GB2413587A

GB2413587A - Plastics lining for a tank or pipe providing a space between the lining and the wall to be lined

Info

Publication number: GB2413587A
Application number: GB0409466A
Authority: GB
Inventors: Christos Sotirious Haritou; Alan Fada; Ian Gimiel Fada; John Harry Rhodes
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-04-28
Filing date: 2004-04-28
Publication date: 2005-11-02
Anticipated expiration: 2024-04-28
Also published as: GB2413587B; GB0419830D0; GB0409466D0

Abstract

A lining comprises a plastics sheet (3) having a first layer and protrusions (5) extending from the first layer, such that in use the protrusions space the first layer from a wall to be lined (1) to leave an interstitial space between the wall and the body of the sheet. Preferably the lining includes a second layer (7) in the form of a plastics membrane adhered to the first layer. The wall to be lined may be prepared by keying and/or pre-coated with an additional layer such as epoxy (2). Adjacent sheets of the lining may be secured together by welding (9, Figure 6). The lining may be supported by ribs (8, Figure 5), of the same material as the lining, which in use, extend away from the surface to be lined. The lining may be temporarily held in place by magnets.

Description

24 1 3587

WALL LINING APPARATUS AND METHOD

Field of the Invention

This invention relates to a lining apparatus and method, and in particular to a lining apparatus and method for use in connection with walls, pipes and tanks in contact with hazardous fluids.

Background of the Invention

Tanks are commonlyused 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. Where tanks are above-ground, they can be monitored by visual inspection. However, in manycircurnstances fluid storage tanks are located underground. Underground fuel storage tanks are used at filling stations for the storage of petroleum products. Leakage of petroleum products from an underground storage tank might go unnoticed for manymonths, during which time water courses maybe polluted, and soil maybe contaminated. Furthermore, people and buildings in the vicinity may be endangered by the presence of highly flammable fuels in the ground.

Historically, underground fuel storage tanks were fashioned from a single skin of mild steel.

Corrosion of such tanks was not a problem whilst petrol fuel contained lead, the lead acting as a corrosion inhibitor. However, in most countries lead is no longer present in petrol fuel. The resulting petrol fuel is corrosive of steel, and there have been a number of incidences of such tanks leaking fuel into the ground with consequent damaging effects. There is therefore a move to line underground fuel storage tanks with linings not susceptible to corrosion by the fuel destined to be stored in the tank.

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. If the pressure changes there is an integrity failure in the inner lining or outer hull.

The replacement of an underground tank is a time consuming and expensive process, since in the case of a filling station, the cost of physicallyremoving the tank from the ground is itself high, but more importantlywhilst the tank is being replaced the fuel station must be closed, resulting loss of revenue for the period of closure, and possible long-term loss of business due to customers going to other firing stations during the period of closure.

Re-lining existing underground tanks provides at least three benefits. First, the lining is selected so as not to be corrodible by the fuel. Second, if there is an interstitial space this space can be monitored to establish whether there is anyleakage of fuel from the tank, and third, lining a tank can be accomplished more quickly then replacement of a 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 anyone time. Due to the toxic nature of the gases given off by the epoxy resin 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 speed 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 epoxy resin used in the laying up of the glass reinforced plastics material. However, the protective clothing available is onlyimpervious 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 hospitalization resulting from exposure to noxious gases during the laying up the glass reinforced plastics material is significant.

It would therefore be desirable to be able to reduce workers exposure to potentially dangerous gases during lining of a tank Surrunaty of the Invention According to an aspect of the invention, there is provided a lining for a tank as specified in Claim 1.

According to another aspect of the invention, there is provided a method of lining a tank according to Claim 36.

The lining and method of application of the invention provide a number of advantages over the tank lining systems of the prior art. In particular, using the lining of the invention rather than linings of the prior art, a tank can be lined much more quickly, safely and with reduced risk to the environment.

The nature of the lining means that the exposure of workers to noxious fumes, such as those produced when laying up glass reinforced plastics is much reduced. In following the lining method of the invention workers are exposed to fumes for a much smaller part of the procedure (only the application of an encapsulating layer to the bare metal inner surface of the tank). Using a lining comprising thermo-plastic sheets welded together significantly reduces the man power required to line a tank.

The lining method of the invention is useful not onlyin the lining of fuel tanks, but also tanks to containing other fluids, and also pipes used to transmit fluids, for example oil, gas, water and sewage pipelines.

