MECHANICAL SEALING TECHNOLOGY USED IN MULTIPHASE PUMP APPLICATIONS
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Date
2022
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Turbomachinery Laboratory, Texas A&M Engineering Experiment Station
Abstract
Multiphase pumps have demonstrated their capability to operate successfully in pumping the product extremes, means 100% liquid up to 100% gas, as well as solids. This duty is difficult for a pump and thus even more difficult for its mechanical seals, which are a critical component of any pump. Mechanical seals are readily available for liquid or gas applications. However, in a multiphase pump the mechanical seals are exposed to multiphase mixtures, sealing liquids like crude oil and formation/produced water, but also natural gas and solids like sand or all kind of debris or cracked hydrocarbon products. Consequently, special mechanical seals had to be developed to handle the product extremes under transient conditions, unpredictable flow composition and a (natural) gas content up to 100%. The biggest challenge for a mechanical seal manufacturer is to design extremely stiff sliding seal faces with the ability to maintain acceptable liquid lubrication to avoiding contact and wear of the mechanical seal faces. Another challenge is the proper selection of the secondary sealing element materials, which are prone to extrusion, excessive wear and explosive decompression associated with sealing gases under high pressures. In this tutorial, we share an overview about the most used multiphase pump technologies, like twin-screw pumps, progressive cavity pumps and helico-axial pumps. We would like to describe the challenges for its mechanical seals, as some pump types use only one mechanical seal, while other pump types require up to four mechanical seals. We focus on a comprehensive overview about the different concepts sealing multiphase with single seals or with dual seal arrangements, handling density variations, viscosity variations, erosion and corrosion effects at high or extremely low temperatures in onshore, offshore and even subsea applications. We also describe specific seal face materials, like Diamond Face Technology, a new face material which offers specific benefits in these multiphase applications.
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