Subsea 7 contracted 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.
Subsea 7 were contracted to perform the tow-out and hook-up of the SPAR FPSO at Aasta Hansteen, 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.
STATS used their pipe end plugs which feature locks and dual seals and are capable of conducting pressure tests up to 200 bar.
Prior to the arrival of the pipe lay vessel the first pipe stalk of 1.5 kilometers was positioned on the spooling rollers and hi-diff pigs were inserted into the vessel end of the stalk. Once installed, a reel flooding head was welded to the pipe stalk and a pull-in head was bolted to the stalk flange. The second pipe stalk of 1.5 kilometers was positioned and welded to the first stalk.
After the arrival of the vessel, the pipe stalk was attached to the vessel using the pull-in head. A STATS E-PEP was then installed to the pipe stalk and a small volume of water was injected through the E-PEP into the stalk.
This water would be used to act as a buffer for the hi-diff pigs which are pigged through the stalk as the pipe is pressurized from the vessel. The pipe stalk was then pressurized to 45 bar and the high-diff pigs were pigged towards the E-PEP.
Once water began to flow through the open valve on the E-PEP, the valve was closed and the pressure held. 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 depressurized 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.
Then the pipe stalks were welded together and non-destructive testing (NDT) was carried out to confirm the integrity of the new weld. The E-PEP was then positioned and installed at the end of the pipe stalk and water was injected through the valve on the E-PEP. The sequence was repeated to pressurize the pipe stalk, pigging the high-diff pigs through the stalk and allowing the mechanically lined stalk to be reeled onto the vessel, the company explained.
Prior to starting the final stage of the spooling operation, STATS installed a 12” I-PEP into the pipe stalk.
Campaigns took place in 2016 which 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 pressurized spooling fluid from the pipe once it was reeled onto the vessel. STATS provided specialist hot tapping cutters and a four stage process to allow the mechanically lined pipe to be hot tapped to eliminate contamination of the flowlines with drilling swarf.