EP0676995A1

EP0676995A1 - Electrically bondable layer to cover an opening

Info

Publication number: EP0676995A1
Application number: EP93924708A
Authority: EP
Inventors: Johannes Maria Cordia; Dirk Raymond Jozef Baert; Marcel Paul Cristens; Karl Heylighen; Jozef Albert Gustaaf Doucet; Jan Lodewijk Maria Frans Ghislain Vansant
Original assignee: Raychem NV SA
Current assignee: Commscope Connectivity Belgium BVBA
Priority date: 1992-11-20
Filing date: 1993-11-05
Publication date: 1995-10-18
Also published as: CA2148833A1; JPH08503429A; FI952452A; PL172669B1; WO1994012338A1; FI952452A0; PL308961A1; KR950704106A

Abstract

A hole in a pipe or polymeric casing associated with a district heating system is sealed by means of a polymeric patch that comprises a backing layer (2), a heat-activatable bonding layer (4) for securing the patch to the pipe or casing, and an electrically heatable layer (4). A further polymeric layer (8) may be included in the patch remote from the backing layer (2) when the substrate itself is not polymeric. The layers may be separate, or one layer may perform more than one function. Tooling (Figure 5) may also be provided to enhance the sealing of the hole when using the patch and method of the invention.

Description

Electrically Bondable Layer to Cover an Opening

This invention relates to an article comprising an electrically heatable layer which itself bonds, or which activates a separate bondable layer, to cover an opening in a polymeric, preferably tubular, substrate such as a pipe or a casing, to a method of covering such an opening, and to a tool which may be used for installing such an article.

Articles comprising electrically heatable bondable, e.g. fusible, layers are known. EP-A-0157640, for example, describes a method of joining, repairing, reinforcing or otherwise modifying a polymeric substrate by placing a tubular conductive polymeric article, preferably one comprising sintered UHMWPE (Ultra High Molecular Weight Polyethylene) adjacent the substrate, and passing electrical current through the article to heat it and to cause the article to adhere directly (e.g. by fusion) or indirectly (e.g. by an insert) to the substrate. In one embodiment, described in Figure 11 of EP-A-0157640, a hole in a plastic pipe is repaired using a non-heat-recoverable, sintered conductive polymeric patch comprising a material that is compatible with the pipe material. This patch is placed over the hole, and kept in place by means of a tape. Electrical current is passed through the patch so it softens and fuses to the pipe.

Another article also relating to an electrically heatable fusible layer is described in WO-A-88/06517. This describes a method of joining articles together with the aid of a conductive polymeric article which comprises sintered ultra high molecular weight polyethylene. The article is typically provided in tape form and positioned, and electrically powered, between two polymeric substrates to bond those substrates to each other.

A known reference describing a separate fusible layer and electrically heatable layer is GB-A-2076489. This describes an impingement layer which may be a thermosetting resin adjacent a heating element in the form of a metal wire braid. This is used to connect pipes or to repair a leaking pipe. All aspects of the present invention are particularly applicable for covering an opening in a casing used in joining district heating pipes. This opening may be a hole of closed outer section, or a longitudinal slit along the casing. District heating pipes typically consist of a steel transport pipe, insulated by a foam usually polyurethane, and an outer polyethylene jacket. When these pipes are joined, a length of insulation is first removed in order that a joint can be easily made. The joints are usually made by welding, and the heat required would damage any insulation close to the weld line. After welding the pipes have to be made good again across the weld, preferably in a water-proof manner. One way of doing this is to encase the exposed regions within a casing (e.g. within two mating half cylindrical shells) and then injecting a curable insulating material e.g. polyurethane foam into the casing through an injection hole left in the casing for that purpose. The casing may then be sealed to the insulation on either side thereof. The foaming hole must then also be sealed to prevent water damage to the insulating material. One method of doing this is first to install a mastic plug in the hole, and then to position a protection sleeve over the mastic plug. Such a protection sleeve may comprise an irradiated modified polyolefin backing coated on the inside with a hot melt adhesive and carrying on the outside a thermo indicating paint. This type of sleeve is sold by the company Raychem under the trademark FOPS. It is installed by heating with a gas torch to activate the adhesive, and then applying pressure to the sleeve using a hand-held compressible plunger to press the sleeve against the casing. Although this method is successful, one problem is that heat applied by the gas torch to activate the adhesive may liberate gasses within the polyurethane foam, and unless pressure is applied and the installation carefully controlled, this may lead to lifting of the FOPS protection sleeve.

We have discovered a new method that can be used to re-cover a hole, inter alia a foaming hole in a casing surrounding thermally insulated pipe, which method involves the use of an electrically heatable layer and a heat-activatable bondable layer, which may or may not be the same layer. We have also discovered new articles that can be used in that method, and a new installation tooling. A first aspect of the invention provides a method of covering a hole in a polymeric, preferably tubular, substrate such as a pipe or casing, comprising:

(a) positioning a laminar polymeric patch comprising:

(i) a backing layer (ii) a heat activatable bondable layer (iii) an electrically heatable layer and

(iv) a further polymeric layer positioned remote from the backing layer,

over the hole in the polymeric substrate so that the further polymeric layer lies within the opening in the substrate, and so that at least a portion of the bondable layer is in contact with a surface of the substrate; and

(b) passing electrical current through the electrically heatable layer for a time, and at a watt density, sufficient to heat the bondable layer to bond it to the substrate.

