PIG-TRAPS

Design and Application Manual

PIG TRAPS

© Copyright 1999Pipeline Engineering & Supply Co Ltd Page 1 Section 6

CONTENTS - SECTION 6.0

6.1 Introduction

6.2 Design Parameters

6.3 Operating Method

6.4 Selection


PIG TRAPS


INTRODUCTION6.1 INTRODUCTION

As part of a complete pigging system, pig traps allow pigs to be inserted into andremoved from a pipeline which is to undergo a pigging program and which is likely tobe under pressure.

Key

a. Pressure Gaugeb. Ventc. Pressure Reliefd. Draine. Pig Signallerf. Kicker Valve (Launcher) Bypass Valve (Receiver)g. Mainline Bypass Valveh. Mainline Trap Valvei. Quick Release Closure

Fig 1. Typical Trap Configuration (Horizontal Launcher/Receiver)

Pig traps can be, and frequently are, referred to bydifferent names some of which may be no morethan alternatives and some which more accuratelydescribe the trap’s function. Popular alternativesare: Launchers, Receivers, Scraper Traps, ScraperBarrels, Universal Traps, Bi-Directional Traps,Sphere Traps. The name may also describe theorientation of the trap, giving a clue to its intendedpurpose: Vertical, Horizontal, Inclined, Declined,Temporary.

If a pipeline is to be pigged, launching andreceiving facilities (pig traps) must be provided.For large diameter pipelines this results in pig trapsup to 56” (nominal pipeline diameter) weighingmany tonnes and represent a significant capitalinvestment. Any company that manufactures thistype of equipment requires the scope andexperience to do so and must possess excellent engineering resources, both in itsequipment and its staff Entrusting the design of these systems to non-specialistsarmed with a few proprietary catalogues is a short-sighted and all too frequent short-lived economy.

Pipeline Engineering’s technical engineers have many years of experience in pig trapdesign and are fully conversant with all the major design codes and make full use ofstate-of-the-art CAD facilities. All welders are fully qualified to both American andBritish welding codes while the Inspection and Quality Assurance systems ensurecontrol at every stage of the manufacturing process from order to delivery.

Fig 2. Trap Types & Orientation


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6.1.1 DESCRIPTION AND PURPOSE

a) What is a Pig Trap? A simple definition is – a piece of pipeline equipmentthat allows easy loading or unloading of a pig into, or out of, the pipeline.

b) What is its purpose? To provide in a safe manner and without flowinterruption the means to either insert and launch a pig into the pipeline orreceive and retrieve a pig from a pipeline.

Although the definitions are simple, in reality it is quite different because a Pig Trap isa vessel that:-

• Gives access to or from a pipeline.• Provides a means by which this access can be closed between the surroundings

and full pressure capability of the pipeline.• Provides for the access to be opened or closed with speed, convenience and

safety.• Provides and internal holding or storage position in which pigs may rest until the

desired travel movement is achieved or after travel is terminated.• Provides a means of converting the pig from its free expanded state into its

compressed travelling state.• Includes, or is associated with, a means of controlling flow, pressure and/or

mechanical movement to give the pigs a positive driving force into or out of thepipeline.

• Has properly engineered safe and practical provisions for connecting to thepipeline.

• Is properly supported in a way which will neither impose excessive strains on thepipeline nor will accept more force than it is safe, or desirable, from the pipelineand its associated systems.

What does a Pig Trap comprise of – simplistically:

I. A quick opening closure or blanked flanged end.II. A major diameter section, referred to as the Barrel.III. A reducer – normally eccentric on a launcher, concentric on receiver.IV. A minor diameter section corresponding to the line pipe size and referred to

as the Neck Pipe.V. Various nozzles such as vent, drain, pressure indicator, kicker, or bypass,

release, equalising and pig signallerVI. Lifting lugs, supports and earthing lugs


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6.1.2 FUNCTION AND CONSTRUCTION

Figures 3a and 3b show typical components found in most types of trap and whichinclude:

