GB2114257A

GB2114257A - Improvements in and relating to flexible barriers

Info

Publication number: GB2114257A
Application number: GB08302114A
Authority: GB
Inventors: Peter Thomas Hale; Ivan Clifford Cheetham; George Arthur Pope
Original assignee: Dunlop Ltd
Current assignee: Dunlop Ltd
Priority date: 1982-01-30
Filing date: 1983-01-26
Publication date: 1983-08-17
Also published as: GB8302114D0; GB2114257B

Abstract

A flexible barrier, such as a high pressure flexible pipe, for containing pressurised fluid, and in particular diphasic fluids, comprises a first layer of polymeric material which in use of the barrier is arranged in proximity with the fluid to be contained, and a second layer which has been formed of a polymeric material of a kind incorporating an additive which when removed results in a substantial increase of the permeability of the material of the second layer in comparison with that of the first layer.

Description

SPECIFICATION Improvements in and relating to flexible barriers This invention relates to flexible barriers and in particular, though not exclusively, to articles such as flexible hose and flexible diaphragms at least one surface of which is exposed, in use, to diphasic mixtures of gas and oil.

Especially in the case of diphasic mixtures which are at a high pressure, resulting in a high pressure differential across the flexible barrier, the diphasic mixture and in particular the gas contained therein tends to permeate through the material of the flexible barrier and cause degradation thereof. Commonly the flexible barrier is of a laminated construction and contains an embedded reinforcement structure, in which case in addition to the risk of a permeating gas causing degradation of the reinforcement it is found that blisters tend to form between and occasionally within the layers and result in a tendency for progressive delamination.

Thus the useful working life of the article is reduced.

To minimise the risk of an undesirable accumulation of gas within the flexible barrier it is known to use, other than at the surface in contact with the diphasic mixture, material of a high permeability, such as silicone rubber and materials of like permeability. Thus any gas permeating through a low permeability surface layer provided in contact with the diphasic mixture is relatively free then to pass through the barrier without any substantial risk of build-up and consequential blistering.

A disadvantage associated with the use of silicone rubber and a number of materials of similar permeability is that they do not possess an adequate level of strength in order satisfactorily to locate successive parts of any reinforcement structure provided within the body of the barrier. Thus although materials such as silicone rubber are suitableforforming an outer surface layer, remote from that surface normally in contact with the diphasic mixture, they are not suitable for use in a central reinforcement region of the flexible barrier, at which region there is thus a tendency for accumulation of gases and consequential blistering and deg radation of the reinforcement structure. A further disadvantage of silicone rubber as compared with, say, neoprene is that of expense.

The present invention seeks to provide a flexible barrier, such as a hose or diaphragm, which in use is capable of containing gases of diphasic fluids under a high pressure differential and in which the aforementioned difficulties are mitigated or overcome.

In accordance with one aspect of the present invention a flexible barrier for containing pressurised fluid comprises a first layer of polymeric material which in use of the barrier is arranged in proximity with the fluid to be contained and a second layer which has been formed of a polymeric material of a kind incorporating additives which when removed result in a substantial increase of the permeability of the material of the second layer in comparison with that of the first layer.

The present invention further provides a flexible barrier wherein said additive has been removed thereby to provide in the second layer of polymeric material fibrillar path formations which relatively readily permit the passage of gas therethrough in comparison with said first layer.

The first layer may be in direct contact or in close proximity but not direct contact with the fluid to be contained.

The term "Fibrillar path formations" is used herein to mean both a discrete formation of an elongate form and also a series of formations each of which is not necessarily elongate or directly in communication with another formation but which together constitute a low permeability path through the second layer.

The fibrillar path formations preferably are provided by using for the second layer a polymeric material of a kind which incorporates additives that are removed from the material subsequent to forming said material to the shape which normally it adopts in the finished article.

The flexible barrier may comprise a reinforced structure, which preferably is embedded in the second layer of polymeric material.

The permeability of the material of the second layer prior to formation of the fibrillar paths may be lower than that of the material of the first layer, the formation of the fibrillar paths thus increasing the extent to which the second layer permeability exceeds that of the first layer. Alternatively, however, the second layer may be formed of a material which, prior to creation of the fibrillar paths has a permeability greater than or equal to that of the first layer.

