JPH0765874B2 - Heat transfer tube for U-shaped heat exchanger and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat transfer tube for a heat exchanger in which cooling water such as seawater, river seawater or fresh water flows, and a method for manufacturing the same, and particularly U
The present invention relates to a heat transfer tube for a U-shaped heat exchanger, which is curved in a V shape and has an inner surface formed with a corrosion-resistant protective coating for preventing corrosion due to cooling water, and a method for manufacturing the same.

[Prior Art] A pipe material made of copper or a copper alloy has been conventionally used as a heat transfer pipe for a heat exchanger that allows sea water, river sea water, or fresh water to flow as cooling water on the inner surface of the pipe. In this case, in order to prevent corrosion due to cooling water, a protective film containing, for example, heat of hydroxylation as a main component is often formed on the inner surface of the pipe. In general, the protective film containing iron hydroxide or the like as a main component is formed by a method of injecting ferrous ions or the like into the cooling water flowing through the heat exchanger. However, this method requires a certain period of time until the protective film is formed after the start of water flow, so when exposed to severe corrosion conditions at the beginning of water flow of cooling water,
There is a drawback that the film formation on the inner surface of the heat transfer tube cannot be completed in time and a sufficient anticorrosion effect cannot be obtained.

Therefore, a method of forming a protective film such as an anticorrosive film in advance before starting to use the heat exchanger has been adopted. In this type of heat exchanger heat exchanger tube, the protective coating must be thin and uniform in order to prevent deterioration of the heat transfer performance due to the coating. Therefore, such a protective film is generally formed by spraying the film-forming substance from the spray nozzle while passing the spray nozzle onto the inner surface of the pipe.

[Problems to be Solved by the Invention] However, conventionally, this heat transfer tube with an inner surface protective film is limited to a straight tube, and for a heat exchanger using a bent tube having a U-shaped curve, There is a problem that this technology has not been put to practical use.

That is, when the protective coating is formed on the inner surface of the heat exchanger tube for heat exchangers, the spray nozzle is passed through the spray nozzle while spraying the coating film-forming substance, as described above. The airless spray method is generally adopted as a method for spraying this film-forming substance, but the spray nozzle for airless spray is 12
Since it is necessary to jet a coating liquid with a high pressure of 0 to 150 kg / cm ² , it is attached to the nozzle of the pump part as the coating liquid pressurizing means and is large in size, and the coating liquid supply hose and the connection part with this hose Has a complicated structure. Therefore, in the case of a U-shaped curved pipe, it is difficult to pass the spray nozzle over the entire length of the pipe, and thus it is difficult to previously form a protective film on the inner surface of the pipe.

Note that, for example, in Japanese Patent Application Laid-Open No. 2-4195, a protective coating made of a silicone resin paint is formed on the inner surface of a pipe in the state of a straight pipe using an airless spray, and then this is bent into a U shape. Manufactures a U-shaped heat transfer tube with an inner protective film. In this case, the protective film needs to have a ductility large enough to follow the deformation of the pipe due to the normal bending process, and in fact, such a resin film is also available.
However, in the case of a copper or copper alloy heat transfer tube, if it is used as a heat exchanger without removing the residual stress generated by bending, there is a possibility that stress corrosion cracking or the like may occur. Therefore, in this case, it is necessary to bend the straight pipe to bend it into a U-shape and then perform a refining treatment for stress relief. For this reason, the film formed on the inner surface of the tube must be resistant to the high temperature of the refining process. However, general organic resins cannot withstand the high temperature in this refining treatment. On the other hand, some inorganic films can withstand the high temperature during the refining process. However, in the case of an inorganic film, since it has no ductility, it cannot follow U-shaped bending.

For these reasons, a protective coating cannot be formed in advance on a U-shaped curved heat transfer tube, and after the heat transfer tube is bonded to the heat exchanger, ferrous ions are injected into the cooling water. The reality is that a protective film is formed. Therefore, when the corrosive environment is severe, a sufficient anticorrosive effect is not obtained.

The present invention has been made in view of such problems,
An object of the present invention is to provide a heat transfer tube for a U-shaped heat exchanger that can avoid corrosion even when used in a severe corrosive environment, and a manufacturing method thereof.

[Means for Solving the Problem] A heat transfer tube for a U-shaped heat exchanger according to the present invention is a copper or copper alloy heat transfer tube for a heat exchanger having a U-shaped curved shape.
A protective film (organic resin film or film mainly composed of inorganic material) with a thickness of 1 to 50 μm is formed on the inner surface of the tube excluding the area from both tube ends up to the length l (mm) shown in the following formula It is characterized by being.

40 ≦ l ≦ 10d, where d is the inner diameter of the pipe (mm).

Further, a method of manufacturing a heat transfer tube for a U-shaped heat exchanger according to the present invention comprises a step of providing a coating on a predetermined portion of the inner surface of the tube at both ends of a copper or copper alloy tube having a U-shaped curve, A spray nozzle connected to a supply source of a resin-based resin paint or an iron powder suspension (film forming substance) is inserted into the pipe from one end of the pipe and moved forward so that the other end of the pipe projects outside the pipe. After spraying the organic resin paint or iron powder suspension from the spray nozzle at a pressure of 50 kg / cm ² or less, the spray nozzle while spraying the organic resin paint or iron powder suspension. A step of applying the organic resin paint or the iron powder suspension to the inner surface of the pipe by continuously moving backward from the other pipe end toward the one pipe end. And

When the iron powder suspension is used as the film forming substance, a step of applying the iron powder suspension to the inner surface of the pipe and then feeding an oxidizing gas into the pipe is added.

[Operation] In the heat transfer tube for U-shaped heat exchanger according to the present invention, the protective film is not formed on the inner surface of the tube in the region from both tube ends to the predetermined length. In the heat transfer tube, usually, the electrocorrosion is performed from the side of the water chamber to which the cooling water is supplied, so that the tube end is sufficiently protected from corrosion by the electrocorrosion. Therefore, the inner surface of the tube end does not require a protective film. Also, when the heat transfer tube is installed in the heat exchanger, both tube ends of the heat transfer tube are expanded and pressed against the holes of the tube plate and fixed to the tube plate, so a protective film is formed on the tube end part. Even if it is done, this protective film is removed when the tube is expanded. Then, since the removed coating substance adheres to the pipe expanding tool, it is necessary to remove the attached coating substance from the pipe expanding tool during maintenance after the pipe expanding process. Therefore, it is not necessary to previously form a protective coating on the inner surface of the tube end portion, and it is advantageous when the protective coating is not formed when the tube is used.

In this case, the area where the protective film is not formed is the distance from the tube end to the length l (mm). However, l is given by the following inequality (1) as a pipe inner diameter of d (mm).

40 ≦ l ≦ 10d (1) If the area where the protective film is not formed on the inner surface of the pipe is less than 40 mm from both ends of the pipe, the coating material cannot be prevented from adhering to the pipe expanding tool during the pipe expanding operation. Further, if the region where the protective film is not formed on the inner surface of the pipe exceeds the length of 10 times the inner diameter of the pipe from both ends of the pipe, it is impossible to protect the inner surface of the pipe from corrosion by the electrocorrosion protection in the region beyond this. Therefore, 40 from both pipe ends
A protective film is formed on the inner surface of the pipe excluding the region of not less than mm and not more than 10 times the length of the pipe inner diameter.

The thickness of the protective film is 1 to 50 μm. When the film thickness of the protective film is 1 μm or less, the anticorrosive effect of the film is not sufficient.
On the other hand, the protective film is preferably thin from the viewpoint of thermal conductivity, and if the film thickness exceeds 50 μm, the thermal conductivity of the heat transfer tube decreases. Therefore, the film pressure of the protective film is 1 to
50 μm.

Examples of the protective film include an epoxy-based or alkyd-based organic resin and an inorganic film containing iron hydroxide as a main component.

Next, in the method of the present invention, first, a coating serving as a mask is provided on a predetermined portion of the inner surface of both tube ends of a copper or copper alloy tube having a U-shaped curve, and a film is formed on the inner surface of the tube in a later step. It prevents the coating from adhering to this tube end when applying the forming substance. Then, the spray nozzle connected to the supply source of the film-forming substance (organic resin paint or iron powder suspension) is inserted into the pipe from one pipe end and moved forward, and the pipe is moved from the other pipe end. Let it stick out. In the present invention, since the pressure when ejecting the film-forming substance is set to a low pressure of 50 kg / cm ² or less, the coating liquid pressure stage of the spray nozzle is not provided in the nozzle, but the coating liquid supply hose connected to the nozzle is provided. This coating liquid pressurizing means can be provided outside the tube.
Therefore, the portion of the spray nozzle can be downsized, and the spray nozzle can be inserted into the U-shaped curved pipe. Then, the film-forming substance is ejected from the spray nozzle. At this time, the spray pattern of the film-forming substance ejected from the spray nozzle to the outside of the tube is visually confirmed. The defects of the film formed on the inner surface of the pipe often occur because the film-forming substance does not uniformly adhere to the inner surface of the pipe due to clogging of the spray nozzle or the like. For this reason,
After visually confirming a good spray pattern, continuously moving the spray nozzle backward from the other pipe end of the curved pipe toward the one pipe end while ejecting the film-forming substance. The coating material is applied to the inner surface of the pipe. Thereby, even if the injection pressure is low, a uniform protective film can be formed.

When an organic resin coating material is used as the film-forming substance, the organic protective coating film is obtained by drying the organic resin coating material. When an iron powder suspension is used as the film-forming substance, the iron powder is oxidized by feeding an oxidizing gas into the pipe, and a film of an inorganic substance containing iron hydroxide or iron oxide as a main component. Is obtained. In this way, the heat transfer tube for U-shaped heat exchanger having a sound protective coating over the entire length of the inner surface of the tube can be easily manufactured.

[Embodiment] Next, an embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a schematic vertical sectional view showing a heat transfer tube for a U-shaped heat exchanger according to this embodiment, FIG. 2 is an enlarged vertical sectional view thereof, and FIG. 3 is a transverse sectional view thereof.

The heat transfer tube for a U-shaped heat exchanger according to the present embodiment is an inorganic material containing an organic resin or iron hydroxide as a main component in the film forming portion 2 on the inner surface of the heat transfer tube raw tube 3 bent into a U shape. A protective film 4 made of is formed. Both tube ends of the raw tube 3 are the film non-forming section 1. The length 1 of the non-coating portion 1 in the pipe axis direction is 40 mm or more from the pipe end and 10 times or less of the inner diameter of the pipe, as shown in the formula (1). Alternatively, the heat transfer tube base pipe 3 made of a copper alloy is exposed. The film thickness of the protective film 4 formed on the film forming part 2 is 1 to 50 μm.

As described above, in the heat transfer tube for the heat exchanger according to the present embodiment, the protective film 4 is formed on the inner surface of the tube that is curved in a U shape, and thus the anticorrosion effect is high. In addition, since the coating 4 is not formed in the area extending 40 mm or more from the pipe end (non-coating portion 1), the coating material adheres to the pipe expanding tool during pipe expanding when incorporating the heat transfer tube into the heat exchanger. Is prevented. The length 1 of the non-coating portion 1 in the tube axis direction is the inner diameter of the tube.
Since it is 10 times or less, it is protected by cathodic protection after the heat transfer tube is installed in the heat exchanger.

Next, the result of manufacturing the above-mentioned heat transfer tube for U-shaped heat exchanger by the method of this embodiment will be described.

Aluminum brass tube with an outer diameter of 19.0 mm and a wall thickness of 1.65 mm (JI
SH 3300 C6872T) was bent into a U shape with a bending radius of 50 mm, 100 mm or 200 mm. The straight portion of this U-shaped bent tube is 2000 mm. Then, an epoxy-based anticorrosive paint was applied to the inner surfaces of these tubes by the method described below.

That is, first, 20, 40, 50, 60 or 200 m from both ends of the inner surface of the pipe.
A removable cover was provided for parts up to m. And 5
After connecting a hose for supplying paint and air to a small air spray nozzle that supports pressure of 0 kg / cm ² or less, insert this spray nozzle into the pipe from one pipe end and The tip of the spray nozzle was made to protrude from the other pipe end by sequentially passing through the pipe portion, the curved pipe portion, and the other straight pipe portion. Next, after spraying the paint from the spray nozzle and visually confirming that the spray pattern is circular, that is, uniform, spray the spray nozzle to the other straight pipe part, curved pipe part and one straight pipe while continuing spraying. The inner surface of the pipe was painted by moving the parts in order. Then, the ends of the tube were uncovered. In this way, test tubes of Examples 1 to 3 and Comparative Examples 1 to 3 having coatings having the film thickness shown in Table 1 below were obtained.

In addition, a heat transfer tube having a film of an inorganic material containing iron hydroxide as a main component was manufactured by the method described below.

That is, first, the bending tube subjected to the above-described bending was covered with a portion up to 10 or 50 mm from both ends. Then, the iron powder suspension was applied to the inner surface of the tube. In this case, the application of the iron powder suspension to the inner surface of the pipe was performed in the same manner as in the case of the epoxy-based anticorrosive paint described above.

Next, moist air was blown from one end of the tube to oxidize the iron, and a protective film of an inorganic material containing iron hydroxide as a main component was formed. In this way, the test tubes of Examples 4 to 6 and Comparative Example 4 having the film having the film thickness shown in the film thickness column of Table 1 were obtained.

Further, as Comparative Examples 5 and 6, the bending radii of the bent pipe portions are 100, respectively.
Alternatively, a U-shaped bent tube having a protective film of 200 mm was prepared.

Each test tube of these Examples and Comparative Examples was attached to a model condenser, and a water flow test was conducted for 6 hours to examine its performance.

This water flow test was carried out by passing S ^{2 −} at a concentration of 0.1 ppm for 2 hours every day to natural seawater in the Kanmon Strait at a flow rate of 2 m / sec through the pipe. After attaching the tube end of each test tube to the tube plate made of Neval brass by tube expansion processing,
Electric current was applied while the tube plate surface potential was kept at -550 mV SCE by a potentiostatic electrolyzer, and water was passed through while electrical protection was applied to the test tube.

After the water flow was completed, the test tube was halved, and the corrosion depth of the inner surface of each test tube was measured at several points. The maximum value of the corrosion depth is also shown in Table 1.

In addition, a straight tube test tube with a length of 1000 mm was cut out from the straight tube portion of each test tube. Then, set the outside of this straight tube test tube to 100
A steam atmosphere at ℃ was used, 2 m / sec room temperature industrial water was allowed to flow through the tube, and the overall heat transfer coefficient under steam condensation conditions was measured. Under the same conditions, the overall heat transfer coefficient of the new tube having no protective coating on the inner surface was measured, and the inner surface heat transfer resistance of the test tube was determined by the following second formula.

1 / K = 1 / K ₀ + γ (2) where K: measured value of overall heat transfer coefficient of test tube K ₀ : measured value of overall heat transfer coefficient of new tube γ: inner surface heat transfer resistance of test tube The results are also shown in Table 1.

Further, the pipe expanding workability was evaluated based on whether or not it took time to clean the pipe expanding tool by adhering coating fragments to the pipe expanding tool when adhering each test tube to the tube sheet. The results are also shown in Table 1. However, in the table, the case where there is no complication during the pipe expanding work is indicated by ◯, and the case where the film adheres to the tool and cleaning thereof takes time is indicated by x.

As is clear from Table 1, even in comparatively severe corrosive environments in which Comparative Examples 5 and 6 having no protective coating are corroded by 0.25 mm or more, all of Examples 1 to 6 according to the present invention have maximum corrosion depths. Of less than 0.01 mm, the corrosion was extremely small.
Moreover, in each of Examples 1 to 6, the heat transfer resistance was 5.4 × 10 5.
^{It was} as small as ^-5 m ² ℃ h / kcal or less, and no film adhered to the tool during pipe expanding work.

On the other hand, in Comparative Example 1 where the thickness of the protective film is as thin as 0.5 μm, the maximum corrosion depth is as deep as 0.20 mm and the thickness of the protective film is 80
In Comparative Example 2 having a large thickness of μm, the heat transfer resistance was 16.0 × 10 ⁻⁵ m ²
It was extremely high at ℃ h / kcal. Further, in Comparative Examples 3 and 4 in which the length of the non-coating portion from the pipe end was short, the coating adhered to the tool used for the pipe expanding operation, and cleaning of the tool was complicated. As described above, in Comparative Examples 5 and 6 having no coating, severe corrosion occurred over the entire length of the inner surface of the pipe, and the length of the portion of the pipe end where the coating was not formed was equal to the inner diameter of the pipe (15.7 mm).
mm), and in Comparative Example 2 exceeding 10 times,
Corrosion occurred in the non-film-formed area near 0 mm.

[Effects of the Invention] As described above, according to the present invention, the U-shaped heat exchanger heat exchanger tube has an organic surface on the inner surface of the tube excluding the area of 40 mm or more and 10 times or less of the inner diameter of the tube from both ends. Since the system resin film or the inorganic film is formed to have a predetermined film thickness, corrosion of the heat transfer tube is prevented and heat transfer efficiency is high even under severe corrosion conditions. Further, when the heat transfer tube is incorporated in the heat exchanger, the film does not adhere to the pipe expanding tool. Therefore, the U-shaped heat exchanger tube according to the present invention is extremely useful as a heat exchanger tube used in a severe situation.

Further, according to the method of the present invention, a coating is provided on the inner surfaces of both ends of a copper or copper alloy tube having a U-shaped curve, and an organic resin ejected from the spray nozzle at a pressure of 50 kg / cm ² or less. After confirming the spray pattern of the paint or the iron powder suspension, the organic resin paint in the pipe is continuously moved by continuously moving the spray nozzle while ejecting the organic resin paint or the iron powder suspension. Alternatively, since the iron powder suspension is applied to form a protective film on the inner surface of the pipe in a region excluding a predetermined portion of the pipe end, the heat transfer pipe for the U-shaped heat exchanger having the above-mentioned excellent properties is formed. INDUSTRIAL APPLICABILITY The present invention has an extremely excellent effect in preventing corrosion of the heat transfer tube for the U-shaped heat exchanger, such as industrial production.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view showing a heat transfer tube for a U-shaped heat exchanger according to an embodiment of the present invention, FIG. 2 is an enlarged vertical sectional view thereof, and FIG. 3 is a transverse sectional view thereof. 1; non-film forming part, 2; film forming part, 3; heat transfer tube, 4; protective film

Claims (4)

[Claims] 1. A U-shaped curved heat transfer tube for copper or copper alloy heat exchangers, excluding a region from both pipe ends to a length l (mm) shown by the following formula: 1 to 50
A heat transfer tube for a U-shaped heat exchanger, characterized in that an organic resin film having a thickness of μm is formed. 40 ≦ l ≦ 10d where d; pipe inner diameter (mm) 2. A copper or copper alloy heat exchanger heat exchanger tube having a U-shaped curve, excluding the area from both tube ends to a length l (mm) shown by the following formula: 1 to 50
A heat transfer tube for a U-shaped heat exchanger, characterized in that a film mainly composed of an inorganic substance having a film thickness of μm is formed. 40 ≦ l ≦ 10d where d; pipe inner diameter (mm) 3. A step of providing a coating on a predetermined portion of the inner surface of a copper or copper alloy tube having a U-shaped curve at both ends, and a spray nozzle connected to an organic resin paint supply source A step of ejecting an organic resin coating from the spray nozzle at a pressure of 50 kg / cm ² or less after inserting the tube end portion into the tube and moving it forward and projecting the other tube end portion to the outside of the tube,
A step of applying the organic resin paint to the inner surface of the pipe by continuously moving the spray nozzle backward from the other pipe end toward the one pipe end while ejecting the organic resin paint. U characterized by having
Method for manufacturing heat transfer tube for letter-shaped heat exchanger. 4. One of a step of providing a coating on a predetermined portion of the inner surface of a copper or copper alloy tube having a U-shaped curve and a spray nozzle connected to an iron powder suspension supply source. A step of ejecting iron powder suspension from the spray nozzle at a pressure of 50 kg / cm ² or less after the tube is inserted into the tube from the tube end and moved forward to project from the other tube end to the outside of the tube, The iron powder suspension is applied to the inner surface of the pipe by continuously moving the spray nozzle backward from the other pipe end toward the one pipe end while ejecting the iron powder suspension. And a step of feeding an oxidizing gas into the tube, the method of manufacturing a heat transfer tube for a U-shaped heat exchanger.