WO2015101718A1

WO2015101718A1 - Method of grounding multilayer pipes and pipeline comprising multilayer pipes

Info

Publication number: WO2015101718A1
Application number: PCT/FI2014/051069
Authority: WO
Inventors: Patrick Jansson
Original assignee: Uponor Infra Oy
Priority date: 2013-12-31
Filing date: 2014-12-31
Publication date: 2015-07-09
Also published as: FI20136341A; FI126591B

Abstract

The present invention relates to a method of grounding a joint (3) between two pipes (1, 2), which pipes comprise a multi-layered wall structure having an inner surface (A) and an outer surface (B) and containing at least a first conductive layer (4'', 7''), which is covered by a non-conductive layer (5, 8), comprising the steps of forming at least one pair of apertures(6) in a pipe wall structure, whereby each aperture of the pair is positioned on opposite sides and in the proximity of the joint, whereby each aperture extends through the wall structure from the inner to the outer surface, and filling the aperture with conductive material (6'), said conductive material forming a conductive link from the at least first conductive layer through the non-conductive layer to the outer surface for grounding the at least first conductive layer. The invention further relates to a pipe comprising said conductive link.

Description

METHOD OF GROUNDING MULTILAYER PIPES AND PIPELINE

COMPRISING MULTILAYER PIPES

Technical Field

The present invention relates to multilayer pipes. In particular, the present invention concerns pipelines or pipings formed by a plurality of multilayer pipes comprising at least a first conductive layer, which pipes are grounded by a conductive link. The present invention also concerns pipes as wells as methods for grounding multilayer pipes comprising at least a first conductive layer to provide a pipe, which allows for grounding of the at least first conductive layer.

Background Art

Flammable liquids and gases, such as gasoline and other hydrocarbons, dry substances, such as dust particles, as well as many other materials are capable of inducing a static charge. If the charge is not conducted out of a system containing these materials, there is a risk of spark ignition. For this reason, only electrically conductive, or at least dissipative, materials can be used in direct contact with media of the above mentioned types.

Suitable conduits for materials of the above kind are represented by multilayer polymer pipes, where the main layer is made of a non-conductive material and conductive layers have been added on the inside or outside (or both) of the pipe. This construction offers a cost effective alternative to pipes made fully of conductive material. However, it also poses some demands on jointing and grounding of the pipes.

Thus, when the conductive layer of the multilayer pipe is located on the inside of the pipe, it is shielded from the surrounding by the insulating main polymer layer. It is necessary to find a specific way to ground the inner conductive layer. It is also of interest to find grounding methods that function as a conductive link between two conductive multilayer pipes that are joined. If the conduction layer is grounded in the proximity of the joint, it is not necessary to ground every single pipe over its entire length, since the whole pipeline is then conductive from end to end. A number of patents deal with jointing of conductive polymer pipes. EP 0 975 911 describes a method of leading away static electricity in mutually joined conductive polymer pipes. According to the method, a sleeve-like body of conductive material is placed in the ends of two pipe-parts to be joined end-to-end, so as to internally bridge the intermediate joint; and a contact pressure is generated between the sleeve-like body and the inner surfaces of the barrier layers at the ends of the two pipe-parts so as to provide an inner, electrically conductive connection between the conductive barrier layers of the mutually joined pipe-parts. US 5 951 812 provides a method of joining two pieces of fiberglass reinforced pipe using a cylindrical joining member adapted to receive the two ends of the pipes. The joining method comprises placing the ends of the pipes inside the joining member and arranging a conductive adhesive between the joining member and the pipes so that the adhesive conducts electricity from one pipe piece to the other pipe piece. The conductive adhesive extends along the inside and the outside pipe conductive surfaces and contacts the inside and the outside conductive surfaces so that static charge on the inside pipe surface can pass to the outside pipe surface.

