January 31, 2020 | 3 minute read
A jack-up oil unit serving the Harding Field in the Central North Sea was experiencing frequent unplanned test separator pump failures caused by the combination of high levels of corrosive naphthenic acid and sandy conditions. The platform’s test separator pump performs a critical function by monitoring well fluids, ultimately determining which well to pump oil and gas and water from, and at what rate.
The oil company grew concerned about rising costs and labor hours required to frequently change the mechanical seals within the pump, as well as potential lost production.
John Crane’s Expertise
The company relied on John Crane’s knowledge and experience to provide a reliable alternative to existing mechanical seals. After a comprehensive analysis of the failed test separator pump seals, John Crane determined that the process fluid properties and contaminants caused an unacceptable MTBF rate. With a long history of oil and gas industry knowledge, coupled with expertise on corrosive fluid applications, John Crane recommended an alternative to mechanical seals that use the process fluid as the interface fluid.
The solution would replace the standard dual-unpressurized seals with a tested, innovative face treatment to reliably handle the less-than-ideal fluid conditions.
Based on the findings, the jack-up platform replaced the existing two test separator pump seals with John Crane’s proprietary Dynamic Lift Up-stream Pumping (USP) seals. These low-volume, high-pressure seals handle the corrosive and sandy fluid by propelling a small amount of buffer liquid along the path usually sealed by a mechanical seal face and into the higher-pressure product side. By employing a series of spiral grooves, these specially designed seals significantly reduced wear on the test separator pumps.
With non-saline water in short supply, extensive testing was required to determine if the seals would operate using filtered seawater as a barrier fluid. This would set up a sealed gap that eliminated physical contact of the faces during operation to form a sealing dam when stationary.
Upon receiving satisfactory test results, a second seal in cartridge form was added to contain the barrier fluid, allowing little or no leakage at the outboard seal at or slightly above atmospheric pressure.
Since upgrading to John Crane’s Dynamic Lift USP technology, the platform has increased seal MTBF rate from approximately one month to 84 months. The platform has been able to adhere to planned maintenance schedules and has embraced the technology adding it to other North Sea offshore operations.