WO2000008368A1

WO2000008368A1 - Venting of plastics lined pipelines

Info

Publication number: WO2000008368A1
Application number: PCT/GB1999/002613
Authority: WO
Inventors: Stuart Mcintyre
Original assignee: Boreas Consultants Ltd
Current assignee: Boreas Consultants Ltd
Priority date: 1998-08-08
Filing date: 1999-08-09
Publication date: 2000-02-17
Anticipated expiration: 2001-02-08
Also published as: GB9817223D0; AU5430299A

Abstract

A vent assembly for venting of plastics lined pipelines is inserted through the wall of a steel pipeline (2). The vent assembly (1) has a main body (3) having a small through-hole (4). A porous element (5) fits in a recess (6) in the main body (3) and a non return valve (7) is held in place by a retaining cap (10). The valve assembly (1) fits flush with the inner surface (11) of the pipeline (2). A micro annulus (13) exists between the pipeline (2) and the liner (12). In use, the pipeline (2) is typically used for hydrocarbons and the plastics liner (12) is permeable to the gas content in the hydrocarbon. Consequently a small quantity of gas finds its way into the micro annulus (13) from where it can escape through a nearby vent assembly (1).

Description

VENTING OF PLASTICS LINED PIPELINES

This invention relates to the venting of plastic lined pipelines, especially but not exclusively those pipelines used for transporting hydrocarbon fluids.

In the North Sea and in many other oil and gas-producing areas throughout the world there are a great many pipelines which carry aggressive hydrocarbon fluids. These fluids are very corrosive which must be taken into consideration in pipeline construction.

This problem can be addressed in two main ways. The first option is to use high-grade corrosion resistant material for pipeline construction. However such materials are very expensive, up to ten times the cost of Carbon Steel that is used in less exacting circumstances. The cost premium means that this option is not practical where any significant length of pipeline is involved. Accordingly the second option, that of providing a cheap corrosion resistant inner surface on a carbon steel pipeline, offers major cost benefits. Various plastics material liners have previously been proposed and are commonly used in process plant pipework. However, the materials used in these systems are not suitable for petrochemical pipelines as they are generally supplied in short lengths that are flanged rather than welded and operate at near ambient temperatures and low pressures.

Plastics lining of non-hydrocarbon pipelines is used in certain applications such as high-pressure seawater injection pipelines. The technique used for lining such pipelines is to weld up lengths of about one kilometre and then to pull a continuous plastics material pipe into the steel pipe to form an inner lining. The process is for the plastics material pipe to be swaged down or squeezed between rollers to make it smaller and temporarily a loose fit. Installation is thus simplified and after some time the plastics material relaxes, or is expanded, to be a close fit with the steel pipeline. The fit between the plastics liner and the steel pipeline is close but there is no physical bond between the two. A small micro-annulus exists which is particularly evident at weld beads where there is greater stand off. The technique described is well established and particularly suited to systems, such as high-pressure water injection pipelines, with no gas content.

The main disadvantage of using such plastics liners for hydrocarbons is that the plastics material is slightly permeable to this and certain other materials. As the steel is impermeable the plastics liner allows the smaller gas molecules to permeate out of the fluid stream and the micro-annulus becomes pressurised over time. In the event that fluid pressure in the pipeline is released, as inevitably happens from time to time for operational reasons, the gas pressure in the annulus can cause the liner to collapse. In such circumstances, it is highly probable that the liner will not re-inflate without damage .

Possible solutions include strengthening the liner so that it is less susceptible to collapse or to make the liner impermeable by including a thin metallic layer within the plastics liner. Both these solutions however are likely to require the production of special liner materials and/or the use of special installation techniques. Additionally the plastics material degrades over time and absorbs water so that the likelihood of collapse when the pipeline is depressurised becomes difficult to predict.

Accordingly it would be a preferable engineering solution to prevent the annulus becoming pressurised and it is an object of the present invention to provide apparatus that seeks to achieve such a result.

According to the present invention there is provided apparatus for use in venting plastics lined pipeline comprising a vent assembly for through fitment in a pipeline wall and having means for resisting deformation of the plastics lining into the vent assembly.

The means for resisting deformation of the plastics lining may for example be by virtue of the provision of a vent hole of small diameter relative to the elasticity of the plastics material or preferably, a gas permeable barrier. More preferably, said gas permeable barrier is provided at an inner end of the vent assembly.

Said gas permeable barrier may for example be a sintered metal, a sintered wire mesh, a ceramic material or a stainless steel wire mesh.

Preferably also, the vent assembly includes non-return valve means .

The non-return valve means may for example comprise a spring biased ball valve assembly, or resilient material closure.

Preferably also, means are provided for allowing gas flow between the plastics lining and the pipeline.

This may be, for example, by virtue of the provision of a spacer element, such as a wire, cable or wire mesh between the lining and the pipeline.