US 3 943 273 discloses a conducting plastic pipe system wherein one part of the pipes is shaped as a male pipe part and the other as a female plastic pipe part with conducting covering layers which are interconnected by means of a conducting sealing ring between the male and female part. In case there are outer covering layers, the covering layer is extended onto the inner side of the muff end of the female pipe part. JP 07310710 relates to a connecting member for antistatic synthetic resin members. To provide a connecting member capable of connecting an antistatic synthetic resin member with the antistatic function thereof maintained. According to the reference, a connecting section for catching the end of an antistatic synthetic resin member is formed at both side ends of a connecting member body. Also, antistatic jointing layers are formed on the surface of the body for jointing antistatic layers formed on the surface of the member inserted and fixed in the section at both side ends.

EP 2 167 861 discloses a method for jointing two multilayer pipes comprising at least one conductive layer covered by a non-conductive layer by grounding the conductive layer at the joint using a conductive bridge that extends from the conductive layer through the non- conductive layer to the outer surface of the pipe.

Further art is disclosed in WO 2013/030621 and US 4 032 708.

As will appear from the above survey, the known solutions are complex and require the use of separate sealing rings and joining members potentially coupled with the use of resins and adhesives. The know solutions require a complex procedure of boring holes in the wall of the pipes at the joints, prior to jointing the pipes and then filling the holes.

Summary of Invention

Technical Problem It is an aim of the present invention to eliminate at least a part of the problems associated with the known solutions and to provide a new way of grounding conductive multilayer pipes made of polymer materials in particular to provide efficient grounding of at least a first conductive layer even if these are covered by a non-conductive layer. It is another aim to provide new pipelines comprising a plurality of multilayer pipes jointed together to form a continuous conduit with proper grounding of the conductive layers.

These and other objects, together with the advantages thereof over known methods and pipe joints, are achieved by the present invention as hereinafter described and claimed.

Solution to Problem

The present invention is based on the idea that at a pipe is provided with at least one conductive contact plug extending from the inside to the outside of the pipe, which plug forms a conductive bridge or link from the conductive inside layer of the pipe to the outside.

Suitably the plug comprises an aperture or hole filled with a conductive material.

Preferably, the aperture(s) or hole(s) is/are filled with a conductive, melt-processible material, which is compatible with the material of the conductive layer. The conductive material that fills the aperture serves as a conductive link from the conductive inner or first conductive layer to the outside surface of the pipe. The aperture preferably extends from the inner surface of the pipe essentially transversally to the central axis of the pipe.

If the outside layer of the pipe is non-conductive, the inside layer can be grounded through grounding of the conductive bridge formed by the plug. If the outside layer of the pipe is at least partially conductive, the inside layer can be grounded through any point on the outside layer of the pipe, as the conductive inner and outside layer are connected through the conductive bridge.

In a particular embodiment, a pipe joint contact from the inside to the outside of the pipe is achieved by forming in the pipe wall at least one pair of aperture or hole, whereby the aperture extends from the outer surface of the pipe to the conductive layer. The pair of apertures is positioned at the joint (or in the following "over the joint"), i.e. one on each (opposite) side of the joint and in the proximity of said joint. Each of the apertures is filled with conductive material.

Based on this method, in a pipeline or piping according to the invention, the conductive layer of the pipe is grounded by the conductive link extending from the conductive layer through any overlapping non-conductive layers. In the pipeline, the pair of apertures present on opposite sides and in the proximity of the joint provide for inductive links that prevent induction of static charges at the joint. More specifically, the method according to the present invention of grounding multilayer pipes is mainly characterized by what is defined in claim 1.

A pipe according to the present invention is characterized by what is stated in the characterizing part of claim 16.

The pipeline or piping according to the present invention is characterized by what is stated in the characterizing part of claim 21. Advantageous Effects of Invention

Considerable advantages are obtained by the present invention. Thus, no production of extra parts is needed - the joint can be processed at the installation site using materials readily available. The inner surface is smooth at the conductive link and the grounding of the conductive layers is secure. A particularly preferred feature resides in the fact that the grounding system does not change the dimensions of the pipe. Furthermore, by mounting a sleeve around the joint, the pressure rating of the pipe can be maintained. By providing the conductive links close to the joints between two pipes it is possible to provide grounding of two pipes at a common grounding site which is located at the jointing area.

