Pushing pig designs into the future

For many years pipeline pigs have remained virtually unchanged from their ‘modern’ layout. Although there have been significant improvements in elastomeric materials (such as polyurethane used for sealing discs, guiding discs and conical cups) which have resulted in pigs that have extended wear life and resilience, the basic design parameters adopted during pig design remain unchanged. Foam pigs, cup pigs and bi-directional disc pigs have been the mainstay of most pigging campaigns, and the pipeline industry has taken a relatively risk-adverse approach, being content to use these well-proven designs.

Changes in subsea completions and the need to find cost and time-savings has introduced an appetite for change and led to the need for more creative pig design thinking. Risk of blockages and the associated costs of repair have also led to increased product testing, which has in-turn allowed the introduction of new designs of pipeline pig.

New design development

Propipe is developing new pipeline pig designs that take their cues from the ‘modern’ layout but also push pig designs into the future. These designs are being proven at Propipe’s In-House Test Facility and then field-proven on projects worldwide. This work is helping to unlock the ‘dark art’ of pig design and allowing pigs to be developed to meet even the most exacting of demands, as well as allowing clients the opportunity to see pigs in action and to both learn and contribute to the pig design and testing process. This open approach enables clients to gain valuable knowledge and an understanding of how the pigs will perform and (more importantly) what to expect if, or when, things change offshore.

With the increasing need for pigs to pass through multi-diameter pipelines this has also forced the development of new pig types. Where traditional multi-diameter pipelines have diameters that have stepped around 50 mm from minimum to maximum bore (such as 8 in. x 10 in. or 18 in. x 20 in.), now diameter changes up to 100 - 200 mm, with lines such as 16 in. x 20 in. or 32 in. x 24 in. are becoming more prevalent.

Propipe wheeled-support pigs were developed specifically for multi-diameter pipelines where good centralisation is required to maintain a constant seal through all ID’s and features. The pigs use a series of wheel mounted arms mounted to a central suspension system. This allows the suspension arms to move as a collective unit and provide constant support and centralisation. This action ensures that the pig does not drop its centreline below the pipeline centreline, which in turn means that the sealing discs are always centrally held within the pipeline, giving 100% seal efficiency.

Conventional pipeline pigs use rigid polyurethane guide discs to support the weight of the pig and guide it through the pipeline, but these guide discs can suffer from compression set or slow recovery (when used for large diameter changes), which can mean a loss of seal. Sealing discs that are held centrally within the pipeline provide maximum sealing ability, which ensures maximum dewatering ability.

In many cases, piggability trials and offshore operations have confirmed that wheeled-support pigs can be run with a small number of seals and provide extremely high dewatering performance. The low running DP also helps to ensure that the pig is allowed to perform at its optimum without any speed-affected loss in performance. Pigs can carry brush modules, bypass jetting units plus both standard gauge and/or Trident SMART gauge systems.

Although the primary aim of the wheeled-support pig is to allow dual or multi-diameter pigging, by utilising a rolling support system and removing the guide/support discs required by conventional bi-di pigs, running pressures through the pipeline system also reduce significantly. This lowering of the running pressure can offer significant cost savings when considering liquids removal operations, such as pipeline dewatering...

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