MXPA96000023A - Coating for pipe plates, and cooling pipes in ac exchangers - Google Patents

Abstract

The present invention relates to a method for coating plates of cooling tubes and tubes used in heat exchangers, in particular in steam condensers, which is based on mixtures of hardenable plastics, the steps of cleaning the surfaces to be coated with the help of abrasive agents, seal the inlets and outlets of the tubes with removable plugs, apply at least one layer of a plastic coating that is hardenable to the tube plate, allow the coating to harden so that further mechanical processing can be performed that still remain reactive sites on the surface and mechanically process the surface, remove the plugs from the inlets and outlets of the tubes and apply at least one plate of a hardenable plastic coating in at least the triple entry of the cooling tubes, characterized by chemically bonding the coating of the tube plate with the coating of the cooling tubes by a suitable application of time, the coating of the cooling tubes has a greater elasticity than the coating of the tube plate with a breaking elongation in accordance with the German industry standard DIN EN ISO 1519 (DIN 53152 ) at least 2% greater than the rupture elongation of the tubing plate

Description

COVERING FOR TUBE PLATES, AND COOLING TUBES IN HEAT EXCHANGES. DESCRIPTION OF THE INVENTION The present invention relates to a coating for tube plates or cooling tubes that are used in heat exchangers, in particular steam condensers based on hardened plastic mixtures, the coating is obtained by cleaning the surface they have to cover. cover with the help of abrasive agents; sealing the inlets and outlets of the tubes with removable plugs; to 11 • at least one layer of a plastic coating - hardenable to the tube plate; allowing the coating to harden so that the mechanical process can take place and process the surface; removing the plugs from the inlets and outlets of the tube and applying at least one layer of a plastic coating hardenable at least to the entrance area of the cooling tubes and letting them harden; and a method for coating pipes and cooling pipes that are used in steam condensers. It is known to provide tube plates in steam condensers, as are used for example in plants to produce electric power with a plastic coating to counteract the signs of corrosion. The tube plates and the cooling tubes used are exposed to a multiplicity of external influences, in particular chemical and electromagnetic mechanical stresses. Mechanical stresses are caused by solid particles roughened by the cooling agent eg sand, also the difference in temperature between the cooling temperature and the vapor to be condensed which may exceed 100 causes expansions in the area of the cooling head. Cooling tubes on the tube plate. Chemical efforts result from the cooling nature, for example when charged with salts or acidic substances. In particular, the known corrosive effect of sea water or highly polluted river water used for cooling purposes should be mentioned. Electrochemical or galvanic corrosion refers to that which is present from the galvanic elements or mechanical limiting surfaces. In particular, in the transitions from the plates of tubes to the cooling tube, and that increases greatly by the action of the liquids that drive the electricity, for example seawater. In addition, the functionality of a tubular plate is controlled by the deposition of undesirable substances forming algae, etc., on a surface that is promoted in particular by rough areas produced by corrosion. The result is that the corrosion and the signal of the deposit is a -celerates with age and a tube plate because new starting points for corrosion as well as deposits are continuously formed. It has started with providing tube plates with an anti-corrosion coating of plastic materials long ago, in particular epoxy resin coatings that were adapted to the inlets and outlets of the tubes by certain techniques, for example using plugs molded during the application. This allows the coating of the tube plate that first smoothly adapts to the inlets and outlets of the tubes, where the tubes u-sually projecting beyond or ending in the coating area are usually not covered with material resistant to corrosion inside, but even such solutions could not prevent for a long time that the water will penetrate through micro cracks or cracks and thus the resulting formation of galvanic elements, the consequence being increased signs of corrosion after the formation of the first cracks Even the inclusion of cooling tubes in the coated surface at least in their entrances and exits only brought about a small improvement since the extreme thermal and mechanical stresses prevailing in those areas lead to the formation of cracks as hair particularly in the sensitive transition area from the tubeplate to the cooling tube. Once the link between the tube plate, that is, between the coating and the re-covering of the tube, the protective effect of the coating decreases constantly. Measures of the aforementioned type are known for example from the patent documents GB-A-1 175 157, OE-U-1 939665, OE-U-7 702 562 and EP-A-0 236 388. In