This paper addresses technologies primarily for the transportation of natural gas by offshore pipelines from remote sources to the downstream transmission and distribution network, and also to land oil and gas from deepwater fields. Emphasis is placed on the possibilities to improve transportation efficiency and to expand present offshore pipeline limitations.
Essential code requirements to the design of pipeline wall thickness have remained unchanged for several decades. The quality standards for design, construction and operation have gradually been improved, and failure statistics for modern pipelines are very good. Present wall thickness criteria may therefore be unnecessarily conservative. Improved transportation capacities may be achievable by the use of probabiiistic design methods and more rational acceptance criteria, associated with the modification of code requirements to allow such an approach.
Recent offshore gas transmission projects, such as the 26" Transmed pipelines to 600 m water depth and the 40 Zeepipe pipeline with 800 km pigging distance, have been made possible by significant advances in the capabilities of pipeline technology. Pipelines to depths beyond 800 m have now been installed in connection with the development of oil and gas resources. The further development of offshore pipeline capabilities, in terms of pipe size, pigging distance, water depth and seabed conditions is discussed in relation to design, construction, commissioning and operation aspects.
TECH NO LOGY STATUS The present overall status of offshore pipeline technology is characterized by achievements within a few projects, discussed below.
The Zeepipe pipeline between the Sleipner field in the North Sea and Zeebrugge has a diameter of 40 and a length of 815 km between pigging stations'.
The water depth is a maximum 80 m along the route, and the relatively shallow water represents a particular challenge to submerged weight design and assessment of self-burial potential to minimize requirements to trenching. The Zeepipe pipeline thus represents the status with respect to length between pigging stations, with corresponding commissioning and operational pigging technology. The Zeepipe pipeline, together with the 40 Europipe pipeline now under construction to Emden, represent the status for the pipe size/submerged weight combination which is layable without trenching for protection in shallow water areas exposed to severe environmental conditions.
The first three Transmed pipelines between Tunisia and Sicily, 20 diameter each were laid in 1979/81 to 600 m water depth. These pipelines were followed in 1992193 by two 26" pipelines to the same water depth'. As part of the same pipeline system, several pipelines of 20" to 26" diameter have been installed across the strait of Messina. in some shallower water depths, but with rather severe en
