JPS63233300A - Thermal conducting pipe for heat exchanging operation - Google Patents

Abstract

PURPOSE:To improve anti-corrosion and thermal conducting characteristics and restrict a reduction in the thermal efficiency of a heat exchanging plant as less as possible by a method wherein silicone resin coating mixed with benzotriasole is spread on the inner surface of a copper or a copper alloy pipe to have a coating film having a thickness of a specified value. CONSTITUTION:Silicone resin coating mixed with benzotriasole is spread on an inner surface of a copper or a copper alloy pipe, a thickness of a coated film is made to have 5-20mum. Then, anti-corrosion and durability characteristics similar to or more than to these of coating with a thickness of about 20mum of alkid resin, epoxy resin, fluorine resin, polyurethane resin, vinyl resin and acryle resin coatings and further superior thermal conducting characteristic is applied. Thus, an amount of mixed benzotriasole is satisfactory with a few percent in respect to a silicone resin coating and a much higher volume mixing may decrease thermal conducting performance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heat exchanger tube for a heat exchanger that uses seawater or river/seawater as cooling water, and in particular has improved corrosion resistance, durability, and heat transfer performance.

[Conventional technology]

Copper or copper alloy tubes are generally used as heat transfer tubes in thermal/nuclear power plants, chemical factories, ships, and other various heat exchangers. Seawater or river/seawater is often used as cooling water for such heat exchangers, and deposits containing corrosion products adhere to the inner surfaces of heat exchanger tubes, reducing the heat transfer performance of the heat exchanger.

In order to suppress such corrosion, a trace amount of Fe is added to the cooling water.
When ions are implanted, the inner surface of the heat transfer tube contains iron compounds.
Kimono gets attached and reduces the heat transfer performance of the heat exchanger.

For this reason, Japanese Patent Publication No. 56-45079 discloses a heat exchanger tube in which the inner surface of a copper or copper alloy tube is coated with a synthetic resin paint.

Special Publication No. Sho 59-50269, Special Publication No. Sho 61-5458
Publication No. 4.

Japanese Patent Publication No. 61-54585, Japanese Patent Publication No. 59-1594
This method has been proposed in Japanese Patent Application Laid-Open No. 59-212696, Japanese Patent Application Laid-Open No. 61-79998, and the like. These heat exchanger tubes have alkyd resin paint on the inner surface of copper or copper alloy tubes.

Paints coated with epoxy resin paints, fluororesin paints, polyurethane resin paints, vinyl resin paints, acrylic resin paints, etc., with a coating thickness of approximately 20 μm in consideration of corrosion resistance and durability, have been put into practical use. There is.

[Problem that the invention seeks to solve]

However, when the above-mentioned paint is applied to a thickness of about 20 μm, the heat transmission coefficient decreases by about 10% compared to that without coating. Further, if the coating film thickness is less than 20 μm, sufficient corrosion resistance and durability cannot be obtained.

If the heat transfer performance of heat exchangers decreases, the thermal efficiency of the plant will decrease, leading to an increase in energy costs, so the decrease in heat transfer performance has become an important problem, as well as the corrosion resistance and durability of heat exchanger tubes.

All of the proposals proposed in the above publications focus on corrosion resistance, durability, and workability, and have only made improvements in these areas.They do not give sufficient consideration to the thermal efficiency of the plant, resulting in an increase in energy costs. It invites

[Failure to solve the problem]

In view of this, as a result of various studies, the present invention has been developed by coating the inner surface of copper or copper alloy tubes with silicone resin paint to a thickness of 5 to 20 μm, thereby achieving corrosion resistance and durability equivalent to or higher than conventional inner-coated heat exchanger tubes. As a result of further study, we developed a heat exchanger tube for heat exchangers that has excellent heat transfer performance as well as corrosion resistance and durability.

That is, the heat exchanger tube of the present invention is characterized by coating the inner surface of a copper or copper alloy tube with a silicone resin paint containing benzotriazole to form a coating film with a thickness of 5 to 20 μm on the inner surface of the tube. .

[For production]

The present invention coats the inner surface of a copper or copper alloy tube with a silicone resin paint containing benzotriazole and makes the coating film 5 to 20 μm thick. Provides corrosion resistance and durability equal to or greater than that of paints, fluororesin paints, polyurethane resin paints, vinyl resin paints, acrylic resin paints, etc. applied to a thickness of approximately 20 μm, and provides far superior heat transfer performance. This is what I did. However, it is sufficient to add benzotriazole to the silicone resin paint in an amount of about several percent, and if it is added in a large amount, the heat transfer performance will deteriorate. In addition, in the present invention, the thickness of the coating film is limited to 5 to 20 μm, because if the thickness of the coating film is less than 5 μm, it will be difficult to form a uniform coating film, and sufficient corrosion resistance and durability will not be obtained.
This is because if the thickness exceeds 20 μm, no improvement in heat transfer performance will be recognized compared to a conventional heat transfer tube coated with the above paint to a thickness of 20 μm.

〔Example〕

Using a commercially available silicone resin paint (Fuji Gamma #1100 manufactured by Gamma Kagaku Co., Ltd.), 1% of benzo 1 to lyazole dissolved in alcohol was added to it (99% silicone resin paint: 1% benzotriazole). and mixed uniformly. This is airless spray painted on the entire length of the inner surface of a brass seamless pipe for condenser (JIS H3300-C6780) whose inner surface has been sandblasted, and the inner surface of the pipe is coated with a thickness of 3.
A heat exchanger tube was formed by forming a coating film of ~30 μm. These were subjected to heat transmission coefficient evaluation, polarization resistance value evaluation, jet jet resistance test, and coating film adhesion evaluation, and the results are shown in Table 1 in comparison with conventional heat exchanger tubes. The thickness of the coating film was calculated from the difference in weight before and after the coating film was formed.

Conventional heat transfer tubes include alkyd resin paint (LZI Primer manufactured by Chugoku Paint Co., Ltd.), epoxy resin paint (Million Nα1A manufactured by Kansai Paint Co., Ltd.), and polyurethane resin paint (New Garmet #50 manufactured by Kansai Paint Co., Ltd.).
00), polyurethane resin paint (Rethane Nα4000 manufactured by Kansai Paint Co., Ltd.), vinyl resin paint (China Vinyl Lead Yen Primer manufactured by Chugoku Paint Co., Ltd.), acrylic resin paint (Door Acron H3O0 manufactured by Toa Paint Co., Ltd.)
), apply airless spray coating to the entire length of the inner surface of the condenser brass seamless pipe in the same manner as above, and coat the inner surface of the pipe with a thickness of 20 μm.
A coating film of m was formed.

To evaluate the heat transfer coefficient, heat transfer tubes with internal coatings and uncoated heat transfer tubes were installed in parallel in a heat transfer coefficient measurement device, water vapor at about 100℃ was flowed outside the tubes, and water vapor at about 90℃ was poured into the tubes as cooling water.
C. hot water was flowed at a flow rate of 2 TrL/SeC, the temperature at the inlet and outlet of the cooling water and the temperature of water vapor were measured, and the rate of decrease in heat transfer coefficient n (%) was determined from the following equation.

) = y-r-Cp(θ2-01) θ2-θ1 (a, Q is the amount of heat exchanged (Kcal/11), K is the heat transmission coefficient (Kcal/TrLh'c), V is the cooling water i (m
/h), r is the specific weight of the cooling water <Kg/rtl>, Cp is the specific heat of the cooling water (Kcal/Ny°C), A is the surface area of the tube (
), θ1 is the inlet temperature of the cooling water (°C), θ2 is the outlet temperature of the cooling water (°C), θS is the saturation temperature of water vapor (°C), K
O is the heat transmission coefficient of unpainted seamless pipe (Kcal/m
k'c), 1 is the heat transmission coefficient (Kc
al/ih'C).

To evaluate the polarization resistance value, the test tube was divided in half, and the test piece was coated with an insulating coating, leaving the painted film surface with a surface area of 100 kg.
STM-D-114, 1-75> After measuring the natural potential with respect to a saturated calomel electrode placed outside via the Luggin tube and a salt bridge, using a platinum wire as a counter electrode,
The test piece was cathodically polarized from its natural potential, the value of the steady current flowing at that time was read, and the polarization resistance value R (Ω~) was calculated using the following formula.

R-ΔEXS/I However, 8E is the potential difference (V) between the potential during polarization and the natural potential
, S is the surface area (10 cffl), ■ is the value of the steady current flowing during polarization (A). For the jet jet resistance test, the test tube was cut in half, and the coating film was measured from the tip of the nozzle 2 mm away from the coating surface of the test tube piece. 3% saline solution containing 3% air by volume perpendicular to the surface at a flow rate of 12m/se
C caused a collision, and this was applied for 30 days.

Adhesion was determined by cutting the test tube in half and applying approximately 10 rM to the painted film surface.
After cutting an X character with a length r with a knife and pasting an adhesive tape on it, the peeled part of the coating film was evaluated in the following three grades by peeling it off vigorously.

○ mark: Good condition (no peeling) △ mark: dotted or partial peeling Inventive products No. 1 to 4 are all conventional products No. 8 to N.
It can be seen that compared to No. 0 and No. 13, No. 13 has corrosion resistance and durability equivalent to or better than No. 13, and has far superior heat transfer performance.

On the other hand, a comparison amount Nα5 with a coating thickness of less than 5 μm of silicone resin containing hensitriazole shows excellent heat transfer performance but poor corrosion resistance, and a comparison amount with a coating thickness of more than 20 μm shows heat transfer performance. Performance improvement is not recognized. Ma I
Comparative amount No. 7, which was coated with a silicone resin paint that did not contain benzotriazole, had improved heat transfer performance, but
It can be seen that this product is inferior to the products of the present invention, and also has inferior corrosion resistance and durability.

〔Effect of the invention〕

A silicone resin paint containing benzotriazole is applied to the inner surface of a copper or copper alloy tube, and the thickness of the coating is 5 to 20 mm.
The heat exchanger tube of the present invention made of μ tiles has corrosion resistance and durability equivalent to or higher than conventionally proposed heat exchanger tubes, and has far superior heat transfer performance, which reduces the reduction in thermal efficiency of heat exchange plants. It has remarkable industrial effects, such as minimizing the amount of damage and enabling highly reliable operation.

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Claims (1)

[Claims] Coat the inner surface of a copper or copper alloy tube with a silicone resin paint containing benzotriazole to a thickness of 5 to 20 μm on the inner surface of the tube.
A heat exchanger tube for a heat exchanger, characterized by forming a coating film of m.