view of the problems mentioned above, the aim is to solve the problem of supplying tube plates and inlets and outlets adyante the cooling tube with a coating that integrates the two effects of a long resistance to the mechanical stresses that act at the transition points and also suitable to resist the chemical efforts from the cooling in a large time period. This problem is solved according to the present invention by means of a coating of the aforementioned type wherein the coating of the cooling tubes is reactively connected to the coating of the tube sheet by a mutually calculated application in time, and wherein the Coating of the cooling tube has a greater elusiveness than that of the coating of the tubular plate with a breaking elongation according to the German Insdustria Norm 53 152 at least two percent greater than the elongation of rupture of the coating of the tube plate . The mutual coincidence in time of the coating operations on the tube plate and in the cooling tubes produces a cross-linked bond across the boundaries of the coating from the coating of the tubes to the coating on the tubular plate, which gives as a result, a particularly stable chemical bond. Simultaneously and additionally the relative greater elasticity of the coating of the cooling tube improves the resistance to mechanical stresses in the areas of entrance and exit of the tubes; where galvanic corrosion occurs. It has been found that a 2% increase in break enlogation according to DIN 53152 is generally sufficient to improve the coating bond, assuming an elongation to the breaking of the coating of the pipe plates of less than 5% and one of the coatings of the cooling tube of less than 10% to ensure the hardness and resistance to abrasion and pressure necessary for the coating to last. On the other hand the elongation of breaking of the coating of the tube plate should not be less than 2% to avoid brittleness. Particularly suitable materials have been shown to have the breaking elongation according to German Industry Standard 53 152 from 2 to k% for the tubular plate and from k to 9% for the cooling tubes. Particularly preferred coatings have longations at break of more than 3% in the tube plate and more than 5% in the cooling tubes. To apply the thickness of layer necessary for the operation to last several years and simultaneously ensure the quality with respect to the freedom of pore freedom and cracks of hair it is convenient to apply the coating of the invention in several layers by applying each layer to the surface of the lower layer, while the latter is still reactive to obtain a chemical cross-link, it is convenient to apply two or three layers to both the 1-tube plate and the cooling tubes, the layers being, if possible, of different colors to allow the thickness of remaining layers check for color in previous inspections. The minimum layer thickness of the total coating is approximately 8 microns for the internal coating of the tubes and 200 microns for the tube plate. Thick layers of 20 mm and more are immediately possible without loss in strength. It is a special advantage when coating tube plates that are already corroded and have deep corrosion points. It has been found very convenient to provide the cleaned surfaces of the tube plate and the cooling tubes before the application of the current coating with a first agent that is sprayed with low viscosity and penetrates the depressions and points of corrosion, thereby obtaining a leveling of the surfaces with iBejor adaptation of the uneven areas and a better alloy of the; coating itself. The coating itself can also be additionally provided with a seal on the surface to obtain in particular a smoother surface which prevents adhesion of the algae, soil particles or the like. Preferably, the seal on the tube plate is standardized so that it is more elastic than the coating on the tube plate, where the elongations to the break indicated above must be maintained for the coatings of the cooling tubes. In general, it is convenient to provide two first and sealing layers in each case; sealing in the tubular area is usually not necessary. Preferred materials for the inventive coating are resins, epoxies that cure cold which are processed together with an amine hardener, these resin compositions contain customary fillers and colorants, normalizing agents, stabilizers and other co-immune advices for ensure the desired properties, in particular the ease of the process and its durability. These are common plastic blends that can also be used for other purposes - the important or essential aspect of the invention coating is not so much the type of hardenable plastic compound as rather its resistance to corrosion and elasticity after curing. Apart from epoxy resins, other plastic mixtures cold-setting with t3l can also be used to meet these requirements. However, epoxy / amine systems are intended for the purposes of the present invention. The plastic mixtures used for pipes and in particular for cooling pipes, preferably containing a proportion of poly tetrafluoroethylene (PTFE), powder in an amount of at least about 5% by weight to obtain the desired values of elasticity and strength, it