Field of the Invention

The present invention relates to wall skins and the provision of a monitorable interstitial space between a surface of a wall and a skin attached to the wall, and in particular to the provision of monitorable interstitial spaces for hulls of tanks and similar objects.

Background of the Invention

Tanks are commonly used for storing fluids. Environmental damage may occur if a fluid storage tank leaks. Obviously the nature and extent of damage caused by leakage from a tank will depend on the nature of the fluid in the tank and the amount of leakage. There are applications both above and below ground where it is desirable to provide a twin walled tank where the space between the twin walls can be monitored to establish whether the integrity of the either tank wall has been compromised.

If a double skinned tank contains an air gap between the outer tank wall and the interior lining, leakage from the tank can be monitored by various leak monitoring devices. One such leak monitoring device monitors a vacuum in the air gap. A change in pressure indicates an integrity failure in the inner lining or the outer tank wall.

Whilst the present invention could be utilised with new single wall tanks, if a twin walled new tank is desired, in all likelihood a twin metal walled tank would be specified. The supported liner of the invention will therefore be most useful as a retro-fit to existing tanks.

Lining an existing tank provides a number of advantages. For example, the lining is selected so as not to be corrodible by the fluid stored in the tank. If there is an interstitial space this space can be monitored to establish whether there is any leakage of fuel from the tank.

The publication WO 00/32394 describes a method of lining a fuel storage tank in which a keying means is applied to the surface of a tank. A corrosion barrier is then applied to the keying means. An interstitial grid is then applied to the tank and pliable glass reinforced plastics material is laid onto the grid. The glass reinforced plastics material is then exposed to ultra violet rays to cure the material and form a hardened inner liner shell for the tank.

To line a tank following the method described in WO 00/32394 requires a team of men working for thirty to forty five days, with one man of the team working in the tank at any one time. Due to the toxic nature of the gases given off by the resins used in the laying up of the pliable glass reinforced plastics material onto the grid, and the ability of those gases to pass through the skin and into the bloodstream of humans, the length of time a worker may spend in the tank is severely limited, and special protective clothing must be worn and breathing apparatus used. Whilst in the tank the workers wear clothing that is impervious to the gases given off by the resins used in the laying up of the glass reinforced plastics material. However, the protective clothing available is only impervious to these gases for a limited period of time, after which the worker must come out of the tank, dispose of the protective clothing and be de-contaminated. The risk of hospitalisation resulting from exposure to noxious gases during the laying up the glass reinforced plastics material is significant.

An apparatus and method for lining a tank so as provide a monitorable interstitial space is described in GB2444486. This apparatus uses sheet material having adhesive applied to both sides to attach itself and the other components of the lining to the wall of a tank. The apparatus and method described in this invention have been found to be particularly effective in the lining of both underground and above-ground fuel storage tanks.

Fuel storage tanks are generally placed in the ground with their longitudinal axis extending in the horizontal plane. It has been found that when such tanks have been empty for long periods, particularly if the vacuum applied to the interstitial space has been removed for lengthy periods of time (for example months or years), the lining in the upper part of the tank and around domed parts of the tank. It has also been found that when used in connection with tanks having their longitudinal axis extending in the vertical plane the weight of the liner can pull the liner from the wall to which it is attached. It would therefore be desirable to provide an improved apparatus and method.

Summary of the Invention

According to an aspect of the present invention there is provided a supported wall skin as specified in Claim 1.

According to another aspect of the invention there is provided a method of providing a wall with a supported skin as specified in Claim 11.

According to another aspect of the invention there is provided a wall having a supported wall skin as specified in any of Claims 1 to 10 attached thereto.

The supported wall skin may be a lining for an inner or outer surface of a wall of a tank for example.

The invention provides for the efficient lining of tanks so as to provide a lining which is impervious to fluids, and which may be specified so as to be impervious to corrosive fluids such as biofuels. Where a suitable fluid impervious layer such as aluminium foil is used, a barrier to fumes is provided. Further, an interstitial space is provided between the lining and the surface being lined. The interstitial space can be monitored. By monitoring the interstitial space it is possible to detect failure of either the lining or the surface which is lined.

The invention provides a fast and safe method of lining a wall. Further, where a vacuum is used during application of the lining any faults in the lining may be identified and made good.

The presence of the mechanical support that passes through some of the layers of the composite material enhances the integrity of the wall skin.

