Pipes and tubular conduits – Distinct layers – With intermediate insulation layer
Patent
1997-03-12
2000-06-27
Hook, James
Pipes and tubular conduits
Distinct layers
With intermediate insulation layer
138146, 427409, F16L 9147
Patent
active
060794526
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the coating of pipelines and the like, particularly subsea pipelines and risers, but also other forms of ducting and piping, for the purpose of providing thermal insulation. The invention provides an improved coating method and an improved coated pipeline formed thereby.
Oil and gas are transported by steel pipes from subsea wells to fixed platforms or moored floating platforms. The oil and gas temperature at the wellhead is in the range of temperatures between 70.degree. C. and 130.degree. C. The sea temperature at seabed level of the North Sea is in the range of temperatures of between 4.degree. C. and 8.degree. C. Over a relatively short distance the oil and gas temperature is reduced to the surrounding sea temperature. This in turn increases oil viscosity and solidifies any waxes present, and in the case of gas will produce hydrate formation, drastically reducing flow and possibly causing blockage of the line.
Methods of overcoming these problems in the past have included: This method is expensive and not always effective, and is environmentally unacceptable as chemicals are entrained in the water which is present in oil wells and which is separated and dumped into the sea. larger diameter pipe concentrically. The annulus formed is filled with a polyurethane foam. Polyurethane foam produces good insulating values but is low in mechanical strength and unable to resist seawater, therefore an outer steel pipe is required to provide resistance to hydrostatic forces and produce a waterproof barrier. This method of construction restricts the way a pipeline can be installed and is most suited to shallow water and short lengths of lines. insulating material particles into a matrix of elastomer plastic or epoxy. The introduction of microspheres or insulation particles into such a matrix greatly reduces the physical properties of the matrix material. The maximum amount normally considered acceptable is approximately 40% which improves the thermal insulation property of the matrix but in many instances not significantly enough to meet common insulation requirements. extruded onto the pipe, a layer of insulation material, such as PVC foam or a similar closed cell foam able to resist hydrostatic pressures, followed by a further coat of elastomer. PVC foam has been applied in the past in the form of pre-formed, part-cylindrical shells and as helically wound strip of relatively thin material. The latter requires multiple layers to be applied. The assembled system is placed into an autoclave and cured under temperature and pressure to crosslink the elastomer and form a bond between the insulation material and the pipe. The laminated system produces a thermally efficient coating but has disadvantages. Spaces exist at the joints of the insulation material which are not filled by the elastomer. During the autoclaving, entrapped air can cause blistering of the outer cover of elastomer. If the outer coating, which is generally of low mechanical property, is breached during installation or on the sea bed, water floods the helical or circumferential joints and penetrates any striations in the insulation destroying thermal efficiency of the system.
The good insulating properties and compressive strength of high density polyurethane foam are widely recognised. However, its use in pipeline coatings has been restricted by its poor resistance to water ingress under hydrostatic pressure. This means that the foam must be encapsulated in a water-tight outer sleeve (pipe-in-a-pipe as discussed above) or coating (such as solid polyurethane elastomer), and makes the foam matrix liable to flooding in the event that the integrity of the outer coating is comprised by impact or stress either during installation or whilst on the sea-bed. Unprotected polyurethane foam will flood completely in a matter of hours and will thus lose all insulation properties. The further problems associated with the pipe-in-a-pipe approach are discussed briefly at (b) above.
It is an object of the present invention to provide an improve
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Arnott Thomas Christopher
Touzel John James
Buskop Wendy K.
Hook James
Liquid Polymers Group
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