Alternatively, gas drainage channels may be provided on the inner surface of the pipeline.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which:

Fig. 1 is a schematic cross-sectional view of a first embodiment of an annulus vent for use in apparatus of the present invention; Fig. 2 is a cross-sectional end view of a segment of plastics lined pipeline in accordance with the present invention;

Fig. 3 is a cross-sectional view of an alternative embodiment of an annulus vent for use in apparatus of the present invention;

Fig. 4 is a cross-sectional view of a further alternative embodiment of an annulus vent for use in apparatus of the present invention;

Fig. 5 is a schematic cross-sectional view of a first arrangement of the application of a vent to an insulated pipeline; and

Fig. 6 is a schematic cross-sectional view of a second arrangement of the application of a vent to an insulated pipeline

Referring to Figs 1 and 2 of the drawings a vent assembly for venting of plastics lined pipelines is shown generally at 1. The vent assembly 1 is inserted through the wall of a steel pipeline 2. This can be done at any convenient time during manufacture but before welding together of long lengths. The spacing of vents may be as frequent as every 12 or 13m (to suit the standard pipe length) up to several hundred metres apart (one vent in every ten or twenty lengths) as appropriate to the circumstances. Plastics liner installation follows the known procedures described above.

The vent assembly 1 is made up of a main body 3 having a small through-hole 4 forming a gas passage. A porous element 5 fits in a recess 6 in the main body 3 and a non return valve 7 comprising a ball 8 and spring 9 is held in place by a retaining cap 10. The valve assembly 1 fits flush with the inner surface 11 of the pipeline 2 so that it does not present an obstruction to the plastics liner 12. A micro annulus 13 exists between the pipeline 2 and the liner 12.

In use, the pipeline 2 is typically used for hydrocarbons, which will generally result in high temperatures and pressures in the pipeline 2. The plastics liner 12 is permeable to the gas content in the hydrocarbon to some extent. Consequently a small quantity of gas finds its way into the micro annulus 13 from where it can escape through a nearby vent assembly 1.

In certain circumstances no specific arrangements need be made to allow the gas to flow from the point where it escapes the plastics liner to the vent assembly along the micro annulus. Much depends on the surface finish of the pipeline 2 and the fit of the liner 12.

In the event that a need to promote gas flow is identified, a small spacer can be provided to ensure a gap exists between the pipeline 2 and the liner 12. The spacer can be glued or taped to the liner 12 as it is inserted in the pipeline 2.

One such arrangement is illustrated in Fig 2. In this construction, a number of power, signal and other cables 14 are inserted between the pipeline 2 and the liner 12 by fixing them to the liner 12 during installation. This results in small channels 15 being created which provide an easy gas passage along the length of the pipeline 2. If necessary filler materials can be included to prevent excessive curvature of the liner 12 that might cause cracking. Other means of providing a small gap are also envisaged such as the use of fine wire mesh. Further or alternative gas flow passages can be provided by the provision of small scores or grooves on the inner surface 11 of the pipeline 2. Typically, these grooves would be in a spiral pattern. The cable system which provides the channels 15 might be a fibre optic sensor system. These systems have previously been deployed downhole and they are capable of measuring temperature and pressure along every metre of their length. In the present application such a system can monitor temperature and pressure as described and also function as a leak detection system in the event of liner rupture.

In addition, conventional or fibre optic conductors could be fitted which would allow the transfer of control and instrumentation signals along the pipeline. This would be particularly helpful in subsea step out developments, where the pipeline typically connects a remote well to a platform and the control functions are performed via a separate umbilical. A degree of control could be provided through the liner spacer.

The porous element 5 on the vent assembly 1 provides a barrier against the liner 12 deforming under pressure and clogging the vent hole. Various materials are envisaged for the porous element 5, for example sintered metal, sintered wire mesh or porcelain/ceramic type material. Additionally the porous element can be made from various plastics and composite materials such as PEEK (Poly Ether Ether Ketone) alloyed with Teflon (PAT) . The specific physical characteristics of the material provide a high resistance to large molecular weight molecules to prevent a fluid leak in case of the liner 12 becoming ruptured.

The presence of a non-return valve 7 ensures that the liner 12 does not collapse as a result of hydrostatic pressure during offshore installation. For land pipelines and in shallow water applications the non- return valve may be omitted to simplify the construction.

In offshore installations in particular corrosion can be a significant problem and as such, especially for such installations, the materials and attachment of the vent assembly are selected to minimise corrosion effects.

The practical effect of the vent assembly 1 is to ensure that the micro annulus is always at or near to ambient pressure. Thus the risk of collapse of the liner 12 when pipeline pressure is reduced is minimised.

Modifications and improvements may be made without departing from the scope of the invention herein intended and some examples of such modified embodiments will now be described.

Referring now to Figs 3 and 4 alternative arrangements of vent assembly are illustrated. Referring firstly to Fig 3 a vent assembly 100 comprises a threaded plug 101 which is screwed into a partially threaded throughole 102 in the pipeline 2. As before the vent assembly has a small throughhole 103 forming a gas passage and a porous element 104. The porous element may either sit flush with the pipeline inner surface 11 or form a slight protrusion, as in this example. The vent assembly 1 can be formed from a range of plastics or composite materials, in the example illustrated this is PEEK material. The selection of this material is primarily dictated by the need for the assembly to be resistant to corrosion and blockage in the harsh environment typically found in pipelines. In this embodiment non return valve means are effectively provided by a rubber, or similar material, band 105 which fits around the pipeline 2 to close off the vent assembly 100. An improved seal is obtained where the throughhole 103 in the vent assembly 100 has a tapered opening as shown in Fig 3.

