Direct heating under study to combat pipeline wax formation

A new system for the direct heating of pipelines in waters down to 3,000 meters is to be developed by Alcatel Kabel Norge for the DeepStar IV project. In this project, the company is partnered by Thermotite, which will provide the pipeline insulation system. The contract, which is worth some NKr 8.4 million, includes the construction of a 400-meter test length, which will be built at Alcatel's Halden plant. Testing will take place in the local fjord through to spring 1999.

The project represents a new initiative in the search for viable methods of combatting the formation of hydrate or wax plugs in production pipelines when the flow has to be stopped. The problem tends to be worse in deeper water depths where the temperature of the water is lower.

A direct heating system has also been specified by Statoil for two pipeline systems to be installed on the Åsgard gas/condensate development, and the oil company is also planning to use it on other subsea projects in the Norwe gian sector, according to marketing manager Ragnvald Graff.

The DeepStar and Åsgard projects involve different types of direct heating systems. In the case of DeepStar, the pipe insulation is used as electrical insulation. All the current passes through the steel pipe. The voltage falls from that of the power supply at the end at which the current is introduced into the pipe to zero at the other end.

For Åsgard, the pipe is to be earthed at both ends, acting electrically as a return conductor in parallel with the sea. This method requires a higher power consumption, but the pipe does not need to be electrically insulated.

Alcatel was also involved in the development of the Combipipe, for which it holds patent rights together with Aker Engineering. Combipipe uses a system of induction heating. A 200-meter test length was successfully tested a few years ago, and the system was considered for installation on Statoil's Sleipner West development. In the end, it was not used, however, due to the operator's concerns over installation costs.

Under a separate DeepStar contract Alcatel has developed a steel-tube umbilical for deep-water applications. This is based on the so-called Seacat tube, which uses a combination of carbon steel and zinc for the steel tube. Seacat, which is now fully qualified, is significantly less expensive than metals such as super duplex which have traditionally been used for this role.

Alcatel already has an order for umbilicals with Seacat steel tubes. This summer, it will supply some 20 km, including both static and dynamic sections, to Shell's Macaroni development in 1,000 meters of water in the Gulf of Mexico.

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