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PIPELINE ENGINEERING

Multi-Diameter Pigging – Factors

affecting the design and selection of 

pigging tools for multi-diameter lines

Karl DawsonPPSA Aberdeen

19th November 2008

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Agenda

• Why Multi-Diameter Lines?

• Definitions

• Pig Selection• Pig Design

• Provision of data for pig design

• Prototype Development and Validation Testing

• Case Study

• Summary• Presentation End

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Definitions 

Industry Accepted Definitions:

• Dual-diameter  – Operates in 2 distinct diameters

• Multi-diameter  – Operates in two or morediameters and may operate in a range diametersor sizes in between

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Why Multi-Diameter Lines?

Multi-Diameter lines are installed due to:

• Cost

 – Procurement

 – Installation

 – Associated features• Standardisation – deepwater 

 – Valves

 – Connectors

• Weight

• Space

• Necessity

 – Tie-in

 – Control Pressure losses

Subsea Pigging Loop

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Pig Selection

Purpose of Pigging Operation:

• Dewatering

• Cleaning – debris removal• Gauging

• Batching

• Inspection

• Camera

• Apply internal treatment Wax Removal

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Pig Design

• Internal Diameters

 – Range of sizes

• Bend Radii

 – 5D, 3D or 1.5D• Feature definition and configuration

 – Valve

• Gate

• Full bore ball

• Check

• Lengths of run

• Transitions

• Location of features

 – In relation to one another and specified diameters

Factors Affecting Pig Design:

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Pig Design Continued

Factors Continued:

• Flow and Pressure Conditions

• Medium

• Expected Debris or Internal Line

Condition

• Pig Trap

 – Dimensions

 – Configuration• Interaction of Pig Characteristics

to Negotiate Features

Build up of Deposits

Dual Diameter with Unbarred Tee

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Provision of Data

Interaction of line and pig features

Influencing factors:

• Interaction

• Variation

• Combination

 All available data is of use in the

process of design: ‘Every LittleHelps’ 

Stick to the facts – never assume

Wye and Bend Combination

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Prototype Development and

Validation Testing 

Why Test?

• Prove design

• Prove Functionality

• Gather Data

• Experience the unpredictable

The overall objective tomaximise tool effectiveness

and to minimise risk Test Rig Example

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Case Study 600m Water Depth: 8” x 10” Flooding,

Cleaning and Dewatering Tool 

Operational Requirements:•  8” Launcher and pipe work ID = 190.5 mm 

• Connector ID = 179.8 mm

• 5D bend ID = 190.5 mm

• Tapered transition = 1 in 6

•  10” Line ID = 241.3 mm 

• Buckle arrestor = 236.5 mm

• Length fixed at 400 mm due to laydown head

• To be back loaded in to laydown head ID = 190.5 mm

• Bi-directional capabilityFunctional Requirements:

• Remove construction debris

• Flood line for hydrotest

• Dewater line

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Pig Design:

• Mandrel Body

• Segmented Supportsactive in all diameters

• Diameter specific seals

for each line section

• Symmetrical disc packs

• Transmitter housing

Initial Design

Case Study 600m Water Depth: 8” x 10” Flooding,

Cleaning and Dewatering Tool 

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Test Rig Design:

Case Study 600m Water Depth: 8” x 10” Flooding,

Cleaning and Dewatering Tool 

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Final Proven Design

Modifications made following trials:

• Extra discs fitted and radial grooves added

to improve support in larger diameter 

• Support flexibility improved in taperedtransitions through reconfiguring the disc

pack

• Quantity of sealing discs reduced to

prevent discs clashing and loss of positiveseal

Pig has successfully been run in field

operations

Case Study 600m Water Depth: 8” x 10” Flooding,

Cleaning and Dewatering Tool 

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Conclusions

• Involvement in the FEED stage is invaluable for both parties

• Free flow of information is key to an effective and suitable

design solution

• Changes are ok, but the impact must be assessed

• Testing of the intended design is essential at reducing the

risk involved in field operations

• With modern design capabilities and functional testing, multi-

diameter pigging need not be a subject to be avoided,

instead with careful consideration even the most arduous of 

diametrical variations may prove piggable

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End 

Thank you kindly for listening

Questions Welcome