesigning and manufacturing the vessel are covered in this code.

Complex vessels

Traditionally the two principal codes and standards BS 5500 and ASME VIII, areemployed in the design and manufacture of pressure vessels within the UnitedKingdom. Importantly both of these demand adherence to satisfaction in the designand manufacturing process of an independent inspection authority. This authority isresponsible for adherence during both the design and construction phases inaccordance with the standard or code.

Design considerations

Factors that should be taken into account in the design process for pressurevessels include:

Internal and external static and dynamic pressures;Ambient and operational temperatures;

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Weight of vessel and contents;Wind loading;Residual stress, localised stress, thermal stress etc.;Stress concentrations;Reaction forces and moments from attachments, piping etc;Fatigue;Corrosion/erosion;Creep;Buckling.

Pressure vessels are subject to a variety of loads and other conditions that causestress and can result in failure and there are a number of design featuresassociated with pressure vessels that need to be carefully considered.

Discontinuities such as vessel ends, changes of cross-section and changesof thickness;Joints (bolted and welded);Bimetallic joints;Holes and openings;Flanges;Nozzles and connections;Bolt seating and tightening;Supports and lugs.

Consideration should also be given to other parts of the vessel not directly within thepressure envelope, but critical to vessel integrity i.e. any failure which could lead tobreach of the pressure boundary e.g. vessel skirt or support legs. Other factorswhich require careful consideration include; a means of in-service periodicexamination i.e. a means of determining the internal condition of the vessel by theprovision of access openings; a means of draining and venting the vessel; andmeans by which the vessel can be safely filled and discharged.

Materials of constructionVesselsMaterials used for the manufacture of pressure vessels should haveappropriate properties for all operating conditions that are reasonablyforeseeable, and for all test conditions. They should be sufficiently chemicallyresistant to the fluid contained and not be significantly affected by ageing. Thematerials should be selected in order to avoid corrosion effects when thevarious materials are put together.

Steel is the most common material of construction, including mild steel, lowalloy steel, and stainless steel. It is often operating process temperature thatdetermines the material used, but other equally important factors such ascorrosion/erosion allowance, low temperature application etc. can determineselection.

Clearly in the choice of material selection it is important that the materialselected not only has properties which are suited to that particular application,but also that its suitability with regard to fabrication is also taken into account.Several different methods are used to construct pressure vessels, mosthowever are constructed using welded joints.

Where an American, British or European code is used for vessel design andspecific materials are quoted within the code it is important that the correctmaterials are used in order that the design is not invalidated.LinersWhere carbon steel will not resist expected corrosion or erosion or couldcause contamination of the product, vessels may be lined with other metals ornon-metals. A lined vessel is usually more economical than one built of solidcorrosion resistant material. Metallic liners are installed in various ways. Theymay be an integral part of the plate material rolled or bonded before fabricationof the vessel, or they may be separate sheets of metal fastened by welding.Metallic liners may be made of ferritic alloy, monel alloy, nickel, lead or anyother metal resistant to the corrosive agent. Non-metallic liners may be used toresist corrosion and erosion or to insulate and reduce the temperature on thewalls of a pressure vessel. The most common materials are reinforcedconcrete, insulating material, carbon brick, rubber, glass and plastic.Internals

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Many pressure vessels have no internals. Others have internals such asbaffles, trays, mesh or strip type packing, grids, bed supports, cyclones, pipecoils, spray nozzles, quench lines, agitators etc. Large vessels may haveinternal bracing and ties and most vacuum vessels have either internal orexternal stiffening rings. Heat exchangers have internal tube bundles withbaffle and support plates. These internals may be made from a wide range ofmaterials but care should be taken that the materials selected for the internalsare compatible with the materials chosen for fabrication of the maincomponents.

Failure modesPressure vessels are subject to a variety of loads and other conditions that causestress and in certain cases may cause serious failure. Any design should take intoaccount the most likely failure modes and causes of deterioration. Deterioration ispossible on all vessel surfaces in contact with any range of organic or inorganiccompounds, with contaminants, or fresh water, with steam or with the atmosphere.The form of deterioration may be electrochemical, chemical, mechanical orcombinations of all.

Mechanical Failure The most common causes of mechanical failure in process plant are:

Faulty materials;Faulty fabrication and assembly;Excessive stress;External loading including reaction forces;Overpressure;Overheating;Mechanical and thermal fatigue;Mechanical shock;Brittle failure;Creep;Corrosion failure.

Corrosion FailureThe most common corrosion mechanisms are:

General corrosion;Crevice corrosion;Corrosion pitting;External corrosion including corrosion beneath lagging;Stress corrosion cracking;Corrosion fatigue.

For more information see Technical Measures Document - Corrosion / Selection ofMaterials.

Design Codes and StandardsTwo principal codes and standards are employed in the design and manufacture ofpressure vessels - the American ASME VIII system and BS 5500 in the UK.Importantly both of these demand adherence to satisfaction in the design andmanufacturing process of an independent inspection authority. This authority isresponsible for adherence during both the design and construction phases inaccordance with the standard code. The codes and standards cover design,materials of construction, fabrication (manufacture and workmanship), inspectionand testing, and form the basis of agreement between the manufacturer andcustomer and the appointed independent inspection authority. These codes relate tovessels fabricated in carbon and alloy steels and aluminium.

