JPS6154584B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a copper alloy tube with an inner surface anti-corrosion coating for a heat exchanger, and in particular to a tube sheet of a heat exchanger.
This invention relates to a copper alloy tube with an anti-corrosion coating coated on the inner surface with excellent coating adhesion. Traditionally, so-called special brass tubes, which are made by adding aluminum, arsenic, silicon, etc. to brass, have been used as heat transfer tubes for condensers and other various heat exchangers in thermal power plants, chemical factories, ships, etc. Copper alloy tubes such as so-called Cypronickel tubes, which are made of copper, nickel, and iron, are widely used, but because these heat exchangers use seawater or river seawater as cooling water, the heat exchanger tubes are On the inside,
Various types of corrosion occur. When such corrosion occurs, deposits containing corrosion products adhere to the inner surfaces of the heat exchanger tubes, reducing the heat transfer coefficient of the heat exchanger. For this reason, in order to use such copper alloy tubes as heat transfer tubes, various methods have been proposed to prevent corrosion on the inner surface of the tubes. As disclosed in Publication No. 56-166271, etc., the method of forming a predetermined anti-corrosion coating film on the inner surface of a pipe with a predetermined thickness is superior to other methods in terms of corrosion resistance and workability. It has already been put into practical use today. In such a heat exchanger tube with an anticorrosive coating formed on the inner surface of the tube, the adhesion of the coating to the inner surface of the heat exchanger tube becomes a problem because a cooling fluid is allowed to flow through the tube. If this adhesion is poor, it is clear that even if an effective anticorrosive coating is formed, it will lack durability. A cathodic protection device will be installed to prevent corrosion in the parts, but it is necessary to prevent the paint film from peeling even under such a cathodic protection environment. In general, as a base treatment for plating copper products or a base treatment for painting iron-based materials, chemical conversion coating treatment, similar chemical treatment, sandplast treatment, etc. are used, and such base treatment also applies to copper alloy pipes. However, if the former chemical conversion coating treatment or similar chemical treatment is adopted,
In addition to requiring troublesome work such as preparing the treatment liquid and setting treatment conditions, and incurring work management costs, the cost of treating the waste liquid was also high, which posed a problem from an economic point of view. On the other hand, the latter sandblasting process is extremely easy to work with and does not increase costs much because the target surface is the inner surface of the round tube, but it requires cleaning to remove fine powder remaining on the blasted surface. It cannot be said that it provides a satisfactory base for painting. The present invention has been made against this background, and its purpose is to provide a copper alloy tube (heat exchanger tube) with an inner anticorrosive coating film that has excellent coating adhesion. In particular, another objective is to develop a product that is easy and economical and can exhibit excellent coating adhesion even under cathodic protection.
An object of the present invention is to provide a heat exchanger tube with an inner surface anticorrosive coating film. In order to achieve this object, the present invention provides a long copper alloy tube with an inner surface anti-corrosion coating as a heat exchanger, which is attached to a heat exchanger and allows cooling fluid to flow inside the tube. On the inner surface, an oxide film formed by annealing is used as a base, and an anticorrosion coating film is formed on the base using a predetermined resin paint. As described above, the copper alloy tube with the inner surface anti-corrosion coating according to the present invention has an anti-corrosion coating formed on the annealing (oxidation) coating, and the presence of such an annealing coating makes it possible to reduce the corrosion of the coating. The adhesion was significantly improved, and no gas was generated at the interface between the tube surface and the annealed film even under cathodic protection.
Therefore, it was possible to effectively prevent the occurrence of blistering, peeling, etc. of the coating film. Furthermore, such an annealed film has good compatibility with paint, and therefore also has excellent adhesion between the annealed film and the paint film.
In order to form such an annealed film on the inner surface of a copper alloy tube, a normal annealing operation is sufficient, so this coating surface treatment is industrially efficient, has good productivity, and does not require any troublesome work, making it economical. It can be achieved. Here, as the copper alloy tube material used in the present invention, all tube materials conventionally used as heat transfer tubes are applicable, but in particular, in the present invention, aluminum brass tubes, aluminum brass tubes,
For example, aluminum brass materials such as JIS-H-3300 C-6870, 6871, 6872, JIS-H-3300 C-
Tubes made of Cypronickel materials such as 7060 and 7150 are preferably used. And such copper alloy pipes have an inner diameter of about 10 to 40 mm, especially
It is used as a long thin tube with a length of about 15 to 25 mm and a length of 4 to 40 m, especially about 5 to 25 m. Such small-diameter, long copper alloy tubes are annealed before a predetermined anticorrosive coating is formed on the inner surface of the tube. It is formed. This annealed film is an oxide film mainly composed of copper oxide, and oxide films with various thicknesses are formed depending on the annealing conditions, but in particular in the present invention, the film thickness does not exceed 6000 Å. It is desirable that the film has a thickness of about 10 to 3000 Å, and it is recognized that it has better performance than an acid-washed surface. Furthermore, it has been found that even when the film thickness is less than 10 Å or greater than 3000 Å, it is better than a sandblasted surface. Further, such annealing treatment can be carried out under normal conditions generally adopted for copper alloy materials, for example, the annealing temperature is about 400 to 700°C, and the annealing time is about 10 to 700°C. 60