By providing the conductive links close to the joint between two pipes it is even possible to conductively join together the adjacent pipes by forming an external conductive bridge between the links of the two pipes.

By providing all pipes of a pipeline with a conductive link according to the invention, the conductive inner layer is connected to form an integral conductive line which can be grounded at one single point. The conductive link can be provided after the pipes have been jointed. This improves the production process for piping.

In a preferred embodiment, the aperture has a conical shape, whereby the apex of the cone is directed toward the inner surface of the pipe and the base of the cone is directed towards the outer surface of the pipe. The conical shape improves conduction or dissipation of electrical charges. The conical shape with the apex directed towards the inner surface will also reduce or eliminate the danger of melt-processible material flowing into the cylindrical cavity of the pipe during the filling of the aperture.

Brief Description of Drawings

Reference is made to the appended drawings, in which Figure 1 shows the longitudinal cross-section of a first embodiment of a pipe comprising a pair of inductive link at opposite sides and in the proximity of a joint formed by two pipes joined together end-to-end; and

Figure 2 shows the longitudinal cross-section of a second embodiment, whereby the inductive link comprises a friction welding plug.

Description of Embodiments

For the purpose of the present invention, "aperture" bears the conventional meaning of "hole" or "opening". The aperture is defined by the edges surrounding it. As will appear from the following description, an aperture can be formed by boring or drilling, i.e. the aperture comprises a "bore". The aperture is formed at a distance from the end of the pipe, as also will be discussed below. As evident from above, and in reference to Fig 1 and Fig 2, the present invention relates to grounding of multi-layered polymer pipes 1, 2, in particular conductive multilayer pipes. The present invention provides for good grounding of the conductive layer 7', 7".

A wall structure of the pipes 1, 2 which may be joined together typically have at least two layers, an outer layer B and an inner layer A. The wall structure may comprise further layers, e.g. at least one middle layer located between the inner and the outer layers.

Preferably, at least a part of the layers is produced from materials, which can be co- extruded. Typically, polyolefms, such as polyethylene or polypropylene, are used for making the structural layers of the pipe wall or wall structure.

At least a first layer 7', 7" is electrically conductive or dissipative. And at least one of the conductive layers is circumferentially covered by an outer non-conductive layer 5, 8.

Typically, there is one or two conductive or dissipative layer(s) 7', 7", which is/are covered by an outer or outermost layer. According to one embodiment, the outermost layer/surface layer 5, 8 of the pipe is non-conductive. In this embodiment, the conductive link according to the invention extends from an inner surface A of the pipes 1, 2 to an outer surface B of the pipes 1, 2 from the first conductive layer 7', 7"' through the non- conductive layer 5, 8 to an outer surface B of the pipes 1, 2. The conductive link provides a conductive tab, which can be grounded. According to another embodiment, the pipes 1, 2 comprise two conductive layers, a first or inner conductive layer 7', 7" and a second or outer conductive layer 4', 4" that is located at a distance from the first conductive layer 7', 7". The outer conductive layer can be continuous or, preferably, in the shape of conductive stripes, for example stripes which are longitudinally (i.e. axially) orientated with respect to the pipe. An intermediate layer 5, 8 is located between the first and the second conductive layer. Typically, the intermediate layer 5, 8 is a structural, non-conductive layer. The second conductive layer 4', 4" forms the outer surface B of the wall structure of the pipes 1, 2, and the two conductive layers are connected through the conductive link. Naturally, it is possible to have pipes with more than two conductive layers. There can be several structural and/or non-conductive layers, also.

