EP1993923B1 - Tank made of a corrosion-resistant composite - Google Patents

Abstract

The present invention relates to a tank that can be used for holding corrosive liquids, for example for the production of hot water, the wall of which is insensitive to chemical attack and more particularly to oxidation and to chlorine. The subject of the invention is a tank having a composite wall that comprises a steel outer shell, a metal or ceramic intermediate layer and an inner layer based on a thermoplastic polymeric compound. Advantageously, the polymeric compound includes polar groups of electronegative character. Such a composite wall may for example comprise a steel outer shell, an aluminium intermediate layer and an inner layer made of maleic anhydride-modified polypropylene. Also claimed is a process for manufacturing a composite-wall tank, called "rotocoating", which consists in depositing, by known techniques, a metal or ceramic coating on the inner face of a steel shell so as to form an intermediate layer and then in melting the polymeric powder compound in the metallized shell rotated by a biaxial rotation system until the formation of a continuous polymeric layer, which solidifies on cooling.

Description

The present invention belongs to the field of equipment intended to contain potentially corrosive fluids, especially intended for the production of hot water.

It relates to a vessel whose wall is made from a composite material comprising three associated layers, which ensures both the rigidity of the wall and its physical and chemical stability vis-à-vis a corrosive fluid or can be in certain conditions of use. Another object of the invention is a method of manufacturing such a composite wall.

The balloons used to supply hot water to individual or collective equipment are generally made from a steel shell, covered with a thermal insulating material. The internal surface must be treated to resist corrosion as the domestic hot water contains impurities and aggressive treatment products with respect to the steel, especially as the temperature is maintained at a high level to be distributed at 65 ° C. Not only does the installation deteriorate, which is a problem in itself, but also corrosion promotes biofouling by bacterial growth on the inner wall. It is obvious that the production of hot water, intended especially for food use, can not be subject to this kind of hazard.

To fight against corrosion, it is resorted to a treatment of depositing a protective material on the inner surface of the steel shell in contact with the liquid (see for example EP 0 143 731 ). The deposited material must be chosen so that its coefficient of expansion is close to that of the steel so that the protective layer remains integral with the steel shell during temperature variations of the system. It is for example known to project a molten metal material on the shell whose surface has previously been roughened. This technique, also known as "metallization" because of the addition of material in the form of fine vaporized and cooled metal droplets, is commonly used with aluminum, which also offers the advantage of cathodic protection of steel.

However, material projection techniques give porous surfaces, which still have some susceptibility to corrosion and biological fouling. Indeed, intragranular microcracks may form inside the deposited layer, and secondly, when the projections are made in the air, which is the least expensive method, the projected metal particles and the substrate. are subject to oxidation phenomena. This fragility, which remained marginal in the usual conditions of use, has now become a major disadvantage.

In recent years, hot water production facilities have been subjected to increased health constraints following the appearance of several cases of legionnaires' disease, particularly in collective accommodation establishments. Strict measures have been taken to ensure that the facilities are free from any germs, by performing a particularly powerful periodic preventive treatment. It consists in increasing for a few hours the concentration of chlorine and bringing the fluid to a temperature above 72 ° C, legionella resistant to temperatures close to 70 ° C. The combination of chlorine and heat is an effective treatment, but repeated monthly is aggressive for the cell walls and leads to accelerated degradation of facilities.

It was therefore necessary to provide a means for improving the resistance of the heating body to this increased corrosion. The solution provided by the present invention is to coat the inner face of the tanks with a corrosion-resistant material, such as a plastic material. The realization of this principle nevertheless raises a number of problems, related to the requirement of cohesion of this layer with the metal wall.

Indeed, the walls of the tanks are commonly made of steel, a material that provides the rigidity and the necessary mechanical strength at a moderate cost price. On the one hand, steel has no particular affinity for plastics, and on the other hand, it has a significant coefficient of expansion in the range of temperatures concerned, ranging from -20 ° C to 100 ° C during various handling, storage, transport and operation, while plastics have a very different coefficient of expansion. In tanks of large volume, the expansion can cause deviations of several millimeters, leading to the dissociation of the coating and the deterioration of the wall. It is therefore imperative to ensure a strong cohesion of the coating with the wall.

