EP0754635A1 - Double-walled tank and method of making the same - Google Patents

Abstract

The outer wall consists of a spacer sheet (15) to which is joined at least one plastic elastomeric layer, preferably formed of a multi-component synthetic resin. The spacer sheet, possibly made of knopped aluminium foil or cardboard, creates a hollow cavity between the inner (13) and outer wall. The spacer sheet is applied to the exterior of the especially steel tank, and finally coated with synthetic resin. The elastomeric layer is applied onto the spacer sheet, and is tested by excess, or under, pressure for leaks.

Description

The present invention relates to a double-walled tank, in particular for storing oil, petrol or solvents, with an inner wall and an outer wall, the outer wall being formed from a spacer film and at least one plastic layer connected to the spacer film and by means of the spacer film a between the inner and the outer wall lying cavity is created, which can be checked for leakage by means of excess or negative pressure.

In the past, metal tanks were often only provided with a bitumen layer as corrosion protection on the outside, with no actual leak protection. The advantage of bitumen layers is that such coatings can be produced inexpensively. On the other hand, it is disadvantageous that they crack over time and therefore do not offer reliable protection against corrosion and the resulting leakage of the tank contents. In addition, a subsequent check of the bitumen layer is often impossible. Wherever conditions permit, the check is complex, since the entire shift must be examined in each case.

Metal tanks coated directly with epoxy resin have also become known on the outside. Epoxy resin layers are resistant and protect the tank from corrosion. On the other hand, it is disadvantageous that epoxy resin layers are relatively brittle and that they can be easily damaged, for example during transport. If there are small damaged areas or even hairline cracks in the dielectric plastic layer, an electrical connection between the metal wall and the surrounding soil, reinforced concrete walls etc. can occur. Electrical currents occur at the damaged areas, causing rapid corrosion of the metal. An effective one Corrosion protection therefore requires good adhesion of the epoxy resin to the outside of the tank. This can only be achieved if the outer wall of the tank is carefully cleaned before the resin is applied, which of course is time-consuming. It is also disadvantageous in terms of production that several coats of epoxy resin are usually necessary and that the drying time is approx. 2-3 days.

As already mentioned above, coated metal tanks have the major disadvantage that the outer coating can usually no longer be checked for possible damage. For this reason, double-walled steel tanks with a cavity between the inner and outer walls have been used increasingly in recent years. Such tanks have the advantage that they e.g. can be checked for leaks using a vacuum applied to the cavity. It is therefore not necessary to examine the entire outer coating, as is the case with the coated tanks mentioned at the beginning. However, double-walled steel tanks have the major disadvantage that they are very expensive to manufacture and that external corrosion protection cannot be dispensed with.

Leak tests using vacuum or overpressure generally have the immense advantage that they can also be used at any time in tanks that are buried in the ground. They are therefore suitable for the continuous monitoring of double-walled tanks. However, the cavity of double-walled tanks can also serve to hold a warning liquid, or sensors protruding into the cavity can be used to detect the penetration of liquid into the cavity.

The CH-PS 471 728 describes a double-walled tank with an inner wall made of steel and an outer wall made of plastic, wherein a flat spacer is arranged between the inner and the outer wall. The glass fiber reinforced Polyester-plastic outer wall is applied to the spacer formed by a film. The cavity formed by the spacer film between the inner and the outer wall is intended to contain a warning liquid in order to be able to detect a possible leakage of the inner or outer wall. The thermosetting plastic layer gives the tank casing good stability, so that the cavity between the inner and outer wall is preserved even under heavy loads. A disadvantage of the double-walled tank described, however, is the brittleness of the outer layer made of polyester. Because of the brittleness, the outer wall can crack as a result of temperature fluctuations or alternating loads. Another disadvantage is the relatively complex production process, in which two layers of glass fiber fabric usually have to be worked into the polyester resin in order to achieve the necessary stability of the outer wall. If GRP laminates are damaged, so-called "open" fibers are formed, on which liquid can penetrate into the cavity (capillary action). This removes the cathode protection at these points. Another disadvantage is that the long curing times required for the polyester resin make it necessary to have large production facilities in which several tanks can be processed at the same time.

