JPH0660296B2 - Copper alloy tube with anticorrosion paint film for heat exchanger - Google Patents

Description

TECHNICAL FIELD The present invention relates to a copper alloy pipe with an inner anticorrosion coating film for a heat exchanger, and particularly to the heat transfer performance of the pipe and the properties of the coating film formed on the inner surface of the pipe as an anticorrosion film. The present invention relates to a copper alloy tube as a heat transfer tube, which has improved anti-corrosion resistance without deteriorating.

(Background Art) Conventionally, in a condenser or other various heat exchangers of a thermal power plant, a chemical factory, or a ship, aluminum, arsenic, other silicon, etc. are added to brass as a heat transfer tube,
So-called special brass pipes and copper alloy pipes such as so-called cupro-nickel pipes made of copper, nickel, and iron have been widely used. In these heat exchangers, seawater or river water is used as cooling water. Due to this, various corrosions occur on the inner surfaces of the heat transfer tubes. When such corrosion occurs, deposits containing corrosion products adhere to the inner surface of the heat transfer tube, which lowers the heat transmission coefficient of the heat exchanger.

Therefore, in order to use such a copper alloy tube as a heat transfer tube, various methods have been proposed to prevent corrosion on the inner surface of the tube. Among them, the inventors of the present invention have proposed a Japanese Patent Publication No. 56-4.
As disclosed in Japanese Patent Publication No. 5079 and Japanese Patent Application Laid-Open No. 56-166271, a method of forming an anticorrosion coating film on a pipe inner surface with a predetermined thickness by using a predetermined resin coating is a method for preventing corrosion and workability. Is superior to other methods in terms of
Today, it is already in practical use. The resin coating which gives such an anticorrosion coating is a film-forming synthetic resin together with pigments such as rust-preventive pigments, extender pigments and coloring pigments, anti-settling agents, pigment dispersants, plasticizers and anti-skinning agents. It is configured by appropriately adding additives such as agents. Among these, chromium- or lead-based pigments such as zinc chromate and basic lead chromate are used as the rust preventive pigment.

By the way, the corrosion of the heat exchanger is not limited to the copper alloy pipe that is the heat exchanger pipe (heat transfer pipe), and other materials that compose the water chamber, such as the water chamber wall, valve, and tube plate, are also considered. In addition, even when a predetermined anticorrosive coating is formed on the inner surface of the heat exchanger tube, the inflow that is mixed in the heat transfer fluid (cooling fluid) that is allowed to flow through the heat exchanger tube. It is not possible to completely prevent the peeling of the coating film on the pipe end portion due to the hitting of foreign matter, and when such peeling is caused, erosion, so-called inlet attack is caused at the peeled portion, In order to solve these problems, a cathodic protection device is generally installed in the water chamber of the heat exchanger.

However, in such a cathodic corrosion protection environment, when a copper alloy tube provided with a predetermined inner surface anticorrosion coating film is placed, the inner surface anticorrosion coating film may be subjected to such an anticorrosion effect depending on the conditions of the cathodic protection film. The generated alkali (OH ⁻ ) causes swelling of the coating film, in other words, alkali deterioration, which accelerates the peeling of the coating film, and the heat transfer resistance value of the coating film also increases. Therefore, it has been experienced that the heat transmission coefficient decreases by about 10%.

Thus, such alkaline deterioration causes H ₂ O and O ₂ existing in seawater or the like as a cooling fluid, which has penetrated into the coating film and reached the metal surface under the coating film, due to cathodic protection. It is a phenomenon of deterioration of the coating film that is caused by reacting with electrons supplied from the inside of the metal to the surface of the metal to generate alkali (OH ⁻ ), but with conventional coating films, it is necessary to prevent such deterioration phenomenon. Was difficult.

Further, according to the study by the present inventors, in order to prevent swelling (deterioration) of such an inner anticorrosion coating film under cathodic protection, the underlying film is improved or the coating film thickness is increased. However, it is clear that such measures are effective to a certain extent, but in those measures, in addition to the effect not being sufficient, there is a negative effect in terms of cost and heat transfer performance. Therefore, more effective measures are required.