The method according to the first aspect of the invention generally envisages using a continuous patch to completely sealingly cover the hole in the substrate. However this aspect of the invention also encompasses the possibility that the patch incorporates a valve e.g. a pressure valve, which is installed via the patch into the hole in the substrate. Therefore the term "covering a hole" is intended to include such a valve installation. Such a patch might be used, for example to install a pressure access valve onto the jacket of a cable or a pipeline. A specific application is described later in the specification.

It is envisaged that the further layer and the heat activatable bondable layer may be the same layers

A second aspect of the present invention provides a method of covering a hole in a polymeric preferably tubular substrate such as a pipe or casing, comprising: (a) positioning a laminar polymeric patch comprising a backing layer, a heat-activatable bondable layer, and an electrically heatable layer over the hole so that it covers the opening and overlaps the substrate in the area around the opening, and so that the bondable layer lies in contact with the substrate; and

(b) passing electrical current through the electrically heatable layer for a time and at a watt density sufficient to heat the bondable layer to bond it to the substrate, but so that the temperature within the substrate remains below 100°C, preferably below 90°C, especially preferably below 80°C.

In the prior art applications, for example, where a gas torch is used to apply a relatively thin FOPS patch over a hole in a district heating casing, it is known for temperatures inside the substrate to exceed 80°C, 90°C or even 100°C. This may lead to problems of lifting of the patch as described earlier, especially where a relatively thin patch is used. Therefore methods according to the invention whereby the electrical heating method restricts the heating to the bond line region can be used in applications where the prior an solution using a gas torch cannot be used, or is less desired. In particular preferred embodiments of all aspects of the invention the patch according to the invention is thicker than the previously used FOPS, and/or is applied with an external supporting installation tool, both of which factors also reduce or eliminate the problem of lifting of the patch.

Referring specifically to the insulated pipe application, a third aspect of the invention provides a method of sealing a joint between two insulated pipes, the insulation of each of which ends short of the joint, the method comprising:

(a) positioning a polymeric casing containing a fluid-entry hole around the exposed portions of the pipe to bridge the cut-back insulations, and sealing the ends of the casing to the cut back insulations;

(b) filling the casing through the fluid entry hole with a pourable composition, for example polyurethane, which solidifies after positioning in the casing; (c) positioning a laminar polymeric patch comprising a backing layer, a heat-activatable bondable layer, and an electrically heatable layer, over the fluid entry hole so that it covers the hole and overlaps the casing in the area around the hole, and so that the bondable layer lies adjacent to the casing; and

(d) passing electrical current through the electrically heatable layer to heat and thereby to bond the bondable layer to the casing.

The pourable composition which later solidifies may, for example, comprise a curable composition, e.g. a polyurethane foam. The pourable composition may solidify immediately on positioning in the casing, or some time thereafter. The pourable composition may be one which gives off gasses if heated to temperatures above 80°C, 90°C or 100°C.

In the first, second and third aspects of the invention, the heat- activatable bondable layer and the electrically heatable layer may be separate layers or may be provided by the same single layer. Where a single layer is used this single layer preferably comprises a conductive polymer layer. The conductive polymer is preferably a polymer matrix comprising a conductive carbon black filler. It may also or instead comprise a polymer matrix with other metal fillers. Preferably it comprises sintered ultra high molecular weight polyethylene containing carbon black filler dispersed at the boundaries of the coalesced particles of the sintered ultra high molecular weight polyethylene particles, as described for example, in EP-A-0157640, the disclosure of which is incorporated herein by reference. As another example a single fusible and electrically heatable layer may comprise a mat of carbon fibre, or a metal mesh.

In other embodiments separate layers may be used for the bondable layer and the electrically heatable layer. For example a metal mesh layer may be used for the electrically heatable layer. In other embodiments wherein the heat-activatable bondable layer and the electrically heatable layer are separate layers, there maybe preferably additionally provided two electrodes which are in electrical contact with the electrically heatable layer, preferably sandwiched between the separate bondable and heatable lavers. The bondable layer, whether or not it is also the electrically heatable layer, is preferably a fusible layer. Such a layer may comprise a non cross-linked polyethylene layer, for example. Other suitable materials include polypropylene, polybutene, copolymers of ethylene, propylene, butene and hexene, copolymers of ethylene with ethyl acrylate, vinyl acetate, acrylic acid, methacrylic acid, acrylic esters or methacrylic esters in which polyethylene predominates, blends of these polymers, and blends of these polymers with elastomers. When the fusible layer is the same layer as the electrically heatable layer, it may comprise a conductive polymeric material, preferably comprising a matrix of sintered UHMWPE containing a conductive filler preferably carbon black.

A definition of "fusible layer" appears later in the specification.

As an alternative the electrically heatable bondable layer may comprise a layer which provides an adhesive bond. Preferably such a material is a hot melt adhesive or a heat curable adhesive. Examples of hot- melt adhesives that may be used include formulations comprising poly amides modified with hydrocarbon waxes, and mixtures of acidic ethylene polymers and tackifiers. Also suitable are compositions based on ethylene vinyl-acetate copolymers, blended with hydrocarbon waxes and optionally buyle rubber. One suitable adhesive is described in GB-A- 2075991. It comprises a blend of a polyamide, an acrylic rubber, and preferably a small amount of an ethylene/acrylic acid/butyl acrylate terpolymer. The hot melt adhesive may be cross-linked , though the degree of cross-linking must not be so high as to reduce the ability of the adhesive to liquefy, and thereby to flow and to wet.