Surprisingly, it has been found that thermoplastic polymeric compounds can be used as anticorrosive inner lining of tanks, when they are applied to a metallized steel shell, i.e. the inner face of the shell has been spray-treated with a molten metal material, which has the effect of rendering the surface porous. The coating technique used is inspired by well-known rotational molding techniques and brings an unexpected result. Indeed, the thermoplastic properties of many polymers are known and implemented to achieve all kinds of objects, by different molding techniques, and among them rotomolding.

This plastics transformation process is carried out in three stages: filling of a mold with a thermoplastic polymer in the form of granules or of powder, melting of the plastic material, then solidification. During cooling, the molded object retracts and unstands itself from the mold. However, this phenomenon is totally contrary to the desired objective, which is to obtain a strong and durable adhesion of the plastic compound to the wall giving it its shape. Nevertheless, the pull-out tests that have been conducted by the inventors have shown that the coating carried out using the rotational molding technique of a thin layer of a thermoplastic polymer on a metallized surface, led to the desired result. . The wall obtained, object of the present invention, can be considered as a composite wall, and the new manufacturing process, also claimed as an object of the invention, can receive the name of "rotoenduction".

It has also been demonstrated that the use of a polymeric compound comprising polar groups of electronegative character further strengthens the cohesion of the composite obtained. Although extensive studies have not been done to explain this state of affairs, the hypothesis has been formulated that the metals used for the metallization of the shell being electropositive, they have a stronger affinity for compounds with groups bearing partial charges. ∂ ^- negative, with which they can form bonds of Van der Waals bonds type.

An object of the present invention is therefore to provide a tank useful for receiving corrosive liquids, for example for the production of hot water, the wall of which, while retaining its previous mechanical properties, is insensitive to chemical attack and more particularly to oxidation and chlorine. Another object of the invention is to provide a vessel whose wall is resistant to stress due to thermal expansion. Another object of the present invention is to provide a tank meeting the above requirements for periods of several years, and with a moderate manufacturing cost. Another object of the invention is to provide a method of manufacturing said tanks which is reliable and easy to implement.

Finally, in achieving these objectives, the present invention makes it possible to offer establishments such as hotels or hospital centers a means of distributing hot water in complete safety, without significant additional cost of equipment or operation.

More specifically, the present invention relates to a vessel for containing a corrosive fluid, original in that it has a composite wall comprising a shell outer steel, a metal or ceramic interlayer, and an inner layer of a thermoplastic polymeric compound.

The outer shell is the element ensuring the mechanical strength of the composite wall. It gives its shape to the tank and also serves as a support for other layers. It is commonly made of steel. It is possible to use, for example, non-alloyed hot-rolled structural steels that meet the standards in force. Its thickness is chosen according to the operating pressure and the diameter of the tank, in accordance with the pressure vessel code and / or the regulations in force in the country of use. It can thus be between 2 mm and 15 mm, more frequently between 4 mm and 8 mm. Manufacturers of heating equipment are familiar with these standards and the qualities of steel to implement.

Preferably, in order to achieve a good mechanical bonding of the intermediate layer, the surface of the part to be coated is previously prepared to remove oxides and calamines, increase its roughness and allow particles to anchor in the irregularities of the surface . Many processes are known to the professionals and can be validly implemented. For example, the method called impact treatment can be used. It consists in projecting a natural or artificial abrasive onto the surface to be treated. The projection can be done by compressed air, either by a vacuum system (suction, suction, Giffard effect), or by a direct pressure system (overpressure). Depending on the size of the abrasive particles we are talking about sanding (fine particles) or shot blasting (larger particles). Here again, since these techniques are commonly used in metallurgy, those skilled in the art are able to choose without difficulty the appropriate procedures. It is estimated that the depth of the roughness profile is between 5% and 25% of the thickness of the subsequent coating, with an optimum value around 25% which has the effect of increasing the contact area by a factor of 3 or 4.