(Problem to be Solved) Here, the present invention has been made in view of such circumstances, and the problem to be solved is that the inner surface anticorrosion coating is attached to the heat exchanger in which the anticorrosion device is installed. The purpose of the present invention is to further improve the electrocorrosion resistance of a coated copper alloy tube without impairing its heat transfer performance and corrosion resistance, thereby increasing the practicality of the copper alloy tube as a heat transfer tube.

(Solution) Then, in order to solve the problem, the present invention is attached to a heat exchanger in which a cathodic protection device is installed, and under a cathodic cathodic protection environment, a predetermined cooling fluid is circulated in the tube. In a copper alloy tube with an inner anticorrosion coating film as a heat transfer tube, the inner anticorrosion coating film is (a) 1 to 50% by weight of condensed aluminum phosphate with respect to the coating solid content, and (b) A synthetic resin coating material containing 0.5 to 15% by weight of zinc oxide and (c) 5 to 50% by weight of clay and / or talc in a total amount of 10 to 70% by weight. It is characterized by being formed by using.

In short, in the copper alloy tube with the inner anticorrosion coating film according to the present invention, as the rust preventive pigment, instead of the conventional chromate system, a predetermined amount of condensed aluminum phosphate and zinc oxide is used, and as an extender pigment. A predetermined anticorrosion coating film is formed on the inner surface of a copper alloy tube with a synthetic resin paint containing a predetermined amount of clay and / or talc, which causes swelling in a cathodic cathodic protection environment ( Alkali deterioration) is effectively suppressed, and thus the anticorrosion resistance thereof can be remarkably improved.

By the way, as the copper alloy tube material used in the present invention, any tube material conventionally used as a heat transfer tube is targeted, but particularly in the present invention, an aluminum brass tube, For example, JIS-H-3300
-C-6870, 6871, 6872 and other tubes made of aluminum brass materials, cupronickel tubes such as J
A tube made of cupro-nickel material such as IS-H-3300-C-7060, 7150 is preferably used. And, such a copper alloy tube has, for example, an inner diameter of 10
-40mm, especially 15-25mm, length 4-40
m, in particular as a long thin tube of about 5 to 25 m.

Then, on such a small-diameter, long copper alloy pipe, a predetermined resin paint is evenly applied to the inner surface of the pipe by a coating method such as spray painting, and a film having a predetermined thickness is formed thereon. Although an anticorrosive coating film is formed, in the present invention, such an anticorrosive coating film is formed by a coating operation using a synthetic resin coating material containing a specific rust preventive pigment and an extender pigment in a predetermined ratio. Of.

That is, as a synthetic resin coating material used for such an anticorrosion coating operation, generally a dry type (normal temperature drying type) coating material is preferably used, and in such a coating material, an alkyd resin is used as a film forming element. , Epoxy resin, polyester resin, epoxy ester resin, vinyl resin (vinyl chloride, vinyl acetate, etc.), polyurethane resin, acrylic resin (acrylic ester, etc.), and other organic polymer resins (including modified products) 1 type (s) or 2 or more types are used. Then, such an organic polymer resin is dissolved in an appropriate solvent (for example, alcohol-based, ester-based, ether-based, ketone-based aliphatic or aromatic hydrocarbon-based), and as a pigment, a rust preventive pigment, An extender pigment is added, and if necessary, other pigments such as a coloring pigment and an antifouling pigment, and other additives such as an anti-settling agent, a pigment dispersant, a plasticizer, and an anti-skinning agent are appropriately added. Then, the composition is prepared into a liquid composition (coating material) that can be dried at room temperature, and in the present invention, the rust preventive pigment in such coating material is (a) aluminum tripolyphosphate. Condensed aluminum phosphate and (b) zinc oxide such as zinc white are used, and (c) clay (Al ₂ O) is used as an extender pigment.
_{3 · 2SiO 2 · 2H 2 O} ) and / or talc (3Mg
O.4SiO ₂ .2H ₂ O) was used.

