GB2528729A - Umbilical - Google Patents

Abstract

A subsea flexible umbilical 2 comprises a plurality of umbilical components, which can include electric cables, optical fibre cables, steel tubes or thermoplastic hoses. An umbilical component comprises a composite tube 6 having a metal liner 10 and a composite outer layer 20. The umbilical 2 achieves the benefit of the mechanical properties and the anti-permeation properties of a metal liner such as a stainless steel tube, whilst minimizing any increase in overall weight of the umbilical by maintaining the use of a composite outer layer or wrap. The composite material can comprise fibres in a polymer matrix, which can be an epoxy matrix. The fibres can be carbon fibre, glass fibre, aramid fibre, or PBO. The umbilical can be reelable and greater than 2000m in length. The umbilical can be structured so the that axial loading is wholly or substantially withstood by the metal liner, which can be steel or stainless steel, and the radial loading is shared by the metal liner and the composite outer layer.

Description

Umbilical The present invention relates to a subsea flexible umbilical for use in the offshore production of hydrocarbons) and in particular to an umbilical for use in deep water applications.

An umbilical for use in the offshore production of hydrocarbons generally comprises a group of one or more types of elongated active umbilical components, such as electrical cables, optical fibre cables, steel tubes and/or thermoplastic hoses for fluid transportation, all cabled together for flexibility, over-sheathed and, when applicable, armoured for mechanical strength. IJmbilicals are typically used for transmitting power, signals, hydrocarbons, and/or working fluids [for example for fluid injection, hydraulic power, gas release, etc.) to and from a subsea installation.

The umbilical cross-section is generally circular, the elongated elements being wound together either in a helical or in a S/Z pattern. In order to fill the interstitial voids between the various umbilical elements and to obtain the desired configuration, filler components may be included within the voids.

ISO 1362 8-5 "Specification for Subsea Umbilicals", provides standards for the design and manufacture of such umbilicals.

Subsea umbilicals are now being installed at increasingly deeper water depths, commonly being deeper than 2000m, for example for use with severe reservoirs'.

Such umbilicals therefore have to be able to withstand the increasingly severe loading conditions during their installation and their service life. Due to the increasing water depth, there is also a need to reduce the weight of the umbilical and/or to increase its resistance to axial loading.

Another problem related to the exploitation of a severe reservoir is the increase in the internal pressure of the fluid transported by the ste& hoses and/or the thermoplastic hoses of the umbilical. There is therefore also a need to increase the pressure rating of the tubes and the hoses, typically up to 1000 bar and more, and preferably up to 1300 bar and more.

A solution to the need to increase the pressure rating of the steel tubes is to increase the wall thickness of the tube. However, this solution increases the overall weight of the subsea umbilical, which has detrimental effects when the umbilical is to be submerged and used at an important water depth. And as the weight of the umbilical increases, more of the total stress capacity of the umbilical must be devoted to tensioning stresses, so that less of the total stress capacity is available for any bending stresses.

In addition, heavier umbilicals require more robust handling equipment, such as winches, spools, clamps, tensioners etc. In further addition, when the tube wall thickness is increased, there is an increased material cost, especially with the use of high strength stainless steels, such as super duplex or even hyper duplex steel.

This solution also decreases the flexibility of the steel tubes, and therefore the flexibility of the umbilical, whilst the umbilical should still have sufficient flexibility to be reelable' with conventional equipment etc. Reeling is the most convenient form of pipeline transportation and laying, generally from a reel in the reel-laying method known in the art.

Another solution for transporting high pressure fluids in an umbilical is to use thermoplastic hoses. A thermoplastic hose generally consists of a plastic liner reinforced externally by a wrapping of aramid fibres, and an outer wrapping of rubber or plastic. Thermoplastic hose are generally lighter and more flexible than the equivalent steel tube. However, thermoplastic hoses are less impermeable than steel tubes) with gas molecules being able to slowly permeate through the polymer layers of the hose. Furthermore, thermoplastic hoses are less secure than steel tubes when the fluid to be transported is both under high pressure and high temperature.

It is an object of the present invention to provide a subsea flexible umbilical that overcomes at least one of the above problems.

