Before I tell you more about pipe-in-pipe, I’ll tell you one fact related with this topic which I just found last night during my research:

How cool is that? Ok, now back to the main purpose of this article: to explain about pipe-in-pipe and to fullfill my task assignment.

Due to the increased number of components in a pipe-in-pipe system compared with conventional pipelines, the design process is therefore more iterative in nature as the interactions of the components may necessitate design alteration.

A pipe-in-pipe system is essentially made up of an insulated inner pipe and a protective outer pipe. The function of the inner pipe is to convey fluids and therefore is designed for internal pressure containment. The inner pipe is insulated with thermal insulation materials to achieve the required arrival temperature. The outer pipe protects the insulation material from external hydrostatic pressure and other mechanical damage. Concrete weight coating is not normally required due to high submerged weight and usually low ocean current speeds in deepwater areas.

For the exploitation of HP/HT reservoirs, pipe-in-pipe system can provide the necessary thermal insulation and integrity for transporting hydrocarbon at high temperature (above 120 ^C) and high pressure (in excess of 10000 psi). Pipe-in-pipe system comprises a rigid steel flowline inside a rigid sleeve pipe. The two pipes are kept apart by some form of spacer at the ends of each joint, and by bulkheads at the ends of the pipeline.

The air gap between the inner and outer pipes provides the means of achieving the high thermal insulation. This air gap accommodates the insulation, which typically consists of either granular material poured into the inter-pipe annulus, or of a blanket form, which is wrapped around the inner pipe. In either case, the insulation material needs to be kept dry in order to maintain its insulation properties.

There are several conditions under which pipe-in-pipe systems (including bundles in this definition) may be considered for a particular flowline application over a conventional or flexible pipeline.

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Source:

Bai, Yong and Bai, Qiang. Subsea Pipelines And Risers. USA: Elsevier Inc. 2005.

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