The Terra Nova FPSO vessel offered attractive capabilities for its owners over the expected 15-17 year life of the Terra Nova reservoir. But there are challenges associated with FPSOs. The conditions are harsh for the operating equipment. On-board turbines are expected to run essentially non-stop in high seas. Heavy wave action can make every maintenance task that much more difficult.
Percy Delaney is a Mechanical Maintenance Engineer with the Terra Nova consortium. He points out that “the Terra Nova FPSO is designed to remain on location for years at a time. It is also designed to withstand severe storms, known as 100 year storms.” As Delaney explains, “On one occasion we observed 14 metre waves washing over the main deck.” Typical conditions are harsh, compounded by extreme cold, high winds and fog as well as seasonal ice and icebergs.”
Among the components that made up the Terra Nova FPSO were a pair of Thomassen/General Electric PG6561B Frame 6B Heavy Duty Gas Turbines that are used for power generation. These turbines employ a geared speed reduction system. In this type of application, the lubricant has to do double duty, lubricating both the turbine bearings and gears. Consequently, this is a challenge for any lubricant because the requirements for gear lubrication are different than those of the turbine shaft bearings. According to Delaney, use of large frame turbines off shore is uncommon. Compared to the more prevalent aero-derivative turbines, frame units enjoy extended operating life but they need to be repaired on-site. The combination of confined, hazardous spaces and sea-state limits on the maintenance cranes makes repairs challenging, so reliability is critical.
Nick Finelli, a Technical Service Advisor with Petro-Canada recollects the first contact with the turbine manufacturer’s representative. “He was pretty cautious. We had no history with Thomassen. These turbines aren’t sitting on a plant floor. On the ocean, a turbine failure can be catastrophic.” Tech Services was looking for an EP turbine product. Petro-Canada Research & Development had been a couple of years in development with Turboflo™ EP 32 at the time. We knew that Thomassen had some concerns about “EP” turbine fluids. The industry had seen problems with varnishing in a similar application in the North Sea. The lube oil coolers had developed a buildup of varnish after only 18 months, while using a competitor product. This led to excessively high lubricant temperatures and an eventual 25% decrease in power before a shutdown was necessary to clean the coolers.