HU205436B - Method for providing steel tube and steel pipelines by anti-corrosive coating - Google Patents

Abstract

The present invention relates to a method for supplying steel tubes and steel pipes with a corrosion protection coating. In the process, plastic-based layers are applied to the surface of the steel tube (1) by lubrication and / or spraying, which are left to cure or cure. The essence of the process is that a primer layer (21) made of two-component water-soluble epoxy resin, cement and water is deposited on the surface of the steel tube (1) as a bottom layer and, after at least partial curing, is a mixture of a two-component, aromatic and epoxy diluent. a first intermediate layer (22) is provided. A second intermediate layer (23) consisting of a mixture of two-component tar-epoxy resin, cement and epoxy diluent, containing a two-component aromatic ring (s), is applied to the first intermediate layer (22) and at least partially cured. a topcoat (24) made of a mixture of two-component tar epoxy resin and diluent is applied. (Figure 2) Figure 2 EN 205 436 B Scope of the description:! ® page (including 3 sheets)

Description

Scope of the description: !!) page (including 3 tabs)

Figure 2

EN 205436 Β

Drinking water pipelines worldwide are mainly made of pipes made of one of the following materials: cast iron, steel of normal strength, reinforced concrete with reinforced concrete, asbestos cement (eternite), plastic. Each material has both advantageous and disadvantageous properties. Cast iron pipes are highly corrosion resistant, but extremely expensive. Steel tubes with abnormal strength can have a smaller wall thickness than cast iron pipes, but have low corrosion resistance. Prestressed reinforced concrete pipes are quite expensive, but their corrosion resistance is limited. Corrosion resistance of asbestos cement pipes is good, but their strength is relatively low, and the diameter of the tubes made of such material can be relatively small, but it would not be economical to make large diameter tubes from eternite. Finally, the corrosion resistance of the various plastic tubes is satisfactory, but their strength is low and their diameter is limited. Regardless of what pipes are made of pipe material, connecting adjacent pipe elements to each other is a delicate operation, requiring very careful work.

Attempts are made to attempt to increase the corrosion resistance of the pipe by applying a coating to the surface of the pipe members. For example, British Patent No. 2137 304 discloses a polyethylene layer applied to a metal tube and solid particles, e.g. sand grains are embedded. Pipes of such roughened pipes are designed to be laid on the seabed, and the roughened surface is intended to prevent pipeline slipping.

A pipeline having a corrosion-resistant plastic layer in addition to its steel tubes is applied to the U.S. Patent Application Publication No. 36 07 459, which, on the other hand, is coated with a concrete or mortar to enhance the safety against mechanical damage. In accordance with European Patent Application Publication No. 0183930, a resin layer curing to the tubes is applied, a hot melt adhesive and a thermoplastic plastic layer. The latter method is extremely costly and cumbersome due to the materials used and the method of application, whereas in the above-mentioned two embodiments, the coating does not provide adequate corrosion protection and, on the other hand, its applicability is limited and coatings are difficult and time consuming to produce.

It is also common to use plastic foil winding and plastic powder melting to form the steel corrosion-resistant coating, but these solutions are also difficult and do not always provide durable and adequate protection.

The purpose of the invention is to provide a method for supplying pipes, particularly drinking water lines, with a corrosion-resistant coating, which allows the most important requirements for such conductors2 to be minimized (namely, the maximum strength, the extension of size to larger diameters, the effective corrosion protection, the precision). , reliable joint end connections, favorable internal friction coefficient).

It is also an object of the invention to allow many elements of conventional piping technology to be retained unchanged while reducing the amount of work to be carried out on site and concentrating it on one site. In addition, it is a requirement that most of the workflows can be carried out in a well-controlled and accurate manner on site or in a confined space.

The invention is based on the discovery that the use of a steel tube of sufficient strength to absorb the stress of low wall thickness, but of internal water pressure or external permanent and potential loads, which is capable of being permanently and efficiently protected against corrosion outside a properly selected multilayer plastic coating, is the basic element. Corrosion and abrasion resistance can be achieved by applying cementitious mortar up to the surface surface, and this layer can provide a pleasant degree of friction.

