Double-walled tank and method of making the same

The present invention relates to a double-walled tank, in particular for the storage of oil, petrol or solvents, having an inner wall and an outer wall, said outer wall is formed by a spacer film and at least one associated with the spacer film plastic layer and the spacer foil between the inner and outer wall lying cavity is created, which can be checked by means of pressure or vacuum leak.

In the past, metal tanks were outside often only provided with a bitumen layer as corrosion protection, wherein an actual leak protection was missing. The advantage of bitumen layers is that such coatings can be produced inexpensively. A disadvantage, however, that these are cracked with time and thus do not offer reliable protection against corrosion and thereby caused leakage of contents. In addition, a retrospective review of the bitumen layer is often impossible. Even where conditions allow that an accrediting is costly, since in each case the entire layer has to be investigated.

Became well-known are also outside directly coated with epoxy metal tanks. Epoxy resin layers are resistant and protect the tank against corrosion. A disadvantage, however, that epoxy resin layers are relatively brittle and that this, for example during transport, can be easily injured. Are small defects or even hairline cracks in the dielectric Kunststsoffschicht available, so there may be an electrical connection between the metal wall and the surrounding soil, reinforced concrete walls, etc.. occur on the defective areas to electrical currents that cause rapid corrosion of the metal. An effective corrosion protection, therefore, requires a good adhesion of the epoxy resin on the tank outer wall. This can only be accomplished if the tank outer wall is cleaned thoroughly before application of the resin, which of course is time consuming. Preparation Moderately disadvantageous is that usually several coats of epoxy resin are necessary and that the drying time is approximately 2-3 days.

As mentioned above, coated metal tanks have the great disadvantage that the outer coating is no longer on any damaged areas is subsequently checked in the rule. In recent years, double-walled steel tanks have been used with a cavity between the inner and the outer wall because of this increased. Such tanks have the advantage that this example can be checked by means of vacuum, which is applied to the cavity, for leaks. In this case, therefore, does not need the whole outer coating are examined, as is the case with the above-mentioned coated tanks. However, double-walled steel tanks have the great disadvantage that they are very expensive to manufacture and that on an outer corrosion protection can not be waived.

Leak testing by vacuum or overpressure have the immense advantage of being displaced even in the ground tanks can be applied at any time in general. They are therefore suitable for continuous monitoring of double-walled tanks. The cavity of double wall tanks can also serve to receive a warning liquid, or it may be employed projecting into the cavity sensors to detect the penetration of liquid into the cavity.

The CH-PS 471 728 discloses a double-walled tank with an existing steel inner wall and an outer wall made of plastic, wherein between the inner and the outer wall of an areally formed spacer is arranged. The outer wall formed from glass fiber reinforced polyester resin 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 receive a warning fluid to detect a possible leakage of the inner or outer wall. The thermosetting plastic layer gives the tank shell, good stability, so that the cavity between the inner and outer wall is maintained even under heavy loads. A disadvantage of the described double-tank, however, the brittleness of the existing polyester outer layer. Due to the brittleness the outer wall as a result of temperature fluctuations or alternating loads can be cracked. Another disadvantage is the relatively complex manufacturing process in which to achieve the necessary stability of the outer wall usually two layers of glass fiber fabric must be incorporated into the polyester resin. Become GRP laminates breached, forming so-called "open" fibers can to which fluid in the cavity penetrate (capillary action). Thus, the cathode protection is removed at these locations. Another disadvantage is that large manufacturing facilities are required by the necessary long curing of the polyester resin, in which several tanks can be processed simultaneously.

