Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16L—PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
  • F16L59/00—Thermal insulation in general
  • F16L59/06—Arrangements using an air layer or vacuum
  • F16L59/07—Arrangements using an air layer or vacuum the air layer being enclosed by one or more layers of insulation

Definitions

• This invention relates to coated pipes, a process for their preparation, and pipelines incorporating them.
• European Patent Application 0188340 describes pipelines having a thermally-insulating coating comprising a continuous matrix of a water- impermeable material having dispersed therein a plurality of discrete hollow units, said units being thermally conductive to a lesser degree than the water- impermeable material.
• a corrosion-resistant layer may be present between the pipeline and the thermally-insulating coating, which layer may be of a rubber product such as polychloroprene.
• a pipeline may be required to carry fluids at very high temperatures.
• oil from some off-shore fields may be at temperatures as high as about 120°C.
• the coating materials used in the hitherto proposed insulated pipelines have not been capable of simultaneously withstanding high temperatures (e.g. over about 75°C) and pressures typically encountered in deep water applications.
• the invention provides a coated pipe having a first coating layer comprising a thermally stable polyurethane elastomer, and a second coating layer comprising a matrix of polyurethane elastomer having dispersed therein a plurality of discrete hollow units.
• the invention provides a process for the preparation of a coated pipe which comprises forming a first coating layer of thermally stable polyurethane elastomer on a pipe and subsequently forming a second coating layer on the pipe, said second coating layer comprising a matrix of polyurethane elastomer having dispersed therein a plurality of discrete hollow units.
• Figure 1 is a sectional front view of a pipe in accordance with the present invention
• Figure 2 is a part sectional side view of the pipe of Figure 1.
• thermally stable is used herein to indicate that the polyurethane elastomer of the first layer is resistant to thermal degradation when the pipe is used to carry materials at relatively high temperatures e.g. above about 75°C and preferably up to about 110°C or even 120°C.
• the polyurethane elastomers of the first and second coating layers may be the same or different.
• the elastomers will be of similar composition to optimize compatibility and thus adhesion between the layers.
• the thermal stability of the material for the second layer i.e. the polyurethane matrix and discrete hollow units therein, is not usually critical since this layer is not in direct contact with the pipe.
• the polyurethane elastomers used in the first and second layers are resilient and this allows flexing of the pipe when being laid as a pipeline. Polyurethane is also abrasion-resistant.
• the first polyurethane layer generally acts as a corrosion-resistant layer between the pipe and the thermally-insulating second layer. This first layer is preferably continuous for maximum resistance to penetration. Thus, even if the second thermally-insulating coating is damaged the pipeline is protected from corrosion.
• the first layer being thermally stable, also serves to protect the second layer from the effects of heat from the pipe contents.
• the discrete hollow units dispersed in the polyurethane matrix or the second layer may be for example walled spheres containing a heat- insulating liquid, a gas (including mixtures of gases such as air and mixtures of air with other gases) or a vacuum.
• Gas-filled microspheres are especially suitable, and their walls may be for example of glass or plastics material such as polyvinylidene chloride. A number of such units can then be mixed with the polyurethane so that they become dispersed therein.
• the units are preferably introduced into the polyurethane by being present in one or more components of a mix which reacts to form the polyurethane, i.e. the units may be dispersed in an isocyanate and/or polyol component.
• the material forming the units may be of the same as or different from the polyurethane of the matrix, although generally it will be different.
• the discrete hollow units may range in size from a few microns to 200 microns in the case of microspheres; the particular units selected will depend on the type and use of the pipeline. Preferably, however, the units will be microspheres of polyvinylidene chloride or glass containing gas.
• the hollow units serve to reduce the thermal conductivity of the polyurethane acting as the matrix in the second layer. In this way, the second layer is provided with good thermal insulation properties. In addition, the presence of the hollow units substantially reduces the material costs for the coating, since the amount of relatively expensive polyurethane required to give a coating of desired insulation properties can be reduced.
• the units may be included in the polyurethane matrix in an amount selected to suit the required properties of the pipeline and preferably reduce the thermal conductivity of the polyurethane matrix material by up to about 60%.
• the units may be dispersed through it in sufficient amount to reduce the thermal conductivity constant of the second layer to around 0.12W.m" 1 .K” 1 .
• the thickness of the first coating layer will generally be chosen to ensure that, in use, the temperature drop across the layer is such that the second layer is not adversely affected by heat from the pipe's contents.
• the thickness of the first layer is conveniently about 5 to 15 mm, preferably about 10 mm.
• the thickness of the second layer will be dictated by ambient conditions and the insulating requirements of the pipeline, but generally for subsea use a thickness of 20 to 80 mm, and about 30-40 mm is preferred.
• the primer conveniently comprises a conventional two component solventless polyol-based polyurethane resin.
• the use of a polyurethane resin for the primer leads to good compatibility with the polyurethane elastomer of the first layer.
• the process of the invention may conveniently be effected as follows.
• the uncoated pipe which may be of the duplex or stainless steel type (although other materials, e.g. carbon steel, may be used), is first cleaned and prepared, for example by steam, solvent and/or shot blasting cleaning.
• the primer if desired, may then be applied, e.g. by spraying or brushing.
• the primed pipe is placed in a mould for application of the first layer. Since the pipe is often relatively flexible, it is usually supported in the mould to ensure a uniform thickness of the layer along the length of the pipe.
