First SPAR platform for Norwegian waters

Specialized equipment & materials

Subsea 7 were contracted to perform the tow-out and hook-up of the SPAR FPSO, including the Steel Catenary Riser (SCR) system and reeled installation of 12” BuBi® mechanically lined pipe. This involved the fabrication of flowlines and SCRs at Subsea 7’s spool base facility at Vigra, Norway. In order to allow the 12” BuBi® pipe to be welded and reeled onto the vessel, STATS Group provided positive isolation of the pressurised pipe during spool reeling operations.

The BuBi® (short for BUTTING – Bi-metal) pipe is a corrosion resistant pipe which is telescopically aligned inside a pipe in carbon-manganese material. The tight mechanical bond between the pipes is achieved in a hydroforming facility. For many years these pipes have been successfully used in very demanding and sensitive onshore and offshore areas of the oil and gas industry where they are used as pipelines, riser pipes and SCR-pipes for highly corrosive media. Mechanically lined pipes provide several advantages in these applications such as:

Cost savings of up to 40 % compared to solid pipes

High corrosion resistance at the inside and high pressure resistance at the outside

Project-specific material combinations

Subsea 7 contracted Aberdeenshire based STATS Group to provide positive isolation of pressurised mechanically lined BuBi® pipe to facilitate reeling onto a pipe lay vessel at their facility in Norway, prior to installation at the Aasta Hansteen gas field. STATS proposed the use of their Pipe End Plugs which feature locks and dual seals and are capable of conducting pressure tests up to 200 bar.

Pipe End Plugs are typically used during the construction and fabrication of pipe spools and piping systems; these fail-safe tools cap open-ended pipe, facilitating hydrostatic leak and strength tests. Pipe End Plugs provide many benefits: hydraulically activated, they are quick and easy to install, providing a safe and cost effective solution. STATS range of Pipe End Plugs cover two separate products, the I-PEP™ which fits internally to the pipe and the E-PEP™ which grips the pipe externally.

Once water began to flow through the open valve on the E-PEP™, the valve was closed and the pressure held. The pressure acting on the E-PEP applies differential pressure across the tool, which self-energises the locks and seal, ensuring fail-safe operation.

The pipe stalk was then reeled onto the vessel until the end of the pipe stalk was located in the welding station. The pipe stalk was then depressurised and the valve on the E-PEP™ was opened allowing the water to drain from the stalk and the E-PEP™ was hydraulically unset and removed from the end of the stalk.

Successful collaboration

The project took place in 2016 and consisted of 17 km of BuBi® mechanically clad flowlines being reeled onto the vessel and installed at the Aasta Hansteen gas field. STATS also supplied a mechanical clamp and 1” hot tapping machine to facilitate the draining of the pressurised spooling fluid from the pipe once it was reeled onto the vessel. Specialist hot tapping cutters and a four stage process allowed the mechanically lined pipe to be hot tapped to eliminate contamination of the flowlines with drilling swarf.