Computer programmes to aid the design of vessels to BS 5500 and the ASME VIIIcodes are commercially available.

Non-metallic materials of constructionAlthough the majority of pressure vessels are constructed from metallic compoundspressure vessels can also be constructed from materials such as glass reinforcedplastic (GRP), or fibre reinforced plastic (FRP). The main relevant standard is BS4994:1987 - Specification for Design and Construction of Vessels and Tanks inReinforced Plastics.

Other Vessels (including storage tanks)Some vessels that are used are not designated as pressure vessels. Thedescription atmospheric storage is applied to any tank that is designed to be used

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description atmospheric storage is applied to any tank that is designed to be usedwithin a limited range of atmospheric pressure, either open to the atmosphere orenclosed.

Vertical storage tanks with flat bases and conical roofs are often used for thestorage of liquids at atmospheric pressure and may vary in size considerably. Themain load to be considered in the design of such tanks is the hydrostatic pressureof the liquid contained within the tank. However consideration should also be givento other parameters and the wind loading and any likely snow loading should alsobe considered.

The design of atmospheric storage tanks in general is governed by API Std 620Design and construction of large, welded, low-pressure storage tanks and API Std650 Welded steel tanks for oil storage.

Tanks should be suitable for their operational duty and all reasonably expectedforces such as tank contents, ground settlement, frost, wind and snow loadings,earthquake and others as appropriate. The selection of the type of tank to be usedfor a particular duty will be influenced by considerations of safety, technical suitabilityand economy. The safety considerations are usually related to fire hazards which inturn are dependent on the physical properties of the stored material e.g. flash point,vapour pressure, electrical conductivity etc.

API Standard 2000 gives guidance on the design of vents to prevent pressurechanges that would otherwise occur as a result of temperature changes or thetransfer in and out of liquids. Excessive loss of vapours from vent systems mayresult from outbreathing and may present a hazard.

Reactor designReactors are often the centre of most processes and their design is of utmostimportance when considering the safety hazards of a plant. Reactors are most oftenconsidered as pressure vessels and the mechanical design should be inaccordance with the codes and standards described earlier.

Reactor design should minimise the possibility of a hazardous situation developingand provide the means for dealing with a hazardous situation should it develop.Arrangements for venting, pressure relief and blowdown need to be adequatelyaddressed in the design. For relief systems consideration should be given to theimplications of the release of reactor contents and containment and control systemsmay be necessary to prevent a hazardous situation from developing as a result ofthe discharge of a relief system.

The design of the reactor may affect the efficiency of the reaction process and hencethe generation of by-products and impurities. The effectiveness of the reaction stepwill often determine the requirement for and complexity of downstream separationprocesses. In addition, low conversions may result in large recycles being required.

Many different types of reactor system are available and some of the importantcriteria to consider are given below:

Addition of reactants - the order and rate of addition of the reactants may affect therate of reaction and the generation of by-products. The generation of unstable by-products or excessive reaction rates may increase the potential for a hazardoussituation to develop. The position of addition of reactants may also be important -sub-surface and directly into an intimate mixing zone within the reactor may result inthe minimisation of the generation of reaction by-products;

Mixing - the agitation system selected for the reactor (if appropriate) maydirectly influence the efficiency of the reaction and hence the generation of by-products. Consideration should also be given to the consequences of agitationfailure in the design of the reaction system. Methods for detecting the failure ofa mixing/agitation system and/or stopping the flow of reactants into the reactormay be appropriate especially if there is the possibility of two phases formingon agitation failure which may react exothermically/vigorously when agitation isrecommenced. See Technical Measures Documents - Reaction / ProductTesting and Control Systems;Heat removal - for exothermic reactions the control of the reaction system andthe heat removal systems should be carefully considered. Considerationshould be given to the modes of failure of the control and cooling systems toensure that the hazards of a runaway exothermic reaction are minimised;Phase - the reaction may take place in the gas, liquid or sometimes solidphase. The way in which the reactants are brought into contact may influencethe efficiency of the reaction and introduce additional hazards into the reactionsystem;

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Catalysts - a reaction may require a catalyst in order to promote the requiredreaction. However the catalyst may present additional hazards andconsideration should be given to the selection of the catalyst system in order tominimise the risks associated. If a catalyst is required then additionalseparation steps to remove the catalyst may subsequently be required.

The safety report should describe how the reactor system has been designed withthe principles of safe design in mind and how the selection of the mixing, chemicaladdition systems and relief systems have been selected in order to minimise thepotential for a major accident.

Heat exchangers/reboilersThe transfer of heat between two process streams is a common activity andrequirement on a chemical plant. A number of direct or indirect techniques can beemployed. The most common form of equipment used to transfer heat is a heatexchanger which can be designed in many different shapes, sizes andconfigurations necessary to obtain the required heat transfer between one streamand another. A number of different heat transfer operations are possible with someinvolving a change of phase of one or more component. Heating, cooling,evaporation or condensation may all need to be considered and the equipmentdesigned accordingly to account for the differing requirements.

