JPS6215271B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for regenerating heat exchange tubes, and particularly relates to a long heat exchange tube installed in a heat exchanger.
The present invention relates to a method for restoring the heat transfer performance and corrosion resistance of a small-diameter copper alloy tube so that it can be used again as a heat exchange tube. Conventionally, so-called heat exchange tubes made of brass with aluminum, arsenic, and other silicon added have been used as heat exchange tubes for condensers and other various heat exchangers in thermal power plants, chemical factories, ships, etc. Special brass tubes and copper alloy tubes such as Cupronickel tubes made of copper, nickel, and iron are widely used, but in these heat exchangers, cooling fluid such as seawater or river seawater is Heat exchange occurs between the high-temperature fluid in contact with the surface of the heat exchange tube and the fluid flowing through the heat exchange tube, which causes various problems. -ing That is, since a cooling fluid such as seawater is passed through the heat exchange pipes, the long-term use of the pipes results in various corrosion products, sulfide films, etc. depending on the cooling fluid.
Alternatively, scale (adhesive matter) such as slime is formed on the inner surface of the heat exchange tube, which lowers its heat transmission coefficient (heat transfer performance) and causes a serious problem of deteriorating the thermal efficiency of the heat exchanger. By the way, the thermal efficiency of a heat exchanger is significantly dependent on the contamination of the heat exchange tube as a heat exchange tube, in other words, the scale generated on the inner surface. This is caused by the adhesion of corrosion products of the exchange pipe itself, mud and sand, or living things such as plankton and bacteria.Although it varies depending on the quality of the cooling water used, such adhering substances (scale) adhere to the inner surface of the pipe. As a result, it is often observed that the heat transmission coefficient of heat exchange tubes in use decreases to about 50 to 70% of that of new, unused tubes. The reduction in thermal efficiency of the entire plant due to such a reduction in heat transfer coefficient is extremely large, and the increase in energy costs in each plant has become a major problem for users of such plants. On the other hand, heat exchange tubes generally have an inner diameter of 10 to 40
It is quite small at mm, and its length is 5~
It is extremely long at 30 m, and many thousands or more of such heat exchange tubes are installed inside the heat exchanger, so it is difficult to remove the scale that has formed on the inner surface of the heat exchange tubes. It's not easy. Conventionally, various methods such as sponge ball cleaning method, water jet cleaning method, nylon or wire brush method have been proposed as methods for removing dirt (scale) from the inner surface of heat exchange tubes. In any of these methods,
There are various problems that need to be solved, and the method is not fully satisfactory especially when applied to heat exchange tubes installed in a heat exchanger. For example, in the sponge ball cleaning method, a large number of sponge balls are suspended in a cooling fluid and only need to be passed through a heat exchange tube, so it is extremely efficient and simple, but the scale removal effect is weak and the removal There is a problem that the capacity is not uniform in the longitudinal direction of the heat exchange tube, and there is a drawback that the removal capacity is insufficient especially for hardened scale. In addition, the waterjet cleaning method uses a high-pressure water stream to remove scale adhering to the internal surface, but in order to spray the high-pressure water stream, it is necessary to move the nozzle from one end of the pipe to the other, so the work is difficult. However, there is also the inherent problem that the removal ability is insufficient for hardened scale. Furthermore, the acid cleaning method, in which scale is removed by flowing an acid solution into the heat exchange tube, is expected to have an excellent removal effect depending on the conditions, but it not only requires a large amount of acid solution; Post-treatment of the discarded acid solution has become a major problem, and there is also a method of removing scale by inserting a nylon brush or wire brush into the pipe and moving it from one end to the other. In some cases, there are problems with its workability, and the removal ability is insufficient for hard scale mainly composed of corrosion products, and the brush itself is not durable.