Thus, in the tank according to the invention, the inner face of the steel shell advantageously has a roughness Ra corresponding to the mean arithmetic mean deviation from the mean line of the surface, between 10 μm and 35 μm, preferably from 10 μm to 35 μm. about 15 μm. It is completely covered by the intermediate layer which adheres to it by a mechanical phenomenon with a force which can vary from 20 to 115 MPa after sanding, according to the processes and the materials.

The intermediate layer of the wall according to the invention is a layer of metallic or ceramic nature. It can consist essentially of a metal chosen from aluminum, zinc, copper, tin, nickel, molibdenum, manganese, or an alloy based on metals selected from zinc, copper, nickel, tin.

According to another embodiment, the intermediate layer consists essentially of a ceramic chosen from nitrides such as NiAl, NiCrBSi, aluminides such as Al ₂ O ₃ , Al ₂ O ₃ -TiO ₂ , or oxides such as Cr ₂ O ₃ , ZrO ₂ -CaO.

It can be obtained by one of the thermal treatment techniques with material input available to those skilled in the art. For example, a treatment with a supply of reactive gas may be used. In this case, a substrate (here the steel shell) is superficially heated with a laser. The reactive chemical species (metal or ceramic to be supplied) are then adsorbed on the surface, dissociate and diffuse into the matrix of the solid or liquid phase substrate (laser-assisted thermodiffusion treatments), or accumulate and lead to the formation deposition on the surface (laser assisted chemical vapor deposition, or LCVD).

It is also possible to use a method of adding material by thermal spraying. In this case, the material to be deposited is in the form of powder, wire, cord or rod. It is melted totally or partially in a source of heat (flame, electric arc, plasma). A carrier gas allows spraying the material, and transporting the droplets thus formed to the surface to be coated on which they solidify. The surface of the substrate does not undergo any fusion.

The intermediate layer is porous, the porosity coming either from microcavities due to imperfect stacking of the droplets, or gas locked during solidification. The porosity rate varies according to the process and the materials used. Whatever the nature of the intermediate layer chosen, it advantageously has a porosity level of 0.1% to 25%, preferably between 5% and 10%.

The deposits include inclusions such as oxides or other materials from the torches themselves, unmelted or partially melted particles that have not undergone a complete heat cycle (because of their size or their heat source). Due to the very fast cooling rate of the particles in contact with the substrate, the presence of intragranular microcracks within the deposits is possible. Furthermore, since the projections are made in the air, the droplets and the substrate are subjected to the oxidation phenomenon. It is not uncommon to see an increase in the oxygen level during the projection. It should be emphasized here that the characteristics of the intermediate layer (metallic or ceramic) should have led the inventors to dismiss such a layer of the solution of the problem posed by the present invention. On the contrary, the invention has made it possible to use, in order to meet the desired objective of chemical stability with respect to corrosive fluids, its fixing properties of a polymeric coating.

According to a particular embodiment of the invention, the wall of the vessel may further comprise an underlayer hooking between the steel shell and the intermediate layer. Indeed, in some cases, especially for metallizations by projection of oxides, the roughness of the shell must be reinforced. An undercoating layer is then used, which can be made of different materials, among which mention may be made of nickel aluminide, molibdene, or alloys of the NiCr (80/20) or MCrAlY (M designating Ni) type. , Co or NiCo). It can be applied by any technique available to those skilled in the art, and advantageously according to the same technique as that used for the metallization of the steel shell.

The wall of the tank according to the present invention comprises a third layer, the innermost, intended to be in contact with a corrosive fluid and thus to protect the outermost layers of chemical attack. It is made of a thermoplastic polymer, that is to say softenable by heating and hardening by cooling without chemical reaction. There are many commercially available compounds available in various forms, for example in the form of powders or granules, which can be conveniently used in plastics processes.

They are often mixed with additives or technological aids, such as a load up to 40% by weight (talc or calcium carbonate for example), reinforcing additives, for example fiberglass or mica at 20 to 30% by weight.