Brief Descnption of the Drawings In the drawings, which are for the purpose of example, there are illustrated a number of embodiments of a lining according to the invention: Figure 1 is a cross-section of a part of a tank hull lined according to a first aspect of the invention; Figure 2 is a cross-section of a part of a tank hull lined according to a second aspect of the invention; Figure 3 is a schematic representation of a first possible material used in one of the layers of the lining of either embodiment of the invention; Figure 4 is a schematic representation of a second possible material used in one of the layers of the lining of either embodiment of the invention; Figure 5 illustrates a tank in cross- section lined with the lining of the first embodiment of the invention as illustrated in Figure 1; and Figure 6 is a schematic representation of a tank partiallylined according tO the method of the mventlon.

Detailed Description of the Drawings

Referring now tO Figure 1, a steel tank wall 1 is coated with an anticorrosion encapsulating layer 2, which in this example is between 300 and 1000,um thick. In this example, the encapsulating layer is an epoxy resin which is sprayed onto the inner surface of the tank wall 1 after grit blasting thereof.

The epoxyresin is applied as a hot spray, i.e. the epoxyis solvent free and must be heated to enable application. As the epoxy resin cools it resolidifies forming a continuous layer that is impervious to petrol fuel. Using a hot spray epoxy resin means that solvents in the epoxy are not required, and thereby removing solvent fumes from the working environment inside the tank and the of fumes into the environment.

Fixed to the encapsulating coating 2 is a plastics sheet 3. Fixing is achieved with adhesive applied tO the plastics sheet 3 at spaced apart locations, the adhesive being pressed onto the encapsulating coating 2. A first side 4 of the sheet facing the encapsulating coating 2 is provided with a plurality of protrusions 5 extending in a substantiallyperpendicular direction tO the plane of the sheet 3. The free ends of these protrusions face the surface of the encapsulating layer 2. An interstitial space is therefore provided between the encapsulating layer 2 and the sheet 3. A second side 6 of the sheet 3 is smooth. The sheet 3 is formed from high densitypolyethylene (3DPE), a member of the polyolefin group of chemicals.

Rather than applying adhesive tO the sheet 3 and pressing the adhesive onto the encapsulating coating, small pads of a suitable material (which in the example is the material from which the sheet 3 is made) are fixed to the sheet 3, with a suitable adhesive 17, and the pads 16 are then fastened to the encapsulating layer 2 with a suitable adhesive 17.

A layer of plastics material 7, which is impervious to petrol fuel and in the example is polyvinyl iodine fluoride (PVDF) is glued tO the second side 6 of the sheet 3. The layer of plastics material 7 is formed from a plurality of sheets of PVDF, adjacent sheets being welded together using a plastics welding material. Adjacent sheets may be butt welded, lap welded or fillet welded, depending on the particular location of the sheets being joined in the tank. This procedure of welding together sheets of PVDF is described in greater detail with reference to Figure 6.

The sheets 3 are either not welded together along their adjacent edges, or are not welded along the full lengths of the adjacent edges. This is so that if there is a failure in any weld between the sheets 7, a failure can be detected by virtue of a change generated in the interstitial space.

Alternatively, rather than the protrusions 5 facing towards and resting on the encapsulating layer 2, the sheet 3 could be turned through 180 degrees so that the second side 6 rests on the encapsulating layer 2, with the protrusions 5 facing away from the wall 1. In such a case, the sheet 7 rests on and is fixed to the protrusions 5.

As an alternative to the layer formed byplastics sheets 7, a second impervious layer maybe formed byinseriing an inflatable flexible membrane inside the tank The membrane may be formed from a material of the polyolefin family, such as a polyethylene with a suitable density, or another material that is flexible and fluid impervious, and in particular impervious to petrol fuel or other liquids.

Figure 2 illustrates a second embodiment of the invention, which is similar to the first embodiment, and comprises the same components with the omission of the PVDF layer 7 (Figure 2 is numbered with the same reference numerals as Figure 1 for the reader's ease of understanding). Sheet 3 is formed from a plastics material that is impervious to a liquid product to be stored in the tank thereby obviating the need for the top layer of PVDF as required in the first embodiment of the invention. In the second embodiment, the plastics material 3 is a high density polyethylene (HDPE).