• the pipe may be conveniently supported using spacer rings of cured polyurethane material.
• the polyurethane first layer is then formed on the pipe by injecting uncured polyurethane into the mould and keeping it there until curing takes place.
• the second layer may then be applied by placing the first coated pipe in a second mould and again, if necessary and/or desired, supporting it therein with suitable spacers.
• the uncured polyurethane matrix material with hollow units dispersed therein may then be injected into the mould and subsequently cured.
• the finished coated pipe may then be removed from the mould.
• pipe lengths may be joined together according to conventional techniques, e.g. by welding.
• the welded joints may be preferably covered with one or more layers of polyurethane elastomer to yield a substantially continuous coating on the pipeline. Most conveniently the joints can be covered with a single layer of the elastomer used for the first layer of the pipe.
• a pipe coating 1 includes a heat-insulating resilient second layer 2, which is approximately 35 mm thick, in the form of a body of polyurethane providing a matrix which has dispersed throughout it a plurality of polyvinylidene chloride-walled hollow microspheres 3 containing gas.
• the microspheres 3 range in size from 10 to 100 microns.
• the second coating 2 surrounds a duplex pipe 4 which is conveniently 150 mm in diameter thickness provided with a first coating layer 5 of polyurethane.
• the first layer 5 is approximately 10 mm thick.
• the pipes can be used to form a pipeline having a length of up to, for example, 20 km or more and can be of any external diameter.
• the pipeline may extend from an offshore wellhead (not shown) at which the oil temperature is about 110°C, and the oil flowing in the pipeline must be kept warm for processing reasons.
• the polyurethane elastomer for the first coating layer 5 is preferably derived from a solventless polyurethane elastomer composition, e.g. it may be derived from a solventless polyether base with an appropriate isocyanate to give an injection mouldable polyurethane elastomer with good hydrolysis resistance and capable of withstanding temperatures up to 120°C.
• An example of such an elastomer composition is Hyperlast 2851/407 available from Macpherson Polymers Limited of Stockport, Lancashire, England.
• the polyurethane elastomer is capable of providing a tough coating which is highly chemical and temperature resistant and impervious to moisture and sea water. It is also resistant to abrasion and has high tear and tensile strength, as well as being highly resistant to ozone attack and flex cracking. It is resistant to oils, waxes and gases and most aliphatic hydrocarbons.
• the polyurethane component of the second layer 2 may be the same as or different to the polyurethane of the first layer 5.
• the insulation properties of the polyurethane are conveniently substantially modified by inco ⁇ orating gas-filled microspheres 3 of polyvinylidene chloride.
• the large number of gas-filled microspheres 3 in the coating 1 thus gives the pipeline a good degree of thermal insulation and also provides a degree of abrasion resistance for the coating.
• the walls of the microspheres 3 prevent water from penetrating through interconnecting bubbles in the coating, as can happen in the case of foamed polyurethane in which air bubbles rather than walled microspheres provide the insulation.
• a particularly preferred polyurethane composition for forming the elastomeric matrix of the second layer is Hyperlast 2851/512 also available from Macpherson Polymers Limited.
• the pipeline of this embodiment can be manufactured as follows.
• the pipe 4 is first cleaned, e.g. by steam cleaning and or shot blasting, and a primer is applied.
• the primer may be a conventional two component solventless polyurethane primer such as, for example, Hyperlast 2874/016 available from Macpherson Polymers Limited.
• the primed pipe 4 is then placed in a mould usually within 30 to 90 minutes of applying the primer, and the polyurethane composition of the first layer 5 in injected into the mould around the primed pipe 4.
• the polyurethane is then allowed to cure, forming the first layer 5.
• the polyurethane composition is derived from isocyanate and polyol components, and prior to their introduction into the mould they are maintained apart in separate holding tanks.
• the isocyanate and polyol components are fed separately to a mixing and dispensing machine in which they are intimately mixed and fed in continuous manner into the mould.
• the isocyanate and polyol react in the mould to form the polyurethane elastomer.
• the intermediate coated pipe is transferred to a second mould and the polyurethane composition of the second layer having the microspheres 3 dispersed therein is injected into the mould around the pipe.
• the polyurethane for the second layer may be formed from isocyanate and polyol components separately stored and mixed immediately prior to injection in the mould.
• the microspheres 3 may be present in either of the starting isocyanate and polyol components, or indeed in both. The microspheres are, however, usually present in the polyol component only.
• the pipe When the second polyurethane layer has cured in the mould, the pipe can be removed therefrom.
• pipes according to the invention can be joined together to form pipelines which are particularly suitable for carrying oil at high temperatures (e.g. up to about 110°C or 120°C) in deep water offshore applications.
• high temperatures e.g. up to about 110°C or 120°C
• the use of a thermally stable first layer helps to prevent thermal degradation of the pipe coating, while the use of microspheres in the second layer provides good thermal insulation and aids in reducing material costs.

Landscapes

• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Laminated Bodies (AREA)
• Thermal Insulation (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=10632867

Family Applications (1)

Country Status (4)

Cited By (4)

Families Citing this family (9)

Citations (2)

Family Cites Families (2)

• 1988
  • 1988-03-04 GB GB8805225A patent/GB2215427B/en not_active Expired - Fee Related
• 1989
  • 1989-02-07 NL NL8920232A patent/NL8920232A/nl not_active Application Discontinuation
  • 1989-02-07 CA CA 590363 patent/CA1318263C/en not_active Expired - Fee Related
  • 1989-02-07 WO PCT/US1989/000478 patent/WO1989008220A1/en unknown

Patent Citations (2)

Also Published As

Similar Documents

Legal Events