The additive may be leached from the polymeric material, thereby to create the fibrillar path formations, either as part of the manufacturing process for the flexible barrier or during subsequent installation or use of the barrier.

Thus for flexible barriers of a kind which are to be used in an underwater environment use may be made of a water-soluble additive so that the fibrillar path formations are created during installation or use instead of during the preceding manufacturing operations.

Particularly suitable additives for the polymeric material of the second layer include polyethylene oxides such as Polyox WSR 30 and PEG 6000, and polyvinyl alcohol of molecularweight 14000 IPVA 14000) (each ex B. D. H. Chemicals Limited), these being water soluble.

The aforementioned additives are particularly suitable in polymeric materials such as neoprene, nitrile rubber, styrene butadiene rubber and natural rubber.

The additives may be soluble in contact with the contained fluid for which it is desired to provide a relatively low permeability path through said second layer, such that the additive is leached from the flexible barrier by the contained fluid. In general, however, it is preferred not to rely on the contained fluid to form the fibrillar paths within the material of the second layer because of the risk of fluid accumulation and blisterformation during the time taken for creation of the fibrillar paths.

The invention is particularly useful in respect of hose ,or use as high pressure flexible pipe to transport hot crude oil from, for example, the seabed to a surface or other remotely positioned station. In the case of this, and other underwater applications, the polymeric material of the second layer may conveniently by rendered relatively permeable whilst in situ by allowing sea water to leach away the additives in the polymeric material.

One embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 shows a pipe cut away step-wise to reveal its successive layers, and Figure 2 shows in detail in cross-section a part of the pipe of Figure 1.

The pipe illustrated is a 3" bore high-pressure flexible pipe for the transportion of crude oil.

The pipe comprises a crush-resisting inner lining layer 10 formed from a twin-start helix of type "316" stainless steel wire, the wires being of substantially trapezoidal section and arranged such that contacting surfaces of the wires between successive turns of the helices have a substantially frusto-conical shape and taper in opposite directions relative to the length of the hose.

An inner lining layer of this type is described in more detail in our U.K. Patent Publication No, 2,002,084.

In addition to resisting crushing loads the layer 10 is intended to provide an abrasion resistant lining which permits the passage of tools through the pipe without causing damage to the inner surface thereof.

The lining layer 10 is surrounded by a pair of wrapping layers 11 of glass fabric material, formed by helically wound strips, to act as a radially inner boundary for a subsequently extruded fluid sealing layer 12 of the fluoro-polymer, e.g. a fluoro-plastics material of a kind highly resistant to oil penetration and which thus serves to contain oil from leaking through pipe wall. Suitable materials for forming the fluid sealing layer, which is analogous to the aforedescribed first layer of polymeric material, include Tefzel, Teflon FEP and Teflon PFA (ex DuPont) and to ensure an adequate barrier to the leakage of the transported oil, and gases therein, it is envisaged that the sealing layer should have a thickness in the range 5 to 9 mm.

The layer 12 is surrounded by a pair of wrapping layers 13 also formed by helically wound strips of glass fabric material. These layers serve to contain the fluoro-plastics material especially when the latter is subjected to high pressures from oil and gas within the bore of the pipe.

The layers 13 are surrounded by a primary rein forcementstructure comprising four layers 14 of sheathed reinforcing elements 15, described in more detail below, the elements in each layer being wound helically at tough pitch with the elements in the successive layers extending in opposite senses.

The layers 14 are surrounded by a pair of wrap ping layers 16 constructed substantially similar to the layers 13 but intended to act as a barrier to resist intrusion of the polymeric material of a relatively outer cover 17 during formation thereof by extrusion. The outer cover 17 is formed of neoprene though in alternative constructions use may be made of for example silicone rubber and nylon 11.

The aforementioned reinforcing elements 15 (see Figure 2) comprise high tensile steel cord coins 15a surrounded by a protective sheath 1 5b which serves to resist deterioration of the high tensile steel by corrosive gases or liquids permeating though the wall of the hose pipe. The protective sheath 15b is formed from a material, such as butyl rubber, nylon or Teflon, having a relatively low permeability to crude oil and the gases associated therewith.