The CH-PS 618 658 also describes a double-walled tank with a spacer fabric located between the inner and outer wall. The spacer fabric consists of wrapping paper. A coating gasoline, oil and alcohol resistant coating color is applied to the wrapping paper (Etoplate 6), which inhibits the diffusion of gasoline, oil and alcohol vapors. Etoplate 6 is a colored epoxy resin. The coating color can be sprayed on or even filled, with fiber chips being added to the coating color. The addition of fiber chips is necessary to give the wall a certain toughness and to reduce the risk of cracking. Due to the open porosity of the According to CH-PS 618 658, packaging paper results in an intimate connection between the first color layer and the packaging paper. In practice, the coating described above was only used as an interior lining. The reason for this lies on the one hand in the brittleness of the epoxy plastic layer, which could undoubtedly be damaged when the tank is transported and moved. On the other hand, it has also been found that leakage currents can occur through the plastic layer due to improperly wetted fiber chips, which then cause gradual corrosion of the metal jacket. Although according to CH-PS 618 658 the epoxy plastic layer has a certain elasticity, the tank inner walls that have been produced have often become leaky. It has happened that the epoxy layer is torn and leaking at certain points when the tank is being filled or, if necessary, when the tank is cleaned later. The manufacture of the double-walled tank disclosed in CH-PS 618 658 is also relatively complex since the fiber chips have to be worked into the synthetic resin with rollers and / or grooved rollers. Another disadvantage is that the curing time of the epoxy layer takes several hours to a day, so that it is not possible to continue working on the tank during this time. Checking for any leaks that may still be present is only possible once the epoxy resin layer has hardened. In summary, it can be said that the known double-walled tanks, in which the outer jacket is formed by a glass fiber reinforced plastic layer, are quite susceptible to injury.

No. 4,844,287 proposes to first clothe a tank on the outside with a first elastomer layer and then with a liquid-permeable textile material which was previously coated with a second elastomer layer. The elastomer layers are preferably polyurethanes with a high solids content. Since such a plastic only to a certain depth in the Penetrates textile material, the coated textile material remains liquid-permeable, so that liquid emerging from the tank penetrate the tissue and can be detected with known detection devices. The tank casing described has the disadvantage that a leak can only be determined with a certain time delay. In addition, once a damaged area has occurred, a later leak check may not be possible, since the textile material is soaked with liquid.

US 5,000,342 discloses a tank with a permeable first separation layer and a second fiber-reinforced plastic layer. The outer plastic layer can be formed from a wide variety of plastics. The separating layer has a large number of holes through which the fiber-reinforced plastic applied to the outside is connected to the tank.

The object of the present invention is to provide a double-walled tank in which the disadvantages mentioned at the outset are largely avoided. In particular, a tank, in particular a steel tank, is to be provided with an outer casing which is not susceptible to injury, so that the tank can be transported and moved without problems. The double-walled tank should continue to be easy and inexpensive to manufacture and e.g. Leakage can be checked at any time by means of vacuum or overpressure.

According to the invention, a double-walled tank of the type mentioned at the outset is characterized in that the plastic layer is an elastomer layer which is formed from a multi-component synthetic resin. Surprisingly, it was found that spacer foils such as, for example, aluminum knobbed foils, if instead of, as is known, coated with a thermosetting plastic, only with an elastomer plastic, practically no or only insignificant even under very high loads Deformations are suffered, so that the cavity between the inner and outer walls necessary for a later leak test, for example using a vacuum, is retained. In contrast to the previously known double-walled tanks with outer walls made of epoxy or polyester resins, tanks with outer coatings made of an elastomer also have the advantage that they can be stored, transported and moved without any problems. The elastomeric outer layers produced have the advantage that their vulnerability is significantly lower than that of thermosetting layers made of epoxy or polyester resin. The risk that the outer wall could be injured is very low due to its rubber-like elasticity. The elasticity is advantageously retained even at low temperatures of, for example, -20 ° C. Conventional coatings made of epoxy resin or polyester are rigid and brittle at temperatures of around 0 to -20 ° C. In addition, epoxy resin or polyester coatings have the disadvantage that residual stresses occur in the plastic layer due to aging.