Thus, according to one aspect of the present invention, there is provided a subsea flexible umbilical comprising a plurality of umbilical components, at least one umbilical component comprising a composite tube having a metal liner and a composite outer layer.

In this way, the umbilical of the present invention achieves the benefit of the mechanical properties and the anti-permeation properties of the steel tube, whilst minimizing any increase in overall weight of the umbilical by maintaining the use of a composite outer layer or wrap.

The metal liner may be any suitable metal, including, individually or in combination, steel, copper or stainless steel. Preferably the metal liner is a steel liner, more preferably a stainless steel liner. Many grades of steel and stainless steel are known in the art, including carbon Steel X65 to X80, austenitic stainless steel 316L UNS 531603, Duplex UNS 531803, Lean Duplex UNS S32001 Super Duplex UNS S32750 or IJNS S32760, and other similar grades of stainless steel.

Composite tube inner diameters in standard or conventional umbilicals are typically in the range 10mm -50mm. However, this range can be extended to a larger inner diameter, typically up to 75mm, especially when the composite tube is used for conveying oil and gas, such as in Integrated Production Umbilicals'.

The wall thickness of a standard composite tube is typically proportional to the pressure rating and to the inner diameter. For very high pressure applications (1300 bar and more), the wall thickness of a standard duplex/superduplex tube is typically around 5mm when the inner diameter is 2 5mm, (and by extension, around 10mm when the inner diameter is 50mm, and around 15 mm when the inner diameter is 75 mm].

According to the present invention, when a composite outer layer is added around a metal liner, it is possible to reduce the wall thickness of the steel tube by at least 30%, and optionally even up to 50% (for example where it is possible that the axial loading including the end cap effect is fully held or withstood by the metal liner only).

Thus, the present invention can achieve by way of example for very high pressure applications (1300 bar and more) and with a composite tube inner diameter of say mm, a wall thickness of a duplex/superduplex steel liner in the range of around 50% -70% of 5 mm, i.e. between around 2.5mm and 3.5mm.

Based on the same parameters, and for a composite tube inner diameter equal to 50 mm, the wall thickness of a duplex/superduplex steel liner of a composite tube of the present invention can be between around 5mm and 7mm.

And based on the same parameters, for a composite tube inner diameter equal to 75 mm, the wall thickness of a duplex/superduplex steel liner of a composite tube to the present invention can be between around 7.5 mm and 10.5 mm.

More generally, where the diameter of the composite hose is in the range 10mm to 75mm, the thickness of the metal liner may be in the range 1mm to 10.5mm. In particular, the thickness of a steel liner could be in the range 1mm -7mm thick when the inner diameter of the composite tube is in the range 10mm -50mm, and up to around 10.5mm thick when the inner diameter of the composite tube is up to around 75mm.

The thickness of the composite outer layer is generally between a third of the metal liner wall thickness, and 3 times the metal liner wall thickness, depending on the composite material which is used.

S

Thus, optionally, the ratio of the thickness of the metal liner to the thickness of the composite outer layer is in the range 2 5:75 to 75:25.

Meanwhile, optionally, the ratio of the thickness of the metal liner to the diameter of the composite hose is in the range 5-15:100, preferably in the range 8-14:100.

Compared with composites, metals, in particular steel, provide superior mechanical properties including greater collapse resistance as well as being easily manufacturable and joinable by the use of welding operations to create a continuous elongate liner for a pipeline.

Metals also provide a lower volumetric expansion than composite thermoplastic hoses, which reduces the response time when the tube is to control a subsea hydraulic actuator from a topside hydraulic power unit.

Thus, the use of a metal liner still provides the umbilical with an amount of the overall strength, in particular loading strength, required for the umbilical, both during laying and during use at or near a seabed. Where the umbilical is being laid and/or used at a depth deeper or greater than 2000 meters, a significant proportion of the overall strength of the umbilical can be a factor, especially with the pressures being applied to the or each tube being used for transportation of a hydrocarbon, including the internal pressure within a transportation tube, and the external pressure from the sea.

The use of a metal liner in the replacement of hoses formed from conventional materials, such as plastics and polymers typical in the formation of hydraulic hoses) also reduces the permeation of a fluid being transported by the composite tube.

Permeation or leakage of the fluid through a thermoplastic hose can be detrimental especially when the fluid is dangerous for the environment.

