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PIPELINE ENGINEERING

Multi-Diameter Pigging – Factors affecting the design and selection of pigging tools for multi-diameter lines

Karl DawsonPPSA Aberdeen19th November 2008


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


Definitions

Industry Accepted Definitions:

• Dual-diameter – Operates in 2 distinct diameters

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


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


Pig Selection

Purpose of Pigging Operation:

• Dewatering• Cleaning – debris removal• Gauging• Batching• Inspection• Camera• Apply internal treatment Wax Removal


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:


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


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 Little Helps’

Stick to the facts – never assume

Wye and Bend Combination


Prototype Development and Validation Testing

Why Test?

• Prove design• Prove Functionality• Gather Data• Experience the unpredictable

The overall objective to maximise tool effectiveness and to minimise risk Test Rig Example


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 capability

Functional Requirements:• Remove construction debris• Flood line for hydrotest• Dewater line


Pig Design:

• Mandrel Body

• Segmented Supports active in all diameters

• Diameter specific seals for each line section

• Symmetrical disc packs

• Transmitter housingInitial Design



Test Rig Design:



Final Proven Design

Modifications made following trials:

• Extra discs fitted and radial grooves added to improve support in larger diameter

• Support flexibility improved in tapered transitions through reconfiguring the disc pack

• Quantity of sealing discs reduced to prevent discs clashing and loss of positive seal

Pig has successfully been run in field operations



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


End

Thank you kindly for listening

Questions Welcome

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