Furthermore, various known atmospheres can be used as the annealing atmosphere, including an inert gas atmosphere such as argon or nitrogen, and a reducing atmosphere containing a small amount of oxygen (on the order of ppm). A gas atmosphere such as a so-called DX gas, which is a gas containing nitrogen and carbon dioxide as main components, carbon monoxide and hydrogen, and a small amount of oxygen, can be suitably used. The copper alloy tube subjected to this annealing operation is
In addition to simply degreasing the pipe obtained by cold drawing, it may also be subjected to sandblasting or other treatments. Then, on top of the annealing oxide film formed to a predetermined thickness on the inner surface of a predetermined copper alloy tube, as in the past, a resin paint capable of forming a predetermined anticorrosive coating is applied in a uniformly thin layer, for example. It is coated with a coating method such as spray painting at a film thickness of about 10 to 30μ,
The desired coating film will be formed. As this resin paint, an air-drying type (room-temperature drying type) paint is generally suitably used, and in such a paint, an alkyd resin, a vinyl resin (vinyl chloride type, vinyl acetate type, etc.) is used as a film forming element. , polyurethane resin, epoxy resin and acrylic resin (acrylic acid ester type, etc.)
One or more organic polymer resins (including modified products) consisting of Alternatively, it is dissolved in an aromatic hydrocarbon (or aromatic hydrocarbon, etc.) to prepare a film-forming liquid composition (paint) that dries at room temperature. In addition, when preparing such paints, pigments such as red lead and iron oxide, and other film-forming auxiliary components are added as necessary, but in particular, the blending of iron oxide components is such that the iron hydroxide film This is desirable because it can be expected to prevent corrosion on the inner surface of the heat exchange tube. In addition, 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, a copper alloy tube with an annealing oxide film formed on its inner surface and an anticorrosive coating formed thereon can be used as a heat exchanger tube by the same method as before. The anti-corrosion coating formed on the inner surface of such copper alloy tubes has an annealing oxide film that causes damage to the inner surface of the tube. It exhibits extremely excellent coating adhesion, and does not generate gas between it and the inner surface of the pipe, even under cathodic protection, and therefore does not cause problems such as blistering or peeling due to such gas. This is where the major feature of the present invention can be found. In addition, when forming the anticorrosion coating film, it is sufficient to simply apply a commonly used annealing treatment to the copper alloy pipe as a base treatment for painting, so the base treatment can be performed extremely easily.
It does not require any troublesome processing or operations, and can be carried out with good productivity and economically. Next, some examples of the present invention will be shown to clarify the present invention more specifically, but it should be understood that the present invention is not limited in any way by the description of these examples. , it goes without saying. Example 1 Aluminum brass material (JIS-H-3300C-
6871) according to the conventional method,
Next, hot rolling, annealing, and acid cleaning were performed, and after further cold rolling, acetone degreasing treatment was performed to obtain a copper alloy sample plate having a thickness of 1 mm. Then,
These sample plates were annealed at a temperature of 650° C. for 30 minutes in various annealing atmospheres shown in Table 1, and specimens each having a width of 10 mm and a length of 50 mm were taken. Note that the DX gas used as the annealing atmosphere in samples No. 6 to 13 was 12% CO ₂ and the remainder
Mainly a mixed gas consisting of _N2 , and a first
It contains a predetermined amount of CO + H ₂ and a trace amount of O ₂ as shown in the table. Next, the various test pieces obtained were subjected to surface conditioning as shown in Table 1, or without any surface conditioning, using an air-drying commercially available alkyd resin-based rust-inhibiting paint. Chrome Coat R, manufactured by Toyo Yoyo Co., Ltd., was applied using the dob coating method to a film thickness of 20 μm. The surface was adjusted by Emery paper finishing using Emery paper #120 polishing, chemical conversion coating treatment using a 2% chromic anhydride and 0.1% sulfuric acid bath, or acid cleaning using a solution containing 3% hydrochloric acid. Regarding the various painted specimens obtained in this way, we examined the adhesion of the paint film immediately after painting, after immersing it in warm water at a temperature of 80°C for 72 hours, and after passing it through artificial seawater at room temperature for 3 months. The adhesion of each coating film was evaluated. Furthermore, each sample was subjected to a water flow test by passing artificial seawater at 2 m/sec for 10 days under cathodic protection, and changing the corrosion protection potential from -500 to -750 mV (calomel electrode standard). The coating film adhesion was also evaluated for each. The adhesion of the coating film was evaluated by the so-called cross-cut tape test. In addition, this cross-cut tape test is to cut an X shape with a length of about 10 mm on the surface of each specimen with a knife, apply adhesive tape on top of it, and then peel it off vigorously. This method evaluates 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 Table 2. Note that Table 2 also shows the evaluation results for the water wettability of each sample before painting as the water wettability angle. As is clear from the results in Tables 1 and 2, the adhesion of the paint film of the specimens with the paint film formed on the annealed film is better than that of the paint film base treatment using emery paper finishing or pickling. It shows excellent coating film adhesion, and depending on the annealing treatment conditions, it can even outperform chemical conversion coating treatment. Thus, the surface altered by annealing (formation of copper oxide) is effective as a paint base and can be transformed into a chemical coating, and is at least better than paper polishing (sandblasting) or pickling. It shows that. It is also clear that those on which an annealed film is formed have excellent water wettability and have good compatibility with paints. Paint film evaluation symbol 〇: No peeling or blistering △: Spot peeling ×: Planar peeling

