Highly corrosion-resistant copper tube

Abstract

Use of a heat transfer tube in a damp environment in air-conditioning equipment and exposed to corrosive action caused by a corrosive medium comprising at least one lower carboxylic acid, the heat transfer tube a copper tube comprising 0.10-1.0% by weight of P and the balance consisting of Cu and inevitable impurities. The corrosive action progresses in the form of an ants' nest from an outer surface of the heat transfer tube in a direction of its wall thickness, wherein. Also, use of a copper tube comprising 0.10-1.0% by weight of P and the balance consisting of Cu and inevitable impurities for improving corrosion-resistance against ant nest corrosion caused by a corrosive medium consisting of a lower carboxylic acid in a damp environment, method of inhibiting ants' nest corrosion in a heat transfer tube, and a method of positioning a tube in an air conditioning apparatus or a refrigeration apparatus.

Claims

1. A method for suppressing ants' nest corrosion, comprising: producing a heat transfer tube, wherein the heat transfer tube consists of copper, phosphorous, and inevitable impurities comprising at least one of Fe, Pb, and Sn, the inevitable impurities being contained in an amount of not higher than 0.05% by weight in total, and the producing of the heat transfer tube includes adding the phosphorous so as to be 0.19-1.0% by weight in total to suppress the ants' nest corrosion, positioning the heat transfer tube in air-conditioning equipment and operating the air-conditioning equipment, whereby the heat transfer tube is exposed to a corrosive action caused by a corrosive medium comprising at least one lower carboxylic acid, in which said corrosive action progresses in the form of said ants' nest corrosion from an outer surface of the heat transfer tube in a direction of its wall thickness.

2. The method as recited in claim 1, wherein the heat transfer tube contains not lower than 0.8% by weight of the phosphorous.

3. The method as recited in claim 1, wherein the heat transfer tube contains not lower than 0.5% by weight of the phosphorous.

4. The method as recited in claim 1, wherein the heat transfer tube contains not lower than 0.3-1.0% by weight of the phosphorous.

5. The method as recited in claim 1, wherein the operating of said air conditioning equipment is such that heat is transferred through said heat transfer tube.

6. The method as recited in claim 1, wherein the corrosion progresses in a direction extending along a surface of the heat transfer tube.

7. The method as recited in claim 1, wherein the producing of the heat transfer tube includes casting an ingot or a billet, and extruding and drawing the ingot or the billet.

8. The method as recited in claim 1, wherein the heat transfer tube contains 0.40% by weight of the phosphorous.

9. The method as recited in claim 1, wherein the heat transfer tube contains 1.00% by weight of the phosphorous.

10. A method for suppressing ants' nest corrosion comprising subjecting a copper tube having a composition consisting of copper, 0.19-1.0% by weight of phosphorous, and inevitable impurities comprising at least one of Fe, Pb and Sn, to a corrosive medium comprising a lower carboxylic acid, the inevitable impurities being contained in an amount of not higher than 0.05% by weight in total, said composition of the copper tube providing corrosion-resistance against ants' nest corrosion caused by said corrosive medium.

11. The method as recited in claim 10, wherein the heat transfer tube contains not lower than 0.8% by weight of the phosphorous.

12. The method as recited in claim 10, wherein the heat transfer tube contains not lower than 0.5% by weight of the phosphorous.

13. The method as recited in claim 10, wherein the heat transfer tube contains not lower than 0.3-1.0% by weight of the phosphorous.

14. The method as recited in claim 10, further comprising positioning the heat transfer tube in air conditioning equipment and operating said air conditioning equipment such that heat is transferred through said heat transfer tube.

15. The method as recited in claim 10, wherein corrosion progresses in a direction extending along a surface of the heat transfer tube.

16. The method as recited in claim 10, wherein the heat transfer tube was produced by casting an ingot or a billet, and extruding and drawing the ingot or the billet.

17. A method of inhibiting ants' nest corrosion in a heat transfer tube, the method comprising: forming a tube having a composition consisting of copper, 0.19-1.0% by weight of phosphorous, and inevitable impurities comprising at least one of Fe, Pb and Sn, the inevitable impurities being contained in an amount of not higher than 0.05% by weight in total; positioning the tube in an air conditioning apparatus or a refrigeration apparatus; and subjecting the tube to a corrosive environment comprising at least one lower carboxylic acid.