Preferably the heat activatable bondable layer and the electrically heatable layer (being the same or separate layers) project beyond the edges of the backing layer. This allows separately applied electrodes to be brought easily into contact with the electrically heatable layer, e.g. on an installation tool. Details of this are given later in the specification.

A further layer (similar or the same as that used according to the first aspect of the invention) may also be included, on the side of the patch remote from the backing layer, in embodiments according to the second and third aspect of the invention.

In certain applications where an electrically heatable layer separate from the bondable layer is used (e.g. a metal mesh or a mat of carbon fibre), the backing layer and the bondable layer may be provided by the same layer. For example the order of layers may be: common backing and bondable layer; electrically heatable layer, further layer.

Also in other applications the further layer and the bondable layer may be provided by a common layer. Indeed the electrically heatable layer, the further layer and the bondable layer may be provided by a common layer.

A fourth aspect of the invention also provides use of a laminar polymeric patch comprising a polymeric ba'cking layer, a heat activatable bondable layer, an electrically heatable layer and a further polymeric layer to cover an opening in a polymeric substrate, wherein the further polymeric layer is shaped and sized to fit within the opening in the substrate.

A fifth aspect of the invention provides the use of a laminar polymeric patch comprising a polymeric backing layer, a bondable layer and an electrically heatable layer to cover a hole in a polymeric substrate, wherein the patch is positioned to cover the hole and electrical current is supplied for a time and at a watt density sufficient to heat the bondable layer to fuse the fusible layer to the casing, but so that the temperature within the casing remains below 100°C, preferably below 90°C, especially preferably below 80°C.

Where the further polymeric layer is used, it is preferably smaller in surface area than the bondable layer and is positioned so that the said further layer projects within the opening and at least the bondable layer and preferably all the other layers cover the opening and overlap the substrate in the area around the opening, with the bondable layer in contact with the substrate. Another possibility, where the further layer is also the bondable, preferably fusible layer, is for the further layer to be a close fit in the opening, and for there to be no overlapping of the region around the opening, by the bondable layer if not all the layers, and for the edges of the further bondable layer to (preferably fuse to) bond to the edge of the opening in the substrate.

Preferably, however, the patch according to the invention is used in methods so that it spans an opening and overlaps an area of the substrate in a region around the opening. When heat is applied to the electrically heatable layer by passage of electrical current, this arrangement means that the portion of the heatable layer lying over the opening is only heat- sunk by the adjacent layer(s) making up the patch, whereas in the region around the opening i.e. over the substrate but beneath the patch, the heatable layer of the patch is also heat-sunk by the substrate itself. Therefore, according to the first and fourth aspects of the invention and preferred methods and uses of patches according to other aspects of the invention, the patch also comprises a further polymeric layer positioned on the opposite side of the fusible layer from the backing layer. This is preferably shaped and sized substantially to correspond to the shape and size of the hole in the substrate or casing. When the further layer is present methods and uses of the patch according to the invention preferably also comprise the step of positioning the patch so that the said further layer of the patch projects within the opening in the substrate or casing. This further layer acts, in use, as a heat sink preventing any overheating of the central region of the patch. Advantageously it may also act as a locating member to locate the patch in the correct position.

The provision of a heat sink in this way is an important feature of the pre jsseenntt i innvveennttiioonn.

Preferably the further layer is so shaped and sized that it is a close fit in the hole whereby when bonding occurs there is partial bonding (e.g. welding) of the further layer (which is preferably fusible) to the substrate, e.g. the edge of the further layer to the inside edge of the hole in the substrate. Generally the arrangement is such that passage of electrical current causes the bondable layer of the patch to bond to the outermost surface of the tubular substrate. However other configurations are possible in which this is not the case. For example, where a further layer is used that is a close fit in the opening, electrodes may be arranged so that the only heated surface is the edge of the further layer which bonds to the inside edge of the opening in the substrate. This could be achieved, for example, for a circular further layer, using a first disc shaped electrode on the inside major surface of the further layer, and an annular electrode on the upper surface corresponding to the outer edge of the further layer. Therefore when the words "bonding or fusing to the substrate" are used no limitation is implied as to which surface of the substrate is intended. It is preferably the outer surface, but need not be.

As mentioned above a technical advantage of the invention is that, since electrical heating is used, heat is supplied only in the bond line area over a small area. This is useful in typical district heating pipe joints, and in pressurised pipe applications where the temperature within a casing surrounding the pipes must be kept low if a live seal around the pipes is to be made. For these and other applications the energy input (which is inter alia both time and temperature dependant) is preferably kept to the minimum possible while achieving the temperature required to effect the said fusion.

Another advantage of supplying heat at the bond line electrically rather than externally by a gas torch is that thicker, and consequently stronger backing layers can be used. This allows the patch to withstand higher pressures through the hole from within the casing both during installation, and in service life, without ballooning, lifting or bursting.

The invention also provides, in another aspect a laminar polymeric patch suitable for use in the methods of the present invention, comprising:

(a) a polymeric backing layer; and

(b) a conductive polymeric layer which is both fusible and electrically conductive, which projects beyond at least part of the edge of the backing layer, which is less than half as thick, preferably less than one quarter as thick as the backing layer; and

(c) preferably an additional further layer smaller than the conductive layer and positioned on the surface of the conductive polymer layer that is remote from the backing layer.