In addition, the invention is based on the recognition that, by lubrication and spraying, i.e. by eliminating heat transfer or winding, the layers can be applied to the outer surface of the tubes in the fastest and fastest way, in the covered work area near the installation site. It is further recognized that the multilayer outer coating provides optimum and durable corrosion protection when these layers work perfectly together, have excellent adhesion, and with sufficient stiffness and waterproofing, the coating is sufficiently flexible to be resistant to moisture to microorganisms. This latter property is recognized by the tar content; the rigidity of the cement filling gives the dampness the dilution, and the adhesion and elasticity can be ensured with epoxy-polyamide-based materials.

Based on the above findings, the object of the present invention has been solved by a method of applying plastic-based layers to the surface of the steel tube by lubrication and / or spraying, which are cured and / or cured and characterized by the fact that it is applied to the surface of the steel tube. as a lower layer, a two-component water-soluble epoxy resin, a cement and water primer layer, and, after at least partial curing, a first intermediate layer of an epoxy diluent mixture comprising a two-component aromatic silicon (s) also having an epoxy diluent; applying a second intermediate layer of a mixture of two-component tar-epoxy resin, cement and epoxy diluent containing a two-component aromatic silicone (s) to the first intermediate layer after at least partial curing, and at least partial curing thereof

After application, a top coat of a mixture of two-component tar epoxy resin and diluent is applied.

The present invention also relates to a method of providing a steel pipe conduit with a corrosion protection coating, wherein a cement mortar layer is applied to the inner surface of the steel tubes, and plastic-based layers are applied to the outer surface by lubrication and / or spraying which are cured or cured. and characterized in that a cement mortar layer is applied to the inner surface of the individual steel tubes at a thickness of 1-3 mm, leaving a section free from the pipe ends; on the outer surface of the same steel tubes, also leaving sections free from the pipe ends inwardly, adjacent steel tubes are welded together at their ends, and the outer protective coating layers at the welding sites are also coated with strips of the same material as the material, and the cement mortar layer used as the inner coating. sealed with a band of the same material or substantially the same material.

In a preferred embodiment of the process, the base layer material is 0.24-0.31 parts by weight of a resin component; 0.32-0.38 parts by weight of resin component B (crosslinker); 0.24-0.31 parts by weight of cement and 25-35% by volume of the listed ingredients are produced by mixing and the mixture is applied at a thickness of 70-110 pm to the surface of the steel tube. Such resins are commercially available e.g. It is known as "EPORESIT Akva 41A + B". Preferably, pc 350 quality Portland cement and tap water are used to prepare the mixture.

In another preferred embodiment of the process, the material of the first intermediate layer is from 0.45 to 0.55 parts by weight of resin component, 0.55 to 0.45 parts by weight of resin component B (crosslinker), and 8 to 12% by volume of these two components. and mixing the mixture with 80-130 µm thickness on the surface of the primer layer. Such a resin is known in the trade as, for example, "KATESIL A + B", and a "KATESIL" diluent is used for this purpose.

• In another embodiment, the material of the second intermediate layer is 0.32 to 0.36 parts by weight of resin component A, 0.32 to 0.36 parts of resin component B (crosslinker); 0.36-0.28 parts by weight of cement and the amount of epoxy thinner containing 5-10% by weight of the listed ingredients are prepared and applied to the surface of the first intermediate layer at a thickness of 270-300. In this case, it is also possible to use “KATESIL A + B product and“ KATESIL ”thinner and pc 350 portland cement.

According to another aspect of the invention, the topsheet material comprises 0.45-0.55 parts by weight of resin component, 0.55-0.45 parts by weight of resin component B (cross-linking agent) and 2 to 5% by weight of the total of the two components. by mixing the epoxy diluent and applying the mixture at a thickness of 70-110 pm to the surface of the second intermediate layer. Such a resin is known in the trade as "KATEPOX A + B", and "KATEPOX thinner can be used to make the mixture."

In addition, the cement mortar layer applied as an internal coating at a high pressure of 1-3 cm is used primarily in cases where the water to be transported is not completely cleaned for some reason in the water supply site (ie, water does not pass through all mechanical, organic and chemical cleaning operations) ; and therefore the pipeline can be subjected to wear and tear on the inside, algae formation, corpus cavities and corrosion. Such problems may arise, for example, when transporting raw water or sea water.