The composite outer layer of the composite tube of the present invention preferably comprises fibers in a polymer matrix. Optionally, the fibers are one or more selected from the group comprising carbon fiber, glass fiber, aramid fiber, Poly (p-phenyene-2, 6-benzobisoxazole) (PBO) or a combination of these. Composite fibers such as graphite, Keviar, fiberglass, etc. have numerous assets including high strength, high stiffness, light weight, etc. as well as possibly being braidable.

Optionally, the p&ymer matrix is made with a thermosetting polymer such as an epoxy. Preferably, the polymer matrix is made with a thermoplastic polymer such as polyamide or PEEK.

The use of a polymer matrix provides a combined material that has high strength whilst still having some element of easy usability to form into the required supporting strength to allow the liner to be formed of a relatively thinner metal.

The composite outer layer is preferably a carbon/peek composite, or a carbon/PPS composite, or a carbon/polyamide composite, or a glass/polyamide composite. The thickness of the composite outer layer may be in the range 0.5mm to 10mm.

Carbon fiber in particular possesses superior wear and strength properties for dynamic flexing applications over various other reinforcing fiber materials.

Optionally, the composite tube has an outer sealing polymer sheath.

The composite tube is designed to mechanically support the metal liner and share with the steel liner the loadings applied onto the composite tube, to allow the metal liner to have a reduced thickness compared to the wall thickness of an equivalent standard steel tube not comprising any composite outer layer and designed for the same loadings.

According to a preferred embodiment, the composite tube is designed so that the axial loads are wholly or substantially withstood by the metal liner only, whereas the radial loads due to the inner pressure are shared between the metal liner and the composite outer layer. Based on such a design, the wall thickness of the metal liner of the composite tube can be almost half the wall thickness an equivalent standard steel tube.

The meta' liner wall thickness reduction compared to an equivalent standard metal tube is generally comprised between 30% and 50%, which reduces significantly the overall weight of the umbilical, especially where the umbilical has a longer length such as >2000m. Optionally the umbilical is >2000m long.

The subsea flexible umbilical of the present invention may include any umbilical intended to extend between one or more subsea and surface apparatus, device or units, including support umbilicals, fluid transportation umbilicals, risers, or a combination of same.

In one embodiment of the present invention, the plurality of umbilical components in the umbilical are one or more selected from the group comprising: electrical cables, optical fibre cables, steel tube, and thermoplastic hoses, including fluid transportation tubes.

Optionally the umbilical includes a composite tube which is a fluid transportation tube.

Preferably, the subsea flexible umbilical is reelable, in particular reelable on and off a reel or spool known in the art) and used in the transportation and/or laying and/or recovery of fluid pipelines.

According to a second aspect of the present invention, there is provided a method of forming a subsea flexible umbilical comprising a plurality of umbilical components, at least one umbilical component comprising a composite tube having a metal liner and a composite outer layer as defined herein, comprising at least the steps of providing the composite outer layer around the metal liner to provide a composite tube, and forming the umbilical by combining the composite tube with the other umbilical components.

An embodiment of the present invention will now be described by way of example only, and with reference to the accompanying schematic drawing Figure 1, being a cross sectional view of a subsea flexible umbilical.

Referring to the drawing Figure 1 shows a subsea flexible umbilical 2 for use in the offshore production of hydrocarbons. It includes an outer sheath 4 surrounding a number of first composite tubes 6, and a central composite tube 8. The umbilical 2 could also include other umbilical components such as optical fiber cables, reinforcing steel or carbon rods, electrical signal cables, electrical power cables, etc., which are not shown in Figure 1.

Each of the first composite tubes 6 and the central composite tube S comprises a steel inner liner 10 and a composite outer layer 20.

The meta' liners 10 can be steel, preferably stainless steel. The metal liner provides the required protection against the nature of the particular fluid being conveyed or transported, in particular aggressive or corrosive fluids. This protection reduces, hopefully completely prevents) the permeation of any fluid within the composite tubes 6, 8, while still achieving required flexibility of the umbilical 2, and providing a degree of the overall strength of the umbilica' 2 especially at increasing lengths.

