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US-12618309-B1 - Methods for preventing corrosion in flexible pipe with passivating agents

US12618309B1US 12618309 B1US12618309 B1US 12618309B1US-12618309-B1

Abstract

Disclosed are methods and apparatus for preventing corrosion within the annulus of a flexible pipe used in a riser in an offshore hydrocarbon production facility. Buffer fluid comprising a passivating agent is introduced into the annulus to form protective layers on metal surfaces within the annulus to resist corrosive materials from contacting the metal surfaces. The passivating agents may be one or more of a polyalphaolefin, a polybutene, or a polysiloxane. A corrosion inhibitor may be combined with the passivating agent in the buffer fluid. Pretreating of the metal surfaces within the annulus prior to introduction of the buffer fluid can be performed with a pretreating corrosion inhibitor.

Inventors

  • Farzan Parsinejad
  • Antonio Critsinelis
  • William R. Ruhe, Jr.
  • Man Kit Ng

Assignees

  • CHEVRON ORONITE COMPANY LLC
  • CHEVRON U.S.A. INC.

Dates

Publication Date
20260505
Application Date
20250507

Claims (20)

  1. 1 . A method for preventing or reducing corrosion in an offshore hydrocarbon production facility, comprising: pumping a buffer fluid comprising one or more passivating agents into an inlet port in a topsides riser end fitting in fluid communication with a plurality of tubes within an annulus of a flexible pipe riser wherein each of the plurality of tubes comprises at least one opening within the annulus, the flexible pipe riser comprising one end terminating at the topsides riser end fitting in fluid communication with the plurality of tubes within the annulus and another end terminating at a subsea riser end fitting; and discharging the fluid from the openings of the plurality of tubes into the annulus such that the fluid flows in the annulus; wherein the one or more passivating agents comprises one or more of a polyalphaolefin, a polybutene, or a polysiloxane.
  2. 2 . The method of claim 1 , wherein the one or more passivating agents comprises the polyalphaolefin and the polyalphaolefin has a kinematic viscosity of 1.5-5 cSt at 100 degrees C. and is formed from C6-C12 alkenes.
  3. 3 . The method of claim 1 , wherein the buffer fluid comprises the polybutene.
  4. 4 . The method of claim 3 , wherein the polybutene has an average molecular weight of 350 to 510 Daltons, a kinematic viscosity of 3-17 cSt at 100 degrees C., and a pour point of −55 to −30 degrees C.
  5. 5 . The method of claim 1 , wherein the buffer fluid further comprises a corrosion inhibitor.
  6. 6 . The method of claim 5 , wherein the corrosion inhibitor is alkenylsuccinic acid-based corrosion inhibitor.
  7. 7 . The method of claim 1 , further comprising, prior to pumping the buffer fluid comprising one or more passivating agents into the inlet port in the topsides riser end fitting, pumping a pretreating corrosion inhibitor into the inlet port in the topsides riser end fitting.
  8. 8 . The method of claim 7 , wherein the pretreating corrosion inhibitor is one or more of a hydrophobic silane, an amine, an imidazoline, a polymer, a Gemini surfactant, a molybdate, an organic nitrate, a carbonate, a silicate, a phosphate, an anthranilic acid, a thiol, an organic phosphonate, and an organic carboxylate.
  9. 9 . The method of claim 7 , wherein the pretreating corrosion inhibitor comprises isooctyltriethoxysilane.
  10. 10 . A flexible pipe apparatus for use in an offshore hydrocarbon production facility, the flexible pipe apparatus comprising: a tubular carcass layer defining a bore therein for transporting produced well fluids; a pressure sheath surrounding the carcass layer; an external sheath surrounding the pressure sheath and defining an annulus therebetween; and a plurality of tubes within the annulus and helically wound around at least the pressure sheath; wherein each of the plurality of tubes has at least one opening through which a buffer fluid comprising one or more passivating agents is introduced; wherein surfaces of the pressure sheath and the external sheath in contact with the buffer fluid passing through the annulus are at least partially coated with the one or more passivating agents; and wherein the one or more passivating agents comprises one or more of a polyalphaolefin, a polybutene, or a polysiloxane.
  11. 11 . The flexible pipe apparatus of claim 10 , further comprising: a topsides end fitting attached to a topsides end of the flexible pipe apparatus, the topsides end fitting having an inlet port in fluid communication with the plurality of tubes within the annulus and an outlet port in fluid communication with the annulus; and a subsea end fitting attached to a subsea end of the flexible pipe apparatus.
  12. 12 . The flexible pipe apparatus of claim 11 , further comprising a segregating wall separating the inlet port from the outlet port.
  13. 13 . The flexible pipe apparatus of claim 10 , wherein the plurality of tubes have solid walls and openings at the ends thereof.
  14. 14 . The flexible pipe apparatus of claim 10 , wherein the plurality of tubes have perforated walls.
  15. 15 . The flexible pipe apparatus of claim 10 , wherein the plurality of tubes are a component of a tape layer free of metal wires and located within the annulus.
  16. 16 . The flexible pipe apparatus of claim 10 , wherein the one or more passivating agents comprises the polyalphaolefin and the polyalphaolefin has a kinematic viscosity of 1.5-5 cSt at 100 degrees C. and is formed from C6-C12 alkenes.
  17. 17 . The flexible pipe apparatus of claim 10 , wherein the one or more passivating agents comprises the polybutene and the polybutene has an average molecular weight of 350 to 510 Daltons, a kinematic viscosity of 3-17 cSt at 100 degrees C., and a pour point of −55 to −30 degrees C.
  18. 18 . The flexible pipe apparatus of claim 10 , wherein the buffer fluid further comprises a corrosion inhibitor.
  19. 19 . The flexible pipe apparatus of claim 18 , wherein the corrosion inhibitor is alkenylsuccinic acid-based corrosion inhibitor.
  20. 20 . The flexible pipe apparatus of claim 10 , further comprising, prior to pumping the buffer fluid comprising the one or more passivating agents into the inlet port in the topsides riser end fitting, pumping a pretreating corrosion inhibitor into the inlet port in the topsides riser end fitting.