Thanks to the use of fast-reacting multi-component synthetic resin mixtures, the outer wall of a tank can be manufactured extremely quickly. Another big advantage is that there is no need for glass fibers or glass fabric in the elastomer layers. So no "open" fibers can form. This not only results in material savings, but also in a much more rational way of production than with conventional tanks. The elastomer layer applied to the spacer is also an excellent dielectric, so it is a good cathode protection for a metal tank wall.

The elastomer layer is advantageously formed from isocyanate / polyol compounds or diamine compounds, in particular urea compounds. Elastomer layers with good material properties, such as hydrolysis, solvent and UV resistance and high dielectric constant. There are multi-component resin systems available on the market today that are highly reactive and sprayable. Elastomer layers formed from isocyanate / polyol compounds or essentially only from urea compounds have good chemical resistance, for example to gasoline or oil. Although polyurea layers are generally less elastic than polyurethane / urea layers, they have the advantage that they are more impermeable to gases. The elongation at break of the elastomer layer is expediently at least 10 to 20 percent at 20 ° C. As a result, the risk of cracking during subsequent tank cleaning, as a result of temperature fluctuations or transport is low. The elastomer layer particularly advantageously has an elongation at break of more than 100%, preferably more than 200% at 20 ° C. In comparison to epoxy resin layers, such layers are much more elastic and hardly vulnerable. If such layers are scratched during transport, for example, no leakage currents can still occur.

The elastomer layer expediently has a layer thickness between approximately 1 and approximately 5 mm, preferably between 2 and 4 mm. Elastomer layers of this thickness have a good insulation effect. Although any foil and / or braid that is suitable for forming a cavity between the tank and the adjacent surface of the foil can be used as a spacer foil, an aluminum knobbed foil is preferably used. An inexpensive variant envisages using a spacer film made of cardboard. In the latter case, it is important to prime the box. This can improve the adhesion of the elastomer layer to the cardboard. However, it is also important that the primer, preferably an epoxy resin, makes the cardboard largely gas-impermeable, that is, gas diffusion through the cardboard is prevented. This is important, otherwise the leak checkability would be affected by vacuum or overpressure. The elastomer plastic forms a firm bond with the cardboard. This can result in such a large reinforcement of the cardboard knobs that, surprisingly, they are not compressed even when the tank is full. The use of cardboard films for the production of an elastomer-coated tank outer wall is therefore a cost-effective and interesting alternative to the more expensive aluminum knobbed films. Elastomer layers with a low gas permeability are preferably used in conjunction with cardboard knobbed films.

The tensile strength of the elastomer layer is advantageously greater than 7 MPa, preferably greater than 10 MPa, in particular greater than 12 MPa. The synthetic resin components expediently have a low viscosity, so that they can be sprayed in a spray gun with forced mixing or, preferably, with direct swirling. In the latter case, the components are mixed with one another and sprayed on directly in the spray nozzle. This allows the outer layer to be produced efficiently. UV stabilizers, dyes or other conventional additives can also be contained in the elastomer layer.

The present invention also relates to a method for producing a double-walled tank, which is characterized in that a layer of a reactive multi-component synthetic resin is applied to the spacer film to form an elastomer layer. In this context, reactive means that the components, once brought together, react practically immediately. The reaction mixture should therefore have a short gel time so that the reaction mixture can be sprayed on without forming webs or dripping from the tank. By using reactive or fast-curing multi-component synthetic resins, the manufacturing time of an outer tank wall can be significant be reduced. There are practically no dead periods during which the layers have to be cured. In addition, the tightness of the layer can be checked practically immediately after its application.

