Seal-tube system vital to gas-pipe pull-in

New, innovative technology from the Jotne Group contributed to the successful pull-in of the Åsgard transport gas pipe. The pipe line, operated by Statoil, brings gas all the way from the Halten bank, northeast of Trondheim, to Kårstø and further to the continent in the Europipe II gas pipe.

This was the third time that pipes were pulled in from the sea to the Kårstø facilities in Rogaland. Various solutions have been found to the challenge of bringing the line safely through the rough waters of the breaking zone and then fixing it to permanent structures. On previous occasions, divers were crucial to the success of the operation. This time, they were no longer necessary.

Jotne SB-Verksted constructed a seal-tube system consisting of four parts: a seal-tube sleeve placed in the actual opening between the sea and the rock chamber, an emergency shutdown (ESD) valve, a receiving chamber, and stripper valves. The entire structure was nearly 20 meters long when it was delivered.

The pull-in of the gas pipe took place at a depth of approximately 55 meters. A specially formed consortium was responsible for the operation, with contracts worth a total of more than NOK 60 million. Extensive use of subsea robots, video cameras, and specially constructed tools and supply vessels were vital to the success of the operation.

During the pull-in, the leakage rate of the seal-tube system varied between 350 and 600 liters per minute, which was well below the maximum limit of 1000 liters per minute. After the pull-in, all three inner sections of the system were removed, leaving the seal-tube sleeve as the only permanent fixture - and a leakage rate of zero.