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© T O U C H B R I E F I N G S 2 0 0 8

For over 35 years Pipeline Engineering (PE) has provided pigging solutions

for the oil and gas and related pipeline industries. PE was a forerunner in

the development of a reliable dual-diameter pigging solution, and

continues to advance this technology into multidiameter lines. With a

track record of engineered design solutions to dual-diameter and related

pigging problems, the application of proven techniques together with

new and innovative concepts has allowed the development of

multidiameter pigs capable of negotiating multiple pipeline diameter

changes and geometry conditions, together with specific launch and

operational parameters.

Historically, pipeline inspection companies required a pipeline to be

of single-diameter construction with a constant bore and bend radii

five times the internal diameter. This was to enable the necessary

clearance between their tools and the pipe wall to allow collection of

the required data. If a pipeline followed this configuration, it was

deemed to be piggable.

The drive for cost-effective design highlighted potential savings in space,

weight, fabrication and installation costs. It was found that if topside pipe

work, risers and subsea manifolds were of a smaller diameter than the

main pipeline, a considerable reduction in cost could be realised. The

reduction in bore necessitated smaller valve configurations, branches and

welded fittings such as tees and bends, which naturally led to reduced

costs. The weight savings in these assemblies also reduced fabrication and

installation outlay, which also contributed to the overall reduction in cost.

The joining of lines within a field from a main transmission line to a

central processing location provides a source of dual and multiple

diameters. It is more cost-efficient to tie into an available existing line

than to lay a new line, with benefits being shared in terms of

maintenance and reduced overall installation lead time. A branch line can

be smaller than the main line, and the former’s size is determined by the

production output of the joining location.

The continuing development of deepwater fields has emphasised the

requirement for economical design. The greater water depths dictate

higher pressure ratings and therefore thicker-walled pipe systems, valves

and fittings. With increasing field water depths come exponentially

escalating construction costs, and as such any potential area for saving

must be explored. With this in mind, connectors, valves and features

have been scrutinised, with the result being that rather than reducing the

overall diameter of the component, it is acceptable to reduce the internal

diameter to achieve the thicknesses and cavities needed for form and

function. This then creates the opportunity for a vast quantity of internal

diameters due to the array of manufacturers producing components to

be included in assemblies.

A prime design consideration is that the line to be installed has to be

piggable. This factor is generally never discounted when applying varying

diameters, as flow assurance is a mandatory aspect to be addressed. A

flow assurance programme ensures line condition is maintained at a pre-

determined level, optimum flow conditions are achieved and product

quality is retained. With the aforementioned factors taken into account,

the drive for savings is still pressing and a direct approach can be

achieved by pushing the boundaries of the term ‘piggable’. A balance

must therefore be struck between economy and functional viability.

The Process of Pig Selection

Suitable pig selection is crucial to ensure that the desired task is

carried out to the standard specified, within the project timescale

and to the allocated budget. Here, the drive for an engineered

solution that has been proved to be successful, the need for accurate

information and provision of operating conditions are essential.

Foam and conical cup construction pigs can negotiate reductions in

diameter, but are not specifically designed to cope with changes

in diameter for considerable lengths of run. To fulfil the requirement

of functioning within a dual- or multidiameter line, the pig needs to

be suitably designed to negotiate the pre-defined diameters and to

pass through the diameter-specific features.

Step-by-step Design Guide

To design a pig capable of negotiating a multidiameter pipeline, the

parameters must first be clearly defined. Within the term ‘parameter’,

the following factors need to be considered:

Multidiameter Pigging – Factors Affecting the Design and Selection ofPigging Tools for Multidiameter Pipelines

a report by

Andrew Cargi l l

Pipeline Engineering

74

Pip

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A flow assurance programmeensures line condition is

maintained at a pre-determinedlevel, optimum flow conditions

are achieved and product qualityis retained.

Suitable pig selection is crucial to ensure that the

desired task is carried out to thestandard specified, within

the project timescale and to the allocated budget.