In the present invention, the condensed aluminum phosphate (a), which is one component of the rust preventive pigment, is added to the coating solid content (total pigment component + resin solid content + additive solid content.
Add 50% by weight to the coating composition, and add zinc oxide (b), which is another rust preventive pigment component, to 0.5 to 15% by weight relative to the coating solid content. Clay and / or talc (c) as an extender pigment in an amount of 5 to 50% by weight based on the solid content of the coating, and (a) condensed aluminum phosphate and ( The total amount of b) zinc oxide and (c) clay and / or talc is 10 relative to the coating solids.
It was adjusted to be ~ 70% by weight. In particular, the effect of anticorrosion resistance in the present invention can be further enhanced by the combined use of clay and talc as the extender pigment, but it is of course possible to use them alone.

In the present invention, if the amount of the condensed aluminum phosphate as the component (a), which is one of the rust preventive pigments, is less than 1% by weight, the improvement in electrocorrosion resistance cannot be achieved, and If the content exceeds 50% by weight, the coating film formed will be pulverized, and the abrasion resistance of the coating film will decrease, and the spray coatability will also decrease. Cause problems. Even if the amount of zinc oxide as the other component (b) of the rust preventive pigment is less than 0.5% by weight, the anti-corrosion resistance is lowered and the adhesion of the coating film is reduced. On the other hand, when the blending amount exceeds 15% by weight, the abrasion resistance of the coating film deteriorates.

Further, the clay and talc as the extender pigment (c) component, in the total amount thereof, in an amount of less than 5% by weight,
There is a problem that the coating film forming property is deteriorated, a thin film part is locally formed, and the anticorrosion resistance in the thin film part part is deteriorated, and when the compounding amount exceeds 50% by weight, Cause problems such as reduced wear resistance.

Furthermore, with respect to the total amount of the above-mentioned components (a), (b) and (c), if it is less than 10% by weight, the film forming property is deteriorated and it is difficult to improve the electrical corrosion resistance. Further, if it exceeds 70% by weight, the coating film is pulverized, so that the abrasion resistance is deteriorated and the spray coatability is also deteriorated. Therefore, their total amount must be maintained within the range of 10 to 70% by weight.

Then, the resin composition containing the above-mentioned components (a), (b) and (c) prepared in such a blending amount is used to carry out an ordinary coating operation such as spray coating by using a desired copper alloy. An anticorrosion coating film will be formed on the inner surface of the tube. The thickness of the anticorrosion coating film formed on the inner surface of the copper alloy tube is generally determined appropriately according to the type of resin coating material at a thickness that does not give a large heat transfer resistance value. Yes, for example, at a maximum coating film thickness of 50 to 300 μm, especially 30 μm
An inner anticorrosion coating film having a lower heat transfer resistance is formed at a coating film thickness of m or less.

(Examples) Hereinafter, several examples of the present invention will be shown to clarify the present invention more specifically, but the present invention does not have any restrictions due to the description of such examples. It goes without saying that you do not receive it.

In addition to the following embodiments, the present invention further includes various changes and modifications based on the knowledge of those skilled in the art, in addition to the above specific description, without departing from the spirit of the present invention. It should be understood that improvements and the like can be added.

The percentages in the following examples are shown by weight unless otherwise specified.

Example 1 First, outer diameter: 25.4 mm, wall thickness: 1.25 mm, length: 150
0mm aluminum brass tube (JIS-H-3300-C
-6871) as a test tube, and the inner surface of the tube was heated to a high temperature DX gas [12 to 13% CO ₂ +0.1 to 0.6% (CO + H ₂ ).
+ 1000-2000 ppm O ₂ + N ₂ ], 57
Annealing was performed under the condition of 0 ° C. × 30 minutes.

Next, various paints shown in Table 1 below were prepared.
As the film-forming resin, a normally dry alkyd resin (Beckcozol P-470 manufactured by Dainippon Ink and Chemicals, Inc.) was used, and the resin was dissolved in a solvent (xylene).
The rust preventive pigment and the extender pigment shown in Table 1 were added thereto in predetermined proportions and sufficiently dispersed, and then a usual coating film forming additive was added.

Further, in the coating composition shown in Table 1 below, as the condensed aluminum phosphate which is the component (a) of the rust preventive pigment, aluminum dihydrogen tripolyphosphate [K White (K-82) manufactured by Teikoku Chemical Co., Ltd.] is used. As the zinc oxide used as the component (b), Zinc Hua No. 3 commercially available for general pigments was used. Further, the clay (Al ₂ O ₃ .2SiO ₂ .2H) as the component (c) as an extender pigment
₂ O) is 5-10% talc (3MgO.4SiO ₂
.2H ₂ O) was used.

