WO2020096458A1 - Power umbilicals for subsea deployment - Google Patents

Power umbilicals for subsea deployment Download PDF

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Publication number
WO2020096458A1
WO2020096458A1 PCT/NO2019/050191 NO2019050191W WO2020096458A1 WO 2020096458 A1 WO2020096458 A1 WO 2020096458A1 NO 2019050191 W NO2019050191 W NO 2019050191W WO 2020096458 A1 WO2020096458 A1 WO 2020096458A1
Authority
WO
WIPO (PCT)
Prior art keywords
power
tubing
umbilical
integrated power
zinc coating
Prior art date
Application number
PCT/NO2019/050191
Other languages
French (fr)
Inventor
Sven Morten Hesjevik
Original Assignee
Equinor Energy As
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Equinor Energy As filed Critical Equinor Energy As
Publication of WO2020096458A1 publication Critical patent/WO2020096458A1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B7/00—Insulated conductors or cables characterised by their form
    • H01B7/17—Protection against damage caused by external factors, e.g. sheaths or armouring
    • H01B7/28—Protection against damage caused by moisture, corrosion, chemical attack or weather
    • H01B7/2806—Protection against damage caused by corrosion
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B7/00—Insulated conductors or cables characterised by their form
    • H01B7/0072—Electrical cables comprising fluid supply conductors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B7/00—Insulated conductors or cables characterised by their form
    • H01B7/14—Submarine cables
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B7/00—Insulated conductors or cables characterised by their form
    • H01B7/17—Protection against damage caused by external factors, e.g. sheaths or armouring
    • H01B7/18—Protection against damage caused by wear, mechanical force or pressure; Sheaths; Armouring
    • H01B7/22—Metal wires or tapes, e.g. made of steel
    • H01B7/221—Longitudinally placed metal wires or tapes
    • H01B7/225—Longitudinally placed metal wires or tapes forming part of an outer sheath
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B7/00—Insulated conductors or cables characterised by their form
    • H01B7/04—Flexible cables, conductors, or cords, e.g. trailing cables
    • H01B7/046—Flexible cables, conductors, or cords, e.g. trailing cables attached to objects sunk in bore holes, e.g. well drilling means, well pumps