Advantageously, for producing the inner layer of the vessel according to the invention, said polymeric compound comprises polar groups of electronegative character. It has indeed been observed that the choice of such polymers leads to an even stronger cohesion between the inner layer and the intermediate layer. These groups may be originally present in the chosen polymer or provided by a suitable chemical reaction, for example by functional grafting or by chemical modification of the polymer.

Whether it comprises polar groups or not, the polymeric compound used for the inner layer according to the invention may for example be selected from ethylene polymers, propylene polymers, fluorocarbon resins, polyoxymethylenes.

It is possible to use a polyethylene taken from the numerous types existing, for example from low density polyethylenes (or LDPE) having a density of between 0.92 g / cm ³ and 0.94 g / cm ³ , or from polyethylenes. high density (HDPE), having a density of between 0.95 g / cm ³ and 0.97 g / cm ³ . It is also possible to use polypropylenes, those used in the industry being almost always isotactic. They are often associated with a copolymer.

The fluorocarbon resins of formula [-CH ₂ -CF ₂ -] _n are also usable for producing the inner layer of the tank according to the invention. The main fluorocarbon resins are PTFE (polytetrafluoroethylene), FEP (fluorinated ethylene-propylene), PFA (perfluoroalkoxy), PVDF (polyfluorovinylidene), ETFE (modified copolymer of ethylene and tetrafluoroethylene) and ECTFE (ethylene / chlorotrifluoroethylene).

Also useful are the compounds of the family of polyoxymethylene (POM). They are technical thermoplastics which are distinguished by a high tensile strength, even at temperatures of -40 ° C, a Young's modulus of the order of 2800 to 3600 MPa, a very good dimensional stability when hot.

In the case where the polymer is not itself carrying electronegative groups, it is possible to associate such groups with any appropriate technique known to those skilled in the art. For example, polypropylenes grafted with acrylic acid, maleic anhydride or styrene, polypropylenes crosslinked with silanes can be used which are thus functionalized as required. This list is not exhaustive and concerns all thermoplastics, including graft thermoplastic sub-families.

According to an interesting embodiment, the polymeric compound is a diacid modified polymer. In particular, the polymeric compound may be a polypropylene modified with maleic anhydride. The insertion rate of the anhydride unit may be higher or lower. Preferably, according to the invention; the polymeric compound is a polypropylene modified with 5% to 50% maleic anhydride, in mole. So particularly preferred, the polymeric compound is a polypropylene modified with 20% maleic anhydride, in mole.

To fulfill its protective function satisfactorily, the intermediate layer must have a thickness of between a few microns and 200 microns. According to the preferred embodiment of the present invention, its thickness is about 120 microns.

In a particularly preferred manner, the tank according to the invention, intended to contain a corrosive fluid, has a composite wall comprising an outer steel shell, an aluminum intermediate layer and an inner layer of polypropylene modified with maleic anhydride.

The tank according to the invention can be manufactured by any known method for the deposition of metal or ceramic layers on the one hand and polymer on the other hand. However, a particularly suitable method has been developed for producing the composite wall as described above. In principle, it involves making the metal or ceramic deposition by the techniques commonly used for the manufacture of conventional metallized tanks, then to coat this surface by an original process, which we will call "rotoenduction".

• une étape de métallisation consistant à déposer un composé métallique ou céramique sur la face interne de ladite coque en acier, pour former ladite couche intermédiaire, et
• une étape d'enduction consistant à :
  • introduire un composé polymérique en poudre dans la coque métallisée fixée à un système de rotation biaxial,
  • mettre la coque métallisée contenant le composé polymérique en poudre en rotation biaxiale et chauffer à une température égale ou supérieure à la température de fusion du composé polymérique, jusqu'à formation d'une couche polymérique continue,
  • refroidir en poursuivant la rotation jusqu'à solidification de la couche polymérique.