However, the density of the HDPE used in the second embodiment of the invention maybe greater than the density of the HDPE used in the first embodiment of the invention, and would be dependent on the characteristics of the fluid to be contained in the tank The plastics material 3 is attached to the encapsulating layer by applying glue to the protrusions 5 of the HDPE layer at spaced apart locations, and pressing the protrusions 5 against the encapsulating layer 2. As the HDPE layer is applied in sheets, the joints between adjacent sheets must be welded to provide an impervious layer. Adjacent sheets of HDPE are butt or fillet welded using a suitable plastics welding material.

The encapsulating layer 2 may be formed from a material other than epoxy. For example: vinylester or polyurethane. Alternatively, the encapsulating layer may be omitted and the protrusions 5 extending from the first side 4 of the plastics sheet 3 maybe glued to the inner surface of the tank.

The encapsulating layer is typically between 500 and 1000 m, and in this example is 500 lam Referring now to Figure 3, a plastics sheet 3 comprises a plurality of hook like protrusions 5 extending from the first side 4 of the sheet 3, the second side of the sheet (not shown) being smooth.

The free ends of the hook]ike projections 5 are glued to, at spaced apart locations, the encapsulating layer 2 (see Figures 1 and 2). In use, the weight of fluid in the tank presses the hook dike projections against the encapsulating layer 2. The hooks ensure that an interstitial space exists between the encapsulating layer 2, covering the inner surface of the tank, and the planar sheet 3. The sheet 3 and hooks 5 are formed in an extrusion process, the hooks 5 being an integral part of the sheet 3.

Referring now to Figure 4, a plastics sheet 10 includes on one side thereof a grid dike structure 11 consisting of a plurality of spaced apart ridges 12 extending in a first direction and a plurality of spaced apart elongate elements 13 extending perpendicular to the said ridges 12. The elongate elements 13 are attached to and spaced apart from the ridges 12 by means of attachment members 14. The sheet 10, ridges 12, elongate elements 13 of the grid like structure are all integral parts of the sheet 10, the sheet 10 being formed in an extrusion process. In use the elongate elements 13 abut, and at spaced apart locations are glued to, the encapsulating layer 2 (see Figures 1 and 2). The grid- like structure 11 ensures that an interstitial space exists between the inner surface of the tank and the planer street 10.

Figure 5 illustrates a tank in cross-section lined with the lining of the first embodiment of the invention as illustrated in Figure 1. For the sake of clarify the encapsulating layer of epoxy resin illustrated in Figure 1 is not indicated in Figure 5. The tank 1 in the figure is substantially cylindrical in cross-section. The plastics sheet 3 covers the inner surface of the tank 1, the layer of plastics 7 being glued to the plastics sheet 3. The plastics layer 7 is fowled from PVDF. As an alternative to PVDF, in certain circumstances perfluorinated vinyether (FE P) , or ethylene- chlorotrifluorethylen (ECIFE) may be used. These materials are much more difficult to work with, in temls of welding and fumes produced, and would therefore only be used where the nature of the product to be stored necessitated extreme resistance to chemical attack or temperature.

Spaced everyone metre or so are arcuate supports 8. The outer edges of these supports are welded to the surface of the plastics layer 7, and are formed from the same material as the plastics layer 7, which in this case is PVDF. If the plastics layer 7 were omitted, and the HDPE layer fowled the impervious barrier, as is the case with the second embodiment of the invention, then the arcuate supports 8 would be formed from HDPE. An alternative to fabricating arcuate supports as shown, would be to build up strips of weld extending circurnferentially over the inner surface of the inner most plastics layer.

The arcuate supports prevent the lining from imploding.

Figure 6 shows how the lining of the invention is built up. The inner surface of the steel tank wall 1 is keyed by grit blasting (altemativelysand or shot maybe used), wet blasting where an abrasive is entrained in a high pressure liquid, or simplyLyElasting the surface with high pressure water. An encapsulating layer of epoxy applied as described above in relation to Figure 1. A plastics sheet 3 is glued to the encapsulating layer 2, the sheet 3 including means to space a first side 4 (see Figure 1) of the planar sheet a small distance from the encapsulating layer to create an interstitial space. A plastics layer 7 impervious to fuel is glued to the second side 6 (see Figure 1) of the plastics sheet 3. The plastics layer 7 is formed from a plurality of discrete sheets of plastics material, adjacent edges of such sheets being joined together by welds 9, welding being carried out in situ.