Definitions

  • the invention relates to power umbilicals for subsea deployment, and in particular power umbilicals having improved corrosion protection.
  • Corrosion in steel components immersed in water is a well-known problem.
  • cathodic protection has been used to prevent corrosion. This is achieved by electrically coupling the steel component to a sacrificial piece of metal (e.g. aluminium) having a lower electrochemical potential.
  • the sacrificial piece of metal supplies electrons to the steel component, which prevents it from corroding.
  • An integrated power umbilical is designed to serve a specific piece of equipment, such as an oil well, and to supply it with power and other services such as telecommunication and fluids.
  • the umbilical consists of power cables as well as tubing containing various types of fluids.
  • the tubing is often made from corrosion resistant alloys, such as Super Duplex Stainless Steel (SDSS).
  • SDSS Super Duplex Stainless Steel
  • This biofilm causes a catalytic effect on the cathode reaction, leading to more noble electrochemical potential on the steel which increases the risk of crevice and pitting corrosion. It is therefore common to extrude a polymeric sheet over the tubing to provide a coating that prevents water from accessing the underlying steel.
  • Figure 1 is a schematic diagram of a cross section of an integrated power umbilical according to an embodiment
  • Figure 2 is a flow diagram illustrating the steps of a method of manufacturing an integrated power umbilical according to an embodiment.
  • a power umbilical provides electric power to consumers, often located subsea. Electric power consumers can be pumps, turbines or other equipment.
  • An integrated power umbilical having an SDSS tubing covered by a polymeric sheet can provide good corrosion protection.
  • the polymeric sheet may be damaged in small areas (e.g. scuffs and bending cracks). Such coating damage is not a problem for most systems, but can be surprisingly detrimental to an integrated power umbilical supplying AC power under water.
  • Recent experiments have shown that coating damage can lead to AC corrosion in an integrated power umbilical.
  • the polymeric sheet being an insulating material, causes a build-up of induced AC voltage in the steel tubing. The resulting current in an area where the coating is damaged causes high AC corrosion rates. Without the polymeric sheet, build-up of induced AC voltage does not occur, but then pitting and crevice corrosion becomes a problem caused by the elevated temperatures from the power cable.
  • FIG. 1 shows a schematic diagram of an embodiment of an integrated power umbilical 2, which addresses at least some of the problems outlined above.
  • the umbilical 2 comprises three power cords 4 for supplying AC power to a subsea component (not shown).
  • the power cords 4 are enclosed by an outer steel armour layer 6.
  • the outer layer 6 is covered by an outer plastic sheet 8.
  • metal tubing 10 (three tubes shown), preferably comprising a corrosion resistant metal such as SDSS.
  • the tubing 10 is covered by a zinc coating 12 (e.g. 200 gm to 300 gm in thickness), which provides an unbroken continuous cover over the tubing 10.
  • the umbilical 2 has been deployed and sea water 14 surrounds the power cords 4 and the tubing 10 in the voids.
  • the zinc coating 12 may prevent water from accessing the tubing 10, like a polymeric sheet would have, and thereby prevent corrosion in the tubing 10.
  • a polymeric sheet because of the electric conductive properties of zinc, there is no build up of induced AC voltage in the tubing 10. Hence, even if the zinc coating 12 is damaged, this does not cause high AC corrosion rates in the damaged area of the tubing 10.
  • the zinc coating 12 having a lower noble electrochemical potential than the tubing 10, also provides cathodic protection. More importantly, zinc acts as a weak biocide in water 14 and will prevent formation of a biofilm on the surface of the tubing 10 at elevated temperatures. Exposed to sea water, the zinc will corrode and it is not expected that the zinc coating 12 will be intact on the tubing surface throughout the design life of the umbilical 2. However, release of zinc ions into the confined water phase (i.e. the sea water that penetrates into the voids of the umbilical when immersed) will prevent the formation of a biofilm and hinder potential ennoblement which could lead to pitting and crevice corrosion.
  • the umbilical 2 would normally also comprise further conduits, for example, to supply water or other fluids.
  • the zinc coating 12 is applied in a thermal spraying process to achieve an adequate (unbroken) coverage and a desired thickness.
  • the coating has a thickness in the range of 200 pm to 1 mm, or preferably a thickness in the range of 200 pm to 300 pm.
  • a thicker coating 8 may provide a longer lifetime, but if the coating 8 is too thick, then bending cracks are more likely to occur. This may not be an important consideration for a fixed and rigid system, but may be important for an integrated power umbilical, which has some mechanical flexibility.
  • FIG 2 shows a flow diagram which illustrates the steps of a method of manufacturing an integrated power umbilical according to an embodiment.
  • the method comprises: providing one or more power cords for supplying AC power (step S1 ), providing a metal tubing adjacent to said power cord(s) (step S2), and applying a zinc coating to an outer surface of said tubing (step S3).
  • the step (S3) of applying the zinc coating may comprise thermally spraying zinc onto the tubing.
  • the thermal spray is used to apply a zinc coating with a submillimetre thickness, e.g. in the range of 200 pm to 300 pm.
  • the illustrated method may be used to manufacture an integrated power umbilical as shown in Figure 1.
  • the metal tubing is provided before the one or more power cords.
  • the invention may be defined as an integrated power umbilical for subsea deployment, comprising one or more power cords for supplying AC power, a metal tubing adjacent to said power cord(s), and a zinc coating covering an outer surface of said tubing.
  • embodiments of the invention can enable the use of subsea integrated power umbilicals without the risk of AC corrosion, whilst also avoiding pitting corrosion and crevice corrosion at elevated temperatures.

Landscapes

  • Rigid Pipes And Flexible Pipes (AREA)
  • Coating By Spraying Or Casting (AREA)

Abstract

An integrated power umbilical (2) for subsea deployment comprises: one or more power cords (4) for supplying AC power; a metal tubing (10) adjacent to said power cord(s) (4); and a zinc coating (12) covering an outer surface of said tubing (10).