In preferred aspects of the invention, the fusible electrically conductive layer comprises conductive sintered UHMWPE containing a carbon black filler. Preferably the fusible electrically conductive layer is pre-bonded to the backing layer.

The present invention can be used to cover openings of any shape. In one example the opening is in the form of a hole of closed outer section, e.g. a foaming hole in a district heating pipe casing. In another embodiment the opening is and elongate slit extending along at least part, preferably along the entire length of a polymeric casing.

Preferably the patch is rectilinear, and both the backing layer and the conductive polymeric layer are also rectilinear, and the conductive polymeric layer projects beyond opposite sides of the backing layer. This design is preferred for easy installation using an installation tool according to the invention as described in more detail later in the specification. Depending on the shape of the opening e.g. a hole such as a foaming hole, or a longitudinal slit, the rectilinear patch may have one side significantly longer than the other side.

The patch according to the present invention is preferably also provided with a further polymeric layer as described above with reference to earlier aspects of the invention.

According to the present invention electrical current is passed through the electrically heatable layer to heat, and thereby to bond the bondable layer to the substrate. Preferably the bondable layer is fusible and the heat applied fuses the fusible layer to the substrate. The terms "to fuse" and "fusible layer" etc are used herein to mean that sufficient molecular compatibility exists between the element and the substrate outer surface that a bond forms which will provide mechanical performance equal to or greater than that of the substrate. This may be through viscoelastic contact as defined by J N Anand in Adhesion 1, 1 69, pages 16 through 23 and Adhesion 2, 1970, pages 16 through 22, or a process of molecular diffusion across the polymer/polymer interface, such that, within the interfacial region there is a continuous gradient of one polymer in the other.

The fusible layer fuses to the substrate and thereby bonds the backing layer (which is preferably pre-bonded thereto either directly or via an intermediate separate heatable layer) to the substrate. According to the article aspect of this invention the fusible layer is preferably at most 1/2 times, preferably at most 1/4 times the thickness of the backing layer. This is also preferred for all aspects of the invention. The backing layer therefore provides the necessary strength to act as a protection sleeve, and the fusible layer provides a bonding layer for the backing layer. As an example the backing layer may comprise Cross-linked HDPE. the backing layer is preferably not heat recoverable, a heat recoverable article being one whose dimensional configuration may be made to change when subjected to an appropriate treatment, as well known in the art.

The present invention, in all its aspects, can be used to span significant sized holes, e.g. typically holes, of closed outer section, with a transverse dimension (e.g. diameter of circular holes) of at least 15 mm, even at least 20 mm or even at least 25 mm, or longitudinal slits, of width 5, 8, 10, 15, 20 or 25 mm, that extend partially or even completely along the length of the substrate, which may be substantially cylindrical and of polymeric material.

The patch according to the invention may also be provided with melt flow indicators to show when the bondable layer has heated to a sufficiently high temperature to bond to the substrate. These may conveniently be formed by forming cylindrical pop-up indicators through the patch, by drilling with an annular bore drill almost through the backing layer. This presents stubs of backing layer connected by a narrow neck of material to the bondable layer. Especially when the bondable layer is a fusible layer, when this fusible, conductive layer heats, it melts that neck of material, and flows into the bore causing the stubs to "pop-up" above the surface of the patch and indicate that sufficient bonding has occurred.

As mentioned above the bondable layer and the electrically heatable layer may be the same or separate layers. An advantage obtained when they are the same layer, e.g. a fusible conductive polymeric layer, is that by appropriate electrode arrangement there are then no discrete conductive parts e.g. metal parts acting as electrical busses or electrodes separating the backing layer from the substrate and interfering with the fusion process.

An appropriate electroding arrangement which inter alia achieves the above advantage is provided by the tooling used in the method according to another aspect of the invention which provides a method of installing a patch comprising a backing layer, an electrically heatable layer, and a heat activatable bondable layer over an opening in a polymeric substrate, comprising:

(a) positioning the patch so that it covers the hole and the bondable layer is in contact with the substrate;

(b) positioning a tool comprising a support, two electrodes, and a fixing member over the patch so that the support lies over the patch and the two electrodes are in electrical contact with the electrically heatable layer;

(c) arranging the fixing member to secure the support and the electrodes against the patch; and

(d) passing electrical current via the electrodes through the electrically heatable layer to bond the bondable layer of the patch to the substrate.

Preferably, the patch also comprises a backing layer and the electrically heatable layer projects beyond the edges of the backing layer and the tool is positioned so the electrodes contact those projecting portions of the electrically heatable layer.

Where "electrical contact" between electrodes and the electrically heatable layer is referred to, this may be direct contact, i.e. the electrodes ^' may be contacted against the electrically heatable layer. Alternatively conductive bus bars may be included between the electrically heatable layer and the electrodes to enhance the electrical current flow to the electrical heatable layer.

Preferably the polymeric substrate is a substantially cylindrical casing or housing and the tool support is arranged to conform to the surface of the substrate when fixed by the fixing member. The tool support may, for example, comprise a series of articulated rigid blocks. Instead, a continuous flexible support may be used. These arrangements allow the patch to be curved around the substrate surface and the tool support to press down on that patch over its entire surface. Preferably the fixing member comprises a strip that can be tightened around the cylindrical housing.

