INSULATING TECHNIQUE TO SEE FIRST USE IN NORTH SEA DEVELOPMENT

A new pipeline-insulating technique that saves heating costs and eliminates or reduces hydrate formation will see its first use as part of Total Oil Marine plc's development of the Dunbar field in the U.K.'s North Sea sector. The proprietary insulation was jointly developed by Interpipe and Total S.A., Paris. It is at least four times more efficient than standard insulation, according to Total, in retarding hydrate formation in the gas, condensate, and produced water that will move 15

May 17, 1993

2 min read

The proprietary insulation was jointly developed by Interpipe and Total S.A., Paris. It is at least four times more efficient than standard insulation, according to Total, in retarding hydrate formation in the gas, condensate, and produced water that will move 15 miles by pipeline from Dunbar to North Alwyn field.

The line will run in 450 ft of water. At this depth typical seabed temperatures of 4-8 C. normally promote hydrate formation in a hydrocarbon pipeline.

READY FOR PROCESSING

Dunbar, in North Sea Block 3/14a, holds 120 million bbl of light oil and 500 bcf of gas. A satellite wellhead platform will be used to send oil and gas to North Alwyn for processing and export (OGJ, Jan. 25, p. 44).

Using Interpipe's thermal insulation, Dunbar's wellstream will arrive on North Alwyn at 50-60 C., the correct temperature for processing.

This will save heating costs and avoid the hydrate formation which, with Dunbar's output, would start at 20 C.

Interpipe said the new system will cost about the same as a standard insulated pipeline.

SPECIAL JOINING

Fabrication will be carried out by Rippin Ltd., Auchtermuchty, Scotland, which will receive 16 and 20-in. pipe in 12-m (40 ft) lengths from British Steel plc.

Rippin will fabricate the lengths into concentric sections, the 16 in. inside the 20 in., and weld up 1,000 24-m sections for the 24-km (15 mile) line. The annulus will then be filled with insulating material and an inert gas and sealed at both ends with a tulip-shaped spacer (Fig. la).

A specially developed joining technique will enable pipelaying to be carried out with conventional barges at about the same speed as normal pipelaying.

In the offshore joining process, the inner pipes are welded and the outer pipes are connected by means of a screwed coupling sleeve. A special resin is injected at the joint to make it watertight (Fig. 1b).

Fabrication of the double-walled sections will be complete by early 1994, ready for pipelaying in summer.