The basic design is commenced by an approximate sizing of the unit based onassumptions made concerning the heat transfer characteristics of the substancesinvolved and the anticipated materials of construction. More detailed calculations arethen required to confirm and refine the original design and to identify an optimumlayout. Once the process design has been completed the mechanical design of theunit can then be carried out.

The design of heat exchangers is covered in many texts. A common reference fordesign engineers however is ̀ Process Heat Transfer - D.Q.Kern, InternationalStudent Edition, McGraw Hill, ISBN 0070341907.

The mechanical design features, fabrication, materials of construction and testing ofshell and tube heat exchangers is covered by ̀ BS 3274: 1960- Tubular HeatExchangers for General Purposes'.

The standards of the American Tubular Heat Exchanger Manufacturers Association(TEMA standards) are also widely used. Many companies also have their ownstandards to supplement these various requirements.

The TEMA standards give the preferred shell and tube dimensions, the design andmanufacturing tolerances, corrosion allowances and the recommended designstresses for materials of construction.

Design temperatures and pressures for exchangers are usually specified with amargin of safety beyond the conditions normally anticipated. Typically the designpressure may be 170 kPa greater than the maximum anticipated during operation orat pump shutoff, and the temperature is commonly 14°C greater than the maximumanticipated service temperature.

Major problems associated with heat exchanger design that may affect safetyinclude fouling, polymerization, solidification, overheating, leakage, tube vibrationand tube rupture. The shell of an exchanger is normally a pressure vessel andshould be designed in accordance with the relevant pressure vessel design code -BS 5500 or ASME VIII (Rules for construction of pressure vessels, Division 1). Morespecific guidance is given in API RP 520:1990.

Special consideration needs to be given to the preventing overheating within heatexchanger equipment especially if sensitive materials are involved, for examplematerials which may undergo exothermic decomposition.

The safety report should demonstrate that heat exchange equipment has beendesigned and maintained in accordance with the relevant codes and standards andthat consideration has been given to the various failure modes that could occur andthe implications of such events. It should be demonstrated that wherever possiblemeasures have been taken to prevent, control or mitigate the consequences of suchevents by the appropriate selection of materials of construction, fabrication methods,instrumentation and control or others.

Furnaces/boilersFurnaces and boilers are items of equipment that are often found as part of processplant and are used for a variety of purposes such as waste heat recovery, steam

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generation, destruction of off-gases etc.

The design may involve the interaction of many different variables includingwater/steam circulation systems, fuel characteristics (liquid, gaseous or solid fuels),ignition control systems, heat input and heat transfer systems.

The design of the furnace or boiler enclosure should be able to withstand thethermal conditions associated with the system and specialist designs are oftenrequired. Many codes and standards exist for boiler design.

The elimination of hazards in burner design is a fundamental design requirement.Explosions can occur during start up if ignition design is not carefully considered.Leaks of fuel can cause explosive atmospheres when ignition is attempted. Forthese reasons consideration should be given to inerting /ventilation systems prior toignition sequences to ensure explosive atmospheres are not present.

Isolation systems should be adequately designed to ensure leakage of fuel doesnot occur. Double block and bleed valves on fuel lines can be considered. Relianceshould never be placed upon single valves for isolation. Careful consideration of theconfiguration of the pipework should also be considered to ensure that the flow offuel into the system after the flame has failed or valves have been closed isminimised.

Purging facilities are essential to ensure that the firing space is free from aflammable atmosphere prior to start-up ignition.

A safety report should demonstrate that any furnace/boiler system is designed andmaintained to the relevant codes and standards and that consideration has beengiven to the major hazards associated with the start-up, shutdown and operation ofthe equipment in terms of the fire and explosion potential of such systems. It shouldbe demonstrated that the risks of an explosion occurring have been minimised bythe design of the burner control management system and the layout and design ofthe fuel supply systems.

Rotating equipmentProcess machines are particularly important items of equipment in process plantsand in relation to pressure systems since they are required to provide the motiveforce necessary to transfer process fluids (liquids, solids and gases) from one areaof operation to another. A machine system is any reciprocating or rotating device thatis used to transfer or to produce a change in properties within a process plant.Examples may include items such as pumps, fans, compressors, turbines,centrifuges, agitators etc.

This type of equipment is a potential source of loss of containment. In addition dueto the rotating/vibrating nature of such equipment pressure and flow fluctuations maybe caused and these can affect the operation of other systems.

The basic requirements to define the application for pumps, fans and compressorsare usually the suction and delivery pressures, the flow rate required and thepressure loss in transmission. Special requirements for certain industrial sectorsmay also impose restrictions on the materials of construction to be used or the typeof device that can be considered. Many designs have become standardised basedon experience and numerous standards (API standards, ASME standards, ANSIstandards) have become available. These standards often specify design,construction and testing details such as material selection, shop inspection andtests, drawings, clearances, construction procedures etc

The choice of material of construction is dictated by consideration of corrosion,erosion, personnel safety and containment and contamination.

