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The use of pigs to clear pipelines is well practiced in the oil industry today. Pipes carrying both crude oil and its derivatives can often suffer from a build-up of waxy deposits, sometimes caused by changes in pressure, or temperature in the pipeline. Significant wax deposits and blockages can be potentially catastrophic for the continued operation of the pipeline.
Waxes can vary greatly in texture from a viscous liquid, to soft deposits with varied properties - textures from boot polish to candle wax at its most solid. The deposits can reduce pipeline diameter which can cause a large pressure drop and in the worse case the build-up of deposits becomes so severe, the pipeline blocks and oil transmission may cease completely.
Ice Pigging versus traditional pigging methods...
A variety of techniques can be used to remove wax accumulations, the most common being to use a solid ‘pig’. Solid pigs are typically a 1 or 2m long device which is propelled along the pipe using high pressure oil, water or air.
The pig scrapes wax deposits as it travels and can return the pipe to a serviceable condition. The major disadvantage of introducing a solid pig into any pipeline is the risk of the pig becoming stuck which in many cases, can risk causing major disruption and cost.
Solid pigs are inherently inflexible, and have been known to become stuck at bends, changes in diameter, where the pipe is heavily soiled, or where there has been deformation in the pipe.
As a result of the risk of solid pigs becoming stuck, many pipes have now been classified as ‘unpiggable’ by their operators.
Click here to watch our Ice Pigging test on Oil Pipes
Before and after Ice Pigging
How Could Ice Pigging help?
Ice Pigging can be applied where the risk of a solid pig becoming stuck is unacceptable, or where the topology of the pipeline limits the use of a solid pig. The ice used in Ice Pigging is capable of navigating bends, changes in diameter, butterfly valves, and obstructions that may otherwise render the pipe work unpiggable. The beauty of ice slurry is that if it were to become stuck it will eventually melt.
The pigs created in Ice Pigging can be injected via small diameter fittings (2” injection points are common), and can be formed easily in large diameter pipes without major enabling works.
Ice Pigs are many times longer than solid pigs - often as long as 500m in length - and work by gradual removal of contaminant. The result is that ‘bulldozing’ and any subsequent risk of blocking is not commonly seen with ice pigging.
Ice Pigging can be applied in pipe diameters from 50mm up to 700mm and can be applied effectively in hot climates, just a bit more ice is needed to counteract some melting. Ice Pigging is best suited for pipe runs of no more than between 5 or 10km, and very suited to short sections of pipe that have previously been judged as unpiggable.
Proof that Ice can remove wax deposits
Tests were conducted to prove that Ice Pigging is capable of removing highly viscous oil-based waxes. The tests, conducted on a specially constructed test rig, used 100kg of paraffin wax (mixed with a black dye) smeared around the inside of a 24” diameter pipeline, to replicate contamination of the pipeline with soft wax deposits.
The pipe was pressurized with water, and then approximately 5 tonnes of very thick ice was injected into the pipe, sufficient to form a semi-solid ‘ice pig’. The ice used was considerably thicker than used in other ice pigging applications. This was necessary to create sufficient shear force on the inside of the pipe to remove the viscous wax.
As with most ice pigging operations, water pressure was used to push the ice pig along the pipe. The ice successfully navigated the bends and changes in diameter, and gradually removed the wax from the pipe. The ice and wax was collected in a container for examination and safe disposal.
Once all of the ice had been pushed through the pipe the rig was disassembled for examination. This revealed that virtually all of the wax had been removed from pipeline save for a very thin film, consistent with results seen with similar contaminants in smaller pipes.