has been seen that the adhesion of -PTEE, in the range of 5 to 20% by weight particularly of -about 10 $ by weight, clearly improves the coating durability in the area of the inlets and outlets -of the tube. The PTFE, aggregate, for example Hostaflon (R), of Hoechst, must have a grain smaller than 50 microns, and in particular - in the range of 10 to 30 microns, it forms a matrix that 1 lena, stabilizes and improves the elasticity and in particular also serves to establish the desired elasticity. To increase the strength in particular of the coating of the tube plate, a content greater than 30% by weight of mineral additives in the mixture is desirable. To further improve the inventive coating strength in the transition area from the cooling tube to the tube plate, it may be desirable to provide a plastic sleeve in the coating in the transition area to the tube plate to produce an effect Stabilized, additional. It has been shown that in the receivers of the invention they must meet certain criteria with respect to their mechanical capacity against stresses, the finally obtained hardness of the coating must thus reach a value of at least about 75 according to the standards. of the German Industry 53153 (Barcol hardness), preferably at least 80, for the tube plate a value in the coating of at least 95, is convenient. In addition, the adhesive strength of the coating on the base must be at least N / mm, according to the DIN / 1 SO standards + 62 * +, preferably from when 2 - 5 N / mm, and in particular of at least 7N / mm2. According to the invention, adhesive resistances of more than 10 N / mm 2 are achieved for the coating of the tubular plate and of more than 5 N / mm 2 for the coating of the cooling tube. The stability of the inventive coatings depends crucially on their resistance to pressure and abrasion. With respect to the resistance to pressure, values of more than 50 N / mm2 must be achieved for the coating of the cooling tube and of more than 100 N / mm2 for the coating of the tubular plate; for abrasion resistance according to the German Industry Standard 53233 (case A), the values are more than kO mg, of more than 55 mg, respectively. The invention also relates to a method for applying the described coating comprising the steps of first cleaning the surfaces to be covered with the aid of abrasive agents by sealing the inlets and outlets of the tubes with removable plugs, applying -when less one layer of a plastic coating hardenable to the tubes, allow it to harden in coating so that other mechanical processing can be performed but, remaining still reactive places on the surface and then mechanically processing the surfaces, then the plugs are removed The at least one plastic coating layer hardens at least in the inlet area of the cooling tubes in order to form a reactive connection with the coating of the plate. tubes, selecting the plastic mixtures, so that the coating of the cooling tube has a greater elasticity than The coating of the tube plate with an elongation in the pipe according to the German Industry Standard 53152, of at least 2% greater than the elongation to the breaking of the coating of the tube plate. It is important, for the inventive method, that the surfaces to be coated be thoroughly cleaned with abrasives to provide a firm and uniform base, the inlets and outlets of the tube are sealed by re-rabies plugs, as is basically known for two reasons. Firstly, the compound for the coating of the tube plate has as an object that it does not penetrate into the inlets of the tube; and second the coating of the tube plate has to adapt to the course of the cooling tubes and thus a corresponding profiling must be effected, for which purpose plugs will be used appropriately. This allows the tubular inlet to have a favorable shape to the flow and ensures a trouble-free connection of the cooling tube liner to the lining of the tube plate. It may be useful especially with old or used tube plates to adequately extend the tubes in cold at the inlet and outlet to ensure a smooth transition to the sausage at the insertion of the tubes -in the coating of the tube plate (DE- U-7 702 562). This in particular, allows the transition between the tube plate and the cooling tube and that does not coincide with the transition between the coating of the tube plate and the cooling tube coating, which increases the life of the coating. The surfaces to be coated are preferably cleaned by blowing with an abrasive agent, for example sand. In the next stage, the inlets of the tube are sealed with specially made plugs. A pore cleaner or lid is then preferably applied, in particular one with the coating mixture which achieves the elastic properties of the coating desired for the cooling tubes, since it is convenient to apply the pore lid by spraying with an apparatus, the mixtures of The corresponding plastic should have a corresponding viscosity as well as the ability to penetrate the corrosion holes of the metal surface. The thickness of the layer must be at least 80 times the drying time is approximately 8 hours, up to a few days at a temperature of 20, for the epoxy resins, making sure that a connection is formed within this