The tooling may be provided with melt flow indicator risers in line with those in the patch (if present) so that the pop-up of the indicator activates an aligned riser rod in the tooling. As an alternative, electrical power may be supplied at a predetermined voltage and for a predetermined time and then the tool removed to view the underlying indicators in the patch (which would not be visible with the tool still present). Preferably the current is passed for a sufficient time and at a sufficient voltage to provide a watt density of at least 3 W/cm2 to activate the melt flow indicators.

As an alternative the tooling may comprise component parts including a plate, e.g. an insulating layer, carrying two electrodes, e.g. of copper. Preferably a metal plate is also included that is electrically insulated from the electrodes but in thermal contact with electrode- carrying plate so that it is thermally heated as the patch heats. The electrical insulation of the metal plate from the electrodes is necessary to prevent a short circuit through the metal plate, rather than electrical current passage, and hence heating through a patch. Preferably a further backing insulating component is also included. The component parts are preferably held together by metal screws or the like. These screws preferably pass into the electrodes, and can therefore conveniently be used as a means of connection to the power source for providing power to the electrically heatable layer. The electrode carrying plate is preferably placed, in use, inwardly of the other components. It may be provided with a release layer, e.g. a Teflon layer or sheet, to facilitate removal of the tool after the patch has been installed.

The tooling is preferably held in place by means of a fixing member such as a tightening strap or the like positioned over the further backing insulating component. The metal plate functions to transfer the clamping force of the fixing member over the width of the tool. It may also serve to enhance uniform heat distribution over the patch surface, and to prevent overheating and distortion of any release layer present on the electrode- carrying plate. The further backing insulating component functions to hold the metal plate in position. It may also serve as a guide for holding the fixing member (e.g. tightening strap) if used.

It will be appreciated that the patch and the materials and relationships of its various layers may be as herein described with respect to the other aspects of the present invention.

Where the electrically heatable layer and the bondable layer are separate layers the electroding can be effected in a similar manner to that described above whereby the heatable layer projects beyond the sides of the backing layer and a separate removable tool is installed above the patch to contact the electrically heatable layer during the installation process.

Alternatively integral electrodes may be included in the patch itself. As an example elongate electrodes, e.g. strips of braid may be incorporated in the patch in electrical contact with the electrically heatable layer. For example they may be embedded between the backing layer and the heatable layer, or between the bondable layer and the heatable layer.

It is also possible to use a separate plugging mass, e.g. of mastic for plugging the hole in the substrate prior to application of the patch.

Where separate heatable and bondable layers are used the typical dimensions for the backing layer and the bondable layer are as follows: Backing layer 1-1.5 mm thick, e.g. about 1.25mm thick; bondable layer 0.15- 0.35mm thick, e.g. about 0.25mm thick. In a particularly preferred embodiment of the present invention, the insulation tooling and the patch are preferably provided with an electrical safety feature whereby power can not accidentally be applied to the exposed electrodes of the tooling, and in the absence of deliberate sabotage, can only be applied to the electrodes on the tooling when the tooling is positioned over (and preferably fixed firmly over) the patch. This is preferably achieved by providing contact points on the tooling and the patch which when mated allow electrical current to flow to the electrodes of the tooling. As an example, the mated electrical contacts may activate a switch, e.g. a solenoid switch, which in turn activates or opens the electrical circuit feeding the electrodes of the installation tooling.

The invention also provides a kit of parts comprising:

(a) a laminar polymer patch comprising

(i) a backing layer

(ii) a heat activatable bonding layer

(iii) an electrically heatable layer and

(iv) a further polymeric layer positioned remote from the backing layer and

(b) an installation tooling comprising a support, two electrodes and a fixing member.

The patch and/or the tooling of this kit of parts preferably have the features mentioned above and in the appended claims with reference to the said methods according to the invention.

The invention also provides a kit of parts for forming a substantially cylindrical casing of closed cross-section, suitable for use in a district heating joint, the kit comprising:

a) a longitudinal slit polymeric cylindrical casing; and

b) an elongate patch comprising an electrically heatable layer and a heat activatable bondable layer, the patch being positionable over the slit in the casing and bondable to the casing to cover the slit. In one embodiment according to the invention the patch is adapted to carry an access member, e.g. a valve, for access through the hole over which the patch is positioned. Thus the inner wall of the hole in the patch may be- provided for example with a valve base. A sealing means may also be incorporated to seal the valve base to the patch, e.g. to the said further layer on the patch. The invention may be particularly advantageous for such an apphcation where it is desired to minimise the heat time or amount applied to the substrate, e.g. where applying the valve to a cable jacket containing conductor parts insulated with a temperature sensitive layer (e.g. PE layer). For such an application the invention is advantageous since a relatively small mass is heated during the installation cycle.