1. A short minor diameter pipe section, often referred to as the NECK PIPE2. A REDUCER. This may be eccentric or concentric3. A longer major diameter pipe section, often referred to as the BARREL4. NOZZLES, SUPPORTS and LIFTING LUGS5. An END CLOSURE or a blanked, removable flange

Fig 3a. Horizontal Pig Launcher

Fig 3b. Horizontal Pig Receiver


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DESIGN PARAMETERS6.2 DESIGN PARAMETERS

We have already said that pig traps are pressure vessels and, as such, pressurevessel design parameters must apply. However, unlike pressure vessels that containonly fluids, pig traps must be capable of retaining line pressure whilst allowing pigs tobe launched and received. It is the type of pigs to be used which determine theoverall trap dimensions.

Metal bodied intelligent pigs are both heavy and long and must be considered alongwith the internal pressure requirements when designing supports, lifting lugs andassessing foundation loadings.

Trap design must also satisfy applicable codes. These may be piping codes, inwhich case the trap is treated as part of the pipeline or there may be a specification‘break’ between the pipeline and trap, resulting in a trap design which must meetpressure vessel codes such as ASME VIII or BS 5500.

Whichever approach is used, the designer must ensure all appropriate loadings andconditions are addressed to produce a safe working design.

Pig traps are designed and manufactured within the limits set by the DesignParameters. These are:

1. Basic design parameters2. Functional design parameters

There are instances where the requirements of the basic and functional designparameters are not compatible and a compromise must be reached. One frequentexample is that of a trap having a design code of BS 5500 with a requirement for afull line size kicker connection. As the code states that the nozzle should not exceedone third of the ‘run’ size some form of compromise is required. In this case a full orreducing tee – designed to one of the major pipeline codes – is often acceptable.

Basic Design Parameters cover the following aspects of pig trap design:

1. Design Code, Pressure and Temperature2. Materials and Certification requirements3. External loadings from pipework or external pressure (e.g. sub-sea)4. Cyclic requirements and nozzle reinforcements5. Support and lifting lug design6. Wind, Blast and Seismic loadings7. Ice and Snow loadings8. Inspection and Welding requirements9. Transportation loads

Design Codes can be any of the National or International standards, such as: BS5500, BS 8010, BS 4515, ASME VIII, ANSI B31.3/4 or 8, Stoomwezen (Dutch), ADMerkblatte or DIN Standards (Germany).

Pressures can be client specific or based upon the ASME/ANSIPressure/Temperature ratings. However, the design pressure of the trap shouldnever be less than that of the pipeline.


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Temperature is also client specific but it should be remembered that the maximumdesign temperature should not be less than the maximum temperature which the pigtrap system could attain, or to which it could be exposed during operation, start-up orshut-down.

Materials are often specified by the client. However, it is better to allow themanufacturers of the pig trap to select the trap materials. This approach ensures thatthe most suitable, cost effective and readily available materials are always selected.

To aid the selection process, the line product must always be specified and whether itis ‘sour’, toxic or corrosive. This will influence the selection of not only the metallicelements, but of the elastomeric materials which, typically, constitute the sealingelements.

All components in sour service should be resistant to HIC (Hydrogen InducedCracking) and conform to NACE specifications.

Finally, all materials should be compatible with its mating material, particularly withregard to its weldability, wall thickness and material grade.

Certification can apply to just materials or extend as far as the manufacturing anddesign appraisal.

• For materials only – this is usually limited to a certificate showing the chemicaland mechanical properties of the materials being used and issued by thesuppliers.

• In the case of material traceability, certificates verified by an independent thirdparty inspection authority may be required, in which case they are issued inaccordance with BS EN 10204.3.1.C.

• Where certification is to cover manufacture and design appraisal, this is carriedout by an independent third party inspection authority, usually appointed by theend client, with the scope of inspection being against an agreed qualitycontrol/inspection plan.

Welding should conform to procedures in accordance with the design code used forthe trap whilst all welders, including operators of automatic welding equipment,should be qualified in the procedures used. All completed welds should be examinedby a qualified weld inspector.