For comparison, a commercially available dry alkyd resin paint (LZI primer manufactured by China Paint Co., Ltd.) was used as No. 20.
Used as. This commercial paint is based on alkyd resin 40
%, Rust preventive pigment (zinc oxide, red lead) 25%, extender pigment (C
aCO ₃ ) 25% and toluene 10%.

Then, a solvent (xylene) was further added to each of the dispersed various coating compositions, and the mixture was diluted so that the flow-down time using a Ford Cup No. 4 viscometer was 26 to 28 seconds, and then, After pouring the coating liquid into the above-mentioned test tube to fill the inside of the pipe and then draining the filled coating liquid,
A film was formed while forcibly removing the volatile solvent component outside the tube. The film thickness of the coating film formed on the inner surface of the pipe is
The target was 15 to 30 μm.

Then, the performance of each of the test tubes on which the inner anticorrosion coating film was formed by using the various paints shown in Table 1 was evaluated, and the effectiveness of the inner coating film as the anticorrosion film was examined, The results are shown in Table 2 below. Each performance evaluation was performed according to the following methods.

(1) Electrocorrosion resistance While a test tube is used as a cathode, an electrocorrosion circuit with a Pb-Ag electrode as an anode is assembled, and a flow rate of 2 m / in each test tube.
The constant potential cathodic protection was continuously performed for one month so that the potential at the end of the test tube was from −800 mV to −1200 mV (based on the calomel electrode) while continuously circulating seawater for 2 seconds. Then, for each test tube that was tested for one month at each potential, after washing the inner surface with water and drying, it was split vertically, and an adhesive tape was attached at a position of 100 mm from the end of the tube, and it was vigorously pushed. After the peeling operation was added, the peeled area was determined by an image diffraction method at three locations of 5 cm × 1 cm in the location.

As a result, when the peeled area of the coating film at the evaluation place exceeds 50%, When the peeled area is small and is less than 25%, the evaluation result of each test tube is shown as Table 2 in Table 2.

(2) Coating film adhesion (wear resistance) Each test tube was immersed in 3% saline solution at a temperature of 80 ° C for 3 days, washed with water and dried, and then an adhesive tape was attached to the coating film surface. The operation of applying and vigorously peeling it off was repeated 10 times at the same place, and the adhesion of the coating film was evaluated by the presence or absence of the exposure of the underlying metal. If the exposed area of the base metal exceeds 50%,
In the case of 50% When the content was less than 25%, the result was shown as ◯ in Table 2.

(3) Coating film forming property When air spray coating is tried on each test tube, it is possible, and at the same time each test tube is left horizontally while forming a coating film by curing at room temperature. When air spray coating is performed, the difference in coating film thickness between the upper and lower portions of the inner surface of the tube is small. For example, when the average film thickness is 20 μm, the film thickness on the lower side is within 50% of the film thickness on the upper side. When the following condition was satisfied, the film forming property was evaluated as good, and when it was not, the film forming property was evaluated as poor, and the result was evaluated. The results are shown in Table 2.

(4) Comprehensive Evaluation Criteria Based on the results of performance evaluation of the above-mentioned electrocorrosion resistance, coating adhesion (wear resistance) and coating formation, the electrocorrosion resistance is -800 mV. In the case of, or in the case of either the coating film adhesion (abrasion resistance) or the coating film forming property ●, it was judged that the film could not be used practically, and the comprehensive evaluation was evaluated as x (impossible).

As is clear from the results shown in Table 2, a test tube having an inner anticorrosion coating film formed by using various coating materials containing the components (a), (b) and (c) according to the present invention in predetermined amounts. (No. 2-5, No. 8-9, No. 12-15 and No. 19)
In each case, both have sufficient coating film adhesion (abrasion resistance) and coating film formability, and are extremely excellent in electrocorrosion resistance.