period. reactive for the next layer, - however, you can also choose a roller technique for its application. From one to three layers of the plastics compound intended for the plate of tubes, pores are applied on the lid, in particular extending with a spatula to ensure its penetration into the depressions to eliminate cavities and prevent the formation of pores and bubbles. It has been found convenient to apply several coats efficiently to obtain the necessary layer thickness of 20mm., or more. The drying time before further processing is approximately 2k hrs ak days for the epoxy resins, after hardening the surface is mechanically smoothed and processed in particular with abrasive materials. that a more uniform surface is obtained that offers less resistance to the coupling of the cooling agent on the plate - of tubes and less starting points for mechanical erosion and attack by the algae. It is preferable that a seal is applied, usually in two layers, to the extended coating with the spatula.; the material used for this is a standard plastic mixture, elastically based on the bottom coating, for example a mixture as described in relation to the coating in the cooling tubes, the thickness of the layers is at least 40 microns, for each layer indj_ vi dual. jointly of at least 80, the times of seado for the subjects epoxi do / amina goes of 6hrs. Until they're free of being sticky. In particular, when the seam is sprayed or applied with rollers, a smoothing over of the surface is provided due to the spread of the compound 1i + To the plastic, thus offering means of starting points for corrosion damage and decomposition, it is convenient to apply the seal only when the cooling tubes are already coated, extending when the last coating of the cooling tube gently coats - towards the coating of the tube plate. The total coating can be mechanically and chemically reactive after approximately 7 days at a hardening temperature of 20 After the coating of the tubular plate is applied to the lid pores and the subsequent mechanical treatment has taken place. the plugs of the entrances are retired in the following stage; then the coating of the cooling tubes is conveniently applied - in several layers to the cleaned surface of the tubes in at least their entrance area but preferably all along them. It has been presented as particularly suitable for spraying for its application, starting at the end-disengagement of the tube plate as a suitable nozzle blowing on the sides, and coating onto the plate of the tubes, alternatively the coating can also be applied to the plate. 1 - Brush with a brush by rotating the brush and extending the compound against the wall of the tube. The plastic blends used are standardized to a viscosity suitable for spraying with simultaneous attention to the maximum penetration capacity and the adhesive power without the formation of a greasy edge. It is also convenient to apply several layers here, firstly, a pore lid in one or two layers on the metal surface that hardens within 3 hrs., To 8 days for the epoxy resins, and then the coating -properly said in one or more layers, with an endu_ recimiento time of 6 hrs., to days. A subsequent treatment for the coating of the cooling tube is not always necessary, as described at least the last layer of the tubular coating, it is also applied in a single operation to the coating of the tubular plaster, where it serves as a seal. The individual layers of the tube coating and the seal are applied in a layer thickness of at least 0 mfcras - being at least the total thickness of the dry plate of 80 microns, to withstand a long corro- sion test. If several layers are applied, it is important - to calculate the time: both the transition to the coating of the plate of tubes and the individual layers of the coating of the cooling tube must be applied in a working coincidence so that the chemical cross-linking se - present with the lower layer already applied. The coating of the cooling tube can - 6 undergo chemical and mechanical stresses after 7 days the indicated times refer to epoxy resin / hardener / amine systems, and at a temperature of 20 S, the coating on the cooling tubes is not applied on the entire surface, then You should thin layer by layer, so that the coating gradually flattens out. It is convenient to make the outer layer - extend inside the cooling tube and on the bare metal, so that the lower layer is completely covered with the top layer. However, the outer layer can also start more outside than the lower layer; With all the coatings, it is convenient to give the individual layers different colors to allow the state of the coating and its thickness to be verified by visual observation; If the pore lid is gray and the layers of the top coatings are alternately red and white, it is possible to immediately verify the thickness of the remaining coating visually, and decide for example when the last second layer has been reached, and also the latter, this makes it possible to fully utilize the life of the coating and selectively repair certain places affected especially by corrosion or erosion, which protrudes from its surroundings, due to the different coloration.

