JPS6154473B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of manufacturing a heat exchange tube with an inner surface anticorrosive coating, and in particular, a method for manufacturing a heat exchange tube with an anticorrosive coating on the inner surface, and in particular,
This invention relates to a manufacturing method that improves the heat resistance, cathodic protection, abrasion resistance, etc. of long, small-diameter heat exchange tubes having an anticorrosive coating on their inner surfaces. Conventionally, heat exchange tubes (heat transfer tubes) used in condensers and other heat exchangers in thermal power plants, chemical factories, ships, etc. have been made using brass with aluminum, arsenic, and other silicon added to them. So-called special brass tubes and copper alloy tubes such as so-called cypronickel tubes made of copper, nickel, and iron are widely used, but these heat exchangers use seawater or river seawater as cooling water. Various types of corrosion occur on the inner surfaces of these heat exchange tubes. and,
When such corrosion occurs, deposits containing corrosion products adhere to the inner surface of the heat exchange tube, reducing the heat transmission coefficient of the heat exchanger. Therefore, as an effective method for preventing internal corrosion of heat exchange tubes, the present inventors have previously proposed a method for preventing corrosion in Japanese Patent Publication No. 56-45079 and Japanese Patent Application Laid-Open No. 56-166271. We have proposed a method of forming a coating film to a predetermined thickness on the inner surface of the pipe, and this method is superior to other methods in terms of corrosion resistance and workability, so it has already been put into practical use today. It's reached. In the case of such a heat exchange tube with an anticorrosive coating formed on the inner surface of the tube, a cooling fluid such as cooling water is allowed to flow inside the heat exchange tube, while water vapor flows outside the heat exchange tube. The above-mentioned anti-corrosion coating has a heat-resistant property because the high-temperature fluid to be cooled, such as In addition, when seawater is used as the cooling fluid, since drifting sand is present in the seawater, it is necessary to prevent wear caused by such drifting sand. In addition, for such heat exchange tubes, a cathodic protection device is installed to prevent corrosion at the end of the tube, but even in such a cathodic protection environment, a cathodic protection device is installed to prevent the coating from peeling off. There is a need to. By the way, at present, when manufacturing such a heat exchange tube with an inner surface anti-corrosion coating film, an ordinary drying (normal temperature drying) type resin paint is selected as the paint used for coating the inner surface of the heat exchange tube. This is because such heat exchange tubes are long thin tubes with a small diameter of about 10 to 40 mmφ and a length of about 10 m to about 40 m, and the inner surface of such long thin tubes is to be painted. Therefore, it is necessary to select a paint that has good heat transfer properties, and has excellent spray coating properties and quick drying properties. As such a paint, an air-drying resin paint, such as an alkyd resin paint or an epoxy resin paint, is generally used. However, in heat exchange tubes in which an anticorrosive coating film is formed using such an air-drying resin paint, generally the heat resistance, cathodic protection, and
The abrasion resistance was poor, and therefore special consideration had to be taken to improve the cathodic protection properties of the pipe ends, and the lack of such properties meant that the durability of the coating film was poor. There was a problem that the heat exchange tube had a bad coating, and for this reason, it was necessary to frequently repaint the inner surface of the heat exchange tube after it was installed in the heat exchanger. The present invention has been made against this background, and its purpose is to provide an improved manufacturing method for heat exchange tubes with an anticorrosive coating on the inner surface, and in particular, The object of the present invention is to provide an effective method for manufacturing heat exchange tubes that improves heat resistance, cathodic protection, and abrasion resistance, which are disadvantages of conventional air-drying resin coatings. In order to achieve this object, in the present invention, the inner surface of the long thin tube to be installed in the heat exchanger is uniformly coated with an air-drying resin paint and allowed to dry at room temperature. Afterwards, the inner-coated thin tube was heat-treated to bake the inner surface coating of the thin tube. As described above, in the manufacturing method of the heat exchange tube with the inner surface anticorrosion coating film according to the present invention, as in the conventional method,
After an air-drying resin coating with a uniform thickness is formed on the inner surface of the heat exchange tube, this resin coating is heat-treated to become baked onto the inner surface of the tube. As a result, it has been found that the durability of the paint film is significantly improved, and in particular, the heat resistance and cathodic protection properties can be improved, which can overcome the drawbacks of conventional air-drying resin paint films. It was. Further, according to the present invention, a predetermined anticorrosion coating film is effectively formed on the inner surface of the heat exchange tube with a uniform thickness using an air-drying resin paint that has excellent spray coating properties and quick drying properties. However, there is no problem of adverse effects on heat conductivity or corrosion resistance due to non-uniformity of the coating film.
In addition, if a baking type resin paint is used instead of an air-drying type, spray painting is extremely difficult, and even if it can be applied, it takes a long time to dry, and it may form. The thickness of the coating film becomes non-uniform, causing considerable problems in terms of heat conductivity and corrosion resistance. By the way, the material for the heat exchange tube used in the present invention is any tube material conventionally used for heat exchange tubes, but in particular, in the present invention, aluminum brass tubes are applicable. , e.g. 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. In addition, such a heat exchange tube has an inner diameter of, for example, 10