On the other hand, in the case of using the commercially available paint (No. 20), although it is excellent in the coating film adhesion (wear resistance) and the coating film forming property, it is remarkably excellent in the electric corrosion resistance. It is recognized that it is inferior. Further, (a) as an anticorrosive pigment
If the amounts of the components, the component (b) and the component (c) as an extender pigment, and further the total amount of those pigments deviates from the range specified in the present invention, No. 1, No. 6 to 7, No. .10
As shown in the results of Nos. 11 to 16 and Nos. 16 to 18, the anticorrosion resistance is lowered, and problems are caused in the coating film adhesion (wear resistance) or the coating film formability.

Example 2 External total: 25.4 mm, wall thickness: 1.25 mm, length: 1500 mm aluminum brass tube (JIS-H-3300-C-68)
71), 10% cupro nickel tube (JIS-H-33
00-C-7060) or a 30% cupro-nickel tube (JIS-H-3300-C-7150) as a test tube, as shown in Table 3 in the same manner as in Example 1.
A variety of resin coatings were prepared.

As the paint resin, the normally dry alkyd resin (resin D) used in Example 1 or the normally dry epoxy ester resin (SB-10V manufactured by Sumitomo Chemical Co., Ltd .: resin E) was used.

In addition, the annealing treatment of the 10% cupro nickel pipe is
_{+ H 2): 2~4%,} N 2: 86~87%, O 2: 10
0 to 200 ppm, CO ₂ : using DX gas of the balance composition, performed under the condition of 680 ° C. × 30 minutes, and further 3
In case of 0% cupro nickel pipe, similar DX
Annealing treatment was performed using gas at 720 ° C. for 30 minutes.

Next, after applying the same spray coating apparatus as in Example 1 to the test tube using these four types of coating compositions, the anticorrosion resistance of the anticorrosion coating film formed on the inner surface of the tube The coating adhesion and coating formability were evaluated in the same manner as in Example 1, and comprehensive evaluation was performed based on the evaluation results. The results are shown in Table 4 below.

As is clear from the results in Table 4, N according to the present invention
It was confirmed that the test tubes of Nos. 21 and Nos. 21 to 24 were all significantly excellent in electrocorrosion resistance as well as excellent coating adhesion and coating formation.

(Effects of the Invention) As is clear from the above description, according to the present invention, a cathodic cathodic protection environment, which has been regarded as unavoidable in an inner anticorrosion coating tube attached to a heat exchanger provided with a cathodic protection device, Swelling of organic resin coating underneath (alkali deterioration)
However, due to such measures for improving the anticorrosion resistance, the heat transfer performance and the anticorrosion property of the copper alloy tube with the inner anticorrosion coating film used as the heat transfer tube are impaired. It was also possible to avoid it.

Moreover, the copper alloy tube with the inner anticorrosion coating film according to the present invention is exactly the same as the conventional product in terms of cost and productivity, there is no problem at all, and in the conventional coating system, The base treatment of the material is extremely important, and in some cases it is painted after chromate treatment, and when the existing pipe is targeted, good adhesion cannot be obtained on the sandblasted surface to be implemented. In many cases, the present invention is characterized in that it is less affected by the underlying surface and can be applied to the sandblasted surface of an existing pipe.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shunichi Matsuo 2-chome, Tamagawa, Takatsuki, Osaka 6-506 (56) Reference JP-A-62-4753 (JP, A) “Revised supplement latest pigments edited by Japan Pigment Technology Association” Handbook ”(Sho 52.10.1) Seibundo Shinkosha P.P. 8-9

Claims (1)

[Claims] 1. A copper alloy tube with an inner anticorrosion coating film as a heat transfer tube, which is attached to a heat exchanger provided with a cathodic protection device and allows a predetermined cooling fluid to flow in the tube under a cathodic cathodic protection environment. In addition, such an inner surface anticorrosion coating film has (a) 1 to 5 with respect to the coating solid content, respectively.
0% by weight of condensed aluminum phosphate, (b) 0.
5 to 15% by weight of zinc oxide and (c) 5 to 50% by weight of clay and / or talc in a total amount of 1
A copper alloy tube with an inner anticorrosion coating film for a heat exchanger, which is formed by using a synthetic resin paint containing 0 to 70% by weight.