18. A method, comprising: forming a heat transfer tube, wherein the heat transfer tube consists of copper, phosphorous, and inevitable impurities comprising at least one of Fe, Pb, and Sn, the inevitable impurities being contained in an amount of not higher than 0.05% by weight in total, and the producing of said heat transfer tube includes adding the phosphorous so as to be 0.19-1.0% by weight in total to suppress ants' nest corrosion, positioning said heat transfer tube in an air conditioning apparatus or a refrigeration apparatus; operating said air conditioning apparatus or refrigeration apparatus such that heat is transferred through said tube; and exposing said tube to a corrosive medium in said air-conditioning apparatus or said refrigeration apparatus, in which said corrosive medium generates ants' nest corrosion that progresses from a surface of said tube.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic cross-sectional view showing an apparatus used for a corrosion resistance test in illustrated Examples;

(2) FIG. 2 is a graph showing a relationship between a P content of copper tubes obtained in the Examples and a maximum corrosion depth of those copper tubes;

(3) FIG. 3 is a schematic view showing a heat transfer tube 31 in air-conditioning equipment 32; and

(4) FIG. 4 is a schematic view showing a heat transfer tube 41 in a refrigeration apparatus 42.

DETAILED DESCRIPTION OF THE INVENTION

(5) A highly corrosion-resistant copper tube according to the invention has a major characteristic that its phosphate (P) content is held within a range of 0.05-1.0% by weight and higher than that of the conventional copper tube. It is considered that owing to such a high P content, the type of corrosion generated in the copper tube shifts from a selective corrosion which progresses in a direction perpendicular to the axial direction of the copper tube (i.e., in a direction of the wall thickness of the copper tube) to a surface corrosion which progresses in a direction parallel to the axial direction of the copper tube (i.e., in a direction extending along the surface of the copper tube). In particular, by setting the P content of the copper tube so as to be not lower than 0.10% by weight, and preferably not lower than 0.15% by weight, generation of the selective corrosion is effectively reduced or prevented, and the copper tube can exhibit corrosion resistance which is considerably higher than that of the conventional copper tube.

(6) Where the P content of the copper tube is as low as 0.05% by weight, the selective corrosion is generated, but a rate of progress of the selective corrosion in the copper tube can be effectively reduced as compared with that in the conventional copper tube, so that the copper tube is recognized to have a higher resistance against the ant nest corrosion. Therefore, the P content of the copper tube is set so as to be not lower than 0.05% by weight, in the present invention. On the other hand, the upper limit of the P content of the copper tube needs to be set at 1.0% by weight, since the P content higher than 1.0% by weight causes almost no change in the resistance of the copper tube against the ant nest corrosion, and even causes deterioration of workability of the copper tube during its production, giving rise to a problem of cracking of the copper tube, for example. From the standpoint of practical production of the copper tube, the P content of the copper tube is preferably set so as to be not higher than 0.8% by weight, and more preferably not higher than 0.5% by weight.

(7) The highly corrosion-resistant copper tube according to the present invention is made of a material having the P content described above with the balance consisting of Cu (copper) and inevitable impurities. A total amount of the inevitable impurities such as Fe, Pb and Sn contained in the copper tube is generally controlled so as to be not higher than 0.05% by weight.

(8) The intended copper tube is produced by using a Cu material having the above-described composition according to the invention, by a method similar to the conventional method. For example, the copper tube is produced by steps of casting an ingot or a billet, and extruding and drawing the ingot or billet. Dimensions such as the outside diameter and the wall thickness of the thus obtained copper tube are adequately determined depending on the intended application of the copper tube. Where the copper tube according to the invention is to be used as a heat transfer tube, the copper tube may have a smooth internal surface, or may advantageously have various kinds of internal grooves formed in its internal surface by various known processes, as is well known in the art.

EXAMPLES

(9) To clarify the present invention more specifically, some examples according to the present invention will be described. It is to be understood that the invention is by no means limited by the details of the illustrated examples, but may be embodied with various changes, modifications and improvements which are not described herein, and which may occur to those skilled in the art, without departing from the spirit of the invention.

(10) Initially, various kinds of copper tube having compositions including respective P contents indicated in Table 1 given below, with the balance consisting of Cu and inevitable impurities were produced as in production of the conventional copper tube, such that each copper tube has an outside diameter of 9.52 mm and a wall thickness of 0.41 mm. The thus produced copper tubes were subjected to an ant nest corrosion test, as described below. Further, a Cu material containing 1.5% by weight of P and the balance consisting of Cu and inevitable impurities was used to produce a copper tube having dimensions similar to those of the above-described copper tubes, but the intended copper tube could not be obtained due to cracking of the tube. A phosphorous deoxidized copper tube and an oxygen-free copper tube each having the same dimensions as those of the above-described copper tubes were provided as comparative copper tubes.