More specifically, there is claimed a method of manufacturing a vessel for containing a corrosive fluid, said vessel having a composite wall comprising an outer shell of steel, a metal or ceramic interlayer and an inner layer of a polymeric compound thermoplastic process, which essentially comprises the following steps:

• a metallization step of depositing a metal or ceramic compound on the inner face of said steel shell, to form said intermediate layer, and
• a coating step consisting of:
  • introducing a powdery polymeric compound into the metallized shell attached to a biaxial rotation system,
  • placing the metallised shell containing the powdered polymeric compound in biaxial rotation and heating to a temperature equal to or greater than the melting temperature of the polymeric compound until a continuous polymeric layer is formed,
  • cool by continuing the rotation until solidification of the polymeric layer.

In the present application, the term "metallization" refers to the operation of depositing a metal or ceramic compound on the inner face of the steel shell, leading to the formation of the intermediate layer. By analogy, the term "metallized shell" means a steel tank whose inner face is covered with a metal or ceramic layer.

• soit i) d'un métal choisi parmi l'aluminium, le zinc, le cuivre, l'étain, le nickel, le molibdène, le manganèse;
• soit ii) d'un alliage à base de métaux choisis parmi le zinc, le cuivre, le nickel, l'étain;
• soit iii) d'une céramique choisie parmi NiAl, NiCrBSi, Al₂O₃-TiO₂, Al₂O₃, Cr₂O₃ , ZrO₂-CaO.

According to an interesting characteristic, in the process according to the invention, the intermediate layer is formed by thermal spraying

• i) a metal selected from aluminum, zinc, copper, tin, nickel, molibdenum, manganese;
• or ii) an alloy based on metals selected from zinc, copper, nickel, tin;
• or iii) a ceramic selected from NiAl, NiCrBSi, Al ₂ O ₃ -TiO ₂ , Al ₂ O ₃ , Cr ₂ O ₃ , ZrO ₂ -CaO.

As already indicated, the deposition of the intermediate layer on the steel shell can be achieved by a technique known per se. The flame-wire projection technique is preferred for the practice of the present invention. In this case, the flame serves to melt the supplied material, which is introduced in the form of wire, cord, or rod at its center. The filler material is then projected onto the surface of the shell by a stream of compressed air.

This operation is performed using a flame-wire projection gun. The wire drive can be driven by an automatically regulated electric motor, which allows a perfect regularity of wire feed. In a common manner, the particle velocity is about 150 m / s and the distance between the nozzle and the substrate is between 100 mm and 200 mm. The deposited thicknesses can range from a few tenths of a millimeter to a few millimeters, at very variable hourly rates depending on the materials, the wire diameters used, and the properties of deposits required: of 1 kg / h, for some ceramics prepared in the form of flexible cord or baguette, more than 30 kg / h for anticorrosive threads such as zinc.

This projection technique makes it possible to deposit all the materials mentioned above. Preferably, the intermediate layer is formed by aluminum projection according to the flame-wire technique.

According to an alternative embodiment of the method according to the invention, before the metallization step, the steel shell may be subjected to an impact treatment to increase its roughness. This treatment consists in projecting a natural or artificial abrasive onto the surface to be treated. The conditions of implementation are chosen easily by the person skilled in the art who already practices these techniques of sanding (fine particles) or blasting (larger particles).

According to another embodiment, before the metallization step, a sub-layer of attachment is applied to the shell. It can be carried out according to the same process as that used for the deposition of the intermediate layer, with different materials, among which mention may be made of nickel aluminide, molibdene, or alloys of the NiCr type (80/20). ) or MCrAIY (M denoting Ni, Co or NiCo).

Once the metallization is done, the third layer can be applied. This is to reproduce the inner shape of a cavity (the inner surface of the wall of the tank) which can range from one to 100,000 liters. For this, according to the invention, one proceeds in three phases, by analogy with discontinuous processes of plastics processing: filling the cavity, melting of the polymeric material, solidification of the polymeric material.

