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.
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
Method
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.
Pipe
in Pipe 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.
Source : http://www.offshore-mag.com/content/dam/etc/medialib/new-lib/offshore/print-articles/2011/sept/75700.res/_jcr_content/renditions/pennwell.web.600.300.jpg
Figure above illustrates Pipe in
Pipe technology for offshore pipeline.
Bibliography:
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