The forming of metal liners 10 is known in the art and not further described herein) but it is a particular development of the present invention that the metal liner may only require a thickness between the half and two-thirds of the thickness of an equivalent standard metal tube made with the same metal and designed for the same loadings.

Meanwhile, a high degree of strength is still achieved in the composite tubes 6, 8 by the use of a composite outer layer, especially a composite outer byer formed of fibers such as carbon, glass, aramid, PBO, in a polymer matrix, especially a thermoplastic matrix. The matrix material preferably has a high elongation, high strength) impact resistant properties and can also include matrix material such as nylon-6, vinylester from a polyester, polyetherketone polyphenylene sulfide, polyethylene) polypropylene and thermoplastic urethanes.

Preferably, the fibers of the composite outer layer extend helically around the metal liner, with a winding angle advantageously comprised between 55° and 900 to increase the inner pressure rating. Optionally) the fibers can be interwoven amongst themselves.

Optionally, the composite outer layer could comprise one or more layers of different material to achieve different properties.

By the use of particular materials and particular thicknesses of materials, the present invention achieves a composite tube balancing the requirement to provide increased protection against the nature of fluids to be transported, such as aggressive and corrosive fluids, and the required mechanical properties induding strength, in particular inner pressure resistance and collapse resistance, loading capacity strength, in balance with the overall weight of the umbilical, especially longer umbilicals required for increasing water depths such as those extending and/or being laid beyond 2000m.

Whilst reinforcement layers can be added to any umbilical in the art) this also increases the weight of the umbilical. The present invention is able to achieve a significant balance between weight and strength, in particular achieving reduced permeation to aggressive and corrosive fluids, and to achieve very high pressure rating whilst still achieving flexibility desired for ease of manufacture, transport and laying, generafly via a reel, using current and/or conventional equipment.

Claims (15)

1. Claims 1. A subsea flexible umbilical comprising a plurality of umbilical components, at least one umbilical component comprising a composite tube having a metal liner and a composite outer layer.
2. 2. An umbilical as claimed in claim 1 wherein the metal liner is a steel liner, preferably a stainless steel liner.
3. 3. An umbilical as claimed in claim 1 or claim 2 wherein the composite outer layer comprises fibres in a polymer matrix.
4. 4. An umbilical as claimed in claim 3 wherein the polymer matrix is an epoxy matrix.
5. 5. An umbilical as claimed in claim 3 or claim 4 wherein the fibres are one or more selected from the group comprising: carbon fiber, glass fiber, aramid fiber, PBO, or a combination of these.
6. 6. An umbilical as claimed in any one of the preceding claims wherein the plurality of umbilical components are one or more selected from the group comprising: electrical cables, optical fibre cables, steel tubes, thermoplastic hoses, including fluid transportation tubes.
7. 7. An umbilical as claimed in any one of the preceding claims wherein the composite tube is a fluid transportation tube.
8. 8. An umbilical as claimed in any preceding claim wherein the umbilical is reelable.
9. 9. An umbilical as claimed in any preceding claim wherein the umbilical is >2000m long.
10. 10. An umbilical as claimed in any one of the preceding claims wherein axial loading on the composite tube is wholly or substantially withstood by the metal liner, and radial loading on the composite tube is shared by the metal liner and the composite outer layer.
11. 11. An umbilical as claimed in any one of the preceding claims wherein the ratio of the thickness of the metal liner to the thickness of the composite outer layer is in the range 25:75 to 75:25.
12. 12. An umbilical as claimed in any one of the preceding claims wherein the ratio of the thickness of the metal liner to the diameter of the composite tube is in the range 5-15:100, preferably in the range 8-14:100.
13. 13. An umbilical as claimed in any one of the preceding claims wherein the diameter of the composite tube is in the range 10mm to 75mm, and the thickness of the metal liner is in the range lrnrn-1O.Smm.
14. 14. A method of forming a subsea flexible umbilical comprising a plurality of umbilical components, at least one umbilical component comprising a composite tube having a metal liner and a composite outer layer as defined in any one of claims 1 to 13, comprising at least the steps of: providing the composite outer layer around the metal liner to provide a composite tube, and forming the umbilical by combining the composite tube with the other umbilical components.
15. 15. An umbilica' substantially as described herein and with reference to Figure 1.