(11) TABLE-US-00001 TABLE 1 Copper P content tube No. Kind of copper tube (% by weight) 1 Copper tube according to 0.11 the invention 2 Copper tube according to 0.19 the invention 3 Copper tube according to 0.30 the invention 4 Copper tube according to 0.40 the invention 5 Copper tube according to 0.50 the invention 6 Copper tube according to 1.00 the invention 7 Phosphorous deoxidized 0.03 copper tube 8 Oxygen-free copper tube <0.004

(12) Each of the thus provided various kinds of copper tube was subjected to the ant nest corrosion test by using a test apparatus shown in FIG. 1. A plastic container 2 shown in FIG. 1 has a capacity of 2 L and can be hermetically sealed with a cap 4. Silicone plugs 6 are attached to the cap 4 such that the plugs 6 extend through the cap 4. Copper tubes 10 to be subjected to the corrosion test were inserted into the plastic container 2 by a predetermined length, such that the copper tubes 10 extend through the respective silicone plugs 6. Lower open ends of the copper tubes 10 were closed with silicone plugs 8. 100 mL of a formic acid aqueous solution having a predetermined concentration was accommodated in the plastic container 2, such that the copper tubes 10 do not contact with the aqueous solution.

(13) The ant nest corrosion test was conducted by using three kinds of formic acid aqueous solutions 12 having respective concentrations of 0.01%, 0.1% and 1%. The copper tubes 10 were set with respect to each of the plastic containers 2 in which the respective formic acid aqueous solutions 12 were accommodated, and the plastic container 2 was left within a constant temperature bath at a temperature of 40° C. The plastic container 2 with the copper tubes 10 was taken out of the bath for two hours each day, and held at the room temperature (15° C.), to cause dewing on surfaces of the copper tubes 10 by the difference between the temperature of the constant temperature bath and the room temperature. The copper tubes 10 were subjected to the corrosion test under the above-described conditions for 20 days.

(14) Each of the copper tubes subjected to the corrosion test using each of the formic acid aqueous solutions having the respective concentrations was examined in its cross section, and measured of its maximum corrosion depth. Results of the measurement are indicated in Table 2 given below. Further, a relationship between the maximum corrosion depth of the copper tubes subjected to the corrosion test using the 0.1% formic acid aqueous solution and the P content of the respective copper tubes is indicated in a graph of FIG. 2.

(15) TABLE-US-00002 TABLE 2 Maximum corrosion depth (mm) Formic acid Formic acid Formic acid Copper concentration: concentration: concentration: tube No. 0.01% 0.1% 1% 1 0.10 0.25 — 2 0.06 0.11 0.12 3 0.08 0.04 0.08 4 0.04 0.05 0.07 5 0.03 0.04 0.10 6 <0.03 0.05 — 7 0.15 0.40 >0.40 8 0.05 0.30 >0.40

(16) As is apparent from the results in Table 2, in the corrosion test conducted by using the formic acid aqueous solution having the concentration of 0.01%, the ant nest corrosion was not generated and only slight corrosion on the surfaces of the copper tubes was recognized in the copper tubes Nos. 1-6 having P contents within a range of 0.1-1.0% by weight, and the copper tube No. 8 which is the oxygen-free copper tube. On the other hand, in the corrosion test conducted by using the formic acid aqueous solutions having the respective concentrations of 0.1% and 1%, the ant nest corrosion was recognized in both of the copper tube No. 7 which is the phosphorous deoxidized copper tube, and the copper tube No. 8 which is the oxygen-free copper tube, and corrosion was recognized in the copper tubes Nos. 1-6 having the P contents within the range of 0.1-1.0% by weight. However, the corrosion generated in the copper tubes Nos. 1-6 was not the ant nest corrosion, and maximum corrosion depths of the copper tubes Nos. 1-6 are smaller than those of the phosphorous deoxidized copper tube and the oxygen-free copper tube.

(17) Further, as indicated in FIG. 2, the copper tubes having P contents higher or lower than the P content of 0.03% by weight of the phosphorous deoxidized copper tube (No. 7) have smaller maximum corrosion depths than the phosphorous deoxidized copper tube (No. 7). It is particularly noted that the copper tubes (Nos. 1-6) according to the present invention having higher P contents than the phosphorous deoxidized copper tube (No. 7) are superior to the oxygen-free copper tube (No. 8) in their maximum corrosion depths.