Large diameter, deep water pipelay Zeepipe IIA project

The 300 km Zeepipe IIA offshore gas pipeline was installed by European marine Contractors Ltd. for Statoil between the Sleipner A Platform and the Kollsness Terminal tunnel exit in the 1994 and 1995 lay seasons. The route passes through the Norwegian Trench and the highly undulating nearshore area at Oygarden. While smaller pipes have been laid in deeper water, with a diameter of 40 inches and a maximum water depth of 365 meters this pipeline represents the most technically demanding combination of diameter and water depth laid in the world to date. The project faced specific challenges, including high lay tensions, heavily concrete coated pipe, pipeline laydown and recovery in deep water, subsea pockmark and boulder fields, stringent lay tolerances and low residual tension requirements. This paper details the planning, installation engineering, equipment modification and innovations required to achieve successful completion of the pipeline installation.