It has problems such as rapid deterioration of scale removal ability. This invention has been made against the background of the present invention, and its purpose is to effectively remove deposits such as scale from heat exchange tubes installed in a heat exchanger, Another object of the present invention is to provide a method for activating a heat exchanger by restoring its heat transfer performance and corrosion resistance. In order to achieve this object, the present invention provides a heat exchanger that is attached to a heat exchanger and allows a cooling fluid to flow through the pipe, thereby preventing corrosion products, scale, etc. from forming on the inner surface of the pipe. 10~40
In a method for regenerating a copper alloy tube as a heat exchange tube with a length of 4 to 40 m, air mixed with abrasive particles is caused to flow through the tube at high speed so that it adheres to the inner surface of the tube. After removing deposits such as corrosion products and scale, the inner surface of the copper alloy tube is cleaned with a cleaning solution made by adding a surfactant to a silicate aqueous solution containing at least 5 ppm of silicate. After the treatment, an anticorrosive coating film of 10 to 30 μm was formed on the inner surface of the tube using a specified resin paint. As described above, according to the present invention, deposits such as corrosion products and scale on the inner surface of the heat exchange tube can be effectively removed by the abrasive action of air mixed with abrasive particles flowing at high speed. After the heat transfer performance is restored, the inner surface of the heat exchange tube is treated with a specific cleaning liquid to provide an effective surface treatment, and then a prescribed cleaning solution is applied. By forming an anticorrosive coating film, it is possible to restore or improve the corrosion resistance of the inner surface of the heat exchange tube, and at the same time, by improving the adhesion of the coating film, it is possible to effectively improve the durability thereof. It was. By the way, in the present invention, the copper alloy tube material used as the heat exchange tube that performs the intended heat exchange by being attached to the heat exchange tube and allowing a cooling fluid to flow through the tube has been conventionally used as a heat exchange tube. The present invention is particularly applicable to aluminum brass pipes, such as JIS-H-3300 C-6870, 6871,
Aluminum brass materials such as 6872, JIS-H-
Tubes made of Cypronickel materials such as 3300 C-7060 and 7150 are preferably used. And such copper alloy tubes, for example, have an inner diameter of 10~40
It will be used as a long thin tube with a length of about 4 to 40 m. When such a small-diameter, long copper alloy tube is installed in a designated heat exchanger, its use, especially over a long period of use, causes scale to form on its inner surface, specifically iron rust, etc. The deposits formed by the adhesion of colloidal substances, corrosion products of pipe materials, mud and sand, or living organisms such as plankton and bacteria are first effectively removed by blowing air mixed with abrasive particles. It will be done. The sandblasting method, which uses air mixed with abrasive particles, is simply a method of cleaning the inner surface of a pipe using air mixed with abrasive particles. ,Preferably
Since it is only necessary to flow at an apparent speed of 1000 m/min or more, it is possible to apply the heat exchange tube as is while it is attached to the heat exchanger, and the work is easy to do. In addition, it has sufficient ability to remove hardened scale attached to the inner surface of the heat exchange tube, and can achieve an extremely effective inner surface cleaning action. The abrasives used in this sandblasting method include various particles such as molten alumina, SiC, silica sand, and steel grit, and they are made to flow together with air through the target heat exchange tube, resulting in a grinding or Any type of abrasive particles can be used as long as they exhibit an abrasive action and can remove corrosion products, scale, etc. adhering to the inner surface, but the particle size of such abrasive particles must be within a specified range. In order to effectively exert the grinding or polishing action of the material, it is desirable that it be as large as possible within the range that maintains a certain flow rate, and generally the size is from several tens of microns to
A material of approximately several thousand micrometers will be used. Further, as the mixing ratio of such abrasive particles to air, a ratio by weight of 0.1 to 10 abrasive particles to 1 part of air is generally effectively adopted. If the amount of abrasive is too large, the flow within the small diameter and long heat exchange tube will be inhibited.
This is because a problem arises in that the flow rate decreases, and if the amount of abrasive is too small, a sufficient effect of removing deposits cannot be obtained. Next, according to the present invention, an alkaline cleaning solution is passed through or sprayed onto the inner surface of the heat exchange tube, the inner surface of which has been cleaned by sandblasting, thereby treating the inner surface of the tube. It will be done. This is because when an anti-corrosion coating is applied directly to the surface of the heat exchange tube after sandblasting as described above to form an anti-corrosion coating, the adhesion of the coating may be insufficient, and this may occur after long-term use. This is because it has become clear through the studies of the present inventors that problems such as blistering are caused in sandblasted surfaces. This improves the adhesion of the anticorrosion coating film formed thereon, increasing its durability. Generally, aqueous solutions of silicates, such as ortho- and meta-silicates of alkali metals such as sodium and potassium, are suitably used as alkaline cleaning liquids that have an effective effect on such blasted surfaces. Therefore, the adhesion of the coating film can be effectively enhanced, and the water wettability can also be effectively improved. The reason why treatment with such an alkaline cleaning solution, especially a silicate cleaning solution, is effective has not yet been clarified, but high-magnification observation (3000x) by the present inventors using a scanning electron microscope revealed that the untreated surface It was found that a large number of fine powders of about 1 μm were attached to the sandblasted surface (as is), while the amount was smaller on the treated surface, so surface cleaning treatment,
In particular, treatment with an alkaline cleaning solution has an effective removal effect on dirt, such as fine powder and oil, on metal surfaces. It is believed that by forming an effective base film, it is possible to improve the excellent adhesion of the coating film as described above. In addition, in the silicate aqueous solution as the alkaline cleaning solution, the silicate concentration is
Improvement in performance was observed even when the content was 5ppm, and when it exceeds 2%, it becomes difficult to treat the waste liquid, so it is not practical.
