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
  • F16L53/00—Heating of pipes or pipe systems; Cooling of pipes or pipe systems
  • F16L53/30—Heating of pipes or pipe systems
  • F16L53/35—Ohmic-resistance heating

Definitions

• the present invention relates to a multi-layer pipe and a method of forming a multi-layer pipe/pipeline for transport of hydrocarbons, e.g. a corrosive multi-phase well flow.
• such laminated transport pipes shall also permit heating by means of electrical power to prevent or defrost any hydrate formation. Likewise, fabrication of the said pipes at an acceptable price shall be possible.
• clad steel pipes consisting of two concentric steel pipes that are metallically interconnected.
• a clad steel pipe can therefore not be heated by means of electrical power to prevent or defrost any hydrate formation if the outer insulation layer is damaged and the steel pipe is in contact with sea water.
• Clad steel pipes moreover are very expensive in fabrication, considerably more expensive than the total cost of the two part pipes separately. For transport of a corrosive multi-phase well flow, the clad steel pipes are not competitive with other pipes price-wise.
• Coaxial steel pipes with thermal insulation are moreover known. Both parts of the pipe here consist of carbon steel, and also the inner pipe is therefore sufficiently strong to resist the internal pressure. In connection with heating to prevent or defrost hydrate formation, the resistance heat developed in the outer pipe outside the insulation will be lost to the sea.
• One object of the present invention is to provide a multi-layer pipe/pipeline for transport of hydrocarbons e.g. in the form of a corrosive multi-phase well flow, where the transport pipeline has the necessary mechanical strength properties, and can be heated by means of electrical power to prevent or defrost hydrate formation, and which can be fabricated at an acceptable price.
• Another object of the present invention is to describe an advantageous method of forming a multi-layer pipe/pipeline.
• a main pipe consists of a strong and cheap material, for example carbon steel.
• a thinner pipe of a non-corrodible material is installed coaxially inside the main pipe, for example an appropriate aluminium alloy, titan or stainless steel.
• the inner pipe will by a subsequently stated method be glued or cast to the outer main pipe by means of a polymer material, which may be a thermosetting plastic, for example epoxy. If desired, a heat- insulating coating may be installed outside the main pipeline, covered by a weight coating.
• a polymer material which may be a thermosetting plastic, for example epoxy.
• a heat- insulating coating may be installed outside the main pipeline, covered by a weight coating.
• the main pipe and inner pipe respectively are welded together to form as long lengths as practicable.
• a sufficient number of plastic spacers of a thickness corresponding to the thickness of the polymer layer later installed are glued on the inside of the outer pipe (the main pipe) or on the outside of the inner pipe, preferably on the former.
• the inner pipe is thereafter introduced into the outer pipe (main pipe) , and the annulus between them is filled with a polymer material, which may be a thermosetting plastic, for example epoxy. When the polymer is hardened, the two pipes are securely fastened to one another.
• Such a transport pipe can be fabricated at a far lower price than known pipes with similar strength properties.
• outer and inner pipes are electrically insulated from one another, one of the following methods of electrical heating can be used: (I) Sending a direct current through the inner pipe. The outer pipe is then free from current and voltage, and can admit electrical contact with the sea water. (II) Sending an alternate current coaxially through the inner and outer pipe. Given normal thickness of the outer pipe, the current will only go on the internal side of the same. The outside remains free from current and voltage, and can still be earthed to the sea water.
• FIG. 1 is a cross-sectional view of a multi-layer pipe/pipeline for transport of a corrosive multi-phase well flow according to the invention.
• Fig. 2 is a longitudinal section on a larger scale through two multi-layer pipes/pipelines that are being welded together to form one section of a pipeline.
• Fig. 3 shows one end of a multi-layer pipe/pipeline where the outer and inner pipes are welded together.
• Fig. 4 shows one end of a multi-layer pipe/pipeline where the outer and inner pipes are mechanically connected and electrically separated by means of a flanged connection.
• the transport pipe according to the invention consists of a main pipe (outer pipe) 1 of a strong and cheap material, for example carbon steel.
• An inner pipe with a smaller external diameter than that of the outer pipe, is designated by reference numeral 2.
• the inner pipe 2 consists of a non-corrodible material, for example an appropriate aluminium alloy, titan or stainless steel.
• the outer and the inner pipes, 1, 2 are coaxially installed in relation to each other and are bound together by means of an intermediate layer 3, preferably a polymer material, that may be a thermosetting plastic, for example epoxy.
• a heat-insulating coating 4 may be applied outside the outer pipe 1, covered by a weight coating 5.
• the fabrication is accomplished by the outer pipe 1 and the inner pipe 2 respectively being welded together to as long pipe lengths as practicable.
• a sufficient number of plastic spacers 6 of a thickness corresponding to that of the polymer layer to be applied should be glued on the inside of the outer pipe 1 or the outside of the inner pipe 2, preferably on the former.
• the inner pipe 2 is subsequently introduced into outer pipe 1, and the annulus between them is filled, preferably with a polymer material 3 that is injected.