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H Y D R O C A R B O N W O R L D V O L U M E 3 I S S U E 276

• internal diameters;

• bend radii;

• feature definition and configuration;

• length of each section;

• transitions between diameters;

• location of features;

• flow and pressure conditions;

• medium and environment;

• expected debris and internal line conditions;

• pig launcher and receiver; and

• interaction of pig characteristics to negotiate features.

Internal Diameters

The diameters present in a line need to be defined as accurately as

possible, as all variations of the stated diameters can have an effect on

the boundary conditions. The range of diameters needs to be broken

down into a range for each core diameter. This could involve grouping

schedules for each major diameter or, more likely, similar sizes to allow

a number of defined ranges to be identified. The pig seal and support

elements would then be sized to suit the ranges. If the ranges are

found to be too great for the elements to accommodate, the ranges

could be broken down further to identify additional elements for

cover. The type of seal and support element and configuration will be

selected based on the range step changes, together with the length of

run in each diameter and transitional conditions. The seal element

could be a range of specially sized sealing discs (see ‘Case Study’,

below) or an overlapping petal-style disc (see Figure 1). The support

element could be a modified traditional style support disc (see ‘Case

Study’, below) or a hybrid paddle support (patent held by PE; see

Figure 2). For larger diameters it may be necessary to employ a

wheeled spring suspension arrangement to maintain alignment to the

pipe centre-line due to the increased weight of the pigging tool (see

Figure 3).

Bend Radii

The bend radii need to be defined together with the specific diameter

in which the bend is formed. The portion of bend in angular terms and

the method in which the bend is formed, such as induction bending

or lobster-back field fabrication, are also key factors for consideration.

The pig length is of major consideration here, as a longer body is less

likely to be able to traverse the bend, but a short pig would be

unstable through straight length runs. The pig length is also

influenced by the combination of features within the pipeline system.

Feature Definition and Configuration

Definition of the feature and its particular configuration in the

application require detailing. An example would be a tee, which

could have a barred branch for pigging, or it could be a flow tee with

through-bore flow-matched pipeline. The pig design needs to provide

a positive seal across the feature to allow an efficient passage with no

loss of drive, which would lead to stalling. A wye piece is another

example of branch that requires careful design consideration.

Length of Each Section

The length of each section in relation to its diameter needs to be

clearly defined to assist the review of the main diameters. This also

provides a basis for the selection of materials resistant to wear for

the stated length.

Transitions Between Diameters

The transitions between different diameters and features need to be

investigated and simulated to ensure that they are not too abrupt,

which could cause loss of a positive seal and therefore drive, and

could also prevent the switch between the two sealing elements, as

required in the transition between major diameters. The length of

run to each feature needs defining so that a map of the pig run can

be built up for analysis purposes to enable the optimum pig design

to be generated. The distance to each feature and the order in which

they occur in the line are key pieces of information, without which a

suitable design cannot be produced.

Flow and Pressure Conditions

The stipulated flow and pressure conditions need to be taken into

account, and recommendations should be made to ensure pig

speeds are kept at the optimum level to prevent unnecessary wear

Figure 1: Petal-style Pig

Figure 2: Paddle Support Pig

Figure 3: Wheeled Suspension Pig

Multidiameter Pigging – Design and Selection of Pigging Tools for Multidiameter Pipelines

To design a pig capable ofnegotiating a multidiameter

pipeline, the parameters mustfirst be clearly defined.


H Y D R O C A R B O N W O R L D V O L U M E 3 I S S U E 2 77

and damage, but also to ensure an optimum cleaning speed, as

required. Bypass can be introduced to maintain flow but reduce pig

speed, while introducing an efficient cleaning mechanism.

Medium and Environment

The medium and environment in which the pig is to transit can be

corrosive, and as such the materials and design need to be resistant

to corrosion. A medium that is not self-lubricating, such as a dry gas

line, can present a particular challenge as the seal and support

elements can wear at a faster rate than they would in a lubricated

line. Careful material selection for the affected elements will ensure

that a suitable pig is designed for the task.