In a first step, after a possible preheating, the cavity is loaded with powder of polymer material, whose weight corresponds to that of the coating to be obtained. The tank is then closed and is rotated by a mechanical system that allows it to rotate about two axes oriented differently, generally perpendicular to each other.

The tank, rotating in all directions, is then heated to the temperature of good melting, the melting temperature of the thermoplastic polymers being generally between 150 ° C and 300 ° C. The molten plastic powder flows by gravity on the walls. The rotational speeds being low the effect of the centrifugal force is negligible. According to a particularly advantageous characteristic of the manufacturing process, the melting of the powdered polymeric compound is obtained by heating the metallized shell containing it by an external heating means. For example, the heat input is achieved by means of an oven, a gas ramp or infrared panels. Thus, the heated tank transmits its heat to the powder whose grains melt and stick on the wall. At the end of the heating period, the thermoplastic whose temperature is above its melting point has a viscous consistency. The device is removed from the oven and allowed to cool. Cooling can be accelerated by projecting fresh air and / or water mist onto the tank.

Different types of thermoplastic polymers can be used in the process as just described. Preferably, the polymers used in the process according to the invention are chosen from those which are implemented in the wall of the tank described above.

A particularly advantageous embodiment of the process according to the invention uses a powdered polymeric compound comprising polar groups of electronegative character.

Whether it comprises polar groups or not, the polymeric powder compound used in the process according to the invention may be chosen from ethylene polymers, propylene polymers, fluorocarbon resins, polyoxymethylenes. Preferably, said polymeric powder compound is a diacid modified polymer. More preferably, said polymeric powder compound is a polypropylene modified with maleic anhydride.

The tank as described and claimed in the present application may be manufactured by the method of the invention or by any other suitable method. It finds application in various industrial fields, such as the production of hot water, but also the industrial production of chemical or biological substances in reactors, or the road or rail transport of corrosive fluids. The fluids used in these applications may be at low, medium to high temperatures and may be more or less aggressive. The characteristics of the tank allow its use in all conditions without long term degradation.

Thus, another object of the present invention is a device for storing, transporting, storing or producing a corrosive fluid, comprising a composite wall vessel as described above. More particularly, is claimed a hot water production device comprising a composite wall vessel according to the invention.

EXAMPLE 1 Composite wall tank for the production of hot water

Other features and advantages of the invention will be better understood with the aid of the nonlimiting example below. It concerns the composite wall of a tank intended for the production of hot water and its method of manufacture.

This wall was made from a steel shell of unalloyed construction, complying with the European standard bearing the EN 10025: 1993 (symbolic designation: S235JR, numerical designation: 1.0037) and to the French standard N ° NF A 35-501 (designation: E 24-2), of thickness 3 mm, and forming a cylindrical tank with a volume of 50 liters.

The inner side has undergone impact treatment using a sandblaster equipped with a cylindrical nozzle projecting corundum with an air pressure of about 7 bars. The projection angle is practically tangential to the surface (30 to 40 degrees). The ambient temperature is at 20 ° C to avoid oxidation as much as possible. At the end of sanding, the inner face of the steel shell has a Ra roughness of 15 microns, which represents 25% of the thickness of the intermediate layer which will now be deposited.

The intermediate layer is high purity aluminum (99.9%). It is deposited by thermal spraying using the flame-wire technique. The spray gun used is automatically regulated. The lead feed is driven by an electric motor at a fixed speed of one meter per minute. For both bottoms, the layer is applied manually. In the shell, the movements of the spray gun are automated and regulated by sensors. The metallization is carried out at 20 ° C., in order to reduce the oxidation. The aluminum layer thus deposited has a thickness of 120 μm with a porosity of 8%.

The inner layer of the wall consists of a polypropylene modified with maleic anhydride. The degree of insertion of the anhydride unit is 20 mol%. The melting point is mp = 162 ° C. Such polypropylene modified with maleic anhydride is obtained by the known methods for producing the polymeric raw materials.

