Prestressed Cryogenic Pipelines

The main technical problem holding up the use of buried, submerged, and long-distance liquified natural gas (LNG) and other cold fluid pipelines is the high longitudinal stress resulting from the temperature difference between operating and nonoperating conditions. Prestressing can solve this main problem, but introduces secondary problems which can be solved within the framework of existing technology. A piping system suitable for prestressing can consist of an inner insulated conveying pipe within a steel casing. The steel casing protects the conveying pipe and insulation from mechanical damage and can furnish restraining load for the prestressing. For cold fluids the inner pipe is preloaded in compression to fully or partially compensate for the contraction forces. If the inner pipe is only partially prestressed, a longitudinal tensile stress will develop at operating temperature. The alignment requirements and the assembly procedures for prestressed LNG pipelines lead to the concept of combining the pipeway with a railway or a highway for minimal overall costs.