Description

TECHNICAL FIELD The present disclosure relates to the use of polysiloxane compounds, polyalphaolefins, and/or polybutene for preventing corrosion on flexible pipelines. BACKGROUND Flexible pipes used in oil and gas production are composed of densely packed steel wires enclosed in an annulus confined by inner and outer thermoplastic sheaths (pressure barriers). Hydrocarbons, water, CO2 and H2S from the bore diffuse through the inner sheath and form a corrosive environment in the confined space between the sheaths. Carbon dioxide-induced stress corrosion cracking is an environmentally assisted corrosion cracking phenomenon that has recently been identified as a new failure mode in flexible pipe armor wires. The phenomenon has been observed to take place notably in severe CO2 environments and is a cause of great concern to the flexible pipe industry. Engineered flexible pipe is frequently used in riser applications in offshore hydrocarbon production facilities which convey hydrocarbon products from a subsea well to a topsides production platform or vessel. Such flexible pipe is formed of multiple layers, each layer designed for a specific function. In general, the innermost layer of the multiple layers is the carcass layer, made of corrosion resistant material, designed to resist collapse of the flexible pipe. Surrounding the carcass is a polymeric sealant layer or pressure sheath which is extruded around the carcass and sealed at flexible pipe end fittings to contain fluid within the bore. Surrounding the polymeric sealant layer is an annulus containing a number of metallic armor layers designed to impart strength against tensile loading (e.g. armor wires) and internal pressure loading (e.g., pressure armor). Surrounding these layers is another polymeric sealant layer or external sheath designed to avoid external sea water ingress into inner layers of the flexible pipe, which acts as an outer protective layer. The space between the two polymeric sealant layers is referred to as “the annulus.” Typically, the annulus contains one or more layers of circumferentially oriented steel members (referred to as pressure armor layers) designed to provide radial strength and burst resistance due to internal pressure. Surrounding the pressure armor layers are layers of helically wound armor wires (referred to as armor wire layers) designed to provide tensile strength in the axial direction. Flexible pipe is terminated at each end by an end fitting which incorporates a flange for mating with other flanges. In use, flexible pipe risers are suspended from an offshore hydrocarbon production platform or host facility, thus placing high tensile loads on the armor wire layers. The loads along the riser are amplified due to the effects of environmental conditions and associated motions of the platform or host facility to which the riser is connected. Within the bore of the flexible pipe, in addition to hydrocarbon products, other components including hydrogen sulfide, carbon dioxide and water may be present. These other components can diffuse through the first polymeric sealant layer (pressure sheath) to the annulus. These components, hydrogen sulfide in particular, as well as water vapor, can accumulate within the annulus and eventually lead to corrosion of the steel wires therein via mechanisms including hydrogen induced cracking and sulfide stress cracking. Additionally, the annulus can be flooded with seawater due to damage of the outermost layer leading to corrosion of the armor wires. As noted, the armor wires in the flexible riser are particularly subject to dynamic cyclic loads, which can result in corrosion fatigue of the metallic armor wires in the annulus. Corrosion of the metallic wires in this region makes these wires particularly vulnerable to corrosion fatigue and potential acceleration of failure mechanism. In view of the foregoing, there is an ongoing need to prevent or reduce corrosion of the armor wires and other steel elements within the annulus of flexible pipe used in risers and in other dynamic applications. SUMMARY This summary is provided to introduce various concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify required or essential features of the claimed subject matter nor is the summary intended to limit the scope of the claimed subject matter. Aspects of this disclosure are directed to methods for preventing or reducing corrosion by circulating buffer fluid comprising one or more passivating agents within the annulus of a flexible pipe used in a riser, flowlines and jumpers in an offshore hydrocarbon production facility. In one aspect of the present disclosure, a flexible pipe apparatus for use in a riser system in an offshore hydrocarbon production facility is provided. The apparatus includes a tubular carcass layer defining a bore therein for transporting produced well fluids, a pressure sheath surrounding the carcass la