Finally, it is also advantageous for the method to be carried out in such a way that the coating layers terminating at the welds on both sides of the weld seam at the welded sites of the steel tubes are sealed with strips of the same material as the material and the top strip, which closes the adjacent tops. a layer of 500-700 µm thick overlapping with adjacent topsheets is applied to the layer by lubrication and / or spray, which is 0.35 to 0.45 parts by weight of component B (cross-linker) of 0.35 to 0.45 parts by weight of the two-component tar epoxy resin. By mixing 0.3-0.1 parts by weight of a fine washed sand of 0.1 to 1 mm in size and an amount of epoxy diluent in an amount of 8-12% by weight of these components. In this case, it is also advisable to use "KATESIL A + B resin and" KATESIL "thinner. Such an arrangement of the connection of adjacent tubular elements enables continuous pipeline construction, i.e. when the present invention refers to the corrosion protection of a steel tube, the term "steel pipe" is to be interpreted as not limiting the length of the pipe, so that the protection requirement extends to the entire wire system.

The invention will now be described in more detail with reference to the accompanying drawings, which include a corrosion-protected tube or pipe connection solution according to the invention, and a possible way of pipe construction from such pipes. the inner and outer surfaces are covered with corrosion protection;

Figure 2 shows a steel section in a longitudinal section. the invention comprises a layer of outer corrosion resistant coating;

Figure 3 is a longitudinal sectional view of an inner corrosion protection coating on a steel tube;

Figure 4 is a cross-sectional view of how the continuity of the inner and outer corrosion protection coatings can be ensured by connecting the adjacent steel tubes to each other;

Figure 5 is a cross-sectional view of a tube 3 with corrosion protection coatings according to the invention

EN 205436 Β phases of pipeline construction in crushed workshops;

Fig. 6 shows the most important phases of the pipeline construction of Fig. 5 in a smaller-scale longitudinal section.

As shown in Fig. 1, the longitudinal geometric center axis 1 of steel X (which is generally of normal strength, large diameter, spiral welded steel tube) is a 2-outer coating of corrosion protection and also has a corrosion protection 3 inner coating. The required (minimum) thickness of the steel tube 1 shall be determined on the basis of forceful calculations taking into account internal and external stresses; this pipe wall thickness is generally between 1022 mm and the diameter of the medium to be transported, primarily from the amount of water, in the size range of 6001000 mm. The length of each piece of pipe is limited by the installation and delivery options; this value is usually between 4.0 and 12.0 m. 1-3. Fig. 3 shows that a tubing is usually made of groundwater.

THE 2. Fig. 2 is an exterior coating 2 shown in the present invention, extending from the inside out from the base layer 21 directly on the outer surface of the steel tube 1; the first intermediate layer 22 applied thereto; the second intermediate layer 23 (i.e., the first and second coating layers); ultimately, the topsheet 24 is formed. The total thickness Vj of the outer coating 2 (Figure 2) is about 0.50.7 mm. In particular, the layer thickness of the primer 21 formed by a two-component mixture of water-soluble epoxy resin and cement is 70-110 µm; a thickness of the first intermediate layer 22 made from a mixture of tar epoxy resin and diluent containing two-component aromatic silicones; the second intermediate layer 23 has a thickness of 270-350 µm; the thickness of the topsheet 24 may be from 70 to 110 µm. The latter is a mixture of two-component tar epoxy and diluent, while the second intermediate layer 23 is composed of a mixture of two-component tar-epoxy, cement and diluent containing aromatic silicones.

THE 2. Figure 1 shows that at the end and end of the steel tube 1 there are no outer coatings on the length _{t t} ; the value of the hj is preferably about 10 cm.

The material of the corrosion protection 3 inner coating shown in Figures 1 and 3 is cementitious mortar v ₂ thickness applied to the inner surface of the steel tube 1, which is made in a manner known per se (DRV - TATÉ tube liner method). The value of v ₂ is 1-3 cm, and the free length of free surface h ₂ at the ends and ends of the steel tube 1 is approx. 15 cm. This inner coating 3 provides an internal corrosion protection of the steel pipe 1, and maintains the level of internal friction of the wire at a low, low level.

The application of 2 outer coatings and 3 inner coatings of steel pipes of 4 to 12 m length 1 can be carried out in a covered work area near the installation site so that after the surfaces of the steel tubes 1 have been properly cleaned, the inner mortar 3 of cement mortar is first formed at the pipe ends ah ₂ after leaving the length sections (Fig. 3), and after sufficient resting (for at least partial binding of the cement), the layers of the outer coating 2 (Fig. 2) are applied in the manner described in detail later on, at the end of the pipe, the lengths of the length are free. leaving. Of course, there is sufficient time for curing the resins between the waxing and spraying operations of each plastic layer. Air temperatures above 20 'C are recommended for lubrication work.