The conductive or dissipative layer(s) discussed above consist of a polymer material, preferably based on a thermoplastic material, which has been made permanently conductive. The properties of electrical conductivity can be obtained by blending the polymer material with conductive particles, such as fillers comprising carbon black or metal particles, conductive fibres or nanocomposites, including conductive carbon nanotubes. The layer may also contain, optionally and preferably in combination with the above conductive particles or fibres, inherently conductive polymers (ICPs), such as polyacetylene, polythiophene, polyaniline or polypyrrole, or ionomers contaning alkaline and/or earth alkaline metal ions or mixtures thereof. Preferably, the material has a surface resistivity in the conductive range, in particular the surface resistivity is from 1 to

10⁶ohm/sq (ASTM D-257). The layer may also be dissipative, which stands for surface resistivity of about 10⁷ to 10¹² ohm/sq (ASTM D-257).

Although the term "conductive" alone is being used in the present description on some occasions to designate the properties of the inner layer, it should be understood that also "dissipative" properties are being referred to.

The term "in the proximity of the joint" means that the distance of each aperture in the pair of apertures is such that no static charge can be induced between the apertures in the pair of apertures over the joint. This distance may vary depending on for example the dimensions of the pipe. Typically, the distance of the bore and, correspondingly, of the conductive plug filling the bore, to the end of the pipe is about 5 to 300 mm, in particular about 7.5 to 200 mm, in particular about 10 to 150 mm, so as to allow for end cutting of the pipe before joining with an adjacent pipe by, e.g. but welding or using a welding sleeve (electro fusion sleeve). The distance is calculated from the rim of the bore closest to the end of the pipe.

The bore is preferably located in an area or zone of the pipe which is not subjected to heating during the forming of a joint between adjacent pipes for example by welding. The aperture or bore can be pre-manufactured, i.e. it can be ready-made in the pipe to be delivered. Alternatively, the pipe can be provided with suitable apertures by boring in the vicinity or at the installation site.

The term "over the joint" means that at least one aperture is present on each site of a joint.

The weight ratio between the structural and the conductive material in the pipe varies depending on the mechanical strength requirements. The structural layer(s) determine(s) the nominal pressure of the pipe. The thickness of the conductive layer(s) varies depending on the application, but typically it is in the range of about 0.01 to 50 mm, in particular about 0.1 to 10 mm, preferably about 0.2 to 5 mm. The total wall thickness of the pipe is about 2 to 150 mm, typically about 3 to 30 mm. The cross-sectional diameter can vary widely between about 32 and 2000 mm, typically from about 63 to 400 mm.

In a preferred embodiment, at least two pipes 1, 2 of the above indicated type are joined together to form a continuous pipeline.

In a pipeline formed by joining together at least two pipes of the above kind, a conductive link is formed from a first conductive layer 7', 7" to the outer surface B of the pipeline 1, 2 to allow for grounding of the layer 7', 7". The conductive link also guarantees undisturbed conductivity. The positioning of conductive links on opposite sides of the joint 3 and in the proximity of the joint 3 prevents induction of electrical charges at the joint 3. Basically, at least one, generally 1 to about 10, and preferably 1 to 4, in particular one or two pairs of apertures are formed in the pipe wall, which apertures extend through the wall from the inner, at least one first conductive layer 7', 7" through the non-conductive layer 5, 8 to the outer surface B of the pipes 1, 2. The pair of apertures can be formed on one side of the pipe wall, but preferably the pairs of apertures 6 are present on opposite sides on the circumference of the pipe wall. When pairs of apertures are placed evenly around the circumference of the pipe, the grounding spots are equally evenly distributed and thus the distance from static charge induction points to the grounding spots is the shortest possible. Thus, generally a symmetrical distribution of the pairs of apertures 6 along the

circumference of the pipe is preferred.