Brief Description of the Drawings

In the drawings, which illustrate preferred embodiments of the invention, and are by way of example:

Figure 1 is a schematic representation of a tank lined with a supported liner according to the invention; and Figure 2 is a cross-sectional elevation of the lined tank illustrated in Figure 1 in a first stage of construction;

Figure 3 is a cross-sectional elevation of the lined tank illustrated in Figures 1 and 2 in a second stage of construction;

Figure 3a is a plan view of a component of the supported liner; and

Figure 4 is a cross-sectional elevation of the lined tank illustrated in Figures 1 to 3 in a final stage of construction.

Detailed Description of the Preferred Embodiments

Referring now to Figure 1, there is shown a tank 20, having its longitudinal axis extending the vertical direction. Figure 1 illustrates the supports 6 and their relative positions on the wall 1.

Figures 2 to 4 illustrate the supported liner and the method of lining a wall 1 in more detail. The liner comprises a first layer of flexible material 2 coated with adhesive on both sides thereof. In the present example the flexible material is a paper impregnated with adhesive. Each side of the flexible material 2 is typically covered with a layer of peel-off material which when peeled off reveals the sticky surface. The peel-off layer is removed from one surface of the flexible material 2 and that surface is presented up to and press on to the inner surface of the wall 1. With the peel-off material removed from the other surface of the flexible material 2 of the first layer, a layer of non-woven grid material 3 is attached to the surface of the flexible material 2 of the first layer that is distal from the wall 1. The non- woven grid is open and highly permeable, and in the present example a thermoplastic. The adhesive applied to the surface of the flexible material 2 is sufficient to hold the layer of non-woven grid material 3 onto the flexible material 2. However, additional adhesive, either in a layer or in spots may be provided between the flexible material 2 and the non-woven grid material 3.

A third layer of the composite material is formed by a fluid impervious layer comprising a foil sheet 4 having adhesive applied to at least one side thereof. Prior to attachment of the foil sheet 4 to the non-woven grid 3 a peel off layer is removed from the adhesive covering one side of the foil sheet. This adhesive attaches the foil sheet to the non-woven grid 3.

A fourth layer of the composite material comprises a scrim layer 5, which in the present example is formed of woven fibre glass or polymer such as polyester. The scrim layer 5 may be a separate layer that is attached to the foil sheet 4 by a suitable adhesive. The adhesive is typically provided on one of the third or fourth layers, with a peel off layer covering the adhesive until it is required.

The function of the non-woven grid material 3 together with the layers of material between which it is sandwiched is to provide a monitor able interstitial space. Monitoring is typically achieved by applying a vacuum to the interstitial space and monitoring the vacuum. If the walll of the tank or the outer layer of the composite material is compromised the vacuum will fail.

In order to better support the composite material a plurality of support elements 6 are provided in the composite material. Each support element 6 comprises a base 7 from one side of which a pin 9 extends. The other side of the base 7 has a layer of material 8 having adhesive on both sides thereof. The adhesive on one side of the material 8 attaches the said material to the base 7, with the adhesive to the other side of the material 8 attaching the support element 6 to the surface of the flexible material 2 distal from the wall 1. However, the material 8 could attach the support element 6 directly to the wall 1 with the base 7 sitting between the wall 1 and the flexible material 2.

In the illustrated example, the pin 9 pierces the flexible material 2, the non-woven grid material 3, the foil 4 and the scrim layer 5. When each of the aforementioned layers are in place a cap 10 (shown best in Figure 3a) is pressed on to the pin 9. The cap 10 includes an opening 10a which is slightly smaller in diameter of the pin 9. Slots 12 are cut in the cap 10 so that when the cap 10 is pressed on to the pin 9 the opening 10a can become larger, thereby allowing the cap 10 to be pressed on to the surface of the scrim layer 5. Any force acting in the opposite direction that would tend to push the cap 10 off the pin 9 causes the opening 10a to close onto the pin 9, friction therebetween resisting movement of the cap along the pin away from the base 7. With the cap 10 in place as shown in Figure 3, the pin 9 is cut off adjacent the cap 10. The final layer of the composite material is then applied to the scrim layer 5. The final layer of the composite material is a sealant layer 13, typically an epoxy layer that is applied as a liquid and which cures to form a fluid impervious layer.

The textile grid 3 is therefore encapsulated within the composite material 1. The interstitial space of the composite material 1 is formed by the non-woven grid 4. The grid 4 is formed by two arrays of elongate elements arranged at an angle to each other, with the elements of each respective array lying in a different plane and thereby allowing for the free passage of fluid (for example air) through the grid. In the present example the grid 4 is formed from high density polyethylene PDPE).

The invention lies in the combination of the support elements, a part of the support element passing through at least some of the layers of sheet material of the lining, and the end of the support element being encapsulated within an outer layer.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise each feature disclosed is one example of a generic series of equivalent or similar features.