To keep the conveyed fluid warm, the pipeline should be heated by active or passive methods. The active heating methods include, electric heat tracing wires wrapped around the pipeline, circulating hot water through the annulus of pipe-in-pipe, etc. The passive heating method is insulation coating, burial, covering, etc.

Oilfield pipelines are insulated mainly to conserve heat. The need to keep the product in the pipeline at a temperature higher than the ambient could exist for the following reasons including:

In liquefied gas pipelines, such as LNG, insulation is required to maintain the cold temperature of the gas to keep it in a liquid state. This chapter describes commonly used insulation materials, insulation finish on pipes, and general requirements for insulation of offshore and deepwater pipeline.

Polypropylene, polyethylene, and polyurethane are three base materials widely used in the industry for pipeline insulation. Their thermal conductivities are given in table below:

Depending on applications, these base materials are used in different forms resulting in different overall conductivities. A 3-layer polypropylene applied to pipe surface has a conductivity of 0.13 BTU/hr-ft-8F, while a 4-layer polypropylene has a conductivity of 0.10 BTU/hr-ft-8F. Solid polypropylene has higher conductivity than polypropylene foam. Polymer syntactic polyurethane has a conductivity of 0.07 BTU/hr-ft-8F, while glass syntactic polyurethane has a conductivity of 0.09 BTU/hr-ft-8F. These materials have lower conductivities in dry conditions such as that in pipe-in-pipe applications.

Because of its low thermal conductivity, more and more polyurethane foams are used in deepwater applications. Physical properties of polyurethane foams include density, compressive strength, thermal conductivity, closed cell content, leachable halides, flammability, tensile strength, tensile modulus, and water absorption. The values of these properties vary depending on density of the foam.

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Source:

Lee, Jaeyoung. Introduction to Offshore Pipelines and Risers. 2007.

Guo, Boyun, Shanhong Song, Jacob Chacko, Ali Ghalambor. USA. 2005.