Description

Power Umbilicals for Subsea Deployment
Technical field
The invention relates to power umbilicals for subsea deployment, and in particular power umbilicals having improved corrosion protection.
Background
Corrosion in steel components immersed in water is a well-known problem. Traditionally cathodic protection has been used to prevent corrosion. This is achieved by electrically coupling the steel component to a sacrificial piece of metal (e.g. aluminium) having a lower electrochemical potential. The sacrificial piece of metal supplies electrons to the steel component, which prevents it from corroding.
It can be difficult to achieve adequate cathodic protection for large or extended systems such as integrated power umbilicals. An integrated power umbilical is designed to serve a specific piece of equipment, such as an oil well, and to supply it with power and other services such as telecommunication and fluids. Furthermore, the umbilical consists of power cables as well as tubing containing various types of fluids. The tubing is often made from corrosion resistant alloys, such as Super Duplex Stainless Steel (SDSS). However, at elevated temperatures (e.g. above 20 °C) there is a risk of pitting and crevice corrosion on SDSS. The reason for this increased risk of corrosion is related to the formation of a biofilm on the surface of the steel. This biofilm causes a catalytic effect on the cathode reaction, leading to more noble electrochemical potential on the steel which increases the risk of crevice and pitting corrosion. It is therefore common to extrude a polymeric sheet over the tubing to provide a coating that prevents water from accessing the underlying steel.
Statement of invention
Aspects of the present invention provide integrated power umbilicals for subsea deployment, and methods of manufacturing such. Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings.
Brief description of figures
Figure 1 is a schematic diagram of a cross section of an integrated power umbilical according to an embodiment; and
Figure 2 is a flow diagram illustrating the steps of a method of manufacturing an integrated power umbilical according to an embodiment.
Description of preferred embodiments
A power umbilical provides electric power to consumers, often located subsea. Electric power consumers can be pumps, turbines or other equipment. An integrated power umbilical having an SDSS tubing covered by a polymeric sheet can provide good corrosion protection. However, during handling, for example when deploying the umbilical, the polymeric sheet may be damaged in small areas (e.g. scuffs and bending cracks). Such coating damage is not a problem for most systems, but can be surprisingly detrimental to an integrated power umbilical supplying AC power under water. Recent experiments have shown that coating damage can lead to AC corrosion in an integrated power umbilical. The polymeric sheet, being an insulating material, causes a build-up of induced AC voltage in the steel tubing. The resulting current in an area where the coating is damaged causes high AC corrosion rates. Without the polymeric sheet, build-up of induced AC voltage does not occur, but then pitting and crevice corrosion becomes a problem caused by the elevated temperatures from the power cable.
Figure 1 shows a schematic diagram of an embodiment of an integrated power umbilical 2, which addresses at least some of the problems outlined above. The umbilical 2 comprises three power cords 4 for supplying AC power to a subsea component (not shown). The power cords 4 are enclosed by an outer steel armour layer 6. The outer layer 6 is covered by an outer plastic sheet 8. Also enclosed by the outer layer 6 is metal tubing 10 (three tubes shown), preferably comprising a corrosion resistant metal such as SDSS. The tubing 10 is covered by a zinc coating 12 (e.g. 200 gm to 300 gm in thickness), which provides an unbroken continuous cover over the tubing 10. In Figure 1 , the umbilical 2 has been deployed and sea water 14 surrounds the power cords 4 and the tubing 10 in the voids.
The zinc coating 12 may prevent water from accessing the tubing 10, like a polymeric sheet would have, and thereby prevent corrosion in the tubing 10. However, unlike a polymeric sheet, because of the electric conductive properties of zinc, there is no build up of induced AC voltage in the tubing 10. Hence, even if the zinc coating 12 is damaged, this does not cause high AC corrosion rates in the damaged area of the tubing 10.
The zinc coating 12, having a lower noble electrochemical potential than the tubing 10, also provides cathodic protection. More importantly, zinc acts as a weak biocide in water 14 and will prevent formation of a biofilm on the surface of the tubing 10 at elevated temperatures. Exposed to sea water, the zinc will corrode and it is not expected that the zinc coating 12 will be intact on the tubing surface throughout the design life of the umbilical 2. However, release of zinc ions into the confined water phase (i.e. the sea water that penetrates into the voids of the umbilical when immersed) will prevent the formation of a biofilm and hinder potential ennoblement which could lead to pitting and crevice corrosion. Although not shown, the umbilical 2 would normally also comprise further conduits, for example, to supply water or other fluids.
Preferably, the zinc coating 12 is applied in a thermal spraying process to achieve an adequate (unbroken) coverage and a desired thickness. The coating has a thickness in the range of 200 pm to 1 mm, or preferably a thickness in the range of 200 pm to 300 pm. A thicker coating 8 may provide a longer lifetime, but if the coating 8 is too thick, then bending cracks are more likely to occur. This may not be an important consideration for a fixed and rigid system, but may be important for an integrated power umbilical, which has some mechanical flexibility.
Figure 2 shows a flow diagram which illustrates the steps of a method of manufacturing an integrated power umbilical according to an embodiment. The method comprises: providing one or more power cords for supplying AC power (step S1 ), providing a metal tubing adjacent to said power cord(s) (step S2), and applying a zinc coating to an outer surface of said tubing (step S3). The step (S3) of applying the zinc coating may comprise thermally spraying zinc onto the tubing. Preferably, the thermal spray is used to apply a zinc coating with a submillimetre thickness, e.g. in the range of 200 pm to 300 pm. The illustrated method may be used to manufacture an integrated power umbilical as shown in Figure 1. In an alternative embodiment, the metal tubing is provided before the one or more power cords.
The invention may be defined as an integrated power umbilical for subsea deployment, comprising one or more power cords for supplying AC power, a metal tubing adjacent to said power cord(s), and a zinc coating covering an outer surface of said tubing.
In summary, embodiments of the invention can enable the use of subsea integrated power umbilicals without the risk of AC corrosion, whilst also avoiding pitting corrosion and crevice corrosion at elevated temperatures.
Each feature disclosed or illustrated in the present specification may be incorporated in the invention, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.

