Pipeline thermal insulation is a prevention due to temperature difference between pipeline outer surface and inner part of the pipeline. Pipeline thermal insulation is considered as important since its contribution to corrosion as well as wax and hydrate problems in offshore pipeline system.
Pipeline insulation as figured below:
1. Condensation That Lead to Corrosion
Pipes operating at relatively low temperature (with hot fluid flows inside, e.g. offshore pipeline) increases the potential for existing water vapour to condense on pipe surface. And this moisture may lead to corrosion on the pipeline surface.
2. Wax and Hydrate Formation
In oil and gas industry, excessive cooling of the product during transportation can result in drop out of high molecular weight waxes and asphalt. This happens due to the working temperature of the pipeline (deep in the depth, above the seabed where the temperature is relatively low). In wet gas systems, hydrate formation can block pipelines (flow).
INSULATION METHODS
There are few methods that can be used for insulation, such as use of cooling spool, material selection, and pipe in pipe (PIP).
Use of Cooling Spools
There can be significant cost benefit from cooling the product stream from very high temperature wells to minimize the thermal expansion forces and then maintaining this lower temperature for through efficient pipeline insulation reducing the volume of post lay rock dump or trenching required or enabling more conventional materials and analysis techniques to be employed.
Material Selection
Typically, pipeline insulation must be able to withstand the stresses imposed as a result of the installation methods and strong enough to withstand constant external pressure and function effectively when submerged and saturated.
The dry, load-free environment within the annulus of the pipe allows non-typical insulation materials with much lower thermal conductivity to be applied subsea than has historically been possible e.g. rock-wool systems etc. There are also few materials used for insulation have been around for a few decades and include polypropylene, polyurethanes, epoxies and rubbers.
Figure below shows installation of material for pipeline insulation:
PIPE IN PIPE (PIP)
Pipe in Pipe (PIP) is installation of a second pipeline around the product pipeline from the seawater surrounding it and creates a dry chamber around the pipeline that can be engineered to accommodate a range of advanced insulation techniques.
Figure above illustrates Pipe in Pipe technology for offshore pipeline.
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