The CH-PS 618 658 also describes a double-walled tank with a located between the inner and outer wall spacer fabric. The spacer fabric is made of kraft paper. On the wrapping paper a petrol, oil and alcohol resistant coating color is applied (Etoplate 6), which inhibits the diffusion of petrol, oil and alcohol vapors. Etoplate 6 is a colored epoxy resin. The coating color can be sprayed or trowel, wherein the coating color fiber cuttings are mixed. The addition of chopped fibers is necessary to give the wall a certain toughness and reduce the risk of cracking. By open porosity of the wrapping paper obtained according to CH-PS 618 658 an intimate connection between the first ink layer and the wrapping paper. The coating described above was used in practice only as an inner cladding. The reason is partly in the Brittle the epoxy resin layer, which could certainly be damaged during transportation and placement of the tank. On the other hand has also been found that because of not properly wetted chopped fibers can pass through the plastic layer leakage currents occur, which then cause gradual corrosion of the metal shell. Although according to CH-PS 618 658, the epoxy resin layer has a certain elasticity, the tank inner walls made often become leaky. So it has happened, that already torn when filling the tank or possibly at later carried out tank cleaning the epoxy layer at certain locations and will become leaky. The production of 618 658 disclosed in CH-PS double-wall tank is also relatively expensive since the fiber cuttings must be incorporated with rollers and / or grooved rollers in the resin. Moreover, it is disadvantageous that the curing of the epoxy layer until one day takes several hours, so during this time can not be continued on the tank. The conversion test for any remaining leaks is only possible if the epoxy resin is cured. In summary it can be stated that the known double-walled tanks, is in which the outer casing is formed by a glass fiber-reinforced plastic layer, are quite susceptible to injury.

US 4,844,287 proposes a tank outside first with a first elastomer layer and then with a liquid-permeable textile material which has been previously coated with a second layer of elastomer, clothe. The elastomeric layers are preferably polyurethanes having a high solids content. Since such a plastic only up to a certain depth penetrates into the fabric, the coated fabric is permeable to liquids, so that permeate from the tank liquid exiting the tissue and can be detected using known detection means. The tank shell, has the disadvantage that a leak can be festgestllt only with a certain time lag. Also likely after even a damaged section has occurred, a subsequent leak check be impossible, because the fabric is soaked with liquid.

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

Object of the present invention is to provide a double-walled tank available, in which the aforementioned disadvantages are largely avoided. In particular, a tank, in particular steel tank, provided with a verletzungsunanfälligen outer jacket so that the tank can be transported and easily moved. The double-walled tank should be able to continue to be produced easily and inexpensively and his example by Vakumm or positive pressure at all times to leak checked.

According to the invention a double-walled tank of the aforementioned kind is characterized in that the plastic layer is an elastomer layer which is formed of a multi-component synthetic resin. Surprisingly, it was found that the spacer films such as aluminum bubble wrap when instead, as is known, with a thermosetting plastic, coated with an elastomer plastic, even under very heavy loads suffer virtually no or only insignificant deformations, so that for a subsequent leak testing is recordable as obtain necessary space between the inner and outer wall by means of vacuum. In contrast to the previously known double-walled tanks with outer walls made of epoxy or polyester resins have tanks with exterior coatings of an elastomer also has the advantage that they can be easily stored, transported and treated. The elastomeric outer layers produced have the advantage that their vulnerability is substantially less than of thermosetting layers of epoxy or polyester resin. The risk that the outer wall could be hurt because of their rubber-like elasticity is very low. The elasticity is advantageously also obtained even at low temperatures, eg -20 ° C. Conventional coatings of epoxy resin or polyester are rigid and brittle at temperatures of about 0 to -20 ° C. Moreover, epoxy resin or polyester coatings have the disadvantage that residual stresses in the plastic layer occur due to aging.

Through the use of fast-reacting multi-component synthetic resin mixtures, the outer wall of a tank can be made extremely time-saving. Another major advantage is that it can be dispensed with in the elastomer layers on glass fibers or fabric. It can not form "open" fibers so. The result is not only a material saving, but also a much more rational method of production than in conventional tanks. The deposited onto the spacer layer of elastomer is also an excellent dielectric, and is therefore a good cathodic protection of a metal tank wall.