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

Figure 1 is a side cross-sectional view through a patch according to and usable in methods according to the invention;

Figure 2 and 3 are top plan and bottom plan views of the patch of Figure 1;

Figure 4 is a cross-sectional view showing a foam filled casing containing a hole that is covered by the patch of Figures 1-3;

Figure 5 is a side view of an installation tool for installing the patch of Figures 1 to 3 on the casing of Figure 4;

Figure 6 is a cross-sectional view through Figure 5;

Figure 7 is a plan view of the tool of Figures 5 and 6;

Figures 8a, 8b and 8c are plan views of component parts of an alternative installation tool for installing the patch of Figures 1 to 3 on the casing of Figure 4; and

Figure 9 is a sectional view through the assembled components of Figures 8a, 8b and 8c along line A-A; Figures 10 and 11 are inside and outside views respectively of an installation tooling and patch respectively, incorporating additional safety features;

Figures 12, 13 and 14 are a longitudinal section, a cross-section and a top view of a second embodiment according to the invention, which can be used to cover a longitudinal slit extending along a polymer casing as shown in Figure 15; and

Figures 16 to 18 shows a patch incorporating a valve base being installed in a hole in a jacketed cable.

Figures 19 and 20 show another embodiment of patch that can be used in the present invention.

Referring now to the drawings, Figures 1, 2 and 3 show a patch according to the invention comprising a HDPE backing layer 2, bonded to a sintered UHMWPE conductive polymeric fusible layer 4. Both layers 2 and 4 are rectangular. The long edges of the rectangular conductive layer 4 are longer than those of the backing layer 2, but their short edges are the same length. This means that the conductive polymeric layer projects out beyond opposite edges of the backing layer to provide two exposed strips 6 at either end thereof. On the opposite side of the conductive layer 4 from the backing layer 2, a central disc shaped layer 8 of HDPE is provided. Its function as described later is to locate the patch in a hole in a casing and also to act as a heat sink.

These Figures also indicate melt flow indicators in the form of stubs 10 made by using a annular bore drill to drill almost through the backing layer at discrete points on the patch. At those point cylindrical stubs 10 of backing layer material are connected by a narrow neck of material 12 to the fusible layer. When heated by the conductive layer 4 these regions melt, releasing the stubs 10. Flow of fusible layer 4 into the bore then causes the stubs 10 to pop-up indicating that fusion is complete.

Figures 1 to 3 also show a fastening pin 13 projecting up from the backing layer. This is to fasten the installation tool as described later. Figure 4 is a sectional view showing a steel pipe 14 surrounded by polyurethane foam 16 and an outer casing 18. The casing 18 contains a circular hole 20 through which the foam 16 was previously inserted. The patch of Figures 1 to 3 has been installed over the hole, the disc 8 sitting within the hole and the conductive fusible layer having being heated to fuse it to the surface of casing 8. The disc 8 acts as a centring disc and also as a heat sink during this operation. Since heat is electrically applied only the bond line is heated and the risk of gasses being liberated from the polyurethane foam 16 is minimised. The indicators 10 have popped up to show fusion is complete. These are now indicated as 10'.

Figures 5 to 7 show a tool for installing the patch of Figures 1 to 3 to the installed position shown in Figure 4. It comprises a tool support 22 comprising articulated segmented pressure blocks 24. The articulation is along lines parallel to the axis of the casing, so that the segments also extend parallel to the axis of the casing. The articulation allows the blocks 24 to bend around the casing 18 of Figure 3 while retaining firm pressure on the patch. The blocks are tightened around the casing 18 by means of a tightening strap 26 which pass around the circumference of the casing. The strap may simply to tied to itself, or an opening 28 extending parallel to the axis of the casing may be provided in the tool support 22 through which the strap 26 is passed and fixed. Elongate electrodes 30 extend along the end segments of the tool support.

The tool has a stepped profile 32 so that the segmented central regions lie above the backing layer conductive fusible layer part of the patch, while the electrodes lie directly on the conductive layer. This arrangement avoids any metallic parts remaining in the final installed patch.

If desired the tool may also be provided with pop-up risers 34 that correspond in position to the indicators on the patch, so that the pop-up action is translated through the installation tool.

The tool is positioned over fastening pin 13 on the patch so that electrodes 30 overlie the exposed conductive strips 6 of the patch, and the pop-up risers 34 line up with the indicators 10 of the patch. Then electrodes 30 are powered to pass current to, and heat the entire conductive polymeric layer 4 causing fusion to the substrate as described above.

Figures 8a, b, c and Figure 9 show an alternative tool that can be used for installing the patch. The tool is provided in three component parts 50, 52 and 54 (see Figs 8a, 8b, 8c respectively).

Component part 50 provides a backing plate and comprises a polymeric insulating material. It contains a depression 56 in its inward facing surface to receive component part 52, and a feed through and guide 59 (see Fig 9) for receiving a tightening strap to hold the tool in place on the patch. It also contains holes 58 to receive screws which hold the tool together and act as power connections as described later.

Component part 52 is a spring steel metal plate that fits within the depressions 56 of component 50. Its functions are inter alia to spread the force introduced by the tightening strap fed through guide 59, and to help to spread the heat generated in the patch uniformly. The metal plate 52 also contains screw holes 60 to receive the screws and bolts 70 that hold the component parts of the tool together and to receive the electrode contact pins 71 (held in housings 73) - see Figure 9, which act as a power connection. Insulating washers 62 are also provided with each hole 60.

Final component part 54, which is positioned adjacent the patch in use comprises a layer 64 of electrically insulating material on which are mounted copper bar electrodes 66. The layer 64 and copper electrodes 66 contain holes therethrough to receive the screws bolts and contact pins 70, 71, 73. A Teflon release layer 68 (not shown in Fig 9) extends between the copper electrodes 66, facilitate removal of the tool from the patch after installation.