PumpsMany pumps are of the centrifugal type, although positive displacement types (suchas reciprocating and screw types) are also used. Pumps are available throughout avast range of sizes and capacities and are also available in a wide range ofmaterials including various metals and plastics. Sealing of pumps is a veryimportant consideration and is discussed later. The primary advantage of acentrifugal pump is its simplicity. Pumps are particularly vulnerable to mal-operationand poor installation practices. Proper installation and high quality maintenance isessential for safe operation.

Problems associated with centrifugal pumps can include bearing and seal failure.Cavitation (the collapse of vapour bubbles in a flowing liquid leading to vibration,noise and erosion) and dead head running (attempting to run a pump without anoutlet for the fluid, for example against a closed valve) can also result in damage to

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the pumping equipment. Misalignment between pump and motor is also a commoncause of catastrophic failure.

Seal-less or ̀ canned pumps' are often used where any leakage is consideredunacceptable. In a canned pump the impeller of the pump and the rotor of the motorare mounted on an integral shaft which is encased so that the process fluid cancirculate in the space which is normally the air gap of the motor.

Key parameters for pump selection are the liquid to be handled, the total dynamichead, the suction and discharge heads, temperature, viscosity, vapour pressure,specific gravity, liquid corrosion characteristics, the presence of solids which maycause erosion etc.

CompressorsBoth positive displacement and centrifugal compressors are used in the processindustry. They are complex machines and their reliability is crucial. It is veryimportant that they are maintained to high operational standards. Centrifugalcompressors are by far the most common although compression is generally lowerthan that given by reciprocating machines. They are used in both process gas andrefrigeration duties. On centrifugal compressors some of the principal malfunctionsinclude rotor or shaft failure, bearing failure, vibration and surge. Reciprocatingcompressors are utilised for higher compression requirements. They may be eithersingle or multi-stage units. Air compressors for dry air require special considerationand specific codes and standards exist.

FansThe main applications for fans are for high flow, low pressure applications such assupplying air for drying, conveying material suspended in a gas stream, removingfumes, or in condensing towers. These units can be either centrifugal or axial flowtype. They are simple machines but proper installation and maintenance is requiredto ensure high reliability and safe operation.

VibrationOne of the main causes of failure of rotating equipment is vibration. This oftencauses seal damage or fatigue failure and subsequent leakage and can result in amajor accident. Numerous factors can result in vibration occurring includingcavitation, impeller imbalance, loose bearings and pulses in the pipe. ASMEstandards recommend that pumps should be periodically monitored to detectvibration that should normally fall within prescribed limits as determined by themanufacturer. This should be initially confirmed on installation and then periodicallychecked. If measured levels exceed prescribed values then preventativemaintenance is required and should be performed. By collection and analysis ofvibration signatures of rotating equipment it is possible to identify whichcomponents of the system are responsible for particular frequencies of the vibrationsignal. It is then possible to identify the component that is deteriorating andresponsible for the vibration that is occurring.

SealsSeals are very important and often critical components in large rotating machineryand in systems which are flanged/jointed such as heat exchangers or pipeworksystems. Failure of a sealing arrangement can lead to loss of containment and apotential for a major accident. Numerous different types of sealing arrangementexist for rotating equipment. There are many factors that govern the selection ofseals for a particular application including the product being handled, theenvironment which the seal is installed in, the arrangement of the seal, theequipment the seal is to be installed in, secondary packing requirements, seal facecombinations, seal gland plate arrangements, and main seal body etc. Thematerials used for seals should always be compatible with the process fluids beinghandled.

There are three principal methods of sealing the point at which a rotating shaftenters a pump, compressor, pressure vessel or similar equipment:

Conventional stuffing box with soft packing;Hydrodynamic seal, where rotating vanes keep the shaft free;Mechanical seals.

Stuffing boxes and glands with packing are commonly used. Some product leakageis normal both lubricating and cooling the packing material. The chief advantages ofthis type of sealing arrangement are the simplicity and the ease of adjustment orreplacement. The disadvantages are the necessity of frequent attention and the

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inherent lack of integrity of such a system.

Mechanical seals are the next most commonly employed arrangement. They areused in applications where a leak tight seal of almost any fluid is required.Mechanical seals find their best application where fluids should be contained undersubstantial pressure. They can range from the simplest single seal arrangement tocomplicated sophisticated double seals with monitoring of the interspace. Somemechanical seals are assemblies of great complexity and consist of componentsmanufactured to very high tolerances. They are often fitted as complete cartridge typeunits. Some sealing arrangements require constant lubrication often from theprocess fluid itself whilst others require external lubrication arrangements.

Maintenance, inspection and monitoringPlant equipment may be monitored during commissioning and throughout itsoperational life. This monitoring may be carried out on the basis of performance orcondition or both. Performance monitoring is not discussed in detail in thisTechnical Measures Document. However the predominant techniques andparameters employed are flow, pressure, temperature, power etc. The alternative toperformance monitoring is condition monitoring of which there are a number oftechniques. The aim of such techniques is to identify deterioration and pre-emptimminent failures and so secure reliable/available plant, particularly for productionand safety critical items. Some of these techniques are identified below:

Vibration monitoring;Shock pulse monitoring;Acoustic emission monitoring;Oil analysis.