Expected Debris and Internal Line Conditions

Depending on the internal condition of a line and the medium

transmitted, varying types and quantities of debris can be present.

The array of types and quantities of debris dictate a specific

approach, for example a bypass pig to allow through-flow to

suspend black powder in front of the pig in order to prevent a

blockage and overloading of the pig receiver facilities.

Pig Launcher and Receiver

The onsite launching and receiving facilities can restrict the overall

length of the pig and hence prevent the pig being designed to best

suit the line geometry of any feature combinations. An example of

this is an ITAG pigging valve, which has a strict maximum length to

allow a pig to be inserted and rotated into the main flow of the line

to be launched.

Interaction of Line Features

The interaction of individual line features may not at first appear to

have a large bearing on pig design, but in fact can never be

sufficiently stressed as an underestimated design premise. The

interaction of pig characteristics designed to negotiate and traverse

separate line features can potentially have an impact on passage

through a feature in which they are not required to be active. An

example of this is when a pig is designed to seal across a wye piece,

where the body is considerably longer than that of a standard pig.

The pig could also be required to traverse a bend, but due to the

revised length the pig may not be able to do this as the increase in

length could have lowered its position in the bend, causing a clash

between the inside of the bend and the body material. Figure 4

shows the layout of such a scenario.

The severity of the clash would be dependent on the radius of the bend

and may result in a loss of seal rather than a clash; this may be able to

be rectified with a modification to the disc pack configuration. If the

disc pack cannot be modified, the tool could be split into two modules

with an articulated joint between two pig bodies. This would allow

passage around the bend and sealing across the wye.

Pipeline Data Are Critical

Line diametrical information and feature details are fundamental

inputs into the design process. As previously stated, in order to

achieve an optimum design all available line data are required, and

where information is found to be missing, measurements need to be

taken – where viable – to allow the full picture to be obtained. If the

aforementioned data are not obtained, the process of design will be

extremely difficult – or, depending on the missing information,

impossible – to complete. The objective is to provide a pig to suit the

application; this must kept in mind when engineering a suitable

solution, and therefore assumptions and estimations must not take

the place of fact: if information is found to be lacking, a halt must be

called to the design process until the information can be provided.

Prototype Development and the Importance of

Testing and Validation

When a design has been developed to suit a particular application, it

is trialled using computer-aided design (CAD) modelling through the

diameters and features to be negotiated. The design basis and

previous trial data are utilised to refine the design to achieve the most

suitable solution. The true test and therefore validation of the design

is to manufacture a prototype of the design solution and test the pig

in a purpose-made test rig. The test rig should be designed to simulate

the worst-case scenario features and diameters to which the pig will

be subjected when running through the field line. When testing, the

conditions under which the pig will operate in the field – such as flow

and pressure – are simulated to ensure the test is as true a

representation of the operational conditions as possible. This will

therefore validate the pig for use in its intended application in the

field. Data collected from testing can be used as a benchmark for flow

and pressure readings in the simulated features; these can be

compared with operational data to review performance. It must be

noted that testing is generally under ideal conditions with no pipe wall

deposits, such as wax, and no corrosion. However, it is possible to

apply such build-ups and replicate corrosion pits and scours to enable

a true assessment of pig performance.

When testing, it may be necessary to amend disc diameters and disc pack

configurations to allow a smoother, more efficient passage through the

features. A particular parameter to be noted when developing a dual- or

multidiameter pig is bypass; where possible, modifications can be made

to keep this to a minimum. Bypass can be reduced when the pig is

traversing a straight pipe section or is in a bend, but it is at the transition

to a larger diameter where it can not be reduced as the sealing elements

respond to the variations and effect a positive seal.

Figure 4: Layout of Pig in Wye and Bend


Line diametrical information andfeature details are fundamentalinputs into the design process.


