The Frigg pipelines with 730 kilometres of 32 inch line constitute one of the largest pipeline systems in the North Sea and will transport in excess of 15 billions cubic mtrs of natural gas per year from the Frigg field to Scotland. In line with the field platform development and with the inshore facilities the pipelines are scheduled for completion in 1977. Construction started in 1974 and involved in 1974, 1975 and 1976 some of the largest and most sophisticated North Sea construction equipment as well as extensive logistics. The simultaneous use of several lay barges required detailed and careful planning of the pipe laying and subsequent operations and made it necessary to have a technique available for tie-in between sections of pipe laid by lay barges. One of the major decisions made in planning the construction was the choice of underwater dry environment hyperbaric welding as this technique.
A first tie-in operation was successfully completed in 1975and was followed by nine more such operations in the summer of 1976. Some of these operations had been initially planned, others resulted from a delay in installation of the intermediate platform or from changes in the. strategy aimed at ensuring a maximum use of the lay barges during their periods of commitment. Two of these operations were repairs following buckling of the pipe.
This paper describes the Frigg pipeline system, reviews the major construction equipment involved in its construction and provides an history of the construction with emphasis on planning decisions in relation with lay barge and tie in and repair operations.
The Frigg field which was discovered in 1971 is located across the continental shelf between Norway and the United Kingdom at a latitude of nearly 60°North. The field is one of the largest gas fields 1n the North Sea and will produce in excess of 15 billions cubic meters of natural gas per year representing approximately one third of the UK present gas requirements. Early in the course of the development planning work, it was decided to divide the operating responsibilities between ELF NORGE A/S a subsidiary of the ELF/AQUITAINE Group and TOTAL OIL MARINE LTD, a subsidiary of TOTAL-COMPAGNIE FRANCAISE DES PETROLES. ELF NORGE was to be in charge of the field development and operation while TOTAL OIL MARINE was to be in charge of the gas transportation system consisting of two identical pipelines to Scotland, an intermediate manifold/compression platform and the shore gas terminal at St. Fergus on the coast of Scotland. The decision to go ahead with the construction of the first pipeline was made in early 1973 and actual operations started in 1974.