After successfully executing the project, CIRCOR PE presented not one, but three new designs to be incorporated into a maintenance pig fleet.
In the North Sea, an aging 18 inch (457 mm) oil export pipeline running between two platforms via a subsea WYE to then combine flow from a third platform began causing concerns for its piggability due to its diminishing flow rates.
To trial this asset, CIRCOR Pipeline Engineering (PE) was contracted to develop a pig capable of pigging these diminished flow rates.
Low flow trials
The low flow trials were conducted to determine the piggability using three different pig designs, including high seal, medium seal and low sealing pigs with data recordings for drive differential pressure (DP) and bypass rates of varying DP’s.
The objective of the trials was to provide a pig design capable of pigging at a flow rate of 0.015 m/s with minimal bypass, as excessive bypass could stall a pig in service.
CIRCOR PE manufactured the three different test pig designs using combinations of conical type cups, seal discs and support discs, with a housing for the PE data logger. The test rig was set up to incorporate a client free issues spool with the same nominal inner diameter to the pipeline.
Pumping equipment was also set up using a high water pump, including a break tank to allow transit of the pigs through the rig. The pigs were then driven through the test rig with a camera located on the open end to assess pigging performance.
CIRCOR PE’s data logging determined its medium seal pig had the best suited drive DP and pigging performance for the low flows demonstrated in the ageing pipeline. Additionally, the trialling of the pig determined that at the drive DP, there was little to no bypass past the pig.
Therefore, three medium seals were mobilised to the launch platform with the first being officially launched in May 2019. CIRCOR PE now says its basic design principle of the pig is well proven and, in different guises, has performed well in the pipeline since its commissioning one year ago.
The anticipated no bypass has been proven in the pipeline with a run DP comparable to the trialling and almost zero bypass. Additionally, the calculated pig speed and actual pig speed were within ±1 mm/s, indicating the bypass in the actual run was negligible.
CIRCOR PE says all three of its pig designs developed in the project have been incorporated into its maintenance pig fleet.
This article was featured in the July 2020 edition of Pipelines International. To view the magazine on your PC, Mac, tablet or mobile device, click here.
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