Advantageously, the elastomeric layer of isocyanate / polyol or diamine compounds, especially urea compounds formed. For these compounds, elastomeric layers with good material properties, such as hydrolysis, solvent and UV-resistance and high dielectric constant can create. There are now multi-component synthetic resin systems available on the market, which are highly reactive and sprayable. Of isocyanate / polyol compounds, or substantially consisting of only urea compounds elastomer layers have a good chemical resistance, for example, compared with petrol or oil on. Polyharnstoffschichten are less elastic than polyurethane / urea layers in general, but have the advantage that they are gas-impermeable. Suitably, the elongation at break of the elastomer layer is at least 10 to 20 percent at 20 ° C. This reduces the risk of cracking during subsequent tank cleaning, due to temperature fluctuations or transport is low. Particularly advantageously, the elastomer layer has a breaking elongation of more than 100%, preferably more than 200% at 20 ° C. Such layers are therefore more elastic and hardly vulnerable compared to epoxy resin layers. If such layers are eg during transport aufgeritzt, then no leakage currents can still adjust.

Conveniently, the elastomer layer has a layer thickness of between about 1 and about 5 mm, preferably 2-4 mm. Elastomer layers of such thickness have a good insulating effect. Although as a spacer film jedwelche foil and / or braid can be used which is suitable to form a cavity between the tank and the adjacent surface of the film preferably is an aluminum blister sheet is used. An inexpensive variant, use a spacer sheet of cardboard. In the latter case it is important to provide the carton with a primer. Thereby, the adhesion of the elastomer layer on the cardboard can be improved. but is also of importance that is made already largely impermeable to gas by the primer, preferably an epoxy resin, the cardboard, so the gas diffusion is prevented by the carton. This is important because otherwise the leak verifiability by vacuum or overpressure would impair. The elastomer material forming the carton a solid bond. Thereby, such a large amplification of the carton nubs causes these are not pressed together, surprisingly, with a filled tank. The use of cardboard sheets for the manufacture of an elastomer coated tank outer wall is thus a cost-effective and attractive alternative to the more expensive aluminum bubble films. Preferably be used in conjunction with carton bubble films elastomer layers having a low gas permeability.

the tensile strength of the elastomer layer is advantageously greater than 7 MPa, preferably greater than 10 MPa, insbesonder greater than 12 MPa. Suitably, the resin components used in a low viscosity so that they can be sprayed in a spray gun with forced mixing or preferably with Direktverwirbelung. In the latter case, the components are mixed together directly in the spray nozzle and sprayed. This allows an efficient production of the outer layer. In the elastomer layer or UV stabilizers, dyes or other conventional additives may be included.

The present invention also provides a process for producing a double-walled tank, which is characterized in that a layer of a reactive multi-component synthetic resin is applied to form an elastomeric layer on the spacer film. Reactive in this context means that the components, once they are brought together, react almost immediately. The reaction mixture is to say have a short gel time so that the reaction mixture without forming webs or dripping from the tank can be sprayed. By using reactive or fast curing multi-component synthetic resins, the production time of a tank outside wall can be substantially reduced. There are virtually no Totzeiträume, during which you have to harden the layers. In addition, the density of the layer can be verified in practice immediately after their application.

Usefully, a fast curing at room temperature multicomponent synthetic resin is used, which has a gel time of up to about 60 seconds, preferably up to about 30 seconds has, so it can be sprayed in one operation. Advantageously achieved, the reaction mixture after the mixing of the components at 25 ° C a viscosity value of about 50,000 mPa * s within a maximum of about 500 seconds, preferably within a maximum of 200 seconds. Thereby, it is possible to coat a cylindrical tank virtually continuously. In this case, the tank can be mounted on rollers, and rotated at the same time sprayed with the reaction mixture. They can also be several layers will plotted successively in time. Further advantageous process measures are specified in the dependent claims.

An embodiment of the invention is shown schematically in FIG. 1 FIG. 1 shows a portion 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 fixed to the spacer film 15 associated elastomeric layer. The spacer film may be made of sheet aluminum, cardboard or plastic. Expedient aluminum spacer sheets 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 tank wall facing side acts as an insulating layer. Since the pits formed by the protuberances are filled with the elastomer-plastic, a pressing in of the nubs is practically impossible. As primers for cardboard sheets can, for example, the epoxy primer or polyurethane / epoxy primer Adisa the company AG, Urdorf, Switzerland, are used.