~40mmφ, especially around 15~25mmφ, length 4~
It will be used as a long thin tube of about 40 m, especially about 5 to 25 m. For such small-diameter, long heat exchange tubes, a predetermined air-drying resin paint is uniformly and thinly applied to the inner surface of the tube using a coating method such as spray painting. An anticorrosive coating film is formed with a predetermined thickness, for example, about 50 microns or less, generally about 10 to 30 microns. In this air-drying resin paint, alkyd resin,
Vinyl resin (vinyl chloride, vinyl acetate, etc.),
One or more organic polymer resins (including modified products) consisting of polyurethane resins, epoxy resins, and acrylic resins (acrylic acid esters, etc.) are used, and such organic polymer resins are It is dissolved in a solvent such as alcohol, ester, ether, ketone, aliphatic or aromatic hydrocarbon to form a film-forming liquid composition (paint) that dries at room temperature. be. 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. Furthermore, as is well known, such paints can be applied as one-component, two-component, or multi-component types. Furthermore, 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 addition, the heat exchange tube whose inner surface is coated with a predetermined air-drying resin paint is dried at normal temperature, for example, naturally, to form an anticorrosion coating film having a predetermined thickness. Then, the heat exchange tube is subjected to heat treatment according to the present invention. This heat treatment is generally carried out by placing the heat exchange tube with the inner surface coated in a heating furnace maintained at a predetermined temperature and holding the tube for a predetermined period of time. In addition to the oxidizing atmosphere, a reducing atmosphere, and even an inert atmosphere such as N ₂ can be used. In addition, as for the heat treatment temperature, there is a desirable temperature range depending on the type of air-drying resin paint used, and it is difficult to limit it unambiguously, but generally the upper limit is 330℃ and the lower limit is 330℃.
It is preferable to heat treat the internally anticorrosive coated pipe at a temperature of 60℃, particularly 100 to 300℃, especially 150 to 250℃, and the heat treatment time is up to about 90 minutes, preferably 10 to 60℃. It will be selected between minutes. Through such heat treatment, the coating film made of the air-drying resin paint formed on the inner surface of the heat exchange tube becomes baked onto the inner surface of the tube.
As a result, heat resistance, cathodic protection, and abrasion resistance, which were disadvantages of conventional air-drying resin coatings as mentioned above, were improved, and the durability was significantly improved. Therefore, it has now become possible to advantageously produce an industrially useful heat exchange tube with an inner surface anticorrosive coating film. Moreover, in the case of the heat exchange tube with the inner surface anticorrosive coating film manufactured according to the present invention, the polarization resistance value R of the coating film after heat treatment (baking) is
Even when the resistance is 1,000,000 (Ωcm ² ) or more, there are almost no problems such as deterioration of heat transfer performance, which has been pointed out in the past, and it is therefore recognized that it can be fully used as a heat exchange tube. ing. Next, Examples will be shown to clarify the present invention more specifically, but it goes without saying that the present invention is not limited in any way by the description of the Examples. Example 1 Aluminum brass material (JIS-H-3300 C-6871; Brass seamless pipe for condenser) with an outer diameter of 25.4 mm, wall thickness of 1.25 mm, and length of 10000 mm was treated with an air-drying commercially available alkyd resin. A rust-preventing paint [LZI Primer manufactured by Chugoku Paint Co., Ltd.] was spray-painted over the entire length to a film thickness of 20 μm to obtain an inner anti-corrosion coated pipe (Sample A). Similarly, using a commercially available air-drying epoxy resin paint [Million 1A manufactured by Kansai Paint Co., Ltd.], paint was applied using a spray coating method to a film thickness of 1.5 μm. One internally anti-corrosion coated tube (sample B) was obtained. Next, after the coating films of the two samples A and B were sufficiently dried, the samples were charged into a kerosene-burning reducing gas furnace (roller hearth type) and heat-treated at a temperature of 200°C for 30 minutes. The inner coating film of each sample was baked. In addition, as comparison materials, samples were taken from each painted tube (samples A and B) without such baking treatment, and samples C and D
I got it. The four types of samples thus obtained were cut into lengths of about 1500 mm, and they were attached to an artificial seawater flow test device to conduct a water flow test. In this water flow test, specified artificial seawater was passed continuously for 6 months at a flow rate of 2 m/s under cathodic protection conditions such that the potential at the end of the tube was -650 mV (calomel electrode reference). . After this water flow test,
Each sample tube was cut in half in the axial direction, and the adhesion of the inner surface coating was evaluated using a cross-cut tape test. The cross-cut tape test involves cutting an X shape with a length of about 10 mm on the inner surface of the half-split part using a knife, pasting adhesive tape on top of it, and then peeling it off vigorously. This is a method of evaluating the area and degree of peeling of the coating film caused by the adhesive tape. The results are shown in Table 1 below, and as is clear from Table 1, in the case of samples A and B, which were subjected to the prescribed heat treatment according to the present invention, the coating film remained strong even under cathodic protection. While the adhesion was not impaired and the coating film had excellent cathodic protection properties, samples C and D, which were not heat treated, were coated with cathodic protection. It was observed that the adhesion of the film was significantly impaired.