It will be used within a range of about 5 ppm to 2%. Further, by further adding a surfactant to such a silicate aqueous solution, the treatment effect can be further enhanced. As the surfactant to be added, any type of surfactant such as anionic, cationic, or nonionic can be used, but nonionic surfactants such as polyoxyethylene and polyoxypropylene are generally used. Polyoxyalkylene block copolymers such as block copolymers of Polyethylene glycol alkyl ethers and the like are used. and,
Such surfactants have approximately 3
It will be added and used at a ratio of less than 2/2.
In particular, the use of such surfactants is such that, relative to the total amount of silicate and surfactant, the surfactant
It is most effective when used at a ratio of ~15% by weight. In order to ensure corrosion resistance and activate the heat exchanger, heat exchange tubes that have been surface-treated with such an alkaline cleaning solution are uniformly coated with resin paint that can form a predetermined anti-corrosion coating. thinly,
For example, the desired coating film is formed by applying a coating method such as spray coating to a film thickness of about 10 to 30 μm. Barefoot,
If you restart the heat exchanger with the sandblasted surface still in place, the contamination of the cooling water may result.
Alternatively, as a result of adding a rust preventive agent, corrosion products, scale, etc. may re-adhere to the inner surface of the heat exchange tube, which not only causes a decrease in heat transfer performance but also may lead to a leakage accident due to corrosion. Therefore, as mentioned above, it is essential to activate the heat exchanger by treating the inner surface, which has been cleaned by the sandblasting method, with a specified alkaline cleaning solution as described above, and then applying a specified anti-corrosion coating. It is valid for its purpose. Note that, as the resin paint used for such anti-corrosion coating, an air-drying type (normal temperature drying type) paint is generally suitably used. In such paints, organic polymer resins consisting of alkyd resins, vinyl resins (vinyl chloride, vinyl acetate, etc.), polyurethane resins, epoxy resins, and acrylic resins (acrylic acid esters, etc.) are used as film-forming elements. One or more types of organic polymer resins (including modified products) are used.
It is dissolved in a hydrocarbon (ether, ketone, aliphatic, or aromatic hydrocarbon, etc.) to prepare a film-forming liquid composition (paint) that dries at room temperature.
In addition, when preparing such a paint, pigments such as red lead zinc chromate and iron oxide, and other film-forming auxiliary components are also added as necessary. Moreover, as such a paint, one that is generally commercially available as a synthetic resin paint (or varnish or primer) of the resin type is suitably used. In this way, the inner surface of a prescribed heat exchange tube, which is a copper alloy tube, is cleaned by sandblasting and treated with an alkaline cleaning solution, and then a prescribed anticorrosion coating film is formed on the inner surface. The electric heating performance as a heat exchange tube has been effectively restored, and the corrosion resistance is also ensured by the formation of an anticorrosive coating, and the adhesion of such an anticorrosion coating to the inner surface of the tube is effective. Since the corrosion resistance has been improved, the corrosion resistance can be made permanent, thereby making it possible to operate the heat exchanger for a long period of time. Next, some examples and reference examples of the present invention will be shown to clarify the present invention more specifically.
It goes without saying that the present invention is not limited in any way by the description of these Examples and Reference Examples. Reference example 1 Aluminum brass material (JIS-H-3300C-
6871) length: 100mm, width: 20mm, thickness;
Air contained as a fused alumina abrasive with an average particle size of 250μ for a 1 mm test material [Abrasive: Air =
1:3 (weight ratio)] at high speed for 30 seconds, and then washed with an aqueous sodium silicate solution at room temperature under conditions according to Table 1 below. Incidentally, a polyoxyethylene/polyoxypropylene block copolymer is added as a surfactant to this sodium silicate cedar solution at a ratio of 5 to 7% based on the sodium silicate. Next, the sample material that had been cleaned with the sodium silicate aqueous solution was coated with an air-drying commercially available alkyd resin rust preventive paint [Chrome Coat R manufactured by Shinto Toyo Co., Ltd.] to a film thickness of 20 μm. It was painted using a spray method. Regarding the various coating test materials thus obtained,
After immersing it in hot water at a temperature of 80°C for 72 hours, the adhesion of the coating film was evaluated by a cross-cut tape test and a 180° bending test. In addition, the cross-cut tape test is to cut an X-shape approximately 10 mm long on the surface of each sample material with a knife.