This particular type of vent assembly also has the advantage that it is fitted to the pipeline externally. Accordingly it may be fitted to a pipeline either under construction or as a retrofit to already lined pipelines, perhaps those with defective venting already in place. Additionally it may be fitted to pipelines which are to be lined as part of a rehabilitation process.

The Fig 4 assembly is similar to the Fig 3 embodiment but additionally shows further alternatives. In this case the threaded plug 101 forming the vent assembly 100 fits into a throughhole 102 threaded completely through the pipeline wall. Valve means are provided in the form of a vapour permeable water barrier member (for example Goretex) 106.

Although not illustrated it is also envisaged that the valve means of the Fig 3 and Fig 4 embodiments might be used together with the rubber band 105 providing a back up or dirt exclusion function to the membrane 106. Figures 5 and 6 illustrate the application of the vent assembly to insulated pipelines. In each case the vent assembly is provided with an extension tube 107 either as a separate component or as an integral part of the vent assembly. The purpose of the extension is to ensure that any escaping gas is discharged outside the insulating layer. In Fig 5 the vent is positioned beyond the extent of any factory coated insulation 108 and is surrounded by site applied insulation 109. In Fig 106 the factory insulation 108 has been removed to allow fitment of the vent assembly and a site applied insulation repair 110 made around it .

The extension tube allows the high integrity requirements of the coating system to be maintained at the vent, and if made from a suitable insulating material, also prevents cold spots on the pipe which may encourage either the formation or hydrates or condensation and the resulting blockage or corrosion.

Claims

CLAIMS : 1. Apparatus for use m venting plastics lined pipeline comprising a vent assembly for through fitment in a pipeline wall and having means for resisting deformation of the plastics lining into the vent assembly.

2. Apparatus for use m venting plastics lined pipeline as claimed m Claim 1 , wherein the means for resisting deformation of the plastics lining is "the provision of a vent hole m the vent assembly of small diameter relative to the elasticity of the plastics material.

3. Apparatus for use m venting plastics lined pipeline as claimed in Claim 1 , wherein the means for resisting deformation of the plastics lining is a gas permeable barrier m the vent assembly.

4. Apparatus for use in venting plastics lined pipeline as claimed in Claim 3, wherein said gas permeable barrier s provided at an inner end of the vent assembly.

5. Apparatus for use in venting plastics lined pipeline as claimed m Claim 4 wherein the gas permeable barrier is flush fitting with the inner surface of the pipeline.

6. Apparatus for use m venting plastics lined pipeline as claimed m any one of Claims 3, 4 and 5 wherein said gas permeable barrier is of sintered metal material.

7. Apparatus for use in venting plastics lined pipeline as claimed in any one of Claims 3, 4 and 5, wherein said gas permeable barrier is of sintered wire mesh material.

8. Apparatus for use in venting plastics lined pipeline as claimed in any one of Claims 3, 4 and 5, wherein said gas permeable barrier is of ceramic material.

9. Apparatus for use in venting plastics lined pipeline as claimed in any one of Claims 3, 4 and 5, wherein said gas permeable barrier is of steel wire mesh material.

10. Apparatus for use in venting plastics lined pipeline as claimed in any one of Claims 3, 4 and 5, wherein said gas permeable barrier is of plastics material.

11. Apparatus for use in venting plastics lined pipeline as claimed in any one of the preceding Claims, wherein the vent assembly includes non-return valve means .

12. Apparatus for use in venting plastics lined pipeline as claimed in Claim 11 , wherein the non-return valve means comprises a spring biased ball valve assembly.

13. Apparatus for use in venting plastics lined pipeline as claimed in Claim 11 wherein the non return valve means comprises a resilient band around the pipeline and engaging the vent assembly.

14. Apparatus for use in venting plastics lined pipeline as claimed in any one of the preceding Claims, wherein means are provided for allowing gas flow between the plastics lining and the pipeline.

15. Apparatus for use in venting plastics lined pipeline as claimed in Claim 14, wherein the means for allowing gas flow comprises a spacer element between the plastics lining and the pipeline.

16. Apparatus for use in venting plastics lined pipeline as claimed in Claim 15, wherein the spacer element comprises one or more elongate elements extending lengthwise along the pipeline.

17. Apparatus for use in venting plastics lined pipeline as claimed in Claim 16, wherein the elongate elements are fibre optic elements.

18. Apparatus for use in venting plastics lined pipeline as claimed in Claim 15, wherein the spacer element is a wire mesh arrangement .

19. A plastics lined pipeline provided with means for venting between the plastics lining and the pipeline comprising a vent assembly as defined in any one of the preceding Claims.