When applying the plastics sheets, whether they tee the sheets creating the interstitial space, or the planar sheets, to a ferrous tank wall, magnets can be used to hold the sheets in place while they are being positioned, and/or whilst the fixing adhesive is curing. Such magnets could be of the type described in GB 2339633.

The integrity of the welds 9 is tested using the Holiday testing method. This is achieved byplacing wires 15 (shown in broken lines) behind each weld. A potential difference, earthed to the steel wall 1, is applied to the surface of the welds 9. If there is a fault in the weld a current will pass through the wires 15.

As an alternative, or in addition, to the Holiday test, other tests may be used to prove the integrity of welds and the lined tank. For example, welds can be tested by applying a positive pressure to the interstitial space, and applying soap over the welds. If there is a failure in a weld, the soap will froth.

This is a well known testing method.

Another method of testing weld integrityis to apply dye to the surface of the weld. The dye will find its way into the weld either by capillary action, or with the aid of positive or negative pressure.

A lined tank may also be tested bypressurizing the tank lining and measuring pressure in the interstitial space. If the pressure in the interstitial space rises, there is a failure in the tank lining.

Once it has been established that the tank lining has been satisfactorilytested, the outer hull can be tested by subjecting the interstitial space to a vacuum. If the vacuum does not hold, the failure must be in the outer hull of the tank.

The lining of the invention may be applied to walls made of materials other than steel. For example, walls could be of other metals, brick or concrete for example.

The plastics material 7 is resistant to corrosion and/or abrasion, and depending on the nature of the product to be stored in, or pass through, a structure lined according to the invention, the selected plastics material 7 maybe resistant to corrosion and/or abrasion by crude oil, diesel oil, petrol fuel, natural gas or water.

In order to monitor the integrity of the tank a monitoring system is provided which can detect a failure in either the tank wall 1, or the tank lining. Such monitoring systems are well known in the art and are typically either vacuum, liquid fill, electronic moisture sensing systems. In a liquid fill system the interstitial space is filled with liquid and the liquid level monitored. If the liquid level falls then there is a failure in the outer wall. If the liquid level rises there is a failure in the lining. In a vacuum system, the interstitial space is subject to a vacuum. If the vacuum pressure changes outside set thresholds, there is a failure in either the outer wall or the lining.