The sheathed core is encapsulated in a matrix of neoprene rubber 15e which has a relatively high permeability in comparison with the material of the sheath 15band this matrix is formed to provide the reinforcing element with a square section external profile such that on winding of the element 15 helically at touch pitch there is facilitated accurate positioning and spacing of the high tensile core in the successive turns of the reinforcement layer.

In the aforedescribed construction the neoprene material of the cover layer 17 and the encapsulating matrix 1 sic of the reinforcing elements contains, during construction of the pipe, a water-soluble additive such as PEG 6000, being a wax-like solid of molecular weight 6,000, or Polyox WSR 301 which is a powder and has a molecular weight of 4,000,000 or PVA 14000. The additive is leached from the polymeric material either as a part of the manufacturing operation or on site when the pipe is submerged in water, sufficient time being allowed for the additive to substantially completely leach from polymeric material before the pipe is used for the transportation of hot crude oil or other diphasic mixtures.

In the resulting pipe the fluoro-plastics sealing layer 12 is the layer which plays the greatest part in containing the oil and gas within the bore of the pipe. However, those fluids which, in view of the high temperatures and pressure differentials acting across the wall of the pipe, do permeate through the fluoro-plastics sealing layer are found to pass relatively freely through the relatively low permeability polymeric material of the matrix 15c and cover 17.

The substantial contribution made to the per meability of the material of the second layer of neoprene by the fibrillar path formations, i.e. the matrix 15cand cover 17 in the aforedescribed example, is illustrated by the following table of test results: TABLE Material Permeability Neoprene per se 0.7 Neoprene with additive PEG 6000 1.5 without water extraction Neoprene with additive PEG 6000, 106,600 water extracted Silicone rubber per se 116 The above permeability figures are measured in terms of cm3/cm/s/cm2bar x 10-8 in respect of air at 20 C.

Preferably the proportion of additive included in the polymeric material is in the range 50 to 100 pphr.

The fibrillar paths resulting from solution of the additive are not required to interconnect, though interconnection is desirable provided that the mechanical integrity of the polymeric material is not thereby impaired.

The relatively high permeability of the neoprene layers 15, 17 results in a high pressure flexible pipe which is substantially impermable to liquids, such as hydrocarbon liquids, but which is able to withstand without damage the permeation of gases associated with the fluid transported by the pipe.

Claims

1. A flexible barrier for containing pressurised fluid comprising a first layer of polymeric material which in use of the barrier is arranged in proximity with the fluid to be contained and a second layer which has been formed of a polymeric material of a kind incorporating an additive which when removed results in a substantial increase in the permeability of the material of the second layer in comparison with that of the first layer.

2. A flexible barrier according to Claim 1 wherein said additive has been removed thereby to provide in the second layer of polymeric material fibrillar path formations which in comparison with the material of said first layer relatively readily permit the passage of gas through said second layer.

3. A flexible barrier according to Claim 2 wherein said fibrillar path formations are provided by using for the second layer an additive that is removed from the material subsequent to forming said material to the shape which it normally adopts in the finished article.

4. A flexible barrier according to any one of the preceding claims wherein the additive is water soluble.

5. A flexible barrier according to Claim 4 wherein the additive is a polyethylene oxide.

6. A flexible barrier according to any one of the preceding claims and provided with a reinforcement structure.

7. A flexible barrier according to Claim 6 wherein said reinforcement structure is embedded in the second layer of polymeric material.

8. A flexible barrier according to any one of the preceding claims wherein the first layer of polymeric material is of tubular shape and is surrounded by the second layer of polymeric material.

9. A flexible barrier constructed and arranged substantially as hereinbefore described with referpence to the accompanying drawings.

10 A high pressure flexible pipe comprising a reinforcement structure and flexible barrier according to any one of the preceding claims wherein said second layer of polymeric material is arranged outwards of said first layer.

11. A high pressure flexible pipe according to Claim 10 wherein said first layer is a lining layer of the pipe.

12. A high pressure flexible pipe according to Claim 10 or Claim 11 wherein said second layer is a cover layer of the pipe.

13. A high pressure flexible pipe according to any one of Claims 10 to 12 wherein the reinforcement structure is embedded in the second layer of polymeric material.

14. A high pressure flexible pipe according to Claim 10 and constructed and arranged substantially as hereinbefore described with reference to the accompanying drawings.