Copper pipes, heat transfer pipes, refrigerant piping, air conditioning equipment and refrigeration equipment

Abstract

To provide a copper pipe having excellent corrosion resistance to ant nest-like corrosion and also excellent corrosion resistance to SCC.SOLUTION: A copper pipe comprises a copper material comprising 0.10-1.0 wt.% of P with the balance being Cu and unavoidable impurities. The external surface of the copper pipe is provided with a coating layer of copper oxide, formed by shot blasting with oxidative gas.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a corrosion-resistant copper tube, and in particular to a copper tube that is suitable for use as a heat transfer tube or refrigerant piping in air conditioners and refrigeration equipment, and that has excellent corrosion resistance against both ant nest corrosion and stress corrosion cracking (SCC). [Background technology]

[0002] Traditionally, phosphorus (P) deoxidized copper pipe (JIS-H3300-C1220T) has been mainly used for pipe materials such as heat transfer pipes in air conditioners and refrigerant piping (internal piping) in refrigeration equipment, due to its excellent corrosion resistance, brazability, thermal conductivity, and bending workability.

[0003] Phosphorus-deoxidized copper pipes, which are used in such air conditioners and refrigeration equipment, can develop an abnormal type of corrosion called ant nest corrosion, which progresses from the surface of the pipe in the direction of the pipe wall thickness. This ant nest corrosion is thought to occur in a humid environment, with low-molecular-weight carboxylic acids such as formic acid and acetic acid as the corrosive agent. Similar corrosion has also been confirmed in environments containing chlorinated organic solvents such as 1,1,1-trichloroethane, certain lubricating oils, and formaldehyde.

[0004] It is known that this phenomenon is particularly pronounced when copper pipes are used as piping for air conditioners and freezers where condensation occurs. Once this type of ant nest corrosion occurs, it progresses rapidly and can penetrate the copper pipe in a short period of time, causing problems such as the equipment becoming unusable.

[0005] For this reason, Patent Document 1 proposes a highly corrosion-resistant copper tube characterized by containing 0.05 to 1.0 wt % P (phosphorus) and the remainder being made of Cu (copper) and unavoidable impurities, and clarifies that this improves corrosion resistance against ant nest corrosion. In other words, it points out the fact that it is possible to practically advantageously obtain a copper tube that has even better corrosion resistance against ant nest corrosion in a range where the P content is higher than that of conventional pipe material made of phosphorus-deoxidized copper.

[0006] Furthermore, Patent Document 2 reveals that by setting the crystal grain size to 0.005 to 0.050 mm, corrosion resistance against ant nest corrosion can be further improved effectively. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2014 / 148127 [Patent Document 2] International Publication No. 2018 / 061270 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the copper tubes of Patent Documents 1 and 2 have a problem in that stress corrosion cracking (hereinafter referred to as SCC) may occur when stress is applied in an ammonia environment.

[0009] Therefore, there is a need for the development of copper pipes that are excellent in corrosion resistance against ant nest corrosion and SCC.

[0010] Therefore, an object of the present invention is to provide a copper tube that has excellent corrosion resistance against ant nest corrosion and excellent corrosion resistance against SCC. [Means for solving the problem]

[0011] Based on the above technical background, the present inventors have conducted extensive research and have found that by subjecting a copper tube that has been straightened by unwinding it from a long coil after the final heat treatment in the manufacture of the copper tube, or a secondary processed tube such as a hairpin bent tube, to shot blasting using an oxidizing gas, an extremely thin and dense layer of copper oxide film can be formed on the outer surface of the copper tube during the shot blasting process, thereby reducing SCC susceptibility, which led to the completion of the present invention.

[0012] That is, the present invention (1) comprises a copper material containing 0.10 to 1.0 wt % of P, with the remainder being Cu and unavoidable impurities, On the outer surface of the copper pipe, Dry air with a relative humidity of less than 10% at 25°C a copper oxide coating formed by shot blasting using a The present invention provides a copper tube characterized by the above.

[0013] The present invention (2) provides the copper tube according to (1), characterized in that the thickness of the copper oxide film is 50 to 300 Å.

[0014] The present invention (3) provides a copper tube according to (1) or (2), characterized in that the copper tube is placed in a humid environment and is exposed to a corrosive agent consisting of a lower carboxylic acid, which corrodes from the surface of the tube in the direction of the tube wall thickness in an ant nest-like pattern.

[0015] The present invention (4) also provides a heat transfer tube made of the copper tube of any one of (1) to (3), which is used as a heat transfer tube for air conditioning equipment or refrigeration equipment.

[0016] The present invention (5) also provides a refrigerant pipe made of the copper pipe of any one of (1) to (3), which is used as a refrigerant pipe for an air conditioner or a refrigeration device.

[0017] The present invention (6) also provides an air conditioner characterized by having the heat transfer tube of (4).

[0018] The present invention (7) also provides a refrigeration device characterized by having the heat transfer tube of (4).

[0019] The present invention (8) also provides an air conditioner characterized by having the refrigerant pipe of (5).

[0020] The present invention (9) also provides a refrigeration device characterized by having the refrigerant pipe of (5). [Effects of the Invention]

[0021] According to the present invention, it is possible to provide a copper pipe that has excellent corrosion resistance against ant nest corrosion and excellent corrosion resistance against SCC. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a diagram showing a test apparatus for carrying out a formicary corrosion test in the examples. [Figure 2] FIG. 1 is a diagram showing a test apparatus for carrying out a stress corrosion cracking test in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0023] The copper tube of the present invention is made of a copper material containing 0.10 to 1.0 wt% of P, with the remainder being Cu and unavoidable impurities, The outer surface of the copper tube has a copper oxide coating formed by shot blasting using an oxidizing gas. It is a copper pipe characterized by the following.

[0024] The copper tube of the present invention is made of a copper material containing 0.10 to 1.0 wt% of P, with the balance being Cu and unavoidable impurities. That is, the copper tube of the present invention is made of a copper material containing 0.10 to 1.0 wt% of P, with the balance being Cu and unavoidable impurities.

[0025] The P content in the copper material forming the copper tube of the present invention is 0.10 to 1.0 wt %, preferably 0.15 to 0.50 wt %. By ensuring that the P content in the copper material forming the copper tube is within this range, the occurrence of selective corrosion, in which ant nest-like corrosion progresses from the tube surface toward the tube wall thickness, can be effectively suppressed or prevented, even in severe corrosive environments, and corrosion resistance superior to that of known corrosion-resistant copper tubes can be advantageously exhibited for a long period of time. On the other hand, if the P content in the copper material forming the copper tube is below this range, ant nest-like corrosion is likely to progress from the tube surface toward the tube wall thickness. Furthermore, even if the P content in the copper material forming the copper tube exceeds this range, there is little change in corrosion resistance against ant nest-like corrosion, and workability is reduced during copper tube production, making problems such as cracking more likely to occur.

[0026] On the other hand, due to the presence of P, an additive element in the copper tube of the present invention, when stress is applied in an ammonia environment, the corrosiveness of the grain boundaries becomes more acute, embrittlement originating from the grain boundaries is promoted, and stress corrosion cracking may occur.

[0027] The copper tube of the present invention has a copper oxide coating formed on its outer surface by shot blasting using an oxidizing gas. In this invention, the outer surface of the copper tube refers to the outer surface of the copper tube. Shot blasting refers to a surface treatment in which metallic or nonmetallic particles with a diameter of 10 to 100 μm are projected at high speed onto the surface of a workpiece, locally altering the surface. The copper oxide coating formed on the outer surface of the copper tube of the present invention is formed by using a compressed oxidizing gas, such as oxygen gas or dry air, to project metallic or nonmetallic particles toward the outer surface of the copper tube at high speed while simultaneously projecting the metallic or nonmetallic particles toward the outer surface of the copper tube. Therefore, the copper tube of the present invention has a copper oxide coating formed on its outer surface by shot blasting using an oxidizing gas as the compressed gas. The compressed gas injection pressure is not particularly limited, but is preferably 0.4 to 0.6 MPa.

[0028] The copper oxide coating formed on the outer surface of the copper tube of the present invention is formed by shot blasting and is dense. The copper tube of the present invention has a dense copper oxide coating formed on the outer surface by shot blasting using an oxidizing gas as the compressed gas, and therefore has excellent corrosion resistance against SCC.

[0029] That is, the copper tube of the present invention is a copper tube obtained by shot blasting the outer surface of a copper tube made of a copper material containing 0.10 to 1.0 wt. % P, with the remainder being Cu and unavoidable impurities, using an oxidizing gas such as oxygen gas or dry air as a compressed gas, and has a copper oxide coating on the outer surface of the copper tube.

[0030] The thickness of the copper oxide coating formed on the outer surface of the copper tube of the present invention is preferably 50 to 300 Å (angstroms). When the thickness of the copper oxide coating is within this range, the copper oxide coating becomes dense and functions as a pseudo-anticorrosion layer, suppressing the occurrence of cracks in the coating that accompany the rapid growth of the copper oxide coating that occurs immediately after exposure to a corrosive medium such as an acid or alkali.

[0031] The copper pipe of the present invention has an outer surface that has been shot blasted, and a compressive residual stress is imparted to the surface layer of the outer surface of the copper pipe.

[0032] The tensile strength (σB) of the copper tube of the present invention is preferably 270 MPa or more, particularly preferably 275 to 290 MPa. The 0.2% proof stress (σ0.2) of the copper tube of the present invention is preferably 90 MPa or more, particularly preferably 95 to 110 MPa. The elongation (δ) of the copper tube of the present invention is preferably 40% or more, particularly preferably 45 to 55%.

[0033] A manufacturing example of the copper tube of the present invention will be described below. Note that the manufacturing example of the copper tube of the present invention described below is one example for manufacturing the copper tube of the present invention, and the copper tube of the present invention is not limited to those manufactured by the method described below.

[0034] The copper tube of the present invention is manufactured by casting a copper ingot of a predetermined chemical composition, followed by various processing and heat treatments. The inventors have discovered that shot blasting of the copper tube after the final heat treatment imparts compressive residual stress to the outer surface layer and simultaneously forms an extremely thin and dense copper oxide film on the outer surface layer, thereby reducing SCC susceptibility.

[0035] The method for producing a copper tube of the present invention includes at least a casting process, hot working, cold working such as cold rolling and cold drawing, final heat treatment, and shot blasting of a copper tube that has undergone secondary processing such as long coil unwinding, straightening, or subsequent hairpin bending. The shot blasting process uses a compressed gas of an oxidizing gas, such as oxygen gas or dry air, to project metallic or nonmetallic particles at high speed. Shot blasting refers to a surface treatment in which metallic or nonmetallic particles with a diameter of 10 to 100 μm are projected at high speed onto the surface of a workpiece, locally modifying the surface. In the method for producing a copper tube of the present invention, the shot blasting process plastically deforms the surface, thereby imparting compressive residual stress and work hardening.

[0036] In the method for producing a copper tube of the present invention, first, a casting step is carried out in which melting and casting are carried out according to a conventional method to obtain a copper ingot (billet) containing 0.10 to 1.0 wt %, preferably 0.15 to 0.50 wt %, of P, with the remainder being Cu and unavoidable impurities.

[0037] Next, in the method for producing a copper tube of the present invention, the copper ingot (billet) is heated and subjected to hot working, and then cold working to form a desired shape. Hot working is generally hot extrusion. Cold working includes cold rolling, cold drawing, and rolling to form inner grooves. In all of the above-mentioned cold working methods, in the process of working to the final dimensions, a long coil ranging from several hundred meters to several thousand meters is generally formed while reducing the outer diameter and wall thickness.

[0038] In the copper tube manufacturing method of the present invention, the final heat treatment is carried out. In the final heat treatment, the copper material that has been work-hardened by cold working is heated and held at a temperature equal to or higher than the recrystallization temperature in a reducing gas atmosphere to adjust the strength and elongation of the material to be suitable for subsequent working.

[0039] In the method for producing a copper tube of the present invention, a heat treatment (intermediate annealing) can be carried out as needed before cold working, between passes of cold working, etc.

[0040] Final heat treatment methods include, for example, a method in which radiant heat from burner combustion is forced to circulate with a stirring fan in an airtight furnace while the material is heated to a predetermined temperature by heat transfer, and then cooled slowly while a low-temperature atmospheric gas is forced to circulate with a stirring fan; and a method in which eddy currents are generated in the material using a high-frequency induction heating coil while the material is rapidly heated, followed immediately by water cooling.

[0041] In the method for producing a copper tube of the present invention, a copper tube is unwound from a long coil that has been subjected to a final heat treatment, and after undergoing straightening processing to straighten the copper tube into a straight piece, shot blasting is uniformly performed on the entire outer surface of the copper tube while the entire length of the coil is gradually fed out. Alternatively, in the method for producing a copper tube of the present invention, a copper tube is unwound from a long coil that has been subjected to a final heat treatment, and after undergoing straightening processing to straighten the copper tube into a straight piece, shot blasting is uniformly performed on the entire outer surface of the copper tube that has been further subjected to secondary processing such as hairpin bending.

[0042] Shot blasting is a surface treatment method in which metallic or nonmetallic particles with diameters of 10 to 100 μm are projected at high speed onto the surface of a workpiece, causing localized plastic deformation near the surface, thereby imparting compressive residual stress and work hardening. In the method for producing a copper tube of the present invention, a compressed oxidizing gas, such as oxygen gas or dry air, is used as the compressed gas for projecting the metallic or nonmetallic particles at high speed toward the outer surface of the copper tube. Shot blasting is performed by projecting the metallic or nonmetallic particles at high speed toward the outer surface of the copper tube while simultaneously projecting the oxidizing gas. Examples of oxidizing gases used for projecting the metallic or nonmetallic particles include oxygen gas and dry air, with dry air being preferred from a cost perspective. Using dry air as the compressed gas allows for the formation of a denser copper oxide coating with fewer voids on the outer surface of the copper tube. The injection pressure of the compressed gas is not particularly limited, but is preferably 0.4 to 0.6 MPa. By using an oxidizing gas as the compressed gas for projecting particles in the shot blasting process, the impact energy of the projected fine particles colliding with the outer surface of the copper tube generates heat on the outer surface of the copper tube according to the frequency of the fine particles' collisions. During this process, an oxidation reaction occurs between the oxygen in the oxidizing gas injected onto the surface and copper, forming a copper oxide film mainly composed of CuO. By forming a CuO-based copper oxide film with a thickness of 50 to 300 Å on the copper substrate, the resulting dense copper oxide film functions as a pseudo-corrosion protection layer, suppressing the occurrence of cracks in the film that accompany the rapid growth of the copper oxide film immediately after exposure to corrosive media such as acids and alkalis. Note that "dry air" refers to air that has been dehumidified to a relative humidity of less than 10% at 25°C by passing it through a dryer.

[0043] In the copper tube manufacturing method of the present invention, the 0.2% proof stress (σ0.2) of the copper tube to be shot blasted, i.e., the copper tube before shot blasting, is preferably 90 MPa or more, and particularly preferably 95 to 110 MPa. When the 0.2% proof stress (σ0.2) of the copper tube to be shot blasted is in the above range, the elastic limit of the copper tube, which is the workpiece, is increased, and warping and deformation are suppressed when fine particle impacts act on the outer surface during shot blasting, and compressive residual stress is appropriately imparted to the surface layer of the outer surface of the tube, resulting in a copper tube with excellent corrosion resistance against SCC.

[0044] In the method for producing a copper tube of the present invention, the copper tube to be subjected to shot blasting, i.e., the copper tube before shot blasting, preferably has a tensile strength (σB) of 270 MPa or more, particularly preferably 275 to 290 MPa. Also, in the method for producing a copper tube of the present invention, the copper tube to be subjected to shot blasting, i.e., the copper tube before shot blasting, preferably has an elongation (δ) of 40% or more, particularly preferably 45 to 55%.

[0045] In the copper tube manufacturing method of the present invention, a copper tube that has undergone straightening or subsequent secondary processing such as hairpin bending is shot blasted to impart a certain level of compressive residual stress to the surface of the copper tube. Additionally, in the copper tube manufacturing method of the present invention, the copper tube is shot blasted using an oxidizing gas as compressed air to form an extremely thin and dense copper oxide film on the surface, thereby suppressing the rapid growth of the copper oxide film that occurs immediately after exposure to a corrosive medium such as an acid or alkali. More specifically, the formation of a dense copper oxide film on the surface of the copper tube suppresses a chain reaction between film cracking due to a sudden increase in the thickness of the copper oxide film at recrystallized grain boundaries and film regeneration due to oxidation of the exposed copper substrate, thereby reducing the susceptibility to stress corrosion cracking that progresses via oxide film destruction.

[0046] The copper tube of the present invention is unwound from a long coil after the final heat treatment, straightened into a straight pipe, and then subjected to shot blasting treatment, or after being straightened into a straight pipe, is further subjected to hairpin bending and shot blasting treatment, and then subjected to bending and other processing, and is then incorporated into a heat exchanger or the like of an air conditioning or refrigeration equipment.

[0047] The copper tube of the present invention and the copper tube obtained by the manufacturing method of the present invention are suitable for use as copper tubes that are placed in a humid environment and exposed to a corrosive agent comprising a lower carboxylic acid that progresses in an ant-nest-like pattern from the surface to the thickness of the tube. Even when placed in a humid environment and exposed to a corrosive agent comprising a lower carboxylic acid that progresses in an ant-nest-like pattern from the surface to the thickness of the tube, the copper tube of the present invention and the copper tube obtained by the manufacturing method of the present invention have excellent corrosion resistance against ant-nest corrosion and excellent corrosion resistance against SCC, thereby extending the life of the copper tube and the heat exchanger in which the copper tube is used.

[0048] The heat transfer tube of the present invention is made of the copper tube of the present invention or a copper tube obtained by the copper tube manufacturing method of the present invention, and is a copper tube for use in air conditioners or refrigeration equipment. That is, the heat transfer tube of the present invention is a heat transfer tube used in air conditioners or refrigeration equipment, and is used as a heat transfer tube constituting a heat exchanger of air conditioners or refrigeration equipment.

[0049] The refrigerant pipe of the present invention is made of the copper pipe of the present invention or a copper pipe obtained by the copper pipe manufacturing method of the present invention, and is a copper pipe for refrigerant pipe of an air conditioner or a refrigeration equipment. In other words, the refrigerant pipe of the present invention is used as a refrigerant pipe through which a refrigerant flows in an air conditioner or a refrigeration equipment.

[0050] The air conditioner of the present invention has the heat transfer tube of the present invention, that is, a heat transfer tube made of the copper tube of the present invention or a copper tube obtained by the method for producing a copper tube of the present invention.

[0051] The refrigeration equipment of the present invention has the heat transfer tube of the present invention, that is, a heat transfer tube made of the copper tube of the present invention or a copper tube obtained by the copper tube manufacturing method of the present invention.

[0052] The air conditioner of the present invention has the refrigerant piping of the present invention, that is, the refrigerant piping made of the copper pipe of the present invention or the copper pipe obtained by the method for producing the copper pipe of the present invention.

[0053] The refrigeration equipment of the present invention has the refrigerant piping of the present invention, that is, the refrigerant piping made of the copper pipe of the present invention or the copper pipe obtained by the method for producing the copper pipe of the present invention.

[0054] The present invention will be described below with reference to examples, but the present invention is not limited to the following examples. [Example]

[0055] Examples and Comparative Examples <Composition of copper pipe> Chemical composition: Contains P as listed in Table 1, with the balance being Cu and unavoidable impurities <Manufacturing process> (1) Casting process Billets having the chemical compositions shown in Table 1 were prepared. (2) Hot processing The billet obtained above was heated to 850°C, hot extruded, and quenched to obtain an extruded raw pipe. (3) Cold working The extruded raw pipe obtained above was cold-rolled and coiled up by a first cold drawing process. Next, the cold drawing process was repeated multiple times to draw it to a diameter of 7 mm and a wall thickness of 0.40 mm. After drawing, it was wound using a drum winder into a long coil with an outer diameter of 900 mm, an inner diameter of 560 mm, and a coil width of 230 mm. (4) Final heat treatment The long coil was subjected to a final heat treatment to obtain a soft copper tube with an outer diameter of 7 mm and a wall thickness of 0.40 mm. The mechanical properties of the obtained copper tube are shown in Table 1.

[0056] [Table 1]

[0057] (5) Straight pipe straightening processing The long copper tube coil that had undergone the final heat treatment described above was placed on a rotating platform, and the copper tube was unwound and straightened by offsetting horizontal and vertical drive rolls arranged in a staggered pattern behind it, resulting in a straight copper tube with a bend of 1 mm / 1000 mm or less.

[0058] (6) Shot blasting Glass beads, which are non-metallic particles with a diameter of 40 μm, were projected at high speed using a compressed gas projection system onto the surface of the copper pipe obtained above, which was the workpiece. For the shot blasting treatment, three projection nozzles were placed at 120° intervals around the circumference of the pipe, and dry air (oxygen concentration approximately 21%, relative humidity less than 10% at 25°C) or 100% nitrogen gas was used at a spray pressure of 0.4 MPa, under the shot blasting conditions shown in Table 2.

[0059] [Table 2]

[0060] <Ant nest corrosion test and evaluation method> For each type of copper tube prepared, an ant nest corrosion test was conducted using the test equipment shown in Figure 1. In Figure 1, reference numeral 2 denotes a 2-L plastic container that can be sealed with a cap 4. A test copper tube 10 was inserted into the plastic container 2 so as to penetrate a silicone plug 6 that was attached to the cap 4. The lower opening of the test copper tube 10 was closed with a silicone plug 8. The test copper tube 10 was 18 cm long, with 15 cm of the portion exposed to the plastic container 2. The plastic container 2 also contained 100 ml of a formic acid solution of a predetermined concentration, in a manner that prevented it from coming into contact with the test copper tube 10. In the ant nest corrosion test, the concentration of the formic acid solution 12 was set to 0.1%, and a predetermined test copper tube 10 was placed in a plastic container 2 containing the formic acid solution 12, which was then left in a thermostatic bath at 40°C, and then removed from the bath for 2 hours per day and kept at room temperature (15°C), thereby promoting condensation on the surface of the test copper tube 10 due to the temperature difference. The corrosion test under these conditions was carried out for 80 days. For each copper tube tested, five cross sections perpendicular to the tube axis direction were examined at random positions in the area exposed in the plastic container 2 shown in Figure 1, and the maximum corrosion depth from the outer surface of the tube was measured. Regarding the obtained maximum corrosion depth, if the maximum corrosion depth was 0.20 mm or less, the ant nest corrosion was shallow and the corrosion resistance was excellent, which was marked as "○", and if the maximum corrosion depth was more than 0.20 mm, the ant nest corrosion was deep and the corrosion resistance was poor, which was marked as "×".

[0061] <Ant nest corrosion test results> An ant nest corrosion test was conducted on Example 1, Comparative Example 1, and Comparative Example 2, which used copper pipe 1 with a P content of 0.27% by mass. As a result, the maximum ant nest corrosion depth was evaluated as ○ in all cases. Furthermore, a ant nest corrosion test was carried out using copper tube 2 with a P content of 0.024 mass %, and the evaluation of the maximum ant nest corrosion depth was poor.

[0062] <Method for evaluating copper oxide film thickness> Length 100mm, outer surface melting area S (cm 2 The test piece was immersed in 200 ml of a 5% aqueous solution of sodium thiosulfate for 15 minutes to dissolve the copper oxide film, and the mass of copper ions w (mg) was measured from the extracted solution using an ICPE emission spectrometer. The chemical formula of copper oxide was considered to be Cu2O, and the lattice constant was 4.27 x 10 -8 The density of two Cu atoms calculated under the condition that two formula amounts of CuO are contained in a unit cell of 1 cm is ρ = 5.4 g / cm 3 Therefore, the thickness of the copper oxide film Δ(Å) = 10 5The thickness of the obtained copper oxide film was calculated by w / (ρS). When the thickness of the obtained copper oxide film was between 0 and less than 50 Å, the copper oxide film was too thin and was evaluated as "× (below the lower limit)" and when it was between 50 Å and 300 Å, the copper oxide film was within the proper range and was evaluated as "○". The evaluation of the copper oxide film thickness is shown in Table 2.

[0063] <Stress corrosion cracking (SCC) testing and evaluation methods> The prepared copper pipes were subjected to an exposure test (SCC evaluation test) in an ammonia atmosphere using the test equipment shown in Figure 2. The test specimen was a straight pipe measuring 7 mm in diameter and 0.40 mm in thickness, with a pressure sensor attached to one end and the other end sealed with a joint. A leak check was performed inside the pipe with nitrogen gas at 4.0 MPa to confirm airtightness in advance. The test vessel was made of polyethylene and 2L, and 200ml of 1vol.% aqueous ammonia solution was placed in the bottom. The test specimen was exposed to the gas layer and the internal pressure was monitored with a sensor. The time it took for the internal pressure to drop below 3.8MPa was measured as the penetration time. When the penetration time was 100 hours or more, the corrosion resistance was excellent and was marked with "◯", and when it was less than 100 hours, the corrosion resistance was poor and was marked with "×".

[0064] <Evaluation of copper oxide film thickness and stress corrosion cracking (SCC) test results> In Example 1, the copper tube 1 was shot blasted using dry air (oxygen concentration approximately 21%), so that a copper oxide film of an appropriate thickness was obtained on the outer surface of the copper tube, and the SCC penetration time was evaluated as ○. On the other hand, in Comparative Example 1, the copper pipe 1 was shot blasted using 100% nitrogen gas, so a copper oxide film of an appropriate thickness could not be obtained on the outer surface of the copper pipe, and the SCC penetration time was evaluated as ×. In Comparative Example 2, shot blasting was not performed, and therefore no copper oxide film was formed on the outer surface of the copper pipe, and the SCC penetration time was evaluated as "poor."

Claims

1. The copper material contains 0.10 to 1.0 wt % of P, with the remainder being Cu and unavoidable impurities; The copper pipe has a copper oxide coating formed on its outer surface by shot blasting using dry air having a relative humidity of less than 10% at 25°C. A copper pipe characterized by:

2. 2. The copper tube according to claim 1, wherein the thickness of the copper oxide film is 50 to 300 Å.

3. 3. The copper tube according to claim 1, wherein the copper tube is placed in a humid environment and is exposed to a corrosive agent comprising a lower carboxylic acid, the corrosion acting in a manner that progresses in an ant nest-like pattern from the surface of the tube in the direction of the thickness of the tube.

4. A heat transfer tube comprising the copper tube according to any one of claims 1 to 3, which is used as a heat transfer tube for air conditioning equipment or refrigeration equipment.

5. 4. A refrigerant pipe comprising the copper pipe according to claim 1, which is used for refrigerant piping in air conditioning equipment or refrigeration equipment.

6. An air conditioning device comprising the heat transfer tube according to claim 4.

7. A refrigeration appliance comprising the heat transfer tube according to claim 4.

8. An air conditioning device comprising the refrigerant pipe according to claim 5.

9. A refrigeration appliance comprising the refrigerant pipe according to claim 5.

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