Typically, the aperture 6 has a conical cross-section, and the diameter at the base of the cone thereof is about 5 to 50 mm, in particular about 10 to 30 mm. The diameter at the apex of the cone is about 1 to 25 mm, in particular about 5 to 15 mm. The depth of the aperture 6 depends on the distance between the first conductive layer 7', 7" and the surface B of the pipes 1, 2. Typically, with the above wall thicknesses, the first conductive layer 7', 7" is located at about 3 to 30 mm from the surface B. When the first conductive layer 7', 7"', which is to be grounded is located on the inside of the pipes 1, 2, the aperture 6 will preferably extend through the whole wall of the pipes 1, 2. The aperture 6 preferably extends essentially transversally to the central axis x of the pipes 1, 2. In practice, since the aperture 6 is formed manually, i.e. by on-site drilling or milling, some inclination is also possible. Preferably, the aperture 6 has a conical shape, whereby the apex of the cone is directed toward the inner surface A of the pipes 1, 2 and the base of the cone is directed towards the outer surface B of the pipes 1, 2. has a conical cross-section, The aperture 6 may have a circular cross-section, and the diameter at the base thereof is about 5 to 50 mm, in particular about 10 to 30 mm.

After the forming of the aperture 6, a conductive link is formed by filling the aperture 6 with conductive material 6', said conductive material 6' forming a conductive link from the first conductive layer 7', 7" through the non-conductive layer 5, 8 to the outer surface B of the pipes 1, 2 for grounding of the at least first conductive layer(s). The conductive material 6' can be introduced by extrusion or by fitting a solid piece of material into the aperture 6. Other ways of producing a suitable link or conductive plug 16' is to use an electro fusion material, which can be heated and melted in the aperture 6. A further way of achieving a suitable conductive plug 16' is by friction welding, by which method the plug 16' is rotated or vibrated at relatively high speed while applying a force. The friction heat generated at the interface between the plug 16' and the pipe wall softens or melts both components, and they thereby weld to each other.

In the grounding method, the ends of two multilayer pipes are fit against each other in abutting relationship. The ends of the pipes 1, 2 are secured to each other to form a joint 3 between the pipes 1, 2. One particular convenient way of securing the pipes 1, 2 is to use an electro fusion fitting, which is placed as a sleeve around the joint 3.

The invention provides various embodiments for achieving grounding of the at least first conductive layer 7', 7". These are shown in more detail in Figures 1 and 2:

Figure 1 relates to a first embodiment of the invention, wherein a plug 16' comprising conductive material is inserted into a hole or aperture 6 drilled into a pipe wall. The two pipes comprise two conductive layers 4', 4" and 7', 7", which are positioned on opposite sides of the structural, non-conductive layer 5, 8.

The method according to this embodiment may be carried out as described below.

First, at least a pair of aperture 6 is drilled through the pipe wall 1 and extends through the wall from the inner surface A to the outer surface B. Each aperture 6 of the pair of aperture is positioned on an opposite side and in the proximity of the joint 3.

The aperture 6 is subsequently filled conductive material 6', whereby the conductive material forms a conductive link from the at least first conductive layer 7', 7" through the non-conductive layer 5, 8 to the outer surface B for grounding the at least first conductive layer 7', 7".

Optionally, in a further method step the filling is performed by extruding a molten mass of the conductive material 6' into the aperture 6 by heating the conductive material and placing it into the aperture 6. The properties of the molten material 6 are such that it is fluid enough to be placed or pushed in the aperture 6 but solid enough not to flow freely into the pipe 1, but only flow over an edge of the surface A, B of the pipes 1, 2. By controlling the temperature and pressure of the molten material 6', a sufficient flow length and profile can be achieved when filling the aperture 6 with the extruder. In one embodiment, he molten material 6' is prevented from flowing into the pipes 1, 2 by using a stopper 9. Alternatively, a balloon can be used. The balloon can be inserted into the pipes 1 , 2 at the area where the hole 6 has been drilled. The balloon is pressurized and allows a certain amount of the molten conductive material to flow to the inside surface of the pipes 1, 2, covering the area around the circumference of the hole 6.

The molten conductive material 6' is subsequently compressed with the stopper 9 as indicated in Fig 1 with the arrows. This way, the inner surface A and the outer surface B are smoothened around the circumference of the aperture 6 in order to increase a contact area of the at least first conductive layer 7', 7".