After adhering an adhesive tape thereon, the adhesive tape is peeled off vigorously, thereby evaluating the presence or absence of peeling of the coating film due to the adhesive tape and the degree of peeling. The evaluation results are shown in Tables A and B. In Tables 1 A and B, the evaluation results of the water wettability of each sample material before coating are also shown as water wettability angles (contact angles).

【table】

[Table] As is clear from the results in Table 1 A and B, the test materials treated with the sodium silicate aqueous solution were superior to those not subjected to such treatment. The higher the concentration of the sodium silicate aqueous solution, in other words, the higher the PH value, and the longer the treatment time, the better the performance. This shows that the surface treated with an aqueous solution is effective as a base for painting. Furthermore, the test materials treated with the sodium silicate aqueous solution showed excellent results in terms of water wettability, indicating good compatibility with paints. In addition, the coating film evaluation symbols in Table 1 A and B are as follows:
It has the following meaning. 〇: No peeling or blistering △: Spot peeling ×: Planar peeling Reference example 2 For an aluminum brass tube with an outer diameter of 25.4 mm, a wall thickness of 1.25 mm, and a length of 1000 mm, the inside of the tube was Air containing 250μ alumina particles as an abrasive [abrasive: air = 1:1 (weight ratio)] is heated at high speed.
After performing sandblasting treatment by flowing the material for 30 seconds, a cleaning operation was performed for 2 minutes using a cleaning solution containing a total of 0.02% of sodium orthosilicate and a polyoxyethylene/polyoxypropylene block copolymer as a surfactant. Then, in the same manner as in Reference Example 1, an anticorrosion coating film with a thickness of 20 μm was formed on the inner surface of the tube. The test tubes treated with various mixing ratios of sodium orthosilicate and surfactant as shown in Table 2 below were evaluated for their respective coating film adhesion, and the results are shown in Table 2. . The coating film evaluation symbols in Table 2 are the same as in Table 1. In addition, the paint film adhesion test for each test tube was conducted after passing hot water at 80℃ for 72 hours as in Reference Example 1, and after passing artificial seawater containing 0.1% sulfur ions for 3 months. In addition,...
1 under cathodic protection of 600mV (calomel electrode standard)
After being exposed for a week, a cross-cut tape test was conducted on each to evaluate the adhesion properties of each coating. As is clear from the results in Table 2, after sandblasting, cleaning the inner surface of the tube is better than not cleaning it, and using sodium orthosilicate and a surfactant together as a cleaning agent improves the adhesion of the paint film. In particular, the most significant effect was obtained when the ratio of sodium orthosilicate to surfactant was in the range of 85 to 95:15 to 5 (weight ratio).

[Table] Example 1 An aluminum brass pipe (JIS-H-3300C-6871; brass seamless pipe for condenser) with an outer diameter of 25.4 mm, a wall thickness of 1.24 mm, and a length of 2000 mm was coated with molten alumina to a particle size of 200μ. While supplying from a blasting nozzle at a rate of 2 kg/min, 5 kg/cm ² of air was sprayed from one end of the tube to the other for 2 minutes to clean the inner surface of the aluminum brass tube. Next, the inside of this aluminum brass tube was filled with an alkaline cleaning solution, held for 2 minutes, the cleaning solution was drained, and the inside of the tube was thoroughly rinsed with tap water, and then dried with hot air. The alkaline cleaning solution used was sodium metasilicate: nonionic surfactant (polyoxyethylene glycol ether of octylphenol) =
At a cleaning agent mixing ratio (weight) of 90:10, the concentration was 0.001-0.02% (PH = 9-10.5). The aluminum brass tube that has been treated with this alkaline cleaning solution is then coated with an air-drying commercially available alkyd resin-based rust preventive paint [LZI Primer manufactured by Chugoku Paint Co., Ltd.] over the entire length of the inner surface of the tube. Spray paint to a film thickness of 20μ,
An aluminum brass tube (heat exchange tube) whose inner surface was coated with anti-corrosion coating was obtained. For comparison, the above-mentioned sandblasted one, the one that was washed with a 5% hydrochloric acid aqueous solution in place of the sandblasting, and the chromate-treated one [Kyuprotecs manufactured by Nippon Paint Co., Ltd.] #3; 1% solution used, 90°C x 5 minutes], cuprous oxide treated [Brass Bond A manufactured by Nippon Parkerizing Co., Ltd.; 3
% solution used, 100°C x 10 minutes], the inner surface anti-corrosion coating was applied in the same manner as above. The various aluminum brass tubes obtained in this way were subjected to the following durability tests A to D, and after such tests, each sample tube was cut vertically, and the coating film on its inner surface was cross-cut. Adhesion was evaluated using a tape test, and the results are shown in Table 3. Durability test (A) Immersed in warm water at 80℃ for 3 days (B) Seawater added with 0.1 ppm of sulfur ions was passed continuously for 6 months at a flow rate of 2 m/sec.