NDE/NDT (Non-Destructive Examination, also known as Non-Destructive Testing)requires that all circumferential and longitudinal butt weld, where practical, should beexamined by radiographic methods. Welds that cannot easily be radiographedshould be examined ultrasonically or by magnetic particle inspection.

Pressure Testing:

• Hydrostatic – upon completion, each vessel should be subject to a hydrostatictest pressure at least equal to 1.25 times the design pressure.

• Generally there is no upper limit for the hydrostatic test pressure, however, anypressure above 1.5 times the maximum working pressure should not be allowedto exceed wither intentionally or accidentally to the degree that the vessel issubjected to visible, permanent distortion.


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• Pneumatic Test – Some codes allow for the vessels to be pneumatically tested inlieu of hydrostatic testing. However, it should be noted that AIR or GAS is highlyhazardous when used as a testing medium. It is strongly recommended thatspecial precautions be taken when air or gas is used for test purposes.

Data Dossiers: Copies of all certificates, examinations and inspection reports,together with weld procedures, other client specified documents and “as built”drawings, should form a data dossier for presentation to the client with the completedvessel.

Functional Design Parameters can be explained most effectively by describing, indetail, each of the trap components.

The barrel comprises the major diameter section of the trap, designed to be oversizeso that the pigs can be easily loaded and unloaded. It is usually equipped with aquick opening end closure or, for temporary traps, a blind flange.

For conventional pigs, the diameter of the barrel is generally 2” larger than thediameter of the line pipe whilst, for intelligent pigs, it is recommended that thediameter of the barrel is at least 4” larger than that of the line pipe.

Barrel length is dependent on operating procedures, service, pig type, availablespace, etc. However, for launchers deploying conventional pigs, the recommendedlength of the barrel should be 1.5 x pig length, measured from the kicker connectionto the reducer weld. For receivers, the recommended barrel length is, again, 1.5 xpig length. However, this dimension is measured from the kicker connection to theclosure weld.

When deploying intelligent pigs, barrel length should be decided only afterconsultation with the pig manufacturer.

For multiple sphere launchers or receivers,inclined or declined trap barrels should beconsidered, along with a mechanism forreleasing the spheres (e.g. fingers, flaps orvalves). Historically, trap barrels have beeninclined at angles anywhere between10° and45°. However, Pipeline Engineeringrecommend that barrels be inclined between2° and 5°.

The barrel is also equipped with a reducer that iseither concentric or eccentric, depending upon theclient’s preference. However, an eccentric reducerallows pigs to be loaded more easily and isrecommended for horizontal traps whilst a concentricreducer is preferred for vertical traps or when aninternal tray, or basket, is fitted to horizontal traps.

Fig 5. Types of Reducer

Fig 4. Recommended angles for Inclined/declined traps

2°-5°


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Neck Pipe is the minor diameter section of the pig trap and is usually only between500 and 1000mm in length (with the exception of intelligent pig receivers where itmay be as long as 4 meters) and is positioned between the reducer and the pig trapvalve. On launchers, the neck pipe provides head space for the pig and, duringpressurisation, prevents contact between the steel nose of the pig and the trap valve,which may be damaged if struck by a pig under sufficient pressure.

For traps up to and including 24” line size, the neck pipe is usually attached to thepipeline system by a flanged connection. For traps above 24”, connections to thepipeline system are usually welded.

For receiving traps, the neck pipe usually incorporates a pig signaller.

Nozzles is the collective term for the connections from the trap to its associatedpiping system.

On simple traps there are normally only 3 nozzles:

• Kicker• Drain• Vent

On more complex traps, additional nozzles are incorporated for:

• Blowdown• Balance lines• Pressurising lines• Thermal relief valves

The kicker nozzle is usually the largest nozzle on a trap and is often referred to asthe ‘bypass’ or ‘bridle’. Pipeline Engineering defines the kicker nozzle as the off-takeon the trap barrel which connects the barrel to the bypass line pipe. The bypass isthe off-take after the trap valve on the main pipeline.

For launchers, kicker connections are attached to the barrel near the closure endwhilst for receivers, the connection is made near the reducer end.