A multicomponent synthetic resin which hardens at room temperature and has a gelling time of up to about 60 seconds, preferably up to about 30 seconds, is expediently used, so that it can be sprayed on in one operation. After mixing the components at 25 ° C., the reaction mixture advantageously reaches a viscosity value of approximately 50,000 mPa * s within a maximum of approximately 500 seconds, preferably within a maximum of 200 seconds. This makes it possible to coat a cylindrical tank almost continuously. The tank can be stored on rollers, rotated and simultaneously sprayed with the reaction mixture. It is also possible to apply several layers in succession. Further advantageous procedural measures can be found in the subclaims.

An embodiment of the invention is shown schematically in Figure 1. Fig. 1 shows a section of a double wall 11 of a tank in section. The double wall 11 has an inner wall 13 made of steel, a spacer film 15 and an elastomer layer firmly connected to the spacer film 15. The spacer film can be made of aluminum sheet, cardboard or plastic. Appropriate aluminum spacers have a thickness between 0.1 and 0.2 mm and are primed on both sides. The primer ensures good adhesion of the elastomer layer, so that a good bond is formed between the spacer film and the plastic. The primer coating on the side facing the tank wall acts as an insulation layer. Since the depressions formed by the knobs are filled with the elastomer plastic, pressing the knobs in is practically impossible. For example, as a primer for cardboard films the epoxy primer or polyurethane / epoxy primer from Adisa AG, Urdorf, Switzerland, are used.

Recommended elastomer coatings made from a 2-component polyurethane / polyol resin have the following material properties: 20 ° C minus 20 ° C Tensile strength (MPa) ¹⁾ about 10-12 about 25-30 Elongation at break (%) about 300-380 about 220-310 (Tear resistance) shore A 80-85 Chemical resistance Well Well ¹⁾ (DIN 53455, 53504, 53430, 53571, 53354)

A double-walled tank is produced as follows: First, strips of preferably gas or liquid-impermeable spacer films are attached to the outside of the tank, usually a steel tank. This can e.g. with the help of double-sided adhesive tape strips, which are previously glued to the tank at certain intervals. Alternatively, the tank can first be sprayed with a contact adhesive. The aluminum or cardboard film webs are laid on the tank outer wall in such a way that the edge areas of the film webs overlap. The overlap zones are then preferably additionally covered with an adhesive tape, e.g. Aluminum adhesive tape, covered to prevent penetration of the sprayed-on synthetic resin mixture into the cavity between the spacer film and the inner wall of the tank. As soon as the tank or parts of it are completely covered with spacer films, the multi-component mixture can be sprayed on.

A reactive polyurethane / polyol mixture which cures rapidly at room temperature is preferably used as the multi-component mixture. Contains quick-curing mixtures Polyisocyanates (eg aliphatic, cycloaliphatic or aromatic di- and triisocyanates and / or mixtures thereof) and polyols and / or diamines or mixtures thereof. The isocyanates are preferably already prepolymers. Aromatic diamines, urea or urea compounds are used as diamines.

Solvent-free two-component systems that can be used in a ratio of 1: 1 are particularly advantageously used. These are then mixed and sprayed directly in the spray nozzle of a spraying system. This process can also be automated. Due to the short curing time of the quick-reacting mixture, the tank can be checked for leaks practically immediately after its completion.

In a load plate test, a maximum load of 20 kN (corresponding to a compressive stress of 2 N / mm2) was applied to a sample material using steel plates with a loading speed of 0.01 N / mm2 per second and the load-path diagram was recorded. After the load, the knobs were examined for traces of deformation. In a further test, a load of 10 kN was applied to check the creep behavior and left on the sample for 3 hours. The increase in strain was recorded.

The 100 x 100 mm sample material consisted of an aluminum studded film coated with Adalastic®. The three-layer elastomer layer had a layer thickness between approximately 2.2 and 3.2 mm (measured on and between the knobs).

The load-path diagram showed a linear course and showed no signs of yielding by pressing in the knobs. The test specimen only deformed by 0.4 mm, with only a very slight flattening of the Pimples was visible. In the creep test, the increase in compression was only about 0.04 mm.