The component parts 52, 54 and 56 are assembled so that part 54 is sandwiched between parts 52 and 56. Part 56, in use, lies against the patch so that the electrodes 66 overlie the exposed conductive strips 6 of the patch in the manner described with reference to Figures 5 to 7, and so that the Teflon patch 68 overlies the remainder of the patch, and part 54 is outermost. An insulation cap 75 covers bolt hole 70 through which no contact pin protrudes. In this second embodiment of installation tool the component parts 50, 52 and 54 provide the "support" referred to in the claims. As with the previous installation tool this tool must be fixed over the patch and onto a polymeric substrate using a fixing member.

Figures 10 and 11 show additional electrical safety features that can be incorporated into the tooling e.g. the tooling of Figures 8 and 9 and patch to avoid inadvertent powering of the tooling when not in place over the patch.

Referring to Figure 10 where like reference numerals are used for like parts referred to in Figures 8 and 9, the tooling comprises, on its underside, additional contact elements 80. These provide a first pair of safety-contact-elements.

Referring now to Figure 11 this shows the outside view of the patch of figures 1 and 2 with the additional features of a second pair of safety contact elements 82.

Elements 80 (on the tooling) and 82 (on the patch) are arranged to contact each other when the tooling is firmly clamped over the patch, thereby completing a low voltage electrical circuit that activates a solenoid switch (not shown), which in turn allows the circuit powering the electrodes 66 of the tooling to be activated. This additional safety feature means that power can only be applied to the exposed contact electrodes of the tooling when it is clamped over the patch (or by deliberate sabotage by shorting the contact points).

Figures 12,13 and 15 show an elongate patch which can be used to cover an opening in the form of a longitudinal slit extending along the length of a polymeric casing. As in the pervious embodiments the patch 40 comprises a polyethylene backing layer 42 and a sintered UHMWPE layer 44. Both layers 42 and 44 are rectangular. Their long edges are significantly longer than their short edges because of the application of the patch to cover a longitudinal slit in a polymer casing. The long edges of layers 42 and 44 are the same length, and the short edges of layer 42 are shorter than those of layer 44 so that the conductive polymer layer 44 projects out beyond the backing layer 42 on two long edges 46. Bus bars 48 extend along these edges 46. Indicators 50 to show when fusion has taken place are also provided, as in the previous embodiment.

Figure 15 shows a polymer casing 52 with a longitudinal slit the edges of which are indicated by dotted lines 54. The patch 40 of Figures 12, 13 and 14 is positioned to cover the slit 54. A tool similar to that previously described, but appropriately shaped, is applied so that electrodes contact the bus bars 48. Then power is supplied to fuse layer 46 to the casing 52 on either side of the slit.

Figure 16 is a cross-sectional view through a patch of the type shown in Figures 1-3 provided with a valve base 84 which extends through a hole centrally punched in the patch. (In Figure 16, parts like those used in the patch of Figures 1-3 are referenced with like reference numbers). The embodiment also includes a sealing ring 86 between the valve base and the further polymeric layer 8 of the patch, an insulating tube 88 extending within the inner walls of the hole in the patch, and a washer and nut 90 holding the inserted valve base in the patch. The outwardly facing end 92 of the valve base 84 is a hollow cylindrical form provided with screw threads on its outer surface to receive a valve.

Figure 17 shows an alternative form of patch for incorporating a valve piece. In this case the backing layer 2, further layer 8 and insulating tube 88 of Figure 16 are replaced by a single injection moulded piece 2' in which is embedded the conductive layer 4. The valve piece is not shown in Figure 17 for simplicity, but is incorporated in the patch in the same way as for Figure 16.

Figure 18 shows the patch of Figure 17 incorporating a valve inserted into a hole 94 in a polymeric jacketed bundle of cables 96. When power is applied (in the manner described with reference to the earlier Figures), fusion occurs over the area indicated in the figures by arrows W.

Figure 19 shows an alternative embodiment of patch that can be used in the methods according to the invention. In this case a separate electrically heatable layer 42 and fusible layer 44 are provided. The heatable layer 42 is a metal mesh e.g. copper. The fusible layer comprises polyethylene. A heat stable backing layer 40 covers part of the surface of layer 42. It does not cover opposed edges which are therefore exposed for application of a separate installation tool comprising electrodes, e.g. as described in Figures 5-7, or similar, to be brought into contact with the mesh 42. Layers 42 and 44 are coterminous. The backing layer comprises cross-linked high density polyethylene. It is not expanded and hence not heat recoverable.

Figure 20 shows an alternative embodiment in which three separate layers, the backing layer 46 and the heater layer 48 and the fusible layer 50 are provided all coterminous with each other. Elongate electrodes 52 are provided as part of the patch, sandwiched between heater layer 48 and backing sheet 46, or weaving through heater layer 48. The electrodes may be connected to a source of electrical power to provide power to the heater 48. Layers 46, 48 and 50 comprise the same materials as described for Figure 19.

