JPH01273998A - Thermal transmitting pipe for heat exchanger - Google Patents

Abstract

PURPOSE:To keep a superior anti-corrosion characteristic of an artificial protective film and improve an anti-staying characteristic by a method wherein an outer-most layer arranged at an outer-most surface of an inner surface of a main body of a pipe made of metal or alloy and having an organic resin with a contact angle in respect to water more than a specified value and an intermediate layer composed of epoxy resin are provided. CONSTITUTION:As a flow speed of sea water flowing within a pipe is 0.5 to 2m/sec, a contact angle more than 80 deg. is required as a lower limited contact angle required for preventing an adhesion of living animals. Due to this fact, as organic resin at the outer-most surface layer, one with a contact angle of more than 80 deg. is applied. In this way, as resin having a contact angle more than 80 deg., for example, a silicone resin can be applied. So, in order to improve a close fitness between the outer-most surface layer composed of resin having a large contact angle and a raw surface, an intermediate layer composed of epoxy resin is arranged between the main body of pipe of metal or alloy and the outer-most surface layer. With this arrangement, adhesiveness between the organic resin at the outer-most surface layer and the base surface metal or alloy is improved. The epoxy resin has a more superior adhesiveness between it and silicone resin preferable for the outer-most surface layer as compared with other resins.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heat exchanger tube for a heat exchanger, the inner surface of which is provided with an anticorrosive coating.

[Prior Art] Aluminum brass or cupronickel tubes are used as heat transfer tubes in condensers and various heat exchangers in thermal power plants, chemical factories, etc. In order to protect the inner surfaces of these tubes from corrosion, a method has conventionally been used in which ferrous ions are injected into flowing cooling water to form a protective film on the inner surfaces of the tubes. However, in recent years, due to environmental conservation issues, instead of forming a protective film by implanting ferrous ions, a method has been adopted in which an artificial protective film is formed using an organic resin on the inner surface of the pipe. Opportunities for heat exchanger tubes to be used are increasing.

[Problems to be Solved by the Invention] However, since the organic resin used in conventional heat transfer tubes does not have antifouling properties, when untreated seawater is used as cooling water, marine organisms such as slime may There was a risk that heat transfer performance would deteriorate due to adhesion of the metal to the inner surface of the tube.

The present invention has been made in view of these problems, and is a heat exchanger transmission film that maintains the excellent anticorrosion properties of an artificial protective film made of organic resin and exhibits excellent antifouling properties. The purpose is to provide heat tubes.

[Means for Solving the Problems] The heat transfer tube for a heat exchanger according to the present invention has an outermost surface layer made of an organic resin and having a contact angle with water of 80 degrees or more, which is provided on the outermost surface of the inner surface of the tube body made of metal or alloy. and an intermediate layer made of epoxy resin and disposed between the outermost surface layer and the tube body.

U action] In the present invention, the outermost layer has a contact angle with water of 80
Since it is made of an organic resin of at least 100% of organic resin, shellfish, seaweed, etc. cannot adhere to this outermost layer, and it has excellent antifouling properties.

In addition, since an intermediate layer made of epoxy resin is placed between this outermost layer and the metal or alloy tube body,
Adhesion between the outermost layer and the base metal is also high.

-A-wise, the mechanism by which shellfish or seaweed attach is thought to be as follows. That is, these shellfish or seaweeds secrete sticky substances (proteins or polysaccharides) from their bodies, and biochemical synthesis reactions occur in the presence of seawater. This reaction produces adhesive cement, which allows the shellfish or seaweed to adhere to the surface of objects that are in contact with seawater.

The organic resins used in conventional heat exchanger tubes with anti-corrosion coatings on their inner surfaces have not been able to avoid such adhesion caused by adhesive cement.

Therefore, the inventors of the present application repeatedly conducted various experimental studies on ways to weaken the adhesion force caused by adhesive cement, and as a result, by forming an organic resin with a large contact angle to water on the outermost layer, the adhesion caused by adhesive cement was effectively avoided. I found out that it can be done. In this case, considering that the flow rate of seawater flowing inside the pipe is 0.5 to 2 m/sec, the lower limit of the contact angle required to prevent biofouling is a contact angle of 80 degrees or more. be. Therefore, as the organic resin for the outermost surface layer, one having a contact angle of 80 degrees or more is used. As described above, examples of resins having a contact angle of 80 degrees or more include silicone resins.

Resins with large contact angles have the disadvantage that, while they are difficult for living things to adhere to, they also have low adhesion to the base metal or alloy. If a resin that has poor adhesion to the substrate is used in this way, the interface between the substrate and the coating film is likely to peel off when the coating film is scratched.

Therefore, in order to improve the adhesion between the outermost layer made of resin having a large contact angle and the substrate, an intermediate layer made of epoxy resin is provided between the metal or alloy tube body and the outermost layer. This improves the adhesion between the organic resin of the outermost layer and the base metal or alloy.

The reason why the resin for the intermediate layer is limited to epoxy resin is that epoxy resin has superior adhesion to silicone resin, which is suitable for the outermost layer, compared to other resins. This is thought to be because hydrogen bonds are formed between oxygen in the epoxy resin and oxygen in the silicone resin.

[Example] Next, the results of actually manufacturing a heat exchanger tube for a heat exchanger according to an example of the present invention and measuring its antifouling performance, anticorrosion performance, heat transfer performance, etc. will be described. The test tube was prepared by using an aluminum brass tube (diameter: 26 mm, thickness: 1.2 mm, length: 1,000 mm) as a raw tube, and paint was applied to its inner surface using an airless spray method. First, the paint for the intermediate layer was prepared by mixing a commercially available epoxy resin and a pigment (Fe203). Then, an amine curing agent was added to this paint to cure it at room temperature.

On the other hand, for comparison, a pipe was prepared whose inner surface was coated with a paint using alkyd resin and vinyl chloride resin. The coating film thickness was 10 μm in both cases.

Next, as the outermost layer, a room temperature curing silicone resin, which is an organic resin having a contact angle with water of 80 degrees or more, was applied onto the intermediate layer. Next, after being cured by standing at room temperature for 48 hours, this tube was subjected to each test described below. For comparison, tubes were prepared in which alkyd resin, vinyl chloride resin, or acrylic resin was coated on the intermediate layer. The coating film thickness was 10 μm in both cases.

In the water flow test, 2 m of natural seawater from the Kanmon Strait was placed inside each test tube.
Water was passed through the tube at a speed of 1/2 for about 5 months from June to November. The antifouling property and adhesion of the coating film after the water flow test were evaluated for the following items.

■Measurement of contact angle The contact angle of the coating film with water was measured before and after the water flow test. To measure this contact angle, a water droplet is formed on the cleaned paint film, and the radius (a) of the contact area between the paint film and the water droplet and the height (h) of the water droplet are measured. From this measurement result, the following (1) ) Calculated based on the formula.

tan (θ/2) = h/a −・−−(1
) However, θ: Contact angle a: Radius of contact part h: Height of water drop ■Contamination status of tube inner surface After water flow, the adhesion status of slime, fujibo, etc. was visually observed.

(2) Measurement of Heat Transfer Resistance The measurement conditions were as follows: saturated steam at 100°C was passed outside the tube, and industrial water at room temperature was passed inside the tube at a flow rate of 2.0 m/sec. The following (2) is obtained from the measured values of the test tube and new tube under the same conditions.
The fouling coefficient was determined using the formula, and this value was taken as the heat transfer resistance.

7=1/K 1/Ko --(2>(at first, γ: contamination coefficient: Thermal transmission coefficient of the test tube KO: Thermal transmission coefficient of the new pipe ■ Adhesion of silicone resin to the coating film before water flow A slit-like scratch was made, and after water was passed through it, the state of deterioration of the coating film in that area was observed using a stereoscopic microscope (20x magnification).

The measurement results of each of these characteristics are summarized in Table 1 below.

The tubes in which silicone resin was formed on the surface layer (Example and Comparative Examples 4.5) had a contact angle as high as 100 degrees after passing water, and as a result, the inner surface of the tube was not contaminated, so the increase in heat transfer resistance was small. On the other hand, with resins such as alkyd, vinyl chloride, and acrylic, the contact angle before and after passing water is low, less than 80 degrees, and as a result,
After water was passed through, the inner surface of the tube became more contaminated, and the heat transfer resistance increased significantly.

In addition, even if the surface layer is silicone resin, if the intermediate layer is alkyd (Comparative Example 4) or vinyl chloride (Comparative Example 5), the scratches on the coating film after water passage are the starting point for peeling of the silicone resin. It was recognized that On the other hand, in the case of the example tube in which the intermediate layer was made of epoxy resin, no such peeling was observed.

Regarding corrosion resistance, excellent properties were obtained in both Examples and Comparative Examples, except for those in which the resin peeled off.

[Effects of the Invention] As described above, according to the present invention, since an organic resin having a large contact angle with water is formed on the outermost surface, excellent antifouling properties are exhibited, and as a result, transmission due to biological fouling is prevented. A heat exchanger tube for a heat exchanger can be obtained in which the increase in thermal resistance is extremely small and the corrosion resistance is also high.

Claims (1)

[Claims] (1) An outermost layer made of an organic resin provided on the inner surface of the metal or alloy tube body and having a contact angle of 80 degrees or more with water, and an epoxy resin disposed between this outermost layer and the tube body. 1. A heat exchanger tube for a heat exchanger, comprising an intermediate layer made of resin.