The construction of the pipe itself, made of corrosion-resistant pipes as described above, is essentially the same as that of the conventional pipe construction method, depending on the respective ground conditions and / or laying depth, and in the appropriate bedding of the pipes as shown in Figures 5 and 6. Figs. The following aspects should be taken into account in the construction of the pipeline: the minimum number of on-site (trench) welding pipe connections required to produce relatively long (4,012,0 m) pipes at the installed (workshop-like) workplace; in stacked workpieces, the possibility of securing a safety clamp at a suitable length to allow the pipe members to be discharged into the ditch can be executed accurately; the joints and attachability of the ends of two corrosion-protected adjacent tubular members must be provided with an accuracy of at least 12 mm; finally, a work space of sufficient size (min. 80 x 40 cm) can be formed underneath the wire and on two sides for the welding of the matching pipe ends. 5 and 6, the workpiece is designated by reference numeral 4; In the construction phase of Fig. 6, when p is externally inserted into the ditch 4 by means of a crane (not shown) (the crane hook is cranked).

Fig. 6 is a reference numeral 7), the clips 5 shown in Fig. 5 are removed from the trench 4. In the phase shown in Figure 6, there were already 9 landings in the 6 pipe sections. The above-mentioned work spaces 8 provide sufficient space at both the depth and side of the welded joints to perform the work necessary to ensure the continuity of the welding and corrosion protection layers, which are illustrated in FIG.

A4. Figure 2 shows the connection between the two adjacent tube members 6 by first welding the two steel tubes 1; the weld seam is designated by reference numeral 11. All welding seam - is

EN 205436 Β can be welded v-seam depending on the wall thickness of steel pipes, or x-seam on two sides. Subsequently, after grinding the surface of the all-weld seam and clearing the bare sections of the bare pipe length, the primer layers 21 of the outer coating 2, the first intermediate layer 22, the second intermediate layer 23, and finally the topsheet 24 are sealed; these subsequently applied layers are indicated by 40 reference numerals in Figure 4 together. Then, overlapping layer H ₃ (about 10-10 cm) extending over both lengths H ₃ (about 10 to 10 cm) over a length of about 40 cm can be applied only over H j = 2 h. This barrier layer 25 is formed from a material corresponding to the material of the first intermediate layer 22, which, however, also contains sanded sand of a particle size of 0.1 to 1.0 mm.

In the final step, the first coatings 3 are sealed to a strip of width H _{2 to 2} h ₂ (about 30 cm) by applying a layer of cement mortar 31, of course after thorough cleaning of the steel surface.

After the pipeline is partly or fully completed, the landfill is carried out in the ditch. This operation should be performed with particular care and caution, since the plastic outer coating 2 should not be damaged.

The invention will now be described in more detail by way of examples.

Example 1

Drinking water pipelines are made of corrosion-resistant, 800 mm diameter, 16 mm thick, normal strength spiral welded steel tubes according to the invention.

On the outer surface of the steel tubes, the plastic corrosion protection layer is shaped at a workshop-like workplace near the construction site as follows:

the outer surface of the steel tubes is made to have K ₂ and K ₃ , respectively, and T-0 clean, stainless, grease-free and oil-free.

Apply a mixture of two-component water-soluble epoxy resin and cement to a 80 µm layer thickness on the prepared surface. The mixture is prepared according to the following formula:.

EporesitAkva 41 ”Component A is 1 part by weight .—— S — 1,5 -“ - cement (350 pc) 1 - “water (tap water) 30 volume% (Water represents 30% of the total volume of the first three components). ), after a waiting time of one hour, the primer layer is completely cured and the first intermediate (overlay) layer prepared on the basis of the following recipe is applied to this layer in a thickness of 100 [mu] m (a mixture of tar epoxy and thinner containing two component aromatic silicones):

KATESIL ”The component is 1 part by weight

Katesil Diluent 10% by volume (The amount of diluent should be projected to the sum of "KATESIL Components A and B.) After one hour wait, apply (also with lubrication) to the cured first intermediate layer the second intermediate coating layer, which is a tar with two component aromatic silicones. a mixture of epoxy resin and cement and thinner. This second intermediate layer is made of 300 pjn (0.3 mm) layer thickness according to the following formula: KATESIL ”Component 1 1 part by weight

KATESIL ”Component B 1 part by weight (350 pc) 1 part by weight

KATESIL ”Thinner 5% by volume (the amount of diluent is calculated as the total amount of the first component).