In summary, it can be said that double-walled tanks for storing petrol and oil with an outer wall made of an elastomer with high tensile strength (elongation at break) and good tensile strength are much less susceptible to injury than known tanks with epoxy resin or polyester layers. It is also important here that such elastomer coatings can be produced in one operation by spraying on using reactive, fast-curing multi-component resins with the shortest possible gelation time. The elastomer layer ensures very good electrical insulation of the metal tank shell (tank inner wall) and at the same time forms a hard-wearing, stable outer wall that can have the necessary toughness without glass fabric or fiber chips and essentially without fillers. It has been shown that the cathode protection achieved with the elastomer coating is considerably more reliable than that of epoxy or polyester coatings. A significant advantage of the tanks according to the invention is that the outer casing can be produced before the tank is moved.

Claims (18)

Double-walled tank, in particular for storing oil, petrol or solvents, with an inner wall and an outer wall, the outer wall being formed from a spacer film and at least one plastic layer connected to the spacer film, and a cavity lying between the inner and outer wall being created by the spacer film which, for example Leak can be checked by means of excess or negative pressure, characterized in that the plastic layer is an elastomer layer, which is preferably formed from a multi-component synthetic resin. Tank according to claim 1, characterized in that the elastomer layer is formed from isocyanate / polyol compounds and / or diamine compounds, in particular urea compounds or mixtures thereof. Tank according to claim 1 or 2, characterized in that the elongation at break of the elastomer layer is at least 10 to 20 percent at 20 ° C. Tank according to claim 1 or 2, characterized in that the elastomer layer has an elongation at break of more than 100%, preferably more than 200% at 20 ° C. Tank according to one of claims 1 to 4, characterized in that the elastomer layer has a layer thickness between approximately 1 and approximately 5 mm, preferably between 2 and 4 mm. Tank according to one of claims 1 to 5, characterized in that the spacer film is an aluminum knob film. Tank according to one of claims 1 to 5, characterized in that the spacer film is made of cardboard. Tank according to one of claims 1 to 7, characterized in that the spacer films are provided on at least one side with a primer. Tank according to one of claims 1 to 8, characterized in that the tensile strength of the elastomer layer is greater than 7 MPa, preferably greater than 10 MPa. Tank according to claim 1 or 2, characterized in that the elastomer layer has an elongation at break of more than 100%, preferably more than 200% at 20 ° C and a layer thickness between approximately 1 and approximately 5 mm, preferably between 2 and 4 mm, and that the elongation at break of the elastomer layer is greater than 7 MPa, preferably greater than 10 MPa. A process for producing a double-walled tank, in which process a spacer film is applied to the outside of the tank, in particular a steel tank, and then coated with a synthetic resin, characterized in that a layer of a reactive multi-component synthetic resin is applied to the spacer film to form an elastomer layer becomes. A method according to claim 11, characterized in that a multi-component synthetic resin which hardens at room temperature is used, which has a gelling time of up to approximately 60 seconds, preferably up to 30 seconds. A method according to claim 11 or 12, characterized in that isocyanate / polyol compounds and / or diamine compounds as multi-component synthetic resin or mixtures thereof, in particular urea compounds, can be used. Method according to one of claims 11 to 13, characterized in that a layer of between approximately 1 and approximately 5 mm, preferably between 2 and 4 mm, is applied. Method according to one of claims 11 to 14, characterized in that a cardboard bubble film is used as a spacer film, which is provided with a primer which inhibits gas diffusion. Method according to one of claims 11 to 15, characterized in that the tank is first sprayed with a contact adhesive on the outside for fastening the spacer films. Method according to one of claims 11 to 16, characterized in that the elastomer plastic layer produced is checked for leaks after manufacture by means of positive or negative pressure. Method according to one of claims 11 to 17, characterized in that the synthetic resin components used have a low viscosity, so that they can be sprayed in a spray gun with positive mixing or preferably with direct swirling.

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