The present invention will now be explained in more detail with reference to the accompanying drawings in which: Figure 1 shows a coffer of the cooling tube inlet of a tube plate in an uncorrored and corroded state, each with a coating , in three -variates (a) to (c), and Figure 2, shows the invective coating of a tube plate and the cooling tube that penetrates its layer structure. Figure 1 a shows a detail of the pipe pipe 1, with a cooling pipe 2, in the area of the cooling pipe by its entrance, the projection of the pipe 3, is bent or widened towards the sides; in the upper half of the dj_bujo (as in Fig. 2 (b) and (c),) the tube plate has an intact smooth surface k, as it exists without protection-especially virtually only when new. In the lower half of the drawing the surface of the tube plate is damaged by the corrosion samples, particularly in the area of the cooling tube inlet, deep corrosion holes have been produced by galvanic corroding. The parts that are blackened in the area of the pipe plate surface h, constitute the coating or with a suitable mixture of plastic that sets or heals in cold; the coating 6, penetrates the coating of the cooling tube, the corrosion hole 5, is completely filled by the coating. Since the mixture of the coating itself is virtually chemically non-existent, the tube plate 1, and tube 2, are completely insulated against the cooling water, thus galvanic corrosion is to a large extent anticipated. Figure 1 (b) and (c), shows variants - commonly used for the chilled tube socket with a flush end (Ib), and a projection without flare (1c), the tube socket 3, is fully integrated in coating 6, 7, in all cases (1a to 1c). Figure 2 shows the layered structure of the inventive coating, the coating of the plate - of tubes and of the tube can be seen more clearly in the - details A and B. Below the covering 6, properly speaking of the plate tube 1, there is an application of cover 8, which also fills in small uneven areas, the smoothed surface of cover 6, is protected ad_iionally with seal 9, which extends inside the tube and forms the outer layer inside of the coating of the tube. The wall 2 of the cooling tube is first provided with the pore lid 11, on the cleaned metal surface, the coating itself of the cooling tube 7, is elastically standardized with respect to the tube plate coating, and is applied the lid pores 11. In the case shown, the cooling tube 2, is not covered in its entire length, but only in the -entrance area. The overall coating is thinned - (detail B), that is, each upper layer penetrates more into the tube than the lower one, the last layer of cooling jacket 9, is at the same time the seal 9, of the coating of the tube plate 6. The curved end of the tube-coating (11, 7, 9), shown in detail A, is given by the contour of the cap provided for the coating of the tube plate, and that it has been removed before -the cooling tube had been coated. The total thickness of all the layers is greater than 2,000 microns in the area of the tube plate, and greater than 80 microns in the area of the tube walls, larger layer thicknesses can be obtained immediately; Partially suitable materials for the coatings according to the invention have epoxy resins proved to be? which are - processed as with a hardener mine, these are usual commercial systems that can be standardized without using; Suitable products are, for example, epoxides based on glycidyl ethers and biphenol A-derived epoxies, which are hardened with a polyamide normally modified. The epoxide and hardener contain common additives - which regulate their processing, chemical stability, and their stability during storage as well as their resistance.