Recommended elastomer coatings of a 2-component polyurethane / polyol resin have the following material properties: <tables id="tabl0001" num="0001"><table frame="all"><tgroup cols="3" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="52.50mm" /><colspec colnum="2" colname="col2" colwidth="52.50mm" /><colspec colnum="3" colname="col3" colwidth="52.50mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="left">20 ° C</entry><entry namest="col3" nameend="col3" align="left">minus 20 ° C</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Tensile strength (MPa)¹⁾</entry><entry namest="col2" nameend="col2" align="left">10-12</entry><entry namest="col3" nameend="col3" align="left">25-30</entry></row><row><entry namest="col1" nameend="col1" align="left">Elongation at break (%)</entry><entry namest="col2" nameend="col2" align="left">ca. 300-380</entry><entry namest="col3" nameend="col3" align="left">ca. 220-310</entry></row><row><entry namest="col1" nameend="col1" align="left">(Tensile strength) shore A</entry><entry namest="col2" nameend="col2" align="left">80-85</entry><entry namest="col3" nameend="col3" /></row><row><entry namest="col1" nameend="col1" align="left">chemical resistance</entry><entry namest="col2" nameend="col2" align="left">Good</entry><entry namest="col3" nameend="col3" align="left">Good</entry></row></tbody></tgroup><tgroup cols="3" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="52.50mm" /><colspec colnum="2" colname="col2" colwidth="52.50mm" /><colspec colnum="3" colname="col3" colwidth="52.50mm" /><tbody valign="top"><row><entry namest="col1" nameend="col3" align="justify">¹⁾ (DIN 53455, 53504, 53430, 53571, 53354)</entry></row></tbody></tgroup></table></tables>

The preparation of a double-walled tank is as follows: First, the outside of the tank, usually gas- a steel tank, webs of preferably liquid or spacer sheets attached. For example, this can be done with the aid of double-sided tape strips which are previously glued at given intervals on the tank. Alternatively, the tank can also first be sprayed with a contact adhesive. The aluminum or cardboard foil webs are laid on the tank outer wall such that the edge portions of the film webs overlap. The Ueberlappungszonen are then preferably additionally with an adhesive tape, for example, aluminum tape, covered to prevent penetration of the sprayed resin mixture in the present between the spacer film and the inner tank wall cavity. Once the tank or parts thereof whole area occupied by spacer films multicomponent mixture can be sprayed.

As multicomponent mixture a reactive and fast hardening at room temperature polyurethane / polyol mixture is used preferably. Fast hardening mixtures contain polyisocyanates (for example, 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. Suitable diamines are aromatic diamines, urea or urea compounds are used.

solvent-free two-component systems are particularly advantageous to use the ratio of 1: 1 can be used. These are then immediately mixed and sprayed in the spray nozzle of a spray system. This process can also be automated. Due to the short curing time of rapidly reacting mixture of the tank can be practically tested immediately after its completion for leaks.

In a plate bearing test a maximum load of 20 kN (corresponding to a compressive stress of 2 N / mm2) was applied to a sample material by means of steel plates with a loading rate of 0.01 N / mm2 per second and record the load-path diagram. Following exposure, the studs were tested for deformation tracks. For review of the creep behavior of a load of 10 kN was applied and left on the sample for 3 hours in a further experiment. The increase of deformation was recorded.

The 100 x 100 mm large sample material consisted of a coated aluminum Adalastic® Noppenfolie. The three layers applied elastomer layer possessed a thickness between about 2.2 and 3.2 mm (measured on and between the studs).

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

In summary it can be noted that double skin tanks for the storage of petrol and oil with an outer wall of an elastomer with high tensile strength (elongation at break) and good tensile strength are much less prone to injury than known tanks with epoxy resin or polyester layers. It is also important that can be produced by spraying such elastomeric coatings using reactive, fast-curing multicomponent resins with the shortest possible gelling time in one operation. The elastomeric layer provides a very good electrical insulation of the metal tank shell (the inner tank wall) and simultaneously forms a durable, stable outer wall, which may have the necessary toughness without glass fabric or chopped fibers and substantially without fillers. It has been found that the achieved with the elastomer coating cathodic protection is much more reliable than that of epoxy or polyester coatings. An important advantage of the tank according to the invention is that the outer jacket can be prepared prior to the offsetting of the tank.