【table】

[Table] Example 2 A cold-rolled material made of the aluminum brass material obtained in Example 1 was degreased and cleaned with alkali, and further degreased with acetone to obtain a product with a width of 30 mm, a length of 100 mm, and a thickness of 1 mm.
samples were obtained. This sample was annealed in an annealing furnace under the annealing conditions shown in Tables 3 and 4 below, and the film thickness of each of the obtained annealed samples was determined by a cathodic reduction method. The annealed samples were stored in a low-humidity thermostat (26°C) to avoid surface oxidation (so-called discoloration) during storage at room temperature until film thickness measurement and painting. In addition, a 20μ anti-corrosion coating was formed on these various annealed samples in the same manner as in Example 1, and the coated samples were circulated at -400 to -800mV (calomel electrode reference) at 2m/sec. in seawater
After being exposed to cathodic protection (potential changed in 50 mV pitch) for 10 days, the coating peeling status of the painted samples was observed using a cross-cut tape test. The respective results are also shown in Tables 3 and 4. As is clear from the results in Tables 3 and 4,
Both annealed samples are superior to sandblasted samples, and for pickled samples, the thickness of the annealed oxide film is also related, but if the oxide film has a thickness of 10 to 1500 Å, the acid It became clear that the coating film adhesion was superior to that of the washed sample.

【table】

【table】

[Table] Example 3 Drawing tubes (sample Nos. 1, 2, 4, 5) made of aluminum brass material (JIS-H-3300 C-6871) with an outer diameter of 25.4 mm, a wall thickness of 1.25 mm, and a length of 15000 mm. Ten%
Cypronickel material (JIS-H-3300 C-
After degreasing the drawing tubes (sample Nos. 3 and 6) consisting of 7060) with trichlene, reducing gas:
650℃× in DX gas (O ₂ ; 1000ppm)
Each was annealed for 15 minutes. In addition, regarding the drawing tube of sample No. 2, after degreasing, the particle size was 200μ.
Alumina blasting treatment was performed for 30 seconds, followed by annealing treatment under the above conditions. The thickness of the annealed oxide film of the annealed sample thus obtained was measured by a cathodic reduction method and was found to be 150 Å. In addition, among the sample tubes obtained in this way,
Samples Nos. 4 and 6 were subjected to sandblasting to remove the oxide film caused by annealing, and sample No. 5 was pickled with hydrochloric acid. Next, the obtained sample tubes of Sample Nos. 1 to 6 were coated with an air-drying commercially available alkyd resin-based rust preventive paint [LZI Primer manufactured by Chugoku Toyo Co., Ltd.] or an epoxy resin-based paint [Shinto Paint Co., Ltd.]. ) neogose
200] was coated on the entire length using a spray coating method so that the film thickness was 20 μm, thereby obtaining internally anti-corrosion coated pipes. The various types of internally anti-corrosion coated tubes obtained in this way were each set in an artificial seawater flow device, and a three-month continuous water flow test was conducted while the tube ends were electrolytically protected at -700 mV (calomel electrode standard). After that, the adhesion of the paint film on the inner surface of the painted pipe after the test was evaluated using the cross-cut tape test method.
The results are shown in Table 5 below.

【table】

[Table] As is clear from the results in Table 5, Samples Nos. 1 to 3 according to the present invention all exhibit excellent coating film adhesion to the cathodic protection of the tube ends. On the other hand, for samples Nos. 4 to 6, which used sandblasted or pickled paint bases, the adhesion of the paint film was impaired due to cathodic protection.
As a result of the cross-cut tape test, it was found that it was easier to peel off.

Claims (1)

[Scope of Claims] 1. A long copper alloy tube with an anti-corrosion coating on the inner surface as a heat exchanger, which is attached to a heat exchanger and allows a cooling fluid to flow inside the tube, and an oxide film formed by annealing is provided as a base layer. A copper alloy tube with an inner surface anticorrosive coating for a heat exchanger, which has an anticorrosive coating coated thereon with a predetermined resin coating. 2. The copper alloy tube according to claim 1, wherein the oxide film is formed with a thickness not exceeding 6000 Å. 3. The copper alloy according to claim 1 or 2, wherein the oxide film is formed by an annealing operation in a reducing gas atmosphere containing a slight amount of oxygen or in an inert gas atmosphere. tube.