atg UV Technology and Aberdeen-based subsea BOP controls specialists Raisepower have recently carried out pilot trials to prove the effectiveness of UV-disinfection in treating hydraulic fluids used for subsea blow out preventer (BOP) operation.
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 bacterias (SRBs) 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:
- Potable-grade freshwater
- Glycol-based antifreeze
- 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 B.O.P. failure and unrepairable damage of the blow out preventer 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 specialised application. This requires advanced engineering to overcome the barriers regarding UV dose delivery into the B.O.P. 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 caramelising and burning the sugars present in the glycol-based additives.
Working with Raisepower, atg UV Technology designed a unique treatment solution that combined UV treatment and filtration. 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, to fine-tune the design and prove the effectiveness of UV light as a sterilization technique for the mixed hydraulic operation fluid.
Following the success of this original research, atg UV Technology and Raisepower installed a fully operational, ATEX Zone 2, IIB, T3 certified UV treatment, filtration and pumping skid package for 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.
Raisepower subsea control solutions technical manager Andy Downs said: "With review of a year’s fluid analysis results, the tanks that feed the BOP fluid mix tank with freshwater, 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. This demonstrates that the filtration and UV disinfection solution is achieving as near perfect result as you can get."
For more information, please contact atg UV Technology.