OPERATIONS & MAINTENANCE SECTION TITLE
these can be found in any kind of offshore/ onshore/desert oil and gas application. Lube oil systems commonly found on oil platforms are used for transporting oil from the main tank to the engine. As Barnett explains, stainless steel-housed filters are required for these systems to protect the turbines. Further applications for filtration include installation workover control systems and chemical injection systems. Some of the more unusual applications for filtration highlighted by Barnett include subsea boosting. “When an oilfield is closed down there can be approximately 20 to 25% of the oil reserve still left in the well,” he says. “To extract some of this remaining reserve, an HPU is put on the seabed. An HPU normally has three filters mounted to its hydraulic system. If the HPU is submerged to 3,000m deep 300 bar is required, so the deeper the wells the higher the pressure required. We have seen 1,400 bar for filters topside and even a few instances – in the case of testing – 2,000 bar.” Remote operated vehicles (ROVs) in seawater is another important but less common application that requires filtration equipment. “Carbon steel filter housings can be used on ROVs, and I’ve also seen aluminium used,” Barnett points out. “However, in many cases they are being swapped out for stainless steel to extend their lifespan.” He adds that another long- term application is subsea control modules (SCMs) used to control each wellhead. Tese SCMs normally have two or four filters fitted to them, one medium pressure (345 bar) and one high pressure (690 bar). Tim Wright from Pall explains that in the case of subsea control systems, there has been a strong trend towards the use of water-based fluids. “However, mineral oil-based systems are still used, which means oil purifiers (dehydration) are also needed to remove water from systems due to the hygroscopic nature of these fluids.” For offshore control applications, filters are normally designed for water glycol-based fluids for the likes of MacDermid Oceanic series production control fluids. With this in mind, Barnett explains that Hydac has developed and fits special elements to its filters to optimise them for these fluids.
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ROVs require filtration equipment
COMPATIBILITY Wright states that typical industry standards for filter media materials include glass fibre, polypropylene and nylon and fluid compatibility issues must be considered carefully for each application. “For example, in the case of diesel, polypropylene filter media should not be used,” Wright stresses. “Light hydrocarbons are also not suitable for long-term use with polypropylene. Similarly, for water applications that are running at above 60°C, glass fibre is not compatible. Compatibility is important, especially with the wide range of chemicals that are used for injection – you must ensure chemical
compatibility for each application.” Further
downstream, there are more fluid power-
M P Filtri monitoring tool
related applications, such as hydraulic motors, pumps, compressors and
various other hydraulic systems in an oil refinery or a gas plant, for example. “For this equipment to remain reliable and operational – with little or no unforeseen and costly downtime – correctly sized and compatible filtration systems are crucial,” explains Wright. “Filtration systems used for these types of onshore applications would normally be constructed of standard industrial-grade carbon steel rather than stainless steel or higher alloys, which are commonly used in offshore applications due to the harsh corrosive environment in which they operate.”
INTEGRITY As with any hydraulic system, cleanliness affords greater reliability and longevity. “Indeed, in the case of applications in the desert or subsea, reliability and longevity are particularly important,” says Barnett. “Tis is because it can be very expensive to replace parts and equipment due to the relative inaccessibility of where they are situated – you can’t train a dolphin
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