[Table] Example 2 Using an aluminum brass tube (length: 1500 mm) similar to that used in Example 1, an air-drying alkyd resin-based rust preventive paint [LZI Primer manufactured by Chugoku Paint Co., Ltd.] was applied to the tube. After adjusting the viscosity to 25 seconds (20°C) using a No. 4 food cup, spray painting with air spray paint so that the coating thickness after drying is 20μ, and then let it air dry overnight. After that, heat treatment was performed in an air atmosphere furnace under the temperature x time conditions shown in FIG. The various test materials thus obtained were subjected to the following evaluation tests for coating film adhesion performance, and the results are shown in Tables 2 and 3. Test method (a) Original condition: Evaluation with the coating film still formed. (b) Heat resistance: Evaluation after being left in an air oven or autoclave (hot water) at a specified temperature for one week. (c) Bending property: Cut the test tube in half, bend it to 90 degrees, and visually observe the condition of the coating on the edges. (d) Water resistance: Evaluation after being immersed in 3% saline solution at 80°C for one day, or after passing room temperature artificial seawater through the pipe at a flow rate of 2 m/sec for one month. (e) Cathodic corrosion resistance: Using the test tube as a cathode, applying cathodic protection using an external power source at a corrosion protection potential of -550 to -750 mV (calomel electrode standard), applying 3% saline at a flow rate of 2 m/sec inside the tube. Evaluation after watering for a week. (f) Crushing corrosion resistance: Evaluation after passing artificial seawater containing 500ppm of alluvial sand with a particle size of 500μ through the pipe at a flow rate of 2m/sec for 6 months. Evaluation method (1) Tests (a), (b), (c), (d), and (e) were evaluated using the cross-cut tape test according to the following criteria. ○: No peeling or blistering △: Spot peeling ×: Planar peeling (2) Regarding test (f), the appearance was evaluated by visual inspection according to the following criteria. ○: Peeling area 10% or less △: 10-30% ×: 30% or more (3) Test (c) was evaluated according to the following criteria. 〇: Healthy △: Cracks ×: Planar peeling As is clear from the results in Tables 2 and 3,
By applying heat treatment according to the present invention to an anticorrosion coating film formed with an air-drying alkyd resin paint, heat resistance and cathodic corrosion resistance are improved, and furthermore, crushing corrosion resistance is improved. It is recognized that In particular, the adhesion of the coating film in high-temperature water is improved for specimens heat-treated at 75°C or higher, and this effect is remarkable for those heat-treated at 200°C. Furthermore, there is a similar tendency with respect to cathodic corrosion resistance, and the effect is produced by heat treatment at 150°C or higher. In addition, instead of the commercially available resin paint used above, use Shinto Paint, which is a similar alkyd resin paint.
A similar tendency was observed when Chrome Coat R manufactured by Co., Ltd. was used. It was also found that if the heat treatment temperature was too high, powdering of the coating film occurred.