After the second intermediate layer is applied, it is waited for 60 hours and then the overcoat is applied, which is made of a two-component mixture of tar epoxy and diluent at 80 µm (0.08 mm) thickness according to the following recipe:

KATEPOX The component is 1 part by weight

KATEPOX ”Component B 1 part by weight

KATEPOX Diluent 2% by volume (in this case the amount of diluent should also be projected to the sum of the two 'KATEPOX' components).

After an hour as described above, tubes with an external corrosion coating as described above can be lowered into the workpieces where the ends of adjacent steel tubes are welded together. In the vicinity of the weld seam, the wire surface is perfectly cleaned, and the plastic layers of the outer protective coating are then sealed with strips of their own material. Apply a 600 µm sealing layer to the top layer, which also overlaps the coatings applied to the adjacent tubes and is made according to the following recipe:

KATESIL ”The component is 0.4 parts by weight

KATESIL ”Component B (crosslinker) 0.4 parts by weight

Fine washed sand with a mesh size of 0.1 to 1.0 mm is 0.2 parts by weight

KATESIL ”Thinner 10% by volume (the amount of thinner must be projected to the sum of the three components above).

In the manner described above, the connections of adjacent steel pipes are formed, and the wire is continuously constructed

Example 2

All of this is carried out as described in Example 1, except that a 2 cm thick cement mortar layer is applied on the inner surface of the tubes under high pressure. Such layers of adjacent steel tubes are bonded by applying a cement mortar band after being welded together, and thereby bel5

EN 205436 ő a high corrosion protection coating is made continuous.

The beneficial effects of the invention can be summarized as follows:

By providing a durable and safe solution to the external corrosion protection of steel pipes, the invention makes it possible to use a pre-tubular type which is economically advantageous. The effectiveness of corrosion protection is achieved by the layered structure of the present invention: the plastic layers which are friendly to each other and neutral in their effect are more resistant to bacteria; the entire outer coating is highly resistant to both alkaline and acidic groundwater and soils; the adhesion of the individual layers to each other is impeccable, there is no "loosening" that usually occurs during foil corrosion protection; cement and forehead components provide increased resistance to mechanical effects. Repairing any possible damage at the installation site can be done quickly and easily. The application of coating layers can also be carried out very simply, with minimal mechanization (spraying equipment and low-power compressor), no need for eg. for use in high-volume and expensive winding and lifting machines and equipment.

It is also an advantage that many details of a long-lasting and practiced construction process can be retained during pipeline construction; in addition, work on the site is partially reduced or restricted to a single location, and most of the workflows can be performed on site, or in a confined space, in a well-controlled, accurate and high-quality manner. Pipeline construction can be strip-like, and can be transported to the site and placed on the schedule sheet for each (already corrosion-resistant) pipe element.

The invention is, of course, not limited to the exemplary implementation of the method, but can be implemented in a variety of ways within the scope defined by the claims.

Claims (6)