It was done in the following way. The tank is mounted on a mechanical system that allows it to rotate about two perpendicular axes. The whole is introduced into an oven and is preheated to 220 ° C for 20 minutes. Then 1.4 kg of modified polypropylene powder is introduced into the cavity of the tank and the tank is closed by quick couplings. It is set in motion and is maintained at a temperature of 220 ° C for 14 minutes. Then the device is removed from the oven and fresh air is projected onto the tank until the temperature reaches 50 ° C. Then cooling is continued to room temperature, at least two hours. The polymeric layer thus obtained has a constant thickness of about 120 microns over the entire internal surface of the vessel.

The composite wall has been subjected to various tests to evaluate its performance. It has been found on the one hand that during temperature variations, the layers remain united even though their coefficient of expansion is different. This result is assumed to be the intermediate layer absorbs the differential expansion between the materials of the outer and inner layers of the wall.

It has also been found that the polymeric layer is very strongly anchored to its substrate, as shown by the tests detailed in Example 2.

EXAMPLE 2 Pullout tests

The pullout tests were carried out using a traction machine specially designed for this purpose (shown in Figure 1 ) on specimens prepared with the materials described in Example 1 and under similar conditions.

Preparation of test pieces

Each test piece 1 consists of an aluminum metallized steel plate 2 covered with a layer 3 of polypropylene melt-modified in an oven at 220 ° C. When the polymer is melted, the specimen 1 is removed from the furnace and a second aluminum metallized steel plate 4 is deposited on its surface, identical to the previous one, and provided with a hook 5 placed perpendicularly to the plane of the test tube 1. Then the whole is put back into the oven for 14 minutes. After cooling, a sandwich structure is obtained with a polymeric layer 3 fixed to the two metal plates 2, 4. The lower plate 2 has a dimension of 200 mm × 100 mm, it is further provided with mass suspension means, by example of rings 6, while the upper plate 4 has a surface of only 50 mm x 50 mm. Their thickness is about 3 mm, as well as that of the polymeric layer.

Measuring the pulling force

The polymer layer 3 is sliced in its thickness around the upper plate 4, so as to laterally isolate a polymeric coating sample 7 of 50 mm side centered on the axis of the hook 5. The test piece 1 is suspended by the hook 5 and attaches loads to the rings 6, mass increasingly high (10 kg in 10 kg). The mass needed to take off the sample 7 from at least one of the plates 2 or 4 is thus measured in less than one minute and the corresponding force, expressed in daNcm ^{-2, is} calculated.

Test results

Five identical test pieces were prepared and subjected to the peel test. The results are shown in Table 1

According to the conventionally accepted conventions, it is considered that one material is secured to another when the tearing force necessary to separate them is greater than 0.8 MPa, ie 8 daNcm ^-2 , with an average value of about 38. daNcm ^-2 , we can say that the composite wall of the test pieces E1 to E5 has a very strong cohesion.

It should also be noted that the five repetitions give the same result (very low standard deviation), which indicates that the manufacturing process is reproducible and reliable and that it makes it possible to obtain a tank wall of constant quality. The fact that the tearing occurs as well on the lower and upper plate goes in the same direction. This is very important from the point of view of the homogeneity of the deposited coating and the longevity of the tanks. TABLE 1 test tube pulling force (daNcm ^-1 ) E1 37 E2 38.2 E3 38.6 E4 38 E5 39 Average 38.2 Type Difference 0.67

Claims (25)