Claims

Claims 1. A fluid impervious lining for a wall comprising at least one

sheets of plastics material the or each sheet being attached to a surface of the wall to form a first layer, and wherein the or each plastics sheet includes spacing means as an integral part thereof, the spacing means providing an interstitial space between the wall to which the or each sheet is attached and the sheet.
2. A fluid impervious lining according to Maim 1, wherein the said sheets of the first layer are formed from a fluid impervious plastics material.
3. A fluid impervious lining according to aaim 2, wherein adjacent sheets of the first layer are joined bywelding.
4. A fluid impervious lining according to Maim 3, wherein the adjacent sheets are joined by butt, lap or fillet welds.
5. A fluid impervious lining according to Maim 1, wherein the lining includes a second layer of plastics material adjacent the first layer, the interstitial space being located between the inner surface of the wall and the surface of the second layer proximal to the wall.
6. A fluid impervious lining according to Maim 5, wherein the second layer consists of sheets of plastics material attached to the first layer.
7. A fluid impervious lining according to Maim 6, wherein the sheets of plastics material of the second layer are attached to the planar surface of the or each plastics sheet of first layer distant from the wall.
8. A fluid impervious lining according to Maim 6, wherein the sheets of plastics material of the second layer are attached to the spacing means.
9. A fluid impervious lining according to Maim 5, wherein the second layer consists of a plastics membrane.
10. A fluid impervious lining according to any of Maims 5 to 9, wherein the said second layer is formed from a fluid impervious plastics material.
11. A fluid impervious lining according to Claim 10, wherein the second layer is more impervious to fluid than the first layer.
12. A fluid impervious lining according to any preceding claim, wherein the first layer and/or the second layer are formed from a fluoropolymer.
13. A fluid impervious lining according to any of Claim 5 to 12, wherein adjacent sheets of the second layer are joined by welding.
14. A fluid impervious lining according to Claim 13, wherein the adjacent sheets are joined by butt, lap or fillet welds.
15. A fluid impervious lining according to anypreceding claim, wherein the plastics material of the first layer is of the polyolefin family.
16. A fluid impervious lining according to Maim 15, wherein the plastics material of the first layer is a high densitypolyethylene (=PE).
17. A fluid impervious lining according to any of Maim 5 to 16, wherein the plastics material of the second layer is polyvinyl iodine fluoride (PVDF).
18. A fluid impervious lining according to C laim 17, wherein the second layer is between l.OOmm and 2.00mm thick
19. A fluid impervious lining according to Maim 18, wherein the second layer is substantially 1.50mm thick
20. A fluid impervious lining according to any preceding claim, wherein the first layer is attached to the wale and the second layer is attached to the first layer, by an adhesive.
21. A fluid impervious lining according to any preceding claim, wherein the surface of the wall to which the first layer is attached is provided with a fluid impervious coating.
22. A fluid impervious lining according to Claim 21, wherein the coating is an epoxy, a glass flake epoxy, a vinylester or a polyurethane.
23. A fluid impervious lining according to Maim 22, wherein the fluid impervious coating is a solvent free.
24. A fluid impervious lining according to Maim 23, wherein the fluid impervious coating requires heating prior to application.
25. A fluid impervious lining according to anypreceding claim, wherein the wall is formed from a metallic material.
26. A fluid impervious lining according to Maim 25, wherein the wall is formed from steel.
27. A fluid impervious lining according to Maim 21, wherein the surface of the wall to which the impervious coating is attached is keyed.
28. A fluid impervious lining according to anypreceding claim, wherein the said spacing members comprise protrusions extending from the plastics sheet towards the wall.
29. A fluid impervious lining according to Maim 27, wherein the said protrusions extend in a substantiallyperpendicular direction to the plane of the sheet.
30. A fluid impervious lining according to Maim 27 or 28, wherein each protrusion comprises a hook extending from the surface of the sheet proximal to the wall, and wherein the free ends of the hooks abut the surface of the wall or a coating applied to the surface of the wall.
31. A fluid impervious lining according to anypreceding claim, wherein the lining is resistant to corrosion and/or abrasion.
32. A fluid impervious lining according to anypreceding claim, wherein the lining is supported at intervals byribs extending away from the surface of the lining most distant from the wall.
33. A fluid impervious lining according to Maim 32, wherein the ribs are of the same material as the material forming the surface of the lining most distant from the wall.
34. A tank including at least one wall, wherein the or each wall is provided with a lining according to any of Maim 1 to 33.
35. A pipe including a wall, wherein the wall is provided with a lining according to any of Maims 1 to 33.
36. A method of building the fluid impervious wall lining according to any of Oairns 1 to 33, comprising the steps of: i) preparing a surface of a wall to be lined; ii) applying at least one sheet of plastics material to the surface to form a first layer, the plastics material including spacing means as an integral part thereof, wherein the spacing means provide an interstitial space between the wall to which the or each sheet is attached and a plastics sheet.
37. A method of building a fluid impervious wall lining according to Maim 36, including the steps of: i) fixing the or each plastics sheet of the first layer to the surface of the wall to be lined with an adhesive; ii) welding the joints between adjacent plastics sheets of the first layer.
38. A method of building a fluid impervious wall lining according to Maim 36, including the steps of: i) fixing the or each plastics sheet of the first layer to the surface of the wall to be lined with an adhesive; ii) fixing the or each plastics sheet of the second layer to the first layer with an adhesive, an interstitial space existing between the second layer and the surface of the wall being lined; and iii) welding the joints between adjacent plastics sheets of the second layer.
39. A method of building a fluid impervious wall lining according to any of Maims 36 to 38, wherein the surface of the wall to be lined is prepared by blasting said surface with an abrasive and/or high pressure water.
40. A method of building a fluid impervious wall lining according to Maim 39, wherein the abrasive is grit, sand or shot.
41. A method of building a fluid impervious wall lining according to any of Maims 36 to 40, including the step of: i) applying an impervious coating to the surface of the wall to be lined.
42. A method of building a fluid impervious wall lining according to Maim 41, including the step of: i) heating a solvent free impervious coating material; and ii) spraying the heated solvent free impervious coating material onto the surface of to be lined.
43. A method of building a fluid impervious wall lining according to any of Maims 36 to 42, comprising the step of temporarily holding a sheet of the first layer and/or the second layer against the wall with at least one magnet.
44. A fluid impervious lining substantially as shown in, and as described with reference to, the drawings.