【table】

【table】

[Table] Example 3 Internal corrosion protection was carried out in the same manner as in Example 2, except that an epoxy resin paint [Million 1A manufactured by Kansai Paint Co., Ltd.] was used as the air-drying resin paint, and the thickness of the coating was 15μ. I got a painted tube. Next, the coated tubes were heat treated under various heat treatment conditions as shown in FIG. 4, and the same tests as in Example 2 were conducted to evaluate the adhesion of the paint film. The results are shown in Tables 4 and 5. As is clear from Tables 4 and 5, even when epoxy resin paints are used, the same high-temperature water resistance and electrolytic corrosion resistance as in the case of alkyd resin paints are observed, especially the former at 150°C. As mentioned above, remarkable results were obtained for the latter when heat-treated at 100°C or higher.

【table】

[Table] Example 4 Using a commercially available epoxy resin paint [Epicorton manufactured by Tanabe Chemical Industry Co., Ltd.] as an air-drying resin paint,
An anti-corrosion coated pipe on the inner surface was obtained in the same manner as in Example 2, except that the thickness of the coating film was 15 μm. Next, this internally anti-corrosive coated pipe was subjected to heat treatment under various heat treatment conditions as shown in Table 6, and the thus treated internally anti-corrosive coated pipe was coated with a coating according to the method of Example 2. The adhesion was evaluated and the results are shown in Tables 6 and 7. As is clear from Tables 6 and 7, in this example, while the heat treatment temperature was 150°C,
Heat treatment has been carried out with various treatment times, but even when the treatment time is about 5 minutes, there are signs of improvement in coating film performance, especially when treatment times of 10 minutes or more and up to about 60 minutes are used. , has brought about remarkable effects. It is also recognized that if the processing time is too long (120 minutes), the performance will actually deteriorate.

【table】

[Table] Example 5 Acrylic resin paint [ESBAR #200 manufactured by Shinto Paint Co., Ltd.] (sample material No. 22~
24) and polyurethane resin paint [Polytan #1000 manufactured by Dainippon Toyo Co., Ltd.] (sample materials No. 25 to 28), inner corrosion-resistant coated pipes were formed in the same manner as in Example 2, and then Heat treatment was performed under various heat treatment conditions shown in Table 8, and then coating film performance was evaluated according to the method of Example 2, and the results are shown in Tables 8 and 9. As is clear from the results in Tables 8 and 9,
Even in the case of paint films formed using air-drying acrylic resin paints or polyurethane resin paints, they are less susceptible to heat treatment than paint films formed with alkyd resin paints or epoxy resin paints. Although the performance improvement effect is not so remarkable, 150
The effect can be recognized by heat treatment and baking operations at temperatures of ~200°C.

【table】

[Table] Example 6 The inner-coated tubes obtained in Examples 2 and 3 were treated under various furnace atmospheres shown in Table 10.
Each was subjected to predetermined heat treatment. In addition, the sample material
Sample materials No. 29 to 32 have a coating film formed with the air-drying alkyd resin paint obtained in Example 2, and sample materials No. 33 to 36 have a coating film formed from the air-drying alkyd resin paint obtained in Example 2. This is an inner-coated tube having a coating film formed from the air-drying epoxy resin paint obtained in Example 3. The performance of the coating film was evaluated using the same method as in Example 2 for the various inner-coated tubes with different heat treatment atmospheres obtained in this way, and the results are shown in Tables 10 and 11.
Shown in the table.

【table】

[Table] As is clear from Tables 10 and 11, the heat treatment atmosphere includes air, N ₂ , and reducing gas (CO + H ₂ ;
Regardless of the use of O ₂ = small amount), no influence of the furnace atmosphere on the heat treatment effect was observed, and in either case, the performance was improved in terms of heat resistance, cathodic protection, and even crushing corrosion resistance. Shows enhanced results,
Further, no deterioration in other properties such as workability and water resistance was observed.

Claims (1)

[Scope of Claims] 1. The inner surface of a long thin tube to be installed in a heat exchanger is uniformly coated with an air-drying resin paint, and after drying at room temperature, the inner surface coated thin tube is heat-treated. A method for producing a heat exchange tube with an inner surface anticorrosive coating, characterized by baking the inner surface coating of the thin tube. 2. The manufacturing method according to claim 1, wherein the air-drying resin paint is an air-drying alkyd resin paint, epoxy resin paint, vinyl resin paint, polyurethane resin paint, or acrylic resin paint. 3. The manufacturing method according to claim 1 or 2, wherein the heat treatment is performed at a temperature of 60 to 330°C for 5 to 60 minutes.