H Y D R O C A R B O N W O R L D V O L U M E 3 I S S U E 278


Together with the validation of pig performance, testing is imperative

to validate the functionality of a new or special pig design. Gaining

data that can be used for operational purposes is a useful exercise,

but testing the pig through the simulated field geometry and

conditions is invaluable as, should a design feature not perform as

intended or an unexpected clash occur between the body and pipe

wall, leading to the pig becoming stuck, it can easily be removed

from the test rig and the design rectified. The number of

modifications and re-tests is unlimited, but when the operation

requiring the pig takes place only a single opportunity exists for

success. The cost of recovering a stuck pig from a subsea manifold

would be substantial and would undoubtedly delay a project, with

further financial impacts. The cost incurred in performing test loop

trials is minimal in comparison, and could prevent a series of events

detrimental to the success of a project.

Case Study – 8x10-inch Pipeline Offshore India

PE was approached to supply a pigging solution to negotiate 8–10-

inch major diameters for commissioning activities and production

pigging. For dewatering on the line the pig was to be propelled with

nitrogen to remove the water. The pig was to be back-loaded into

an 8-inch vertical subsea launcher, which was then to be connected

to a pipeline end termination through a reduced-bore mechanical

connector and into a 90° 5D bend. The pig was to perform a

mandrel body roll flip and pass though the connector and 5D bend,

then pass into a 10-inch pipeline section, in which it was to travel

3.2km before negotiating a reduction into an 8-inch pipe via a 90°

5D bend and a reduced bore connector before being received at the

subsea manifold (see Figure 5).

Pig Operational Requirement

The operations were to be carried out subsea with both launch and

receipt at 600m water depth. The pig was extensively tested and

developed to ensure functionality was maintained under the

parameters. The pig was required to negotiate the following:

• 8-inch launcher and pipe work (internal diameter 190.5mm);

• connector (internal diameter 179.8mm);

• 5D bend (internal diameter 190.5mm);

• 10-inch line (internal diameter 241.3mm);

• tapered 1 in 6 transition; and

• length fixed at 400mm due to laydown head design.

Figure 5: Test Rig Layout

Figure 6: Initial 8x10-inch Pig Design

Launcher spoolID 189.0

ConnectorID 180.0

10”NS pipework241.25

10”NS pipework241.25

8“NS pipeworkID 189.0



5D bendID 189.0

ConnectorID 180.0


6 in 1 transitionID 202.74 x ID 254.46

6 in 1 transitionID 202.74 x ID 254.46

ID = internal diameter.

When a design has beendeveloped to suit a particularapplication, it is trialled using

computer-aided designmodelling through thediameters and features

to be negotiated.

When testing, it may benecessary to amend discdiameters and disc packconfigurations to allow asmoother, more efficient

passage through the features.


The Pigging Products andServices AssociationAn international trade associationserving the pipeline industry

The Pigging Products andServices AssociationAn international trade associationserving the pipeline industry

Pigging seminars – next one18th November 2009 Aberdeen

PPSA newsletter:“Pigging Industry News”

PPSA’s book:“An Introduction to Pipeline Pigging”

Training coursesPPSA website

www.ppsa-online.com

Services include:Free technical information service

available to allComplimentary Buyers Guide and

Directory of MembersSourcing of pigs and

pigging services

Want to join?Full members: piggingmanufacturers and serviceprovidersAssociate members: pipelineoperators, suppliers and alliedindustriesIndividual members: anyone with aninterest in pigging

To find out more visit our websitewww.ppsa-online.com

or contact the Secretary [email protected]

Pigging Products andServices Association

PO Box 2, Stroud, Glos GL6 8YB, UKTelephone: +44 1285 760597Facsimile: +44 1285 760470Email: [email protected]

www.ppsa-online.com

Our aims are to promote the knowledge of pigging and itsrelated products and services by providing a channel ofcommunication between the members themselves, and

with users and other interested parties

background image © iStockphoto.com/P Wei

PPSA_ad.qxp 17/12/08 12:39 pm Page 79

Pig Functional Requirements

The pig functional requirements were as follows:

• remove construction debris;

• flood line for hydrotest; and

• dewater line.