Claims

CLAIMS:
1 . An integrated power umbilical for subsea deployment, comprising:
one or more power cords for supplying AC power;
a metal tubing adjacent to said power cord(s); and
a zinc coating covering an outer surface of said tubing, wherein the zinc coating has a thickness in the range of 200 pm to 1 mm.
2. An integrated power umbilical according to claim 1 , wherein the zinc coating has a thickness in the range of 200 pm to 300 pm.
3. An integrated power umbilical according to claim 1 or 2, wherein the tubing comprises Super Duplex Stainless Steel, SDSS.
4. An integrated power umbilical according to any preceding claims, further comprising one or more conduits for supplying fluids.
5. An integrated power umbilical according to any preceding claims, wherein said zinc coating is a thermally sprayed zinc coating.
6. An integrated power umbilical according to any preceding claims, further comprising an outer layer enclosing said one or more power cords and said metal tubing.
7. An integrated power umbilical according to claim 6, wherein said outer layer comprises a steel armour layer.
8. A method of manufacturing an integrated power umbilical for subsea deployment, the method comprising;
providing one or more power cords for supplying AC power;
providing a metal tubing adjacent to said power cord(s); and
applying a zinc coating to an outer surface of said tubing, wherein said step of applying comprises applying a layer of zinc having a thickness in the range of 200 pm to 1 mm.
9. A method according to claim 8, wherein said step of applying comprises thermally spraying zinc onto said tubing.
10. A method according to claim 8 or 9, wherein said step of applying a zinc coating comprises applying a layer of zinc having a thickness in the range of 200 pm to
300 pm.
1 1. A method according to claim 8, 9 or 10, wherein said step of providing the metal tubing comprises providing a tubing comprising Super Duplex Stainless Steel, SDSS.
12. A method according to any one of claims 8 to 1 1 , further comprising providing one or more conduits for supplying fluids.
13. A method according to any one of claims 8 to 12, further comprising enclosing said one or more power cords and said metal tubing in an outer layer.
14. A method according to claim 13, wherein said outer layer comprises a steel armour layer.
PCT/NO2019/050191 2018-11-07 2019-09-20 Power umbilicals for subsea deployment WO2020096458A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB1818146.1A GB2578763B (en) 2018-11-07 2018-11-07 Power umbilicals for subsea deployment
GB1818146.1 2018-11-07

Publications (1)

Publication Number Publication Date
WO2020096458A1 true WO2020096458A1 (en) 2020-05-14

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PCT/NO2019/050191 WO2020096458A1 (en) 2018-11-07 2019-09-20 Power umbilicals for subsea deployment

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2255104A (en) * 1991-04-25 1992-10-28 Alcatel Stk As Corrosion protection for flexible submarine line
US6012495A (en) * 1996-09-05 2000-01-11 Alcatel Corrosion protection for subsea lines
US6472614B1 (en) * 2000-01-07 2002-10-29 Coflexip Dynamic umbilicals with internal steel rods
US20070251694A1 (en) * 2005-11-18 2007-11-01 Gwo-Tarng Ju Umbilical assembly, subsea system, and methods of use
WO2015038002A1 (en) * 2013-09-12 2015-03-19 Aker Subsea As Load carrying bundle intended for use in a power cable or a power umbilical

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB506813A (en) * 1936-12-03 1939-06-05 Siemens Ag Improvements in or relating to pressure-proof trunk communication deep-sea cables
DE2939971A1 (en) * 1978-10-02 1980-04-10 Texas Instruments Inc ELECTRIC POWER CORD
US6960724B2 (en) * 2002-09-30 2005-11-01 Schlumberger Technology Corporation Dual stress member conductive cable
US7903914B2 (en) * 2008-05-19 2011-03-08 Deep Down, Inc. Method and apparatus for manufacture of a non-helical subsea umbilical
WO2011008568A2 (en) * 2009-07-16 2011-01-20 3M Innovative Properties Company Submersible composite cable and methods
GB2554087B (en) * 2016-09-19 2020-01-01 Equinor Energy As Sacrificial anode protection of a subsea umbilical

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2255104A (en) * 1991-04-25 1992-10-28 Alcatel Stk As Corrosion protection for flexible submarine line
US6012495A (en) * 1996-09-05 2000-01-11 Alcatel Corrosion protection for subsea lines
US6472614B1 (en) * 2000-01-07 2002-10-29 Coflexip Dynamic umbilicals with internal steel rods
US20070251694A1 (en) * 2005-11-18 2007-11-01 Gwo-Tarng Ju Umbilical assembly, subsea system, and methods of use
WO2015038002A1 (en) * 2013-09-12 2015-03-19 Aker Subsea As Load carrying bundle intended for use in a power cable or a power umbilical

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Publication number Publication date
GB2578763A (en) 2020-05-27
GB201818146D0 (en) 2018-12-19
GB2578763B (en) 2020-12-16

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