Claims (3)

1. NOVELTY OF THE INVENTION Having described the invention as above, the following content is claimed as property: CLAIMS 1.- A coating for tube plates -and cooling tubes used in heat exchangers, in particular in steam condensers, which It is based on mixtures of hardened plastics, and is made by cleaning the surfaces to be coated with the help of - abrasive agents; sealing the entrances and exits of the -tubes with removable plugs; applying at least one layer of a plastic coating hardenable to the plate - of tubes; allowing the coating to harden so that mechanical processing can be performed, mechanically processing the surface; remove the plugs from the inlets and outlets of the tubes and apply at least one layer of a hardened plastic coating at least in the inlet area of the cooling tubes and leaving it to harden; characterized in that, the coating of the cooling tubes is connected to the coating of the plate of tubes reactively by a suitable papl ication of the time and the coating of the cooling tubes, has a greater elasticity than that of the coating of the plate of your bos, with an elongation to the break according to the Ñor-ma of the German Industry 53 152, of at least 2% greater than the elongation of rupture of the coating of the tube pipe.
2. 2. The coating according to claim 1, characterized by an elongation to the rupture of the coating of the tube plate according to the Standard of the German Industry 53 152, from 2 to 4%, and an elongation to the breaking of the cooling tube coating from k to - 9%.
3. 3. The coating according to claims 1, 2, characterized by an elongation to the breakage of the coating of the tube plate according to the German Industry Standard 53 152, of at least 3%, and a resistance to the breakage of the coating of the cooling tube of at least 5%. k. - The coating according to some of the preceding claims, characterized in that it comprises several individual layers, each of which is apllied to the surface of the initial layer while the surface is still reactive. 5. The coating according to claim 1, characterized in that the individual layers have different colors. 6. The coating according to any of the preceding claims, characterized by a greasy layer of at least 80 microns in the cooling tubes and at least about 2,000 microns on the tube plate. 7. The coating according to one of the preceding claims, wherein an epoxy resin / amine hardener system is used. 8. The coating according to some of the previous remarks, because the plastic mixtures contain fillers and colorants, standardizing agents, stabilizers and other common additives. 9. The coating according to any of the preceding claims, characterized in that the plastic mixture for the coating of the cooling tubes contains poly tetrafluoroethanol in powder form, preferably with a grain size of less than 50 microns and in - an amount of 5 to 20% by weight. 10. The coating according to any of the preceding claims, characterized in that it is applied on a first pore or gripper agent, or has a seal. 11. The coating according to claim 10, characterized in that the plastic layer with the properties of the coating of the cooling tube forms the seal. 12. A method for coating tube plates and cooling tubes used in heat exchangers, particularly in steam condensers, based on epochs of hardenable plastics, a method comprising the steps of cleaning the surfaces to be coated with the aid of abrasive agents; seal the inlets and outlets - of the tubes with removable plugs, apply at least one layer of a plastic coating hardenable to the tube plate, allow the coating to harden so that mechanical processing can be performed but still have reactive locations on the surface, mechanically process the surface; remove the plugs from the inlets and outlets of the tube and apply at least one layer-of a hardenable plastic coating in at least the inlet area of the cooling tubes to form a reactive connection to the coating of the tube plate, having the coating of the cooling tubes a greater elasticity than the coating of the tubular plate, with an elongation to the break according to the Norm of the German Industry 53 152, of at least 2% greater than the elongation to the breaking of the coating of the tu-bular plate. 13. The method according to claim 12, characterized in that the surfaces to be coated are cleaned by blowing with an abrasive agent. 14. Method according to claims 12, 13, characterized in that the coating of the plates of tubes extends with a spatula after polishing of the surface has been carried out. 15. Method according to any of claims 12 to 14, characterized in that the coating of the cooling tube is applied by spraying or with roller in the tubes, starting at the far end of the tube plate. 16. The method according to any of claims 12 to 15, characterized in that the surfaces to be coated first receive a pore lid by rolling or with a roller before being coated or, a seal is applied to the coating. 17. Method according to claim 16, characterized in that several layers are applied in each case of the cover pores, coating or seal. 18. Method according to claim 17, characterized in that layers of different colors are applied. 19. Method according to claims 16 to 18, characterized in that a plastic layer with the properties of the coating of the cooling tube is used as a seal.