Figure 1 To that EN 205 436 Β A method of supplying a steel tube with a corrosion protection coating, comprising applying plastic-based layers to the surface of a steel tube by lubrication and / or spraying, which are cured or cured, characterized in that the steel tube (1) has a two-component water-soluble epoxy in the lower layer. a first intermediate layer (22) consisting of a mixture of a two-component, epoxy resin and an epoxy diluent containing at least a partial hardening of the two-component aromatic silicone (s), made of resin, cement and water; applying a second intermediate layer (23) of a mixture of two-component tar epoxy resin, cement and epoxy thinner containing at least partial curing to the first intermediate layer (22) after at least partial curing, and at least partially curing thereof a topcoat (24) made of a mixture of two-component tar epoxy resin and diluent is applied. A method according to claim 1, characterized in that the material of the primer layer (21) is 0.24 to 0.31 parts by weight of resin component A; 0.32-0.38 parts by weight of resin component B (crosslinker); 0.24-0.31 parts by weight of cement and 25-35% by volume of the listed ingredients are prepared by mixing and the mixture is applied at a thickness of 70-110 pm to the surface of the steel tube (1). Method according to claim 1 or 2, characterized in that the material of the first intermediate layer (22) is 0.45-0.55 parts by weight of the resin component, 0.55-0.45 parts by weight of resin component (crosslinking agent) and mixing these two components with 8-12% by volume of water and applying the mixture at a thickness of 80130 μm to the surface of the primer layer (21). 4. Referring to 1-3. Method according to one of Claims 1 to 3, characterized in that the material of the second intermediate layer (23) is 0.32-0.36 parts by weight of resin component B (cross-linking agent), 0.36-0.28 parts by weight of cement, and the listed components 5-10. by mixing an amount of epoxy diluent equal to about 1% by volume, and applying the mixture at a thickness of 270-300 µm to the surface of the first intermediate layer (22), 5. Method according to one of Claims 1 to 4, characterized in that the material of the topsheet (24) is 0.450.55 parts by weight of resin component A, 0.55-0.45 parts by weight of resin component B (cross-linking agent) and the total of the two components is 2-5 volumes. by mixing an amount of epoxy-diluent in an amount of about 50%, and applying the mixture at a thickness of 70-110 µm to the surface of the second intermediate layer (23). A method of supplying an outer and inner corrosion protection coating of steel tubes, comprising applying a cement mortar layer to the inner surface of the steel tubes, and applying plastic-based layers to the outer surface by lubrication and / or spraying, which are cured or cured, characterized by: to apply a cement mortar layer as internal coating (3) at a thickness of 1-3 cm to the inner surface of each steel tube (1), leaving a section free from the pipe ends inwardly); the same steel tubes (1) also have a primer layer (21) made of water-soluble epoxy resin, cement, and water, at least partially cured, on the outer surface of the pipe (1) leaving the bottom of the pipe (free of h szakasz). a first intermediate layer (22) consisting of a mixture of an epoxy resin and an epoxy diluent comprising a tar comprising a two-component tar epoxy resin containing at least a partial curing of the first intermediate layer (22); a second intermediate layer (23) consisting of a mixture of cement and epoxy diluent is applied and then, after at least partial curing, a two-component tar epoxy resin and diluent. EN 205436 Β, the adjacent steel tubes (1) are welded to each other at their ends, and the outer protective coating layers at the welding sites are applied with strip layers of the same material as their own, applied as the inner coating (3). the cement mortar layer is also sealed with a band of the same or substantially identical material. The method according to claim 6, wherein the material of the primer layer (21) is 0.24 to 0.31 parts by weight of resin component A; 0.32-0.38 parts by weight of resin component B (crosslinker); 0.24-0.31 parts by weight of cement and 25-35% by volume of the listed ingredients are prepared by mixing the mixture at a thickness of 70-110 pm on the surface of the steel tube (1). Method according to claim 6 or 7, characterized in that the material of the first intermediate layer (22) is 0.450.55 parts of resin component A, 0.55-0.45 parts by weight of resin component B (crosslinking agent), and mixing these two components with 8-12% by volume of water and applying the mixture at a thickness of 80-130 µm to the surface of the primer layer (21). 9. The 6-8. Method according to one of Claims 1 to 3, characterized in that the material of the second intermediate layer (23) is 0.32-0.36 parts by weight of resin component B (cross-linking agent), 0.36-0.28 parts by weight of cement, and the listed components 5-10. the mixture is prepared by mixing an amount of epoxy diluent in a volume of about 1% by volume and applying the mixture at a thickness of 270-300 µm to the surface of the first intermediate layer (22). 10. From 6-9. Method according to one of Claims 1 to 4, characterized in that the material of the topsheet (24) is 0.450.55 parts by weight of resin component A, 0.55-0.45 parts by weight of resin component B (cross-linking agent) and the total of the two components is 2-5 volumes. by mixing an amount of epoxy-diluent in an amount of about 50%, and applying the mixture at a thickness of 70-110 µm to the surface of the second intermediate layer (23). 11. A6-10. Method according to one of Claims 1 to 3, characterized in that a top layer (25) of over 700 700 µm thickness (25) overlapping the adjacent topsheets is applied to the layer of banding applied to the welded seams connecting the steel tubes (1) to the adjacent covering layers (24). and / or by spraying, from 0.35 to 0.45 parts by weight of component B (cross-linking) from component A of a two-component tar epoxy resin, 0.35 to 0.45 parts by weight of a fine washed sand of 0.1 to 1 mm in size, 0.30.1 parts by weight, and mixing an amount of epoxy diluent in an amount of 8 to 12% by volume of these components. EN 205436 Β Int Cl ⁵ : F16 L 58/02 6. abra Published by: National Office of Invention, Budapest Publisher: dr. Gabriella Svoboda CODE