At the same time, a sponge ball 2 mm larger than the inner diameter of the tube was passed through the tube 20 times each day. (C) Seawater containing 250 ppm of alluvial sand having a particle size of 250 μ was continuously circulated at a flow rate of 2 m/sec for 2 months. (D) While seawater is being passed continuously at a flow rate of 2 m/s, a current is applied using the sample tube as a cathode so that the potential at the end of the tube is -650 mV (calomel electrode reference), and the state is maintained at 1 It was kept for a week. Paint film evaluation symbol ◎: No peeling 〇: Spot peeling (5 pieces/10 cm length or less) △: Spot peeling (5 pieces/10 cm length or more) ×: Planar peeling, band-like peeling

[Table] As is clear from the results in Table 3, when a sodium silicate aqueous solution is used as the alkaline cleaning solution according to the present invention, sandblasting only, cuprous oxide treatment, and acid cleaning It was found that excellent coating film adhesion was obtained in the durability test, and the performance was comparable to that of chromate-treated products. Example 2 A copper alloy pipe that was installed in a condenser of a power generation plant and used for many years was removed from the condenser.
After performing a predetermined operation such as sandblasting to remove deposits on the inner surface of the tube, the inner surface was coated with an anticorrosive coating using an alkyd resin paint by spray coating, with or without treatment with a predetermined alkaline cleaning solution. Details of each step are as follows. In addition to the sandblasting method, we also take into consideration the possibility of working with the actual plant installed.
The conventional sponge ball cleaning method and the combined acid cleaning + wire brush method were used to remove deposits on the inner surface of the tubes, and the heat exchange tubes obtained by these methods were also evaluated. The test tubes subjected to various treatments thus obtained were subjected to durability test B in Example 1, and the adhesion of the coating film (presence or absence of corrosion) and heat conductivity were examined, and the results are shown in Table 4. Indicated. Note that the heat conductivity is expressed as a value relative to the new pipe made of the same alloy material as 100%. (i) The following used pipes and new pipes (outer diameter 25.4 mm, wall thickness 0.25 mm, length 2 m) A: Aluminum brass pipe (C-6871) using clean seawater, iron ion implantation, and condenser for approx. Used for 8 years. Scale adhesion amount: 8 mg/cm ² , heat transfer coefficient reduction rate: 24% B: AP bronze tube (Sn: 8.2%, Al: 1%,
Si: 0.1%, Cu: remainder) Used in contaminated seawater, iron ion implantation, and condenser use for approximately 12 years. Scale adhesion amount: 26mg/cm ² , thermal transmission coefficient reduction rate: 32% (ii) Sandblasting Alumina with a particle size of 150 to 250μ is sprayed for 3 minutes (spray amount: approx. 6 kg) for sample A, and for 5 minutes (spray amount for sample B). Amount of approximately 10 kg) is blown into the end of the test tube and allowed to flow through the test tube, polishing the inner surface of the tube. Substances (CuS, CuCl ₂ , SnO _{2 ,} etc.) and iron rust were almost completely removed. However, due to pitting corrosion at the bottom
Occasionally, spots of residual oxides thought to be Cu ₂ O were observed. (iii) Other scale removal treatments (a) Sponge ball cleaning A sponge ball, which is 2 mm larger than the inner diameter of the pipe and has carborundum adhered to its surface, is passed through the test pipe together with tap water to remove deposits that have adhered to the inner surface of the pipe. The removal operation was performed.