Pig Design Development and Validation Testing

The pig design could not incorporate a suspension system or a

paddle support system due to the bi-directional and back-loading

requirements and the restriction on length. A segmented support

system was employed for pliability through the reduced-diameter

connector and to provide support in both the minor and major

diameters. Dual seals were utilised for the 10-inch section and single

seals for the 8-inch section (see Figure 6).

When the trials commenced, the design was found to be unsuccessful

at negotiating the features due to the reduced bore connector

damaging the disc packs, preventing formation of an effective seal in

the 10-inch pipe work. It was found that the annular clearance in the

8-inch pipe work was too small to allow the compression of the 10-inch

seal discs and the required proportion of the support discs. The pig was

subsequently re-designed and the prototype modified for further trials.

A combination of radially grooved supports arranged in a petal

formation was applied to support the pig in both diameters. Two 10-

inch seal discs were removed and the disc pack spacing and body

flange positions were revised for compression in the 8-inch pipe work

(see Figure 7). The pig was run through the test rig to fine-tune the disc

diameters, with the pig found to be successful.

The 8x10-inch pig will be used to flood and dewater lines in the

field. It was therefore a requirement to test the pig using gas as a

pigging medium to dewater the test rig. The main criterion for the

dewatering test was that the pig was able to be received into the 8-

inch pipe section with gas as the pigging medium. This test was

carried out and the design was again found to be successful.

Testing Results

As stated in the previous section, the final pig design was found to be

successful in the trials and was therefore validated as fit for purpose.

The following information details the differential pressures in each

feature for water to water pigging:

• flip launch: 8.0 bar;

• 8-inch pipe work: 7.5 bar;

• connector: 15.6 bar;

• 5D 90° bend: 13.6 bar;

• 10-inch pipe work: 0.9 bar; and

• pass through reducer: 17.4 bar.

The differential pressures were quite high in the 8-inch diameter

pipe work due to the compression of the 10-inch elements, with

the main length of run having a differential as would be expected in

this diameter. The above results were mirrored with the air water

test exercises. The pig design was successfully launched and received

in a number of field operations, and performed as required during

these operations.

Summary

The process of pig design can be eased by the interaction between client

and vendor where a free flow of information is present. It is only under

these circumstances that a true appreciation of the impact of line

geometry on the final pig design and operational capabilities can be

gained. When developing a pigging tool suitable for a specific task, it is

essential that knowledge of the operations to be carried out is held by

both parties. Dual- and multidiameter pigs have long been proved to be

successful during validation testing and field usage. Each design diameter

difference has to be approached and appraised on a case-by-case basis,

with minor individual changes being considered together with the overall

major change. The interaction of the changes with the features must also

be considered in order for a suitable design solution to be engineered.

With the cost of pipeline recovery and deepwater operations,

validation testing is a necessary step to ensure that a successful

design solution has been supplied and that the risk to the project has

been reduced to as low as reasonably practicable. ■

About Pipeline Engineering

Pipeline Engineering provides products and services for pipelinepigging and flow assurance. Products include utility pigs, pigsignallers, rapid opening closures, pig launchers and receivers,bend restrictors, polyurethane products and other pipelineproducts, including AMPL, an automatic multiple pig launchingsystem. Support services include project management,engineering consultancy and operational support. This includesproduction cleaning services, design, development testing andproduction of special cleaning pigs, product deployment andretrieval, pipeline modifications, caliper surveys and piggingcampaign management.

Figure 7: Successful Final 8x10-inch Pig Design


80 H Y D R O C A R B O N W O R L D V O L U M E 3 I S S U E 2

Together with the validation ofpig performance, testing isimperative to validate thefunctionality of a new or

special pig design.


2009 National Safety Conference

The National Safety Conference takes place on Tuesday 12 May to

Wednesday 13 May 2009 and features an overview of safety challenges

and issues affecting refineries and petrochemical plants. The exhibition,

held as part of the conference, gives attendees the opportunity to meet

and talk with representatives of companies offering a variety of safety-

related services to the refining and petrochemical industries.