Critical machinesAll machine systems should be assessed according to the hazard presented if themachine or any associated protective system should fail.

Machine systems that have been assessed to present unacceptable consequencesif the machine or protective system should fail may be classified as a ̀ CriticalMachine System' and given specific attention during operation including additionalmaintenance and monitoring.

Assessments should be based on:

Potential consequences of any loss of containment);Potential consequences of the failure of the process;Potential damage caused by mechanical failure.

Structural design considerationsStructures are required to provide support for plant and should be able to withstandall foreseeable loadings and operational extremes throughout the life of the plant.Failure of any structural component could lead to initiation of a major accident. Forfull guidance on Design Codes - Buildings / Structures see relevant TechnicalMeasures Document. Structural design should take into account natural events suchas wind loadings, snow loadings and seismic activity and also plant excursions

Maps showing the wind speeds to be used in the design of structures at locations inthe UK are given in British Standards Code of Practice BS CP 3: 1972: Basic Data forthe Design of Buildings, Chapter V Loading: Part 2 Wind Loads. Typical values arearound 50 m/s (112 miles per hour). The code of practice also gives methodsestimating the dynamic wind pressure on buildings and structures of variousshapes.

LightningProtection against lightning strikes on process plant located outside buildings isrequired since lightning is a potential ignition source especially for fires involvingstorage tanks. Lightning protection should be provided and guidance is available inBS 6651 : 1992 Code of Practice for Protection of Structures against Lightning.

See also Technical Measures Document - Earthing.

Special casesFor the following substances general published codes exist giving full designdetails for storage and handling.

Chlorine storage

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The design of systems for chlorine requires special consideration since chlorine ishighly toxic and, if wet, also very corrosive.

Chlorine is usually stored under pressure at atmospheric temperature, but may alsobe stored fully refrigerated (-34°C) at atmospheric pressure.

A number of publications are dedicated to the handling of chlorine and specificguidance is given in:

HS(G)28 Safety advice for bulk chlorine installations, HSE, 1999.This guidance was originally published in 1986 and has been substantiallyrevised.The HS(G)28 document has replaced earlier guidance from the CIA and theChlorine Institute which included:

Chlorine Manual, 1986, Pamphlet 1, Chlorine Institute.Non-refrigerated Liquid Chlorine Storage, 1982, Pamphlet 5, Chlorine Institute.Refrigerated Liquid Chlorine Storage, 1984, Pamphlet 78, Chlorine Institute.Code of Practice for Chemicals with Major Hazards: Chlorine, (the ChlorineCode), CIA, 1975.Guidelines for Bulk Handling of Chlorine at Customer Installations (the CIAChlorine Storage Guide), CIA, 1980/9.

Also see:

HS(G)40 Safe handling of chlorine from drums and cylinders, HSE.CS16 Chlorine vaporisers, HSE.

The Euro Chlor organisation is an affiliate of the European Chemical IndustryCouncil (CEFIC) and represents European chlorine producers at 85 plants in 19countries. Euro Chlor produces a number of publications. Further details can beobtained via the website http://www.eurochlor.org .

ST 79/82, ̀ Choice of materials of construction for use in contact with chlorine',Euro Chlor.This is a typical industry sector standard containing specific guidance on theuse of materials of construction for chlorine systems.

Ammonia storageAnhydrous ammonia, boiling point -33°C, is normally stored as a liquid either underpressure or at atmospheric pressure in refrigerated facilities.

A number of publications are dedicated to the handling of ammonia and specificguidance is given in:

HS(G)30 Storage of anhydrous ammonia under pressure in the UK : spherical andcylindrical vessels, HSE, 1986 (Not in current HSE list).

Gives advice for the appropriate materials of construction for ammonia storagevessels.

CIA Refrigerated Ammonia Storage Code

CIA Code of Practice for the storage of anhydrous ammonia under pressure in theUK: Spherical and cylindrical vessels. (The CIA has withdrawn this document).

CIA Guidance for the large scale storage of fully refrigerated anhydrous ammonia inthe UK.

CIA Guidance on transfer connections for the safe handling of anhydrous ammoniain the UK.

LPG storagePropane and Butane are referred to as liquefied petroleum gas (LPG) in accordancewith BS 4250: Specification for commercial butane and propane. Fully refrigeratedstorage is required at atmospheric pressure and at the boiling points of thesubstances concerned. LPG can also be stored under pressure in horizontalcylindrical or spherical pressure vessels.

HS(G)34 Storage of LPG at fixed installations, HSE, 1987.

HS(G)15 Storage of liquefied petroleum gas at factories, HSE.

CS5 Storage of LPG at fixed installations, HSE.

LPGA CoP 1 Bulk LPG storage at fixed installations. Part 1 : Design, installation and

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operation of vessels located above ground, 2000.

LPGA CoP 1 Bulk LPG storage at fixed installations. Part 2: Small bulk propaneinstallations for domestic and similar purposes, 2000.

LPGA CoP 1 Bulk LPG storage at fixed installations. Part 3 : Periodic inspection andtesting, 2000.

LPGA CoP 1 Bulk LPG storage at fixed installations. Part 4 : Buried/mounded LPGstorage vessels, 2000.

LPGA CoP 15 Valves and fittings for LPG service, Part 1 Safety valves, 2000.

LPGA CoP 17 Purging LPG vessels and systems, 2000.

EEMUA 147. Recommendations for the design and construction of refrigeratedliquefied gas storage tanks.

Liquefied petroleum gas. IP Model code of safe practice: Part 9.

Hydrocarbons storageA number of standards and codes exist for the storage of petroleum products andflammable liquids generally. A range of different main types of storage tanks andvessels for liquids and liquefied gases can be considered:

Atmospheric storage tanks:Low pressure storage tanks;Pressure or refrigerated pressure storage tanks;Refrigerated storage tanks.

The relevant standards and codes are:

API Std 620 Design and construction of large, welded, low-pressure storage tanks,American Petroleum Institute, 1990.

API Std 650 Welded steel tanks for oil storage, American Petroleum Institute, 1988.

BS 2594 : 1975 Specification for carbon steel welded horizontal cylindrical storagetanks.

BS 2654 : 1989 Specification for manufacture of vertical steel welded non-refrigerated storage tanks with butt-welded shells for the petroleum industry.

BS 4741: 1971 Specification for vertical cylindrical welded steel storage tanks for lowtemperature service: single-wall tanks for temperatures down to -50°C.

BS 5387: 1976 Specification for vertical cylindrical welded steel storage tanks for lowtemperature service: double-wall tanks for temperatures down to -196°C.

BS 7777 : 1993 Flat-bottomed, vertical, cylindrical storage tanks for low temperatureservice.

This BS supersedes BS 4741:1971 and BS 5387: 1976 both of which are withdrawn.

BS 799: 1972 Oil Burning Equipment, Part 5 Specification for oil storage tanks.

NFPA 30: 1990 Flammable and Combustible Liquids Code.

IP MSCP Part 3, 1981 Refining Safety Code.

HS(G)50 The storage of flammable liquids in fixed tanks (up to 10000 cu. m in totalcapacity), HSE, 1990.

HS(G)51 Storage of flammable liquids in containers, HSE, 1998.

HS(G)52 The storage of flammable liquids in fixed tanks (exceeding 10000 cu. m intotal capacity), HSE, 1991.

HS(G)140 Safe use and handling of flammable liquids, HSE, 1996.

HS(G)176 The storage of flammable liquids in tanks, HSE, 1998.

CS2 The storage of highly flammable liquids, HSE, 1977.

IGE SR7 Bulk storage and handling of highly flammable liquids used within the gasindustry, 1989.

IGE SR14 High pressure gas storage: Part 1 - Above ground storage vessels

CS15 The cleaning and gas freeing of tanks containing flammable residues, HSE,1997.

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RC 20 Recommendations for the storage and use of flammable liquids, LPC, 1997.

EEMUA 147. Recommendations for the design and construction of refrigeratedliquefied gas storage tanks, 1986.

Construction of plantIt is critically important that following the detailed design of a plant that theconstruction phase is carried out according to the original specification and that noadditional hazards are introduced to the plant during the construction phase. Poorconstruction can result in the integrity of the whole system being compromisedresulting in an increased risk of a major accident.

Building and construction are covered by a series of different building regulationincluding the following:

Construction (General Provisions) Regulations, 1961;

Construction (Lifting Operations) Regulations, 1961;

Construction (Health and Welfare) Regulations, 1966;

Construction (Working Places) Regulations, 1966.

In addition the Construction (Design and Management) Regulations (CDM) clarifythe responsibilities of the various parties in a construction project. Also available isthe Approved Code of Practice for the CDM Regs: Managing Construction for Healthand Safety. Construction (Design and Management) Regulations 1994, ref L54, HSEBooks 1995, ISBN 0 7176 0792 5.

Commissioning/verification of manufacture andconstruction standardsIt is important to demonstrate that the correct materials of construction have beenused and that appropriate construction techniques have been employed so as not tointroduce construction faults and flaws into the plant. Evidence in the form ofdocumentation which shows that checks were carried out during the constructionphase are important to prove that the construction phase of the project has beenadequately supervised.

Documentation should show that the equipment supplied and installed is of thecorrect material of construction (and has received the correct heat treatment ifappropriate), is the correct item/part/unit number and is as specified in the designschedule.

Documentation should also show that the workmanship is of the quality specifiedand that inspection and acceptance tests were carried out as required under thecontract.

Commissioning of equipment should be carried out and records kept of thecommissioning exercises.

Evidence of the following should be available:

Certificates of mechanical completion and hand over certificates;Mechanical completion checks - check that installed equipment is ready forcommissioning, is installed correctly and that the component parts operate asspecified and that any ancillary equipment is installed and working;Certificates of acceptance of plant performance;Witnessing of performance tests;Witnessing of inspection and testing;Performance tests;Cleaning and pressure testing of systems;Visual inspection checks; Check that pipework and equipment is installed inaccordance with engineering drawings. Identify as built discrepancies;Check that mechanical equipment conforms to specified codes andstandards, is installed in accordance with the relevant drawings and meets theperformance tests specified;Each item of equipment should be checked for compliance with thespecification. This may mean witnessing aspects such as examination ortesting at the manufacturers works;· Check any internal fittings are installed,are of the correct dimensions and are firmly secured;Check on the materials of construction;Check rotating equipment for noise and vibration;

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Check plant against P&IDs and isometrics;Pressure vessel and system tests : inspection, pressure tests, leak tests,protective devices tests;Sub-system and system tests - dynamic safe fluid test (water test), dynamicprocess fluid test;Test utilities, instruments, etc. Simulate faults for testing purposes.

The following documentation should be available:

Modification records;Equipment examination records - pressure vessels, pressure piping,protective devices;Equipment Test Records - pressure & leak tests, pressure relief valve tests,rotating machinery tests, instrument tests, computer system tests;Computer tests;Spares inventories;Safety review records;Environmental review records;Reservation lists.

The management of the commissioning and verification stages should be identifiedunder the Safety Management System. The system should focus on ensuring thatthe design intent is met, and that deviations are properly assessed and controlled.Systems should be in place to ensure that corrective action is taken on theidentification of discrepancies between installed equipment and the design intentand to control any deviations from normal operation.

Evidence of a number of pre-commissioning and commissioning checks should bepresented to verify that the equipment as installed has been tested and is suitablefor operation and meets the design intent. These may include:

Pre-commissioning Hazops;Check that information is installed as per the process flow diagrams andengineering line diagrams;Electrical installation checks;Mechanical installation checks - including rotation checks;Civil installation checks - bunds, drains, hardstanding etc;Safety system checks - relief devices installed etc;Instrumentation and control checks - verification of set points, alarm and triptesting etc:Inert material tests using water and air as appropriate;Commissioning tests using process materials.

Codes of Practice and guidanceThe following codes of practice may be useful reading for the assessor whenconsidering the process design of plant and equipment. Codes and guidanceassociated with the design of specific items of equipment (as discussed in previoussections) are given below. Not all the codes or guidance documents identified beloware currently available and many have been superseded. However equipmentdesigned to these original standards may still be in operation.

Pressure vessel designASME Boiler and pressure vessel code : 1998BS 5500 : 1997 - Specification for Unfired Fusion Welded pressure Vessels

Other Standards and Codes of Practice relating to Pressure Vessel Design

In the UK pressure systems are covered by the Pressure Systems SafetyRegulations 2000 (PSSR regs) .

Other useful documents include:

ACOP: Safety of Pressure Systems. Pressure Systems Safety Regulations 2000. RefL122. ISBN 0 7176 1767 X. Published by HSE Books 2000.

HS(G)93 The assessment of pressure vessels operating at low temperature, HSE,1993.

BS 1500: 1958 - Fusion Welded Pressure Vessels for General Purposes.BS 5500 replaced this conventional code in the UK in 1976.

BS 1515: 1965 - Fusion Welded Pressure Vessels for Use in the Chemical,

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Petroleum and Allied Industries.BS 5500 replaced this advanced code in 1976.

BS EN 286-1:1991. Simple unfired pressure vessels designed to contain air ornitrogen.

API 510 Pressure vessel inspection code: Maintenance inspection, rating, repair,and alteration

API RP 572 Inspection of pressure vessels

API Standard 653 Tank inspection, repair, alteration and reconstruction.

API RP 520 Sizing, selection, and installation of pressure relieving devices inrefineries

ASME B16.9 Factory made wrought steel butt welding fittings : 1978

ASME B16.11 Forged steel fittings socket-welded and threaded : 1980

BS 1501: 1970 - Steels for Pressure Purposes:Part 1 (1990) - Specification for carbon and carbon manganese steelsPart 2 (1988) - Specification for alloy steelsPart 3 (1990) - Specification for corrosion and heat resisting steels

BS 1502: 1990 - Specification for steels for fired and unfired pressure vessels:sections and bars

BS 1503: 1989 - Specification for steel forgings for pressure purposes

BS 1504: 1984 - Specification for steel castings for pressure purposes

BS 1506: 1990 - Specification for carbon, low alloy and stainless bars and billets forbolting material to be used in pressure retaining applications.

BS 2594: 1975 - Specification for carbon steel welded horizontal cylindrical storagetanks.

BS 2654: 1989 - Specification for vertical steel welded non-refrigerated storagetanks with butt-welded shells for the petroleum industry

BS 2790: 1992 - Specification for design and manufacture of shell boilers of weldedconstruction

BS 5276: 1977 - Pressure Vessel details (dimensions)

BS 5387: 1976 - Specification for vertical cylindrical welded steel storage tanks forlow temperature service: double wall tanks for temperatures down to -196°C.

ISO R831: Recommendations for Stationary Boilers which is applicable to pressurevessels.

Pressure Vessels : Non-metallic materials of construction

BS 4994: 1987 - Specification for Design and Construction of Vessels and Tanks inReinforced Plastics.

BS 6374: 1984 - Lining of equipment with polymeric materials for the processindustries.

ASME Boiler and Pressure Code Part X, Fiberglass Reinforced Plastic PressureVessels (1992).

ASTM D 4021-86 Standard Specification for Contact Moulded Glass-fiber-reinforcedThermosetting Resin Underground Petroleum Storage Tanks.

ASTM D 4097-88 Standard Specification for Contact Moulded Glass-fiber-reinforcedThermosetting Resin Chemical Resistant Tanks.

Pressure vessel systems examination. IP Model code of safe practice: Part 13

Other Vessels (including Storage Tanks)

API Std 620 Design and construction of large, welded, low-pressure storage tanks,American Petroleum Institute, 1990.

API Std 650 Welded steel tanks for oil storage, American Petroleum Institute, 1988.

API Std 653 Tank inspection, repair, alteration, and reconstruction, AmericanPetroleum Institute, 1991.

API 12B - Bolted Production Tanks.

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API 12D - Large Welded Production Tanks.

API 12F - Small Welded Production Tanks.

API Std 2000 Venting atmospheric and low pressure storage tanks: Nonrefrigeratedand refrigerated, American Petroleum Institute, 1998.

Heat Exchangers

BS 3274: 1960- Tubular Heat Exchangers for General Purposes.

American Tubular Heat Exchanger Manufacturers Association (TEMA standards).

The TEMA standards cover three classes of heat exchanger:

Class R - generally severe duties in the petroleum and related industries;Class C - moderate duties in commercial and general process applications;Class B - exchangers for use in the chemical process industries.

API Standard 660: 1987 - ̀ Shell and Tube heat Exchangers for General RefineryServices' supplements both the TEMA standards and the ASME code.

API Standard 661: 1992 - Air Cooled Heat Exchangers for General Refinery Services.

Furnaces/boilersBS 1113: 1992 - Specification for design and manufacture of water-tube steamgenerating plant (including superheaters, reheaters and steel tube economisers).

BS: 799: 1981 - Oil Burning Equipment

BS 5410: 1976 - Code of Practice for Oil Firing

British Gas Code of Practice for Large Gas and Dual Fuel Burners (the BG BurnerCode)

API Standard 560 - Fired heaters for general refinery services, 1986.

Rotating equipmentBS 7322: 1990 Specification for the Design and Construction of Reciprocating TypeCompressors for the Process Industry

API Standard 610: 1989 Centrifugal Pumps for General Refinery Services.

API Standard 611: 1988 General Purpose Steam Turbines for Refinery Services.

API Standard 612: 1987 Special Purpose Steam Turbines for Refinery Services.

API Standard 613: 1988 Special Purpose Gear Units for Refinery Services.

API Standard 614: 1992 Lubrication, shaft-sealing, and Control Oil systems forspecial purpose applications.

API Standard 616: 1992 Gas Turbines for Refinery Services.

API Standard 617: 1988 Centrifugal Compressors for General Refinery Services.

API Standard 618: 1986 Reciprocating Compressors for General Refinery Services.

API Standard 619: 1985 Rotary Type Positive Displacement Compressors forGeneral Refinery Services.

API Standard 674: 1987 Positive Displacement Pumps - Reciprocating.

API Standard 676: 1987 Positive Displacement Pumps - Rotary.

ASME 19.1 - 1990 Air Compressor Systems.

ASME 19.3 - 1991 Safety Standards for Compressors for the Process Industries.

ASME B73.1M - 1991 Specifications for Horizontal End Suction Centrifugal Pumpsfor Chemical Industries.

ASME B73.2M - 1991 Specifications for Vertical In-line Centrifugal Pumps forChemical Industries.

BS 767: 1987 - Specification for centrifuges of the basket and bowl type for use inindustrial and commercial applications.

BS 4082: 1969 - Specification for external dimensions for vertical in-line centrifugalpumps.

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BS 5257: 1975 - Specification for horizontal end suction centrifugal pumps (16 bar).

BS 7322: 1990 - Specification for the design and construction of reciprocating typecompressors for the process Industry.

BS 4675: 1976 - Mechanical vibration in rotating machinery

Further reading materialLees, F.P., Loss Prevention in the Process Industries: Hazard Identification,Assessment and Control', Volumes 1-3, Second Edition, 1996. ButterworthHeinemann. ISBN 0750615478.

Mecklenburgh, J.C., ̀ Process Plant Layout', George Godwin/IChemE, London, 1985.ISBN 0711457549.

Perry, Robert H., Green Don W., ̀ Perry's Chemical Engineer's Handbook', SeventhEdition, 1997, McGraw-Hill. ISBN 0070498415.

Kern, D.Q., ̀ Process Heat Transfer', International Student Edition, McGraw Hill,ISBN 0070341907.

Coulson J.M. and Richardson J.F., ̀ Chemical Engineering Volumes 1-6'. ThirdEdition, Pergamon Press.

Case studies illustrating the Importance of DesignCodes - PlantAbbeystead Explosion (23/5/1984)

Beek (7/11/1975)

Bhopal - Union Carbide (3/12/1984)

BP Oil West Glamorgan (17/1/1981)

Explosion Caused by Explosion Suppression System

Feyzin (4/1/1966)

Polymerisation Runaway Reaction (May 1992)

Seveso - Icmesa Chemical Company (9/7/1976)

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