1. Tank intended to contain a corrosive fluid, characterised in that it has a composite wall comprising an external shell made of steel, an intermediate metallic or ceramic layer and an internal layer based on a thermoplastic polymeric compound in direct contact with the intermediate layer.
2. Tank according to claim 1, characterised in that the internal layer essentially comprises a polymeric compound including polar groups of an electronegative character.
3. Tank according to claim 1 or 2, characterised in that the polymeric compound is chosen from ethylene polymers, propylene polymers, fluorocarbonated resins, polyoxymethylenes.
4. Tank according to claim 2, characterised in that the polymeric compound is a polymer modified by a diacid.
5. Tank according to claim 4, characterised in that the polymeric compound is a polypropylene modified by maleic anhydride.
6. Tank according to the preceding claim, characterised in that the polymeric compound is a polypropylene modified by 5% to 50% of maleic anhydride by mol.
7. Tank according to the preceding claim, characterised in that the polymeric compound is a polypropylene modified by 20% of maleic anhydride by mol.
8. Tank according to one of the claims 1 to 7, characterised in that the intermediate layer is formed essentially from a metal chosen from aluminium, zinc, copper, tin, nickel, molybdenum, manganese or an alloy based on metals chosen from zinc, copper, nickel, tin.
9. Tank according to one of the claims 1 to 7, characterised in that the intermediate layer is formed essentially from a ceramic chosen from NiAl, NiCrBSi, Al₂O₃, Al₂O₃-TiO₂, Cr₂O₃, ZrO₂-CaO.
10. Tank according to one of the claims 8 or 9, characterised in that the intermediate layer has a porosity ratio of 0.1% to 25%, preferably of 5% to 10%.
11. Tank according to any of the preceding claims, characterised in that the interior face of the steel shell has a roughness between 10 and 35 µm, preferably 15 µm.
12. Tank according to one of the preceding claims, characterised in that it comprises a sub-layer for bonding between the steel shell and the intermediate layer.
13. Tank intended to contain an aqueous fluid according to claim 1, characterised in that it has a composite wall comprising an external shell made of steel, an intermediate layer made of aluminium and an internal layer made of polypropylene modified by maleic anhydride.
14. Method for manufacturing a tank intended to contain a corrosive fluid, having a composite wall comprising an external shell made of steel, an intermediate metallic or ceramic layer and an internal layer based on a thermoplastic polymeric compound, characterised in that it essentially comprises the following steps in succession:

    - a metallisation step consisting in depositing a metallic or ceramic compound on the internal face of said steel shell in order to form said intermediate layer, and

    - a coating step consisting in

    - introducing a polymeric compound made of powder into the metallised shell fixed to a biaxial system of rotation,

    - setting the metallised shell containing the polymeric compound made of powder into biaxial rotation and heating to a temperature equal to or greater than the melting temperature of the polymeric compound until a continuous polymeric layer is formed,

    - cooling whilst continuing the rotation until the polymeric layer solidifies.
15. Method according to claim 14, characterised in that the intermediate layer is formed by thermal projection i) of a metal chosen from aluminium, zinc, copper, tin, nickel, molybdenum, manganese; or ii) of an alloy based on metals chosen from zinc, copper, nickel, tin; or iii) of a ceramic chosen from NiAl, NiCrBSi, Al₂O₃-TiO₂, Al₂O₃, Cr₂O₃, ZrO₂-CaO.
16. Method according to claim 15, characterised in that the intermediate layer is formed by projection of aluminium according to the flame-wire technique.
17. Method according to any of the claims 14 to 16, characterised in that, before the metallisation step, the steel shell is subjected to treatment by impact in order to increase the roughness thereof.
18. Method according to one of the claims 14 to 17, characterised in that , before the metallisation step, a bonding sub-layer is applied on the shell.
19. Method according to one of the claims 14 to 18, characterised in that the fusion of the polymeric compound made of powder is obtained by heating the metallised shell which contains it by an external heating means.
20. Method according to one of the claims 14 to 19, characterised in that said polymeric compound made of powder includes polar groups of an electronegative character.
21. Method according to one of the claims 14 to 20, characterised in that said polymeric compound made of powder is chosen from ethylene polymers, propylene polymers, fluorocarbonated resins, polyoxymethylenes.
22. Method according to claim 14 to 20, characterised in that said polymeric compound made of powder is a polymer modified by a diacid.
23. Method according to the preceding claim, characterised in that said polymeric compound made of powder is a polypropylene modified by maleic anhydride.
24. Device intended for storing, transporting, stockpiling or producing a corrosive fluid, characterised in that it comprises a tank according to one of the claims 1 to 13.
25. Device for the production of hot water, comprising a tank according to one of the claims 1 to 13.

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