The total number of passes reached 500. In all samples, the deposits on the inner surface were not completely removed, and a considerable amount of scale remained in the form of streaks. Particularly in sample B, the degree of this was remarkable. The sponge ball used for cleaning was replaced with a new one every 50 times. (b) Acid cleaning + wire brush method Fill the test tube with 5% hydrochloric acid aqueous solution,
After holding for an hour, the water was drained. Thereafter, the entire length of the test tube was moved while rotating the wire brush. The above acid cleaning operation and wire brush cleaning operation were repeated a total of three times, and as a result, scale was almost completely removed from all samples. (iv) Surface treatment with alkaline cleaning solution Sodium orthosilicate and nonionic surfactant (polyoxyethylene ether of alkyl phenol) are mixed in a ratio such that the former is about 80% and the latter is about 20% in total amount. but
Prepare an alkaline cleaning solution to a concentration of 0.01%, and spray it from a designated nozzle.
The sample was moved from one end to the other, thereby cleaning the inner surface of the tube wall of the sample. The discharge amount of the cleaning liquid was 30 ml/sec, and the nozzle moving speed was 100 mm/sec. After spraying the alkaline cleaning solution, the inner surface of the tube was washed with about 10 times the amount of tap water to ensure that no alkaline cleaning solution remained on the inner surface of the tube, and warm air was blown at a speed of 1 m/sec for about half a day. ,
The inner surface of the tube was thoroughly dried. (v) Anti-corrosion coating treatment In the same manner as in Example 1, an anti-corrosion coating film with a thickness of about 20 μm was formed on the inner wall surface of each sample using a commercially available alkyd resin rust-inhibiting paint. As is clear from the results in Table 4, regarding heat exchange tubes made of aluminum brass materials, Nos. 2 and 6, which were not coated with an anti-corrosion coating, suffered from severe corrosion due to contaminated seawater and scale formation. The corrosion depth also increases significantly. In addition, even in the case of No. 1, although there was no anti-corrosion coating, the degree of corrosion was shallower than in No. 2 because the old scale served as a substitute for the anti-corrosion coating to some extent. Also, sample no.
Samples 3, 4, and 5 (without alkaline cleaning solution treatment, with anticorrosive coating) have uniform coatings remaining, and no progress of corrosion is observed. However, the adhesion of the paint film is poor,
A sufficient lifespan of the anticorrosion coating cannot be expected. On the other hand, in No. 7 according to the present invention, the heat transfer performance decreased only slightly (decreased due to adhesion of mud) as in Nos. 3, 4, and 5, and the adhesion of the coating film is large enough. Therefore, by extending the heat exchange tubes regenerated according to the present invention to the entire area of the heat exchanger, it is possible to obtain a state with excellent heat conductivity and corrosion resistance. Regarding the heat exchange tube made of AP bronze material, since such alloy material is originally a contaminated seawater corrosion resistant alloy, sample No. 10 showed lower heat conductivity and corrosion depth than that of No. 6. Sample No. 11 according to the present invention exhibits excellent characteristics similar to sample No. 7.
Furthermore, as seen in sample No. 12, the adhesion of the paint film was good even when the surface was treated with an alkaline cleaning solution on a surface that had been treated with a combination of acid treatment and wire brush treatment. However, such descaling work requires a large number of steps and there are also problems with waste liquid treatment, so it was judged that it would be difficult to employ it practically.

【table】

【table】

Claims (1)

[Claims] 1. A pipe with an inner diameter of 10 to 40 mm and a length of 4 to 40 m, with corrosion products, scale, etc. attached to the inner surface of the pipe by being attached to a heat exchanger and allowing cooling fluid to flow through the pipe. A method for regenerating copper alloy tubes used as heat exchange tubes, in which corrosion products, scale, etc. on the inner surface of the tubes are removed by circulating air mixed with abrasive particles at high speed inside the tubes. After removing the deposits, the inner surface of the copper alloy pipe is treated with at least 5 ppm
The tube is treated with a cleaning solution made by adding a surfactant to a silicate aqueous solution containing silicate at the above ratio, and then the inner surface of the tube is coated with a specified resin paint for 10 to 30 minutes.
A method for recycling heat exchange tubes characterized by forming a 30μ anti-corrosion coating film. 2. The method according to claim 1, wherein the surfactant is added to the aqueous solution at a ratio of about 2/3 or less to the silicate.