atg UV Technology and Aberdeen-based subsea blowout preventer controls specialists Raisepower have designed a treatment solution that combined UV treatment and filtration to prove the effectiveness of UV disinfection in treating hydraulic fluids used for subsea BOP operation.
A fully operational, ATEX Zone 2, IIB, T3 certified UV treatment, filtration and pumping skid package was installed on the Transocean SEDCO 712 rig in September 2013. After more than a year’s operation, the results have been highly impressive with the fluid mix tank continuously showing zero bacterial growth.
“With review of a year’s fluid analysis results the tanks that feed the BOP fluid mix tank with fresh water, glycol and soluble oil are all showing levels of bacterial growth and notable particle contamination. However, the mix tank which features the UV treatment package is showing undetectable results in both bacteria and solid particle counts,” said Andy Downs, technical manager, Raisepower subsea control solutions
UV light is a chemical-free, physical disinfection technique that is widely used throughout the offshore sector for applications such as potable water disinfection, RO membrane protection and for the reduction of sulphate reducing bacteria from well injection fluids and produced water.
BOPs are critical safety devices used to prevent the uncontrolled flow of liquids and gases during drilling operations. Typically, BOPs are controlled and operated by hydraulic fluids comprised of potable grade fresh water, glycol based antifreeze and soluble lubricants with corrosion inhibitors. If left untreated, the levels of bacteria present in the BOP controls fluid can quickly begin to rise. This growth is quickly accelerated by the sugars present in the glycol mixture. Bacterial growth is now a hot topic with operators, as even small amounts of biological activity can lead to a range of negative consequences including; microbial corrosion on the fluid lines, corrosion of the BOP and control unit components and seals and control system blockages caused by the formation of particles and solids in the fluid. These can lead to critical BOP failure and unrepairable damage of the BOP itself.
Unlike standard water treatment applications that use UV disinfection to control bacterial growth such as drinking water, the treatment of BOP fluid using UV is a highly specialized application. This requires advanced engineering to overcome the barriers regarding UV dose delivery into the BOP fluid, which typically features an extremely low UV transmittance (UVT) of nearly 0% (standard UV systems are not effective below 30% UVT). In addition, the design of the UV solution needs to avoid the possibility of caramelizing and burning the sugars present in the glycol based additives.
A key aspect of the design was to establish the optimum treatment rate in order to overcome the many disinfection barriers associated with BOP fluid. A number of lab and pilot trials were undertaken at atg UV Technology’s facility in Wigan, UK to fine tune the design and prove the effectiveness of UV light as a sterilization technique for the mixed hydraulic operation fluid.
Image: ATEX Ex d UV treatment package/atg UV Technology
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