WO1981002562A1 - Double walled storage tank provided with an internal shell of plastic material - Google Patents

Abstract

The storing tank, is particularly for fluids exposed to the action of water, such as oil and petrol, has an internal shell (2) of a plastic material. The material used for the internal shell is a glass fiber reinforced polyester. The polyester is however not chemically stable with respect to mixtures of petrol and alcohol, respectively petrol and methanol. In this case stable materials are more expensive than polyester, therefore, for economic reasons, only a layer of the internal shell is made of a stable material. In order to make the layer controlable with respect to its porosity and thickness, by using the electric penetration test, it is proposed, that the internal shell (2), at least on the innermost side, should by provided with a layer (4) of an electrically insulating material also chemically stable with respect to the action of the stored product and that the upper surface of the shell adjacent to the layer should be electrically conductive.

Description

 Double-walled storage tank with an inner jacket made of plastic

It is known sigkeit.en storage tanks for water polluting liquid-, such as heating oil and gasoline, reindeer double auszufüh¬, wherein the outer jacket, for example made of concrete or metal and often only later attached to inner shell for example from glass fiber-reinforced ^'plastic. In the self-contained cavity between the two container walls there is usually a test medium serving for leak warning, for example a liquid or a gas kept under positive or negative pressure.

In the most common embodiment, the inner jacket is made of glass fiber reinforced polyester. However, there are storage liquids against which polyester is not chemically resistant. For example, certain amounts of alcohol or methanol have been added to gasoline for several years. Such a mixture can soften and destroy the inner jacket made of polyester.

In order to remedy this disadvantage, it is obvious to use a material that is resistant to storage for the inner jacket instead of polyester, in the case of petrol with an additive as storage, for example, an epoxy resin. Since epoxy resin is considerably more expensive than polyester, however, a solution will be sought, particularly in the case of a self-supporting, therefore relatively thick-walled inner jacket, in which only the surface of the inner jacket on the stored product side is resistant to stored goods. In the example mentioned, an inner jacket consisting mainly of polyester could be lined with an epoxy resin covering. However, this measure alone is insufficient. The covering made of material resistant to stored goods must have a minimum layer thickness and be free of pores, and it must be possible to test these properties of the covering on the finished storage tank in a simple and reliable manner. It is known to subject container walls made of plastic to an electrical breakdown test for this purpose. With this procedure, even the smallest leaks can be found. The electrical breakdown test is handled in such a way that the plastic sheath to be tested is scanned with an electrode which is under high voltage (for example a metal broom). For this purpose, however, a counterelectrode is required on the back of the plastic jacket, and since the level of the test voltage is matched to the normal thickness of the plastic jacket, so that there is a breakdown in the event of a leaky or abnormal, thin area of the plastic jacket this counter electrode should lie on the back of the plastic jacket without any space. If such an undesirable intermediate space is present, the breakdown voltage may increase so much that the test voltage is no longer sufficient to cause an electrical breakdown at the location of a leak. A metal container wall is therefore not suitable as a counterelectrode if the plastic jacket is arranged at a distance from the metal container wall in order to achieve a cavity for the above-mentioned purpose. The same problem arises when testing a plastic covering applied to an electrically non-conductive plastic base using the method mentioned.

The invention now relates to a double-walled storage tank with an inner jacket made of plastic, in which the difficulties mentioned are eliminated in that According to the invention, the inner jacket is provided at least on the inside with a cover layer made of a material which is chemically resistant to the action of the stored goods and is not electrically conductive, and that the surface of the inner jacket adjacent to the cover layer is electrically conductive.

Some exemplary embodiments of the invention are explained in more detail below with reference to the drawing. 1 to 4 of the drawing each show a partial cross section of the wall of a double-walled storage tank, which has an outer jacket 1 made of steel, an inner jacket -2 made of plastic, with spacer cams 3, and one on the inside of the inner jacket 2 Cover layer 4 made of a chemically resistant to the action of the stored goods, electrically non-conductive material. The surface of the inner jacket 2 adjoining the corner layer 4 is electrically conductive, so that the top layer 4 can be checked in a known manner for freedom from pores and layer thickness using electrical high voltage and suitable measuring instruments.

The electrical conductivity on the inner surface on the back of the storage-resistant cover layer 4 can be achieved in various ways.

1, the inner jacket 2, which essentially consists, for example, of fiberglass-reinforced polyester, has an electrically conductive plastic layer 5 on the inside, which can be sprayed on or rolled on, for example. Electrically conductive plastic in the form suitable for the processing mentioned is known per se. Then the cover layer 4, which is resistant to stored goods, is applied to the electrically conductive plastic layer 5 with a layer thickness of, for example, 0.5 to 0.7 mm. Suitable epoxy resins are available for a top layer that is resistant to petrol with the addition of alcohol or methanol. The coating of the inner jacket 2 can be carried out both before and after it is installed in the outer tank 1 of the storage tank.

In the embodiment according to FIG. 2, an electrically conductive plastic is itself used for the inner jacket 2, so that the additional application of a layer (5 in FIG. 1) made of conductive plastic can be omitted.

According to FIG. 3, there is also the possibility of producing the inner shell 2 during its manufacture, i.e. in the wet or sticky state, to be coated with an electrically conductive layer 6 on its surface on the side of the goods to be stored

'see, i.e. only use layer-by-layer conductive plastic or electrically conductive particles, e.g. Incorporate graphite or metal powder or semolina into the non-conductive material of the inner shell 2 on its inner surface. The top layer 4, which is stable in storage, is again located above this.

A further embodiment for particularly stringent requirements is shown in FIG. 4. The inner shell 2 consists of glass-fiber reinforced plastic in the supporting part, e.g. Polyester, and has a storage-resistant cover layer 4 and 7 both on the inside and on the outside. This measure has the advantage that the inner casing 2 cannot be chemically destroyed from the outside by the stored goods in the event of any leaks. The surfaces of the inner casing 2 adjoining the cover layers 4 and 7 can be made electrically conductive in one or other of the described ways.

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Claims

 Claim Double-walled storage tank with an inner jacket made of plastic, characterized in that the inner jacket (2) is provided at least on the inside with a cover layer (4) made of an electrically non-conductive material that is chemically resistant to the action of the stored goods, and that the Cover layer adjacent surface of the inner jacket (2) is electrically conductive.