• a polymer material 3 that is injected.
• the heat insulation 4 and weight coating 5, if any, are applied to the outside in the ordinary way.
• the polymer material e.g. epoxy, will bind the outer and inner pipes together and absorb most of the shear forces produced by varying expansion in the pipes.
• the outer and inner pipes In the other end, the outer and inner pipes must be electrically insulated from each other and connected to a power generator. Mechanical locking of the pipe ends can then be effected bv means of some kind of flange coupling with electrical insulation. Also the end to be electrically short-circuited can be advantageously locked with the same type of electrically insulated flange coupling.
• the outer and inner pipes can then be separated or electrically short-circuited as desired by means of a contactor/switch located outside the pipe.
• the pipeline When the switch is open, the pipeline can be used as an electrical power cable for transmission of electrical energy for the operation e.g. of seabed control installations and/or machinery, or a platform offshore.
• the switch For heating of the pipes, the switch is short-circuited.
• a ring 7 of a heat-resisting, for example ceramic, material is introduced into the annulus, which is moreover filled with polymer 3.
• Two pipe ends are thereafter put butt-in-butt and welded together.
• the outer pipe 1 of the two adjoining multi-layer pipes is welded together from the outside, as indicated by 8, while the inner pipe 2 of the two abutting multi-layer pipes is welded together from the inside, as indicated by 9, by means of an arc welding machine.
• the ceramic ring 7 prevents the polymer material from being destroyed by the heat from the welding, and the two part pipes 1, 2 from getting in metallic contact with one another. If desired, the diameter of the pipe ends 1 to be welded together may be increased to give more room for the ceramic ring 7.
• a single short-circuited end can be accomplished as shown on a longitudinal section in fig. 3 by means of welding.
• a ring 11 of the same material as pipe 2 can be explosion welded to a larger ring 10 of carbon steel, which can then be machined e.g. to a flange-form for further connection.
• the composite end section 10 and 11 can then be welded together to pipes 1 and 2 by means of welds 8 and 9 as for a pipe joint described above.
• FIG. 4 An example of an electrically insulated pipe end is shown in fig. 4 in a longitudinal section.
• a flange-formed ring 12 of the same material as the pipe 2 is located inside an end ring 13 of carbon steel.
• a flanged ring 15 of carbon steel is subsequently connected with the end ring 13 by the weld 18.
• the rings 12 and 13 feature holes permitting a metal rod to be screwed to the ring 12 through ring 13 without being in contact with the ring.
• the rings 13 and 12 can then be connected with pipes 1 and 2 respectively by means of the welds 8 and 9, as for a pipe joint described above.
• a polymer 16 can subsequently be injected, e.g. epoxy.
• the flange 15 can be covered with an electrically insulating composite material 17, which has a higher tensile strength than polymer 14.
• the outer pipe 1 of carbon steel alone can be presupposed to absorb the pressure forces of the well flow.
• the thin inner pipe 2 of non-corrodible material aluminium alloy, titan or stainless steel
• the polymer layer 3 With an internal pressure of edeemg. 100 bars, the polymer layer 3 will be exposed to a surface pressure of somewhat below 100 bars and will be slightly compressed. Since the polymer layer is thin, the absolute compression limit will be low, since the inner LCF pipe 2 is insignificantly strained. An estimate shows that with a 6 mm thick polymer layer 3, a thin inner pipe 2 will be strained far below the yield point.
• a coaxial pipeline as described above, will electrically
• the pipe line 15 behave like a coaxial transmission line.
• the difference in practise is that the pipe line has a relatively high ohmic resistance and capacitance.
• the ohmic resistance is here advantageously exploited for electrical heating. In very long pipelines, the high capacitance will cause part of the
• An average insulation thickness of 6 mm or more will also be desirable on account of dimension tolerances in the outer and inner pipes.
• An epoxy layer of 6 mm has an electrical breakdown voltage of approx. 150 kV, which is approx. 10 times higher than relevant voltages during heating.
• the typical current intensity of alternate current heating will be approx. 500 A per pipe circumference metre for an inner pipe of stainless steel, which will give a voltage drop of approx. 60 V/km.
• a multi-layer pipe/pipeline according to the invention for transport of oil and gas in the form of corrosive multi-phase well flow has outstanding electrical properties with regard to heating to prevent or defrost hydrate formation, and can be fabricated at a far lower price than known multi-layer pipes/pipelines, e.g. clad steel pipes, with similar mechanical strength properties.

Landscapes

• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Rigid Pipes And Flexible Pipes (AREA)
• Physical Deposition Of Substances That Are Components Of Semiconductor Devices (AREA)
• Led Devices (AREA)
• Heating, Cooling, Or Curing Plastics Or The Like In General (AREA)

Applications Claiming Priority (2)

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• 1988
  • 1988-05-27 NO NO882330A patent/NO165462C/no not_active IP Right Cessation
• 1989
  • 1989-05-18 WO PCT/NO1989/000049 patent/WO1989011616A1/en not_active Application Discontinuation
  • 1989-05-18 EP EP89905796A patent/EP0415977A1/en not_active Withdrawn
• 1990
  • 1990-11-26 DK DK280290A patent/DK280290A/da not_active Application Discontinuation

Non-Patent Citations (1)

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