JPH0514199B2 - - Google Patents

Description

[Detailed description of the invention]

(Technical field) The present invention relates to a heat exchange tube in a heat exchanger,
Particularly in heat exchange pipes in which seawater or freshwater containing seawater, such as river and seawater, is used as cooling water and is allowed to flow through the pipes, this effectively prevents the adhesion of marine organisms in the cooling water. Regarding. (Background technology) Conventionally, in multi-tube heat exchangers equipped with a large number of heat exchange tubes such as condensers, when seawater or river water containing seawater is used as cooling water, heat exchange tubes are used as heat transfer tubes. It has been recognized that damage may occur due to the adhesion of marine organisms to the inner surface of the vessel or the resulting blockage. That is, such problems include a decrease in heat transfer performance, an increase in head loss, and corrosion of heat exchange tubes, and the decrease in economic efficiency and increase in pump power costs due to these failures have become serious problems. For this reason, mechanical methods such as sponge ball cleaning and nylon brush cleaning are generally adopted as antifouling measures for heat exchange tubes installed in existing heat exchangers. In a heat exchanger equipped with as many as 10,000 heat exchange tubes, due to the non-uniformity of flow conditions, the above-mentioned biological damage may occur in a small number of tubes, or temporary plant damage may occur. Cleaning each heat exchange tube one by one following a plant shutdown is an extremely tedious task, and the cost of such cleaning, as well as the losses associated with plant shutdowns, are enormous. There is. On the other hand, heat exchange tubes for heat exchangers that use seawater as cooling water are generally copper alloy tubes specified in JIS-H3300, but this copper alloy material is made of titanium, iron,
Compared to other materials, it is difficult for living organisms such as shellfish and seaweed to adhere to it, and it is recognized that it is highly resistant to biological fouling. It is believed that this effect of inhibiting biofouling is due to trace amounts of copper ions eluted from these copper alloy tubes. Therefore, in the case of this copper alloy pipe, it is considered necessary for the material to be corroded to an appropriate degree in order to prevent biofouling. However, the various alloys specified in JIS-H3300 are materials developed from the viewpoint of corrosion prevention, and are said to elute less copper ions, so they are less effective in inhibiting biofouling. Prone to problems due to biofouling. In addition, the present inventors have utilized the biofouling inhibiting effect of such copper alloy materials to provide corrosion protection and
As anti-fouling heat exchange tubes, the first application was made in 1983.
No. 195009 (refer to Utility Model Application Publication No. 1987-105990) discloses a double-tube structure tube material using a copper alloy tube specified in JIS-H3300 as the inner tube and a thin-walled titanium tube as the outer tube. was found to be optimal. (Problems to be Solved) However, even with the heat exchange tube having the structure of the copper alloy-titanium double tube proposed by the present inventors, there are still problems to be solved. That is, for the reasons mentioned above, the copper alloy pipe used as the inner pipe does not necessarily exhibit sufficient biofouling resistance. For example, when the flow velocity in the pipe is 0.8 m/sec or less, significant biofouling occurs.
For this reason, heat exchangers in chemical plants and heat exchangers using seawater other than condensers in power plants, which are often designed with a cooling seawater flow velocity of 0.5 to 1 m/s in the pipes, are not sufficiently effective. There is a problem that it is difficult to expect, and the scope of its practical use is narrowly limited. In addition, in a heat exchanger operated at a relatively low flow rate, the corrosion peculiar to copper alloy tubes is less likely to occur, and therefore alloys specified in JIS-H3300, which emphasize prevention of corrosion, are used, such as C6870~6872, C7060,
There is no need to use C7150 etc. in such equipment; instead, as long as it does not cause selective corrosion such as Zn removal corrosion, it is sufficient for the inner pipe of the double pipe mentioned above. Available for use. Furthermore, the manufacturing cost of the pipe material of copper alloy-titanium double pipe is higher than that of conventional single pipe, so if copper alloy pipe with low metal cost can be used, it would be cost-effective. Because of their effectiveness, such materials are expected to be widely available. However, it goes without saying that such a material must satisfy the mechanical properties required for heat exchanger tubes as specified in JIS-H3300. (Solution Means) Here, the present invention has been made to solve such problems, and has biological fouling resistance,
We focused on Cu-Zn alloy as an alloy system that satisfies appropriate corrosion resistance (mainly general corrosion) and low cost, and developed new Cu-Zn-As alloy and Cu-Zn-
The present invention was completed by developing an Al-As alloy and creating a heat exchange tube with a double tube structure using the tube material made of the new copper alloy as the inner tube. That is, the present invention is characterized in that, in a heat exchange tube in which seawater or fresh water containing seawater is made to flow inside the tube as cooling water, the heat exchange tube is made of (a) an outer tube made of a corrosion-resistant material, and (b) ) 65 to 90% by weight of Cu closely adhered to the inner surface of the outer tube;
0 to less than 1.8 wt% Al and 0.02 to 0.06 wt%
It has a double-tube structure consisting of a copper alloy inner tube that contains As and the remainder is Zn and other inevitable impurities. (Specific explanation of the structure) As described above, in the present invention, a novel Cu
-Zn-As alloy or Cu-Zn-Al-As alloy is used, and these new alloys have a wider range of Zn content than existing aluminum brass, and reduce the Al content to improve copper ion elution. (Biological fouling resistance) is increased, and dezincing prevention property is also improved by adding As. By the way, when the amount of Cu in the new copper alloy used in the present invention exceeds 90% (by weight, the same applies hereinafter), the corrosion resistance of the alloy itself becomes insufficient. As the Cu content decreases, the number of eluted Cu ions decreases, so the biofouling resistance decreases, while the corrosion resistance of the alloy improves. However, when the Cu content becomes lower than 65%, a second phase appears,
The corrosion resistance of the alloy begins to deteriorate. Also, Cu
Reducing quantity leads to cost reduction, so
It is desirable to use an alloy with as low Cu as possible. For this reason, the amount of Cu in the alloy is selected to be 65 to 90%. In addition, in the copper alloy used in the present invention, an increase in the amount of Al has the effect of suppressing the amount of Cu ions eluted, and therefore inhibits biological fouling resistance. - When added to Zn alloys, it leads to the formation of a second phase together with the amount of Al, and when the amount of Al exceeds 1.8%,
These obstacles will be noticeable. Of course,
The smaller the amount of Al, the more desirable it is, and there is no problem even if the amount is set to zero. Furthermore, As is intended to prevent dezincification, and in the range of 0.02 to 0.06% contained in conventional alloys, the dezincing prevention effect is brought about without impairing the biofouling resistance of the alloy of the present invention. And the alloy components specified in this way: Cu,
The remaining alloy components other than Al and As are Zn and inevitable impurities, but the content of such Zn is
The range of Zn content is wider than conventional aluminum brass,
Such a Cu-Zn alloy satisfies the mechanical properties required for heat exchanger tubes. In addition, unavoidable impurities contained in the alloy, such as impurities contained in copper metal when melting the alloy, trace elements mixed in from scrap, and elements contained as deoxidizing agents, such as Fe, Si, Ni,
There is no problem with Mn, Sn, Pb, Ti, P, etc. as long as they are within the range specified by JIS-H3300 or their total amount is 0.3% or less. Further, when the tube material made of the novel copper alloy according to the present invention is used as the inner tube of a heat exchange tube having a double tube structure, the tube wall thickness is appropriately selected depending on the purpose. However, even if a corrosion hole were to occur through the wall thickness due to the elution of copper ions, no problem would occur because the outer tube is backed up on the outside. In this sense, the material constituting such an outer tube must be a corrosion-resistant material, and especially considering the problem of ammonia attack when used in a condenser, such an outer tube must be made of a corrosion-resistant material.
Preferably, the tubing is made of titanium material (including alloys). In manufacturing a heat exchange tube having a double tube structure consisting of an inner tube made of a novel copper alloy and an outer tube made of a predetermined corrosion-resistant material according to the present invention, known drawing methods and hydraulic tube expansion methods are used. By applying such methods as appropriate, a copper alloy inner tube having the desired characteristics is brought into close contact with the inner surface of a predetermined outer tube. Although tensile residual stress occurs when the drawing method is used, under the environment in which the heat exchanger is used, this does not cause problems such as stress corrosion cracking, and when using the hydraulic pipe expansion method, residual compressive stress occurs. However, this does not pose any practical problems. In addition, when attaching the heat exchange tube according to the present invention obtained in this way to the tube plate of a predetermined heat exchanger, it is possible to apply a technique such as a normal roll tube expansion method. When installing this heat exchange tube, an anaerobic adhesive may be used to increase adhesion and water density, and if necessary, a cathode may be used to prevent galvanic corrosion between the tube and the tube sheet. It goes without saying that the anti-corrosion mechanism should be installed appropriately. (Effects of the Invention) As described above, in the heat exchange tube according to the present invention, in a heat exchanger that uses seawater or fresh water containing seawater as cooling water, a specific copper alloy tube is provided on the inner surface of the heat exchange tube. is placed as an inner tube, and copper ions, which have a biological adhesion prevention effect, are advantageously eluted into the cooling water flowing through the tube, so it effectively prevents marine organisms from adhering to the inner surface of the heat exchange tube. Furthermore, even if the inner tube section were to disappear due to seawater corrosion, there is an outer tube made of corrosion-resistant material, especially titanium material, which effectively prevents seawater from leaking outside the tube. It will be blocked. Moreover, the heat exchange tube according to the present invention can be used in a heat exchanger operated at a relatively low flow rate, compared to a heat exchange tube made of a copper alloy-titanium double tube previously proposed by the present inventors. It exhibits excellent resistance to biological fouling and satisfactorily meets the demand for cost reduction. (Examples) Next, some examples of the present invention will be shown to clarify the present invention more specifically, but the present invention is not limited in any way by the description of those examples. It goes without saying that it is nothing.
Note that the percentages in the examples are expressed on a weight basis. First, copper alloys having various alloy compositions shown in Table 1 below are melted in the atmosphere in a graphite crucible using a high-frequency electric furnace, and from the obtained molten metal, a copper alloy of 100 mm x 150 mm x 50 mm is melted. were cast respectively. Next, the obtained copper alloy ingot was faceted, hot rolled at approximately 800℃ to a thickness of 10mm, and further cold rolled to a plate material with a thickness of 1mm, and finally Various prototype alloy plates were obtained by annealing at a temperature of 580°C for 1 hour. Furthermore,
Thereafter, from these alloy plates, plates with dimensions of 200 mm width x 300 mm length x 1 mm plate thickness were taken as plates for the bioadhesion test.

[Table] Next, a biofouling test was conducted using various test plates taken from this alloy plate, and the results are shown in Table 2 below. In addition, the biofouling test involves hanging vertically in seawater at a depth of about 3 m in normal seawater with relatively weak ocean currents, leaving it for one year, and observing the occurrence of biofouling and local corrosion. So I went. As is clear from the results in Table 2 below, the copper alloy plates Nos. 1 to 7 used as inner tube materials in the present invention have very little barnacle adhesion, and are No. 1 in terms of occurrence of corrosion. All but one exception were negligible. On the contrary,
Comparative material No. 8 has no barnacles attached, but corrosion is noticeable, and comparative material No. 9 has no corrosion, but has extremely large numbers of barnacles attached, and Comparative material No. 10 was found to be inferior in both properties. In addition, the test piece No. 11, which is a conventional copper alloy material, showed similar trends to the comparative material No. 9.
It was found that the biofouling prevention properties were inferior. From these results, it can be seen that the copper alloy materials Nos. 1 to 7 according to the present invention have excellent biological fouling resistance and are also excellent in corrosion resistance in an environment where flow conditions are not strong. This was obvious and was considered useful as the inner pipe (seawater side) of a stain-proof double pipe in which the outer pipe is made of a corrosion-resistant material such as titanium.

[Table] In fact, copper alloy welded pipes and welded titanium pipes (JIS
-H4631, TTH35) are used as the inner and outer tubes, respectively, and the former is brought into close contact with the inner surface of the latter tube using the usual hydraulic pipe expansion method to create the desired double-tube structure. As a result of manufacturing a heat exchange tube and using it in a heat exchanger that uses seawater as cooling water, results similar to those shown in Table 2 above were obtained.

Claims (1)

[Scope of Claims] 1. A heat exchange tube through which seawater or fresh water containing seawater flows as cooling water, comprising: (a) an outer tube made of a corrosion-resistant material; and (b) tightly attached to the inner surface of the outer tube. 65-90 wt% Cu and 0-1.8 wt%
1. A heat exchange tube having a double-pipe structure comprising a copper alloy inner tube containing less than 1% Al and 0.02 to 0.06% by weight of As, with the remainder being Zn and inevitable impurities. 2. The heat exchange tube according to claim 1, wherein the outer tube is made of titanium material.