The stopper 9 is then removed or the balloon is then de-pressurized and pulled out when the extrusion is finished and the material 6' has been allowed to cool down to a level well below the melting point of the material 6'. In an alternative variant of the first embodiment, a solid plug 16' is used instead of the extrusion method described above. In this alternative, a hole 16 is drilled through the pipe wall, and a plug 16' of conductive material is mechanically inserted.

Figure 2 shows a second embodiment comprising the use of a friction welding plug 16'.

The methods steps are largely the same as above explained for the first embodiment. Thus, the pipe ends 1 and 2 are brought together. A hole 16 is milled from the outside of the pipes 1, 2 to the inner layers 7', 7". The shape of the milling bit is preferably conical. A plug 16' made of conductive material and having same shape as the milling bit is friction welded to the milled opening 16. Jointing is continued preferably with an electro fusion fitting (not shown).

In an alternative embodiment, a hole or aperture 6, 16 is drilled or milled into the pipes 1, 2, from the outside as far as to the conductive layer 7', 7". However, it should be noted that with pipes 1, 2 having a larger diameter, the hole 6, 16 can also be drilled /milled and filled from the inside of the pipes 1, 2.

To avoid perforating the pipe wall, the drilling or milling means can be provided with an indicator light, e.g. a led light, with a voltage source could be connected. Using the inner layer as grounding, the indicator light can be switched on when the bore or bit is touching the surface and an electric circuit is formed. This embodiment provides for exact indication of the drilling/milling depth. As discussed briefly above, the above description and the drawings mainly relate to an interesting embodiment, wherein there are at least two conductive plugs at abutting ends of two pipes, which plugs are positioned close to the joint between the pipes. Thus, in practice, a pipe produced for use in such a method will exhibit at least two conductive plugs extending through its pipe wall - preferably one at each end.

It is however also possible to achieve grounding of the pipes by merely providing one conductive plug for each pipe. Such a conductive plug can be located at any part of the pipe, i.e. in the middle or at one of the ends. Industrial Applicability

The present technology can be used for any kind of pipelines in which multilayered polymer pipes, in which at least one dissipating or conductive layer is included. Typical applications included are pipelines, for example underground pipelines, for waste collecting systems, pipelines for conducting powders and other solid matters which may give rise to static electric charges, as well as pipelines for collecting and conducting gases which contain potentially explosive gas, such as biogas containing hydrogen, methane and carbon dioxide, collected from landfill sites.

Reference Signs List

A inner surface

B outer surface

1 ; 2 multi-layered polymer pipe 7; 7" inner conductive layer

5; 8 non-conductive layer

4', 4" outer conductive layer

3 joint

6; 16 aperture

6'; 16' conductive material/plug

9 stopper

Citation List

Patent Literature

EP 0 975 911

US 5 951 812

US 3 943 273

JP 07310710

EP 2 167 861

WO 2013/030621

US 4 032 708

Claims

Claims:

1. Method of grounding a pipe (1, 2) comprising a multi-layered wall structure having an inner surface (A) and an outer surface (B) and containing at least a first conductive layer (7', 7"), which is covered by a non-conductive layer (5, 8), which is positioned on the outside of the first conductive layer (7', 7"), comprising the steps of

- forming at least one aperture (6) in the wall structure, whereby each aperture (6) extends through the wall structure from the inner surface (A) to the outer surface (B), and

- filling the aperture (6) with conductive material (6'), said conductive material

forming a conductive link from the at least first conductive layer (7', 7") through the non-conductive layer (5, 8) to the outer surface (B) for grounding the at least first conductive layer (7', 7") .