Example

As an example, a patch of the type shown in Figures 1-3 was made according to the following method. The following components were provided:

a) A backing layer (2) manufactured from a UV-resistant pipe grade high density polyethylene, type 3408, as defined in ASTM D1248 and ASTM D2513. This material has the following properties:

(i) density (23°C) 0.941-0.959 g/cm3, typically 0.954 g/cm3. (ii) Melt How Index (190°C, 2160g load) 0.4 - 1 g/lOmin, typically

0.596 g/lOmin (iii) tensile strength (23°C, cross head speed 50mm/min) 22 MPa or more, typically 25 MPa. (iv) ultimate elongation (23°C, cross head speed 50mm/min) 500% or more, typically 800%.

The dimensions of the backing layer were 50mm x .50mm x 3 mm thick. Cylindrical pop up indicator channels were made through this backing 4 mm in diameter. b) A fusible, electrically heatable layer (4) manufactured from electrically conductive (carbon black loaded) ultra high molecular weight polyethylene, with a molecular weight greater than 4 x 106 g/mol. This material has the following properties:

(ii) tensile strength (23"C), 0.93 - 0.94 g/cm3, typically 0.935 g/cm3 (iii) ultimate elongation (23°C, cross head speed 50mm/min) of

350% or more, typically 375% (iv) ultimate elongation (150°C, cross head speed 50mm/min) of

1000% or more, typically 1150%.

The dimensions of the fusible, electrically heatable layer (4) were 50mm x 70mm x 3 mm thick.

c) A further layer 98) made of the same material as that of the backing layer (2). This was circular, of diameter 25mm, and thickness 3 mm.

The above three elements were positioned in a laminating mould in the order and relative position shown in Figure 1. A pressure of 4 bars/cm2 was applied and electrical power passed through the electrically heatable fusible layer from a 220V supply for a few seconds to cause prelamination of the component parts of the patch to each other.

Claims

1. A method of covering a hole in a polymeric, preferably tubular, substrate such as a pipe or casing, comprising:

(a) positioning a laminar polymeric patch comprising:

(i) a backing layer (ii) a heat-activatable bondable layer (iii) an electrically heatable layer and (iv) a further polymeric layer positioned remote from the backing layer,

over the hole in the polymeric substrate so that the further polymeric layer lies within the hole in the substrate, and so that at least a portion of the bondable layer is in contact with a surface of the substrate; and

2. A method of sealing a joint between two insulated pipes, the insulation of each of which ends short of the joint, the method comprising:

(a) positioning a polymeric casing containing a fluid-entry hole around the exposed portions of the pipe to bridge the cut-back insulations, and sealing the ends of the casing to the pipe insulations;

(b) filling the casing through the fluid entry hole with a pourable composition which solidifies after positioning in the casing;

(c) positioning a laminar polymeric patch comprising a backing layer, a heat-activatable bondable layer, and an electrically heatable layer, over the fluid entry hole so that it covers the hole and overlaps the casing in the area around the hole, and so that the bondable layer lies adjacent to the casing; and

(d) passing electrical current through the electrically heatable layer to heat and thereby to bond the fusible layer to the casing.

3. Use of a laminar polymeric patch comprising a polymeric backing layer, a heat-activatable bondable layer, an electrically heatable layer and a further polymeric layer to cover an opening in a polymeric substrate, wherein the further polymeric layer is shaped and sized to fit within the hole in the substrate, preferably as a close fit.

4. A laminar polymeric patch suitable for use in methods according to any of the preceding claims, comprising:

(a) a polymeric backing layer and

(b) a conductive polymeric layer which is both fusible and electrically conductive, which projects beyond at least part of the edge of the backing layer, which is less than half as thick, preferably less than one quarter as thick as the backing layer, and;

(c) preferably an additional further layer, smaller than the conductive layer and positioned on the surface of the conductive polymer layer that is remote from the backing layer.

5. A method of installing a patch comprising a backing layer, an electrically heatable layer, and a heat activatable bondable layer over a hole in a polymeric substrate, comprising:

(a) positioning the patch so that it covers the opening and the bondable layer is in contact with the substrate; (b) positioning a tool comprising a support, two electrodes, and a fixing member over the patch so that the support lies over the patch and the two electrodes are in electrical contact with the electrically heatable layer;

(d) passing electrical current via the electrodes through the electrically heatable layer to bond the bondable layer of the patch to the substrate

6. A method according to claim 5, wherein the tool is provided on its inward facing surface with one or more first-safety-contacts, and the patch is provided on its outward facing surface with one or more second-safety-contacts, wherein securement of the fixing member causes contact between the said first and second safety contacts, and wherein in the absence of such contact, electrical power can not be supplied to the said electrodes on the tooling.

7. A kit of parts for forming a substantially cylindrical casing of closed cross-section, suitable for use in a district heating joint, the kit comprising:

a) A longitudinal slit polymeric cylindrical casing; and

b) an elongate patch comprising an electrically heatable layer and a heat activatable bondable layer, the patch being positioned over the slit in the casing and bondable to the casing to cover the slit.

8. A kit of parts according to claim 7, wherein the elongate patch also comprises a backing layer, and the electrically heatable layer projects beyond the edges of the backing layer so that a tool carrying electrodes can be brought into electrical contact with the exposed parts of the electrically heatable layer.

9. A kit of parts according to claim 7 or 8, wherein the electrically heatable layer and the heat activatable bondable layer are provided by a single conductive polymeric layer.

10. A method or kit of parts according to any preceding claim wherein the patch is provided with, or adapted to receive, a valve, preferably a pressure access valve, to allow controlled access of fluid through the hole in the polymeric substrate.