JPH10140271A - Copper alloy pipe for steam piping - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a copper alloy pipe for steam piping, excellent in corrosion resistance to steam, by forming a pipe by the use of a Zn-containing copper alloy, specifying P content in the copper alloy, forming Sn and Cu-Sn alloy layers on the internal surface of the pipe, and specifying the roughness of the internal surface. SOLUTION: This copper alloy pipe for steam piping is composed of a copper alloy containing, by weight, 0.01-10% Zn and having <=0.04% P content, and a protective coating layer of 0.1-3μ, composed of Sn or/and Cu-Sn alloy layers, is formed on the internal surface, and also the center line average height (Ra) of the internal surface is <=1.2μ. Although the velocity of the diffusion of Zn in a base material through the coating layer is very high and Zn is diffused into the surface layer part of the coating layer soon after the formation of the coating layer, a compound oxide of Sn-Zn cannot be formed in this state and this compound oxide of Sn-Zn can be formed only when this pipe is used as a steam pipe and brought into contact with steam, and as a result, excellent corrosion resistance can be produced. When the above Ra exceeds 1.2μ, peeling of the protective coating layer becomes liable to occur.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copper alloy pipe for an inner surface coated steam pipe through which water vapor and / or its drain water passes.

[0002]

2. Description of the Related Art Conventionally, carbon steel pipes,
Stainless steel tube, phosphorus deoxidized copper tube (JISH3300 C1
220T) and the like, and in particular, phosphorous deoxidized copper tubes have been widely used because of their excellent bending workability and low cost.

[0003]

However, when a phosphorus deoxidized copper tube is used, corrosion due to water vapor passing through the tube may occur. This corrosion often occurs when the oxygen concentration in the water vapor is high or when the flow of the water vapor is fast. On the other hand, as a water supply / hot water supply pipe, a copper alloy pipe having an inner surface provided with an Sn plating and having a copper ion elution suppressing effect is used (Japanese Patent Application Laid-Open No. Hei 7-118873). Therefore, it is naturally conceivable to use such an Sn-plated copper alloy pipe as a pipe for steam so as to have corrosion resistance to steam. That is, in the former environment, the inner surface of the tube is in contact only with the liquid phase and the temperature is up to 100 ° C. (normally 60 to 80 ° C.), but in the latter environment the temperature is high (100 ° C. or more). In most cases), there is a difference that the gas phase or the mixed phase of the gas phase and the liquid phase is in contact with each other. Therefore, it has been found that the use of the Sn-plated copper alloy tube of the above publication has little effect.

[0004] The present invention has been made in view of the above-mentioned conventional problems, and has as its object to obtain a copper alloy pipe for steam piping having excellent corrosion resistance to steam.

[0005]

Based on the above-mentioned object, the present inventor has conducted various studies, and as a result, formed a tube from a copper alloy containing Zn and regulated the P content in the copper alloy. Further, a Sn or / and Cu-Sn alloy layer is formed on the inner surface of the tube, and the center line average roughness (R
By controlling a), it was found that the corrosion resistance against water vapor was greatly improved, and the present invention was completed.

That is, the copper alloy tube for steam piping according to the present invention comprises a copper alloy tube containing 0.01 to 10% by weight of Zn and having a P content of 0.04% or less.
It has a protective coating layer made of a Sn or / and Cu-Sn alloy layer of 1 to 3 µm, and the center line average roughness (Ra) of its inner surface is 1.2 µm or less.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The mechanism of the improvement of corrosion resistance in the present invention is that Zn contained in a copper alloy pipe base material diffuses in the coating layer Sn and / or Cu-Sn alloy layer to reach the coating layer surface. A protective coating of a stable Sn—Zn composite oxide is formed on the surface layer of the coating layer, and this improves the corrosion resistance. The rate at which Zn in the base material diffuses in the coating layer is very fast, and Zn diffuses into the surface layer of the coating layer soon after the formation of the coating layer. However, the composite oxide of Sn-Zn is not formed as it is, and the composite oxide of Sn-Zn is formed only when it is used as a steam pipe and comes into contact with water vapor, and exhibits excellent corrosion resistance. Therefore, there is no effect even when a tube containing only the Zn-containing copper alloy and having no coating layer has no effect.
And / or using a coating layer other than the Cu-Sn alloy layer has no effect, and using a copper alloy containing no Zn as a tube base has no effect.

When the Zn concentration in the copper alloy base material is 0.0
If the content is less than 1%, there is no clear effect, and if the content exceeds 10%, stress corrosion cracking of the tube itself occurs. Therefore, it is necessary to regulate the Zn content within the range of 0.01 to 10%.
Further, the thickness of the Sn or / and Cu-Sn alloy layer is 0.1
When the thickness is less than μm, no clear effect is obtained. When the thickness exceeds 3 μm, the effect is saturated and only the cost is increased. Further, when the center line average roughness (Ra) of the coating layer exceeds 1.2 μm, the generated Sn
Since the protective film of the composite oxide of -Zn is easily peeled off physically and the effect is reduced, the center line average roughness (Ra) is 1.
It needs to be 2 μm or less.

[0009] The coating layer of the copper alloy tube of the present invention is made of Sn or /
And Cu—Sn alloy layer, which is
It means any of an n layer, a Cu-Sn alloy layer, and a mixed layer of Sn and a Cu-Sn alloy. At the beginning of use, even if only Sn or a mixed layer of Sn and Cu-Sn alloy is used, the entire coating layer changes to a Cu-Sn alloy layer with use. As a method of forming a coating layer on the inner surface of the copper alloy tube, for example, a method of flowing an electroless Sn plating solution through the Zn-containing copper alloy tube to coat the same, a method of passing molten Sn through the Zn-containing copper alloy tube, and the like. Conceivable. At this time, it is important that the center line average roughness Ra of the inner surface of the tube after coating is 1.2 μm or less. For this purpose, the center line surface roughness Ra of the inner surface of the copper alloy tube before coating is set to 1. It is necessary to keep it at 2 μm or less.

[0010] The copper alloy tube base material of the present invention exhibits an effect as long as it contains a predetermined amount of Zn, and there is no problem even if several types of other components coexist with Zn. Therefore, when manufacturing the copper alloy tube of the present invention, P, Si, Mg, B, etc. can be added as a deoxidizing agent in the Zn-containing copper alloy during the manufacturing process of the base material. However, if the P content exceeds 0.04%, Sn-Z
Although there is no problem in the formation of the composite oxide of n, the amount of P must be 0.04% or less because separation easily occurs between the coating layer and the base material. Note that Si, Mg
If the content exceeds 0.1%, processing becomes difficult, so the total content is preferably 0.1% or less. Further, in order to improve the strength of the base material, Ni, Sn, Fe, Mn, Cr, Co, Ti and the like can be added in a total of 2% or less. If it exceeds 2% in total, the workability is reduced.

[0011]

Next, the results of a corrosion test performed on steam for a copper alloy tube according to the present invention will be described in comparison with a comparative example.

Ingots of copper alloys of various components shown in Table 1 (cylinders having an outer diameter of 300 mm and a length of 500 mm) were manufactured and subjