When Shell Exploration & Production subcontractor Jacobs Engineering was tasked to make modifications to a potable water system aboard Perdido, changes included a requirement for a positive break tank.
FiberSystems explains that, moored in the Gulf of Mexico, Perdido is the world’s deepest offshore oil drilling and production platform. Specifications for the tank, which allows trapped gases in the service line to escape through atmospheric vents while letting seawater pass through to water-makers to be turned into drinking water, called for material that iscorrosion resistant, light weight and low maintenance.
FiberSystems say that Jacobs approached it, “FiberSystems was the only company we could find that was capable of designing and fabricating the FRP vessel,” says Jesse LeBoeuf, a Mechanical Engineer for Jacobs. “The alternatives we considered were heavier, more costly and more difficult to maintain; issues that are problematic for offshore platforms.”
FiberSystems was given a preliminary CAD drawing and 12 to 14 weeks to design, fabricate and ship the tank. “It was a concept we hadn’t seen before,” says the FRP manufacturer’s Production Supervisor Dave Orr. “One of the problems we had to solve was how to anchor a free standing pipe on the inside of the tank. Fabricating the tank’s cradle and determining the best method for adhering the top dome to the main body of the tank was also challenging. Unlike a commodity shop though, we’re accustomed to taking on unique projects like this one. It’s one of our core strengths.”
FiberSystems filament wound the main body of the tank along with eight stubs and flanges using a high-performance grade of methacrylate epoxy resin pigmented gray. Holes were pre-drilled and cut. “We used 113 yield fibreglass because we wanted to build tank walls up quickly, twice as fast as the thickest glass,” notes Orr. The tank’s flat base and cradle were also filament wound. A hand lay-up process was used to fabricate the tank’s upper and lower domes which were bonded to the tank with adhesive. “We then butt welded and wrapped the joints for added strength,” says Orr. Interior layups, the free standing pipe inside the tank and the exposed openings were sealed with a resin wax coating. Weighing 1000 pounds, the tank measured 11 feet, 8 inches tall with a 30-inch inside diameter.