The culmination of the meeting will be the Safety Awards Reception and

Banquet from 6pm to 9:30pm on 13 May. The event celebrates and

honours the industry’s excellent safety achievements. Be sure to purchase

your tickets for this event when you register.

The Board of Certified Safety Professionals will grant CSP Continuance of

Certification (COC) points for attendance at the National Safety Conference

without pre-approval. The American Board of Industrial Hygiene (ABIH)

grants certification maintenance (CM) points.

Who Should Attend

Over 300 industry safety managers, engineers and experts are expected to

attend the conference. ■

For further information please visit the National Petrochemical & Refiners

Association’s website at www.npradc.org

Research and Development Center Garners International Recognition

The Research and Development Center (R&DC) is a leading research

facility, but what is the proof? To reach a level of excellence that is well-

defined and recognised worldwide demands precise measurement by an

independent and respected international standards organisation.

Reaching a high level of excellence does not happen overnight. It is a

long journey – a journey overseen by Dr Abdulrahman Vogel, R&DC’s

Quality Co-ordinator. Vogel, a mountaineer, compares striving for

excellence to climbing Mount Everest. “You climb a difficult mountain in

stages, taking time to make yourself safe and rested before continuing

up the cliff.” These stages are vital because testing occurs every year and

it is possible that your organisation could lose ground. As Vogel says, the

true key to excellence is sustainability. Meeting quality milestones is

valueless if you reach a high point only to slide back down the mountain.

When it came to selecting a standard to follow in the pursuit of

excellence, R&DC faced several choices. In the end, the European

Foundation for Quality Management (EFQM) was selected. “EFQM is a

well-respected international standard that fits well with our quality

philosophy at R&DC,” Vogel said. “We can progress in stages and earn

points as long as we are well focused on meeting the EFQM

requirements. In fact, the highest level of EFQM, the tip of the peak,

which equates to a maximum of 1,000 points, can take companies 15

years or more to reach.” Quality is just one aspect of R&DC’s drive for

excellence. “Excellence in everything we do, is the true objective,” Vogel

said. That encompasses more than doing good work.

The approach is QSE plus E, which stands for quality, safety and

environment plus excellence. To measure success, ISO and OHSAS

systems are applied to specific R&D-relevant areas. ISO stands for the

International Organization for Standardization, which sets standards in

several fields. OHSAS is an internationally recognised standard for

occupational health and safety management.

R&DC earned ISO 17025 accreditation in 2006 and recently obtained, as

a first in the Middle East, an accredited ISO 29001 certification for its

core R&D activities. ISO 29001 is the latest oil and gas industry sector-

specific quality management system, a result of intensive co-operation

between the American Petroleum Institute (API) and ISO. Next month,

the R&DC will be certified for its ISO 14001 environment-management

systems. These are important milestones. Take, for instance, the ISO

17025 accreditation, which is for competence of testing and calibration

laboratories. By earning that accreditation, R&DC’s analytical data are

respected around the world and can even be presented as part of legal

procedures or specification product sheets for international trade. That

is what a research institute requires – respect.

OHSAS 18001 certification, in addition to corporate safety standards, is

also vital, according to Vogel. This international health and safety

standard was developed to:

• reduce risk to employees, customers and suppliers;

• reduce or eliminate the damage associated with accidents at work;

• enhance staff morale and motivation;

• demonstrate legal and international compliance;

• ensure competitive advantage;

• build trust and confidence;

• achieve external recognition for safety excellence; and

• guarantee sustainability.

R&DC’s approach to excellence is leading the way not only for Saudi

Aramco, but also for the entire Middle East. This has not come easily.

Training staff to focus on excellence is a journey in itself, but the result

is worth the effort as professionals around the world are taking notice

of Saudi Aramco and its research and management capabilities. For

more information, visit www.saudiaramco.com ■

H Y D R O C A R B O N W O R L D V O L U M E 3 I S S U E 2 81

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