2. The method according to claim 1 for grounding a joint (3) between two pipes (1, 2), each of which pipes (1, 2) comprising a multi-layered wall structure having an inner surface (A) and an outer surface (B) and containing at least a first conductive layer (7', 7"), which is covered by a non-conductive layer (5, 8), which is positioned on the outside of the first conductive layer (7', 7"), comprising the steps of

- forming at least one pair of apertures (6) in the wall structure, whereby each

aperture (6) of the pair of apertures is positioned on an opposite side and in the proximity of the joint (3), whereby each aperture (6) extends through the wall structure from the inner surface (A) to the outer surface (B), and

3. The method according to claim 1 or 2, wherein the filling of the aperture (6) comprises further method steps of

- extruding a molten mass of the conductive material (6') into the aperture (6), and

- restricting the flow of the molten material (6') into the pipe (1, 2) with a stopper (9), while still allowing some of the molten material (6') to flow over the inner surface (A) and the outer surface (B) of the wall structure of the pipe (1, 2), and compressing the molten material (6') with the stopper (9) to smoothen the surface (A, B) around the circumference of the aperture (6) in order to increase a contact area of the at least first conductive layer (7', 7").

4. The method according to claim 1 or 2, wherein the aperture (6) is formed by milling from the outer surface (B) of the pipe (1, 2) to the at least first conductive layer (7', 7"), and a plug (16') comprising conductive material and having the same shape as the milled aperture (6) is friction welded to the milled aperture (6).

5. The method according to claim 1 or 2, wherein the aperture (6) is formed by milling from the inner surface (A) of the pipe (1, 2) to the at least first conductive layer (7', 7"), and a plug (16') comprising conductive material and having the same shape as the milled aperture (6) is friction welded to the milled aperture (6).

6. The method according to any of the preceding claims, wherein the wall structure of the pipe (1, 2) comprises the first conductive layer (7', 7") and the non-conductive layer (5, 8), the latter forming the outer surface (B) of the pipe (1, 2), whereby the first conductive layer (7', 7") is grounded by the conductive link.

7. The method according to any of the preceding claims, wherein the conductive link is formed by an extruded or solid piece of conductive material.

8. The method according to any of the preceding claims, wherein the conductive material (6') is a conductive polymer.

9. The method according to any of the preceding claims, wherein the aperture (6) has a conical shape, whereby the apex of the cone is directed towards the inner surface (A) of the pipe (1, 2).

10. The method according to any of the preceding claims, wherein 1 to 10, preferably about 1 to 4, pairs of conductive links which ground the first conductive layer (7', 7") are formed.

11. The method according to any of the preceding claims for jointing two pipes (1, 2) having a multi- layered wall structure having an inner surface (A) and an outer surface (B) and containing at least a first conductive layer (7', 7"), which is covered by a non- conductive layer (5, 8), which is located on the outside of the conductive layer (7', 7"), in which method

- the ends of two multilayer pipes (1, 2) are fit against each other in abutting

relationship,

- the ends of the pipes (1, 2) are secured to each other to form a joint (3) between the pipes (1, 2), and

- said at least first conductive layer (7 ', 7") is grounded.

12. The method according to any of the preceding claims, wherein each of the layers of the pipes is formed by a polymeric material.

13. The method according to any of the preceding claims, wherein the layers of the pipes are formed by polymeric materials which are

- co-extrudable;

- capable of being welded together; or

- both.

14. The method according to any of the preceding claims, wherein the two pipes are joined together by butt fusion welding or electrofusion welding using electrofusion sleeves.

15. The method according to any of the preceding claims, wherein the wall structure of the pipe (1, 2) comprises a first conductive layer (7', 7"), a second conductive layer (4', 4") located at a distance from the first conductive layer (7', 7"), and an intermediate non- conductive layer (5, 8) located between the first and second conductive layer, whereby the second conductive layer (4', 4") forms the outer surface (B) of the pipe (1, 2) and the first and second conductive layers are connected through the conductive link, said first conductive layer (7', 7") being grounded through any point on the second conductive layer (4', 4").

16. Polymeric pipe (1) having a wall structure (1, 2) comprising an inner surface (A) and an outer surface (B) and containing at least a first conductive layer (7', 7"), which is covered by a non-conductive layer (5, 8), which is located on the outside of the first conductive layer (7', 7"), c h a r a c t e r i z e d in that the pipe (1, 2) comprises at least one aperture (6) in the wall structure, which aperture (6) extends through the wall structure from the inner surface (A) to the outer surface (B), and whereby the aperture (6) is filled with conductive material, said conductive material forming a conductive link from the at least first conductive layer (7', 7") through the non-conductive layer (5, 8) to the outer surface (B) for grounding the at least first conductive layer (7', 7").

17. The polymeric pipe (1) according to claim 16, wherein the aperture is position in an area which is not heated up when the pipe is coupled to another pipe by wielding.

18. The polymeric pipe (1) according to claim 16 or 17, having a first and a second, opposite end, wherein the area of the pipe wall in the proximity of the first end exhibits at least one aperture filled with conductive material, whereas the area in the proximity of the opposite, second end is free from such apertures.

19. The polymeric pipe (1) according to any of claims 16 to 18, wherein the wall structure of the pipe (1 , 2) comprises a first conductive layer (7', 7"), a second conductive layer (4', 4") located at a distance from the first conductive layer (7', 7"), and an intermediate non- conductive layer (5, 8) located between the first and second conductive layer, whereby the second conductive layer (4', 4") forms the outer surface (B) of the pipe (1, 2) and the first and second conductive layers are connected through the conductive link, said first conductive layer (7', 7") being grounded through any point on the second conductive layer (4', 4").

20. The polymeric pipe (1) according to any of claims 16 to 19, wherein the wall structure of the pipe (1, 2) comprises a second conductive layer (4', 4") located on the outer surface of the wall structure, said second conductive layer being in the form of a continuous conductive layer or, preferably, in the shape of conductive stripes.

21. Pipeline comprising at least two multi-layer pipes (1, 2) attached by a joint (3) between the pipes (1, 2), whereby a wall structure of each pipe (1, 2) comprises an inner surface (A) and an outer surface (B) and containing at least a first conductive layer (7', 7"), which is covered by a non-conductive layer (5, 8), which is located on the outside of the first conductive layer (7', 7"), c h a r a c t e r i z e d in that the pipes (1, 2) of the pipeline comprise each at least one aperture (6) in the wall structure, each aperture (6) extending through the wall structure from the inner surface (A) to the outer surface (B), and whereby the aperture (6) is filled with conductive material, said conductive material forming a conductive link from the at least first conductive layer (7', 7") through the non-conductive layer (5, 8) to the outer surface (B) for grounding the at least first conductive layer (7', 7").

22. The pipeline according to claim 21, wherein the pipes (1, 2) comprise at least one pair of apertures (6) in the wall structure, whereby each aperture (6) of the pair of apertures is positioned on an opposite side and in the proximity of the joint (3).

23. The pipeline according to claim 21 or 22, wherein the wall structure of the pipe (1, 2) comprises the first conductive layer (7', 7"), a second conductive layer (4', 4") located at a distance from the first conductive layer (7', 7"), and the intermediate non-conductive layer (5, 8) located between the first and second conductive layer, whereby the second conductive layer (4', 4") forms the outer surface (B) of the pipe (1, 2) and the first and second conductive layers are connected through the conductive link, said first conductive layer (7', 7") being grounded through any point on the second conductive layer (4', 4").

24. The pipeline according to any of claims 21 to 23, wherein the conductive material (6') is a conductive polymer.

25. The pipeline according to any one of claims 21 to 24, wherein the conducting link extends from the first conductive layer (7', 7") through the non-conductive layer (5, 8) essentially transversally to the central axis (x) of the pipes (1, 2), and wherein the aperture (6) has a conical shape, whereby the apex of the cone is directed towards the inner surface (A) of the pipe (1, 2).

26. The pipeline according to any of claims 21 to 25, wherein the wall structure of the pipes (1, 2) comprises a second conductive layer (4', 4") located on the outer surface of the wall structure, said second conductive layer being in the form of a continuous conductive layer or, preferably, in the shape of conductive stripes.