Universal and Bi-directional traps incorporate a single connection located midwayalong the barrel, or twin connections with one connection in the launch position andthe other in the receive position. Ideally, the diameter of the kicker nozzle should notexceed 25% of the main line pipe diameter.

Kicker connections should not be positioned at the 6 o’clock position, historically thisposition causes most damage to pigs.

Drain connections should be provided near the end closure for horizontal launchersand near the pig trap valve for vertical launchers. For receivers on liquid or gas lineswhere liquids could be present, a drain point should be provided near the trap valve.For receivers that are sloped for the use of spheres, two drain points may be locatedtogether near the end closure but should be separated by half a sphere diameter.This prevents the drains being blocked by the spheres.

For traps up to and including 14”ns (nominal diameter of the pipeline), the diameter ofthe drain nozzle should be 2”. For traps above 14” ns the diameter should be 4”.


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Vent connections should be provided near the closure end or highest point. A furtherconnection may be considered near the trap neck end flange to ensuredepressurisation behind the pig in the event of it becoming stuck in the neck pipe.

Size of vent connections should not be less that ½” ns.

Blowdown. On high pressure gas systems, consideration should be given to theprovision of a blowdown line incorporating a globe valve or restriction orifice forcontrolled depressurisation.

Size should not exceed 2” ns.

Balance Lines can be provided on launchers to enable the barrel to be filled andpressurised on both sides of the pig at the same time. This prevents a pig movingforward from the launch position hitting, and possibly damaging, the trap valve ormoving backwards and losing the seal in the reducer. For receivers, balance lineswill prevent any possible pressure differential across the pig and should always beconsidered for inclusion. Balance line connections are approximately 2” in diameter.

Pressurising Lines may be required around kicker valves for several reasons:

• Speed of operation• Control of barrel pressurisation• To avoid damage to the kicker valve seats or other internals

Pressurising lines around bypass valves should also be considered to equalisepossible high pressure differentials. Pressurising line connections are usually smallerthan balancing line diameters.

Thermal Relief Valve connections can be provided at locations where theanticipated shut-in pressure of trapped fluid could exceed the design pressure.

Pressure Indicator (Pressure Gauge) should be fitted towards the closure end andvisible to the operator. May be incorporated with the vent connection. Size shouldbe in the region of ½” to 1”. Gauge dial to be 4” or 6” size.

Other items that may be fitted to the Pig Traps:

Supports, as the name suggests, should permanently support and restrain the PigTrap. They should be designed to carry the weight of the pig trap system filled withwater (or other fluid if their density is greater), together with the weight of theassociated heaviest pig.

Supports under the barrel should normally be of the sliding type to compensate forexpansion of the unrestrained part of the pipeline. Other supports may be fixed if thedesign calculations indicate that sufficient flexibility is incorporated in the pipework tocompensate for any axial and transverse movements. Where cathodic protectionisolation joints are used, the supports should allow sufficient movement to avoidstressing of the joint above its design limits. Where isolation joints are not used thesupports may need to be electrically isolated.

Lifting Lugs are designed to facilitate the lifting of the complete trap duringinstallation stage. Unless specifically requested, they are not proof tested.


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Earthing Lugs are designed to help prevent the build-up of static electricity. Static isa seriously under-estimated yet ever present hazard. Being invisible to the nakedeye, it tends to be ignored. Yet an undischarged build-up of electrostatic can takehours, even days, to relax back into equilibrium, resulting in a potentially lethalworkplace. If the accumulated static is suddenly discharged within a hazardousatmosphere, the resulting spark may easily act as the ignition source for anexplosion.

End Closures are fittings, including removable parts and assemblies, which providequick and easy access to the barrel when open and which seal the barrel whenclosed. All closures should be fitted with a vent/safety bleed device that forms part ofthe door locking mechanism and which, along with a system of interlocks sequencingthe operation of the various valves and end closures, is designed to ensure the safetyof personnel operating the trap.

Pig Signallers (also known as Pig/Scraper Detectors) are devices set on or intothe pipeline which indicate the momentary presence of a pig at a precise location.Signallers should be installed on both sides of the trap valve. For launchers, thesignaller should be sited on the main pipeline and separated from the pig trap valveby a distance that is at least the length of the longest pig. For receivers, the signallershould be positioned on the neck pipe and separated from the pig trap valve by adistance that is equal to the length of the longest pig.

Sphere Release Mechanisms may involve any of the following:

• Mechanical fingers• Flaps• Valves

Mechanical Fingers are the most popular butare not really practical for use with traps inwhich the spheres exceed 20”ns. Above thisdiameter it is more practical to use flapswhich are designed to absorb the high loadsthat a large sphere, weighing up to 500 kilos,can impose.

Fig 6. Sphere Release Fingers

It is normal to fit two fingers or flaps to launchers so that multiple spheres can beloaded into the barrel after which single spheres can then be launched, at a pre-determined rate, by sequencing the operation of the fingers or flaps.

For declined receivers, it is common to fit a single finger to prevent the sphere fromrolling onto the operator as the closure door is opened.

Fingers and flaps can also be used in traps intended for conventional and intelligentpigs.

Sphere Valves are basically ball valves where the hole in the ball does not go all theway through. A sphere enters the valve and on rotation through 180 degrees thesphere drops out to roll and engage with an inclined tee for pick up by the productflow. On rotation back through 180 degrees the valve is reloaded.


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If pigging facilities are required then consideration had to be given to providingvertical launcher for the pigs with the sphere valve and its storage magazine formingan angled branch into this. Naturally this method is both costly and bulky.

Other factors also influence pig trap design. These are related to:

• Layout• Ancillary Facilities

Layout involves the siting of pig trap systems and the possible adverseenvironmental effects that could result during construction and operation.

Pig traps should also be sited so that the end closures are pointing away frompersonnel areas and critical items of equipment. This will minimise any damageresulting from the unlikely event of a pig being ejected from the trap whilst underpressure.

Ancillary Facilities generally refer to pig handling equipment and systems. Nothingdoes more to improve efficiency, safety and cleanliness of pigging operations than apurpose designed system. With the correct equipment, heavy pigs and spheres canbe moved efficiently between traps, benches and vehicles, free of the danger anddirty conditions usually associated with manual operations and the largest pigs andspheres can be correctly and safely handled into, and out of, their traps.

Handling equipment should always be designed as an integral part of trapinstallations. Typical arrangements are as follows:

• Davit and Bench• Cassettes• Cradles

Davit and Bench refers to a manually operated system consisting of a cradle benchwith a winch and a free-standing swing jib crane. The cradle bench can be eithertrolley mounted or suitable for fixing to the floor next to the end closure door.

For positive launching, the pig is inserted into the reducer by a winch-operatedpusher mechanism on the cradle bench. At the receiving trap the pig is attached bycable to the winch and withdrawn onto the cradle bench. The free-standing jib craneis used for hoisting and positioning of pigs.

On multiple trap installations, all traps can be served by a single mobile handlingsystem.

Cassettes, also known as magazines, offer a solution to the problem of limited spaceon offshore platforms. They enable pig or spheres to be pre-loaded in multiples atthe onshore terminal and then transported to the platform as a single unit. Thecassette is loaded into the launching trap from where the pig or spheres can then belaunched at a pre-determined rate. At the receiving trap the loaded cassette isremoved and the complete unit can again be transferred, after inspection, to thelauncher for re-loading.


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Cradles, also known as half baskets or trays, can handle pigs or spheres of any type.When used with launching traps, the cradle is loaded externally and then moves thepig or sphere into its launch position inside the trap. For receivers, the incoming pigcomes to rest on the cradle that can then be withdrawn from the trap. Any debriscollected in the trap as a result of pigging will also be removed. A free-standing jibcrane can be sited next to the trap to handle and position the pigs.

The systems described are designed to provide a cost-effective means of handlingpigs and spheres throughout the operational lifetime of the pipeline. It is importantthat all pig handling systems are manufactured as an integrated part of the trap inorder to preserve its integrity as a pressure vessel.

There are several types of trap which do not confirm to the conventional horizontallayout and which are known as Special traps. The following are examples:

• Vertical traps• Temporary traps• Bi-directional traps• Sphere Launcher and Receiver

Vertical Traps are usually used wherespace is at a premium (e.g. offshoreplatforms). Their design andconfiguration shows very little differenceto that of horizontal traps. In fact, theonly major differences occur in thedesign of the supports and of the endclosure hinging. End closures swing tothe side on horizontal traps but, forvertical traps they have to be eithersprung, fitted with a counterweight orjacked out on a davit and screwed rod).

Vertical receivers are usually fitted with an internal stepped basket into which the pigarrives. As the pig cups expand, the step prevents the pig dropping back into thereducer. The basket also allows the pigs to be removed easily.

Temporary Pig Traps should never be used as an excuse to avoid the designparameters previously discussed as most of them still apply with equal force.Because of the circumstances which prevail onconstruction sites (where there is often an absenceof trained routine) greater attention must be given tosafety. Remember – pressure can kill. However,where there is less incentive towards the time andlabour saving properties of modern quick openingclosures, temporary traps can be designed and madeto less stringent codes than those required for longterm capital equipment – although quality assurancemust never be neglected.

Fig 7. Vertical Trap with Stepped Basket (and pig)

Fig 8. Temporary Launcher (With Pig)


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Bi-Directional Traps, with sleeves, were originally designed for shuttling spheresback and forth but are equally suitablefor use with bi-directional pigs. Theseunits comprise a sliding sleeve insidethe major barrel that can bepositioned so that a single pig orsphere can be pre-loaded and held inthe trap until it is ready for launch.Initially, the flow inside the trapbypasses the pig until the sleeve ismoved into the launch position atwhich point the flow is directed behindthe pig launching it into the pipeline.At the receiving end, the sleeve ispositioned so that flow passes throughit (the sleeve) until the pig arrives.The incoming pig is then captured bythe sleeve and moves along the trapuntil the flow can bypass the pig.

Sphere Launchers and Receivers (Automated Pig Traps)

Automatic pig launching and, to a lesser extent, receiving may be considered forunmanned installations where there is a requirement for frequent pigging of lines.The types of pigs used are either sphere or batching pigs. The general principle forthe handling of each is the same. However, advantage is taken of the spheres abilityto roll.

Pig launching is usually achieved from a vertical launcher whilst for sphere launchingvertical or inclined can be utilised.

The rolling feature of the spheres makes them readily adaptable to unmannedfaciliti4es in that the operator can load a trap with several spheres and the launchingcan be activated either manually or automatically. Various launching mechanismsare available, as already described, and the selection is largely a matter of clientpreference, bearing in mind the design constraints of each.

In the case of sphere receivers, the barrel is declined and it is best to have ahorizontal pup pipe near the closure with a sphere stop fitted so that incomingspheres do not impact against the closure door and also to prevent spillage onto theoperator when he opens the closure door for unloading.

Fig 9. Bi-Directional Trap


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Safety and Interlock Systems

Safety issues are always at the heart of pig trap design. Whilst pigging is a commonprocedure, typically carried out when a pipeline needs purging, cleaning or surveying,it can involve a high risk of human error, high enough to warrant pig traps beingdescribed as ‘primary grade sources of hazard’.

Probably the greatest associated danger is when a trap is opened accidentally whilststill under pressure – usually to insert or remove a pig. To overcome this danger it isvital that a system is incorporated which ensures that the trap is fully vented beforethe door can be opened. Venting depressurises the trap and removes the forcenecessary to propel the pig.

Pig trap systems also involve other more complex, procedures. Even in a basicsystem, safe operation of the closure require it to be correctly sequenced with certainvalves which are incorporated into the trap – these being the pig trap valves, drainand kicker valves. The pig trap line valve governs the piping connection between thepig trap and the main pipeline whilst the kicker valve is on a secondary pipingconnection used to move the pig into and out of the trap. Both valves must beclosed, isolating the trap from the main pipeline, before the trap is drained.

By establishing safety guidelines, a certain level of control over pig trap operationscan be imposed but these usually rely on the voluntary compliance of personneloperating the plant, pig traps and handling equipment. IF these guidelines arecontravened due to human error, or malicious malpractice, serious accidents willoccur. Accordingly, the need for a safety system that positively controls the entireprocess, without dependence on human judgement, is clear. The many separateoperations involved when launching and receiving pigs must be made to follow asafe, predetermined path and the most widely accepted and reliable method forachieving this is by Key Transfer Interlocking.

Mechanical key transfer interlocking has developed from the principle that actionsperformed in the correct sequence are safe but potentially lethal if performed out ofsequence. Therefore, the use of trapped key interlocks in pig trap operations will limitthe sequence of valve and end closure operations to a single, unchanging path. Byfitting interlocks to all relevant valves, as well as to the end closures, it becomesimpossible to load or retrieve a pig without first depressurising the pig trap.

In summary, key transfer interlocking provides a logical method or controlling piglaunching and receiving procedures, no matter how complex. It ensures thatprocedures can only be performed in the correct sequence and eliminates thepossibility of human error.


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OPERATING METHOD6.3 OPERATING METHOD

The following section describes typical operating sequences for launching andreceiving pigs in liquid service pipelines. The sequences are general in nature andare intended solely as a means of explaining the working principles of some of themany types of trap in existence. They (the sequences) are not definitive and shouldnot be used for training pig trap operators, nor should they form any part of theoperating procedures for specific launching and receiving installations.

1. Launching Key

a. Pressure Gaugeb. Ventc. Pressure Reliefd. Draine. Pig Signallerf. Kicker Valveg. Mainline Bypass Valveh. Mainline Trap Valvei. Quick Release Closure

Assumptions prior to launching:

• Trap is full (of pipeline product) and is under pressure• Valves (f), (g), (h) are open• Valves (d) and (b) are closed

Launching Procedure:

1. Close valves (f) and (h)2. Open valve (d) followed by valve (b). Air will displace the liquid and the trap will

drain.3. When the trap has been fully drained (0 psig), open the closure door and push

the pig into the trap until the first cup (or seal) forms a tight fit in the reducer4. Close and secure the closure door, following the manufacturer’s operating

procedure, and close valve (d)5. Open valve (f) slowly. The trap will begin to fill and any residual air will be

forced out through valve (b).6. Slowly continue to fill the trap. When the trap is full, close valve (b) and allow

the pressure to equalise.7. Close valve (f)8. Open valve (h) and then open valve (f). The pig is now ready for launching9. Partially close valve (g). The liquid flow through valve (f) behind the pig will

increase. Continue to close valve (g) until the pig signaller (e) indicates that thepig has moved out of the trap into the mainline stream.

10. When the pig signaller (e) has indicated that the pig has left the trap, fully openvalve (g)


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3. ReceivingKey

a. Pressure Gaugeb. Ventc. Pressure Reliefd. Draine. Pig Signallerf. Bypass Valveg. Mainline Bypass Valveh. Mainline Trap Valvei. Quick Release Closure

Assumptions Prior to Receiving:

• Trap is empty of all product and is at atmospheric pressure• Valves (b), (d) and (g) are open• Valve (f) and (h) are closed• Closure door is closed in accordance with the manufacturer’s operating

procedures

Receiving Procedure:

1. Close valve (d) and slowly open valve (f). Th trap will begin to fill and anyresidual air will be vented through valve (b)

2. Close valve (b) and allow trap pressure to equalise through valve (f)3. Open valve (h). Trap is now ready to receive pig4. On its arrival, if the pig stops at the point marked ‘X’, partially close valve (g).

Increased flow through valve (f) will force the pig into the trap5. When the pig signaller (e) indicated that the pig has entered the trap, fully

open valve (g) and close valve (f) and (h)6. Open valves (d) and (b). The trap will drain

6.4 SELECTION

To provide the user with the most suitable equipment for their application, PipelineEngineering would appreciate the following information:

• Pipeline diameter and wall thickness• Pipeline pressure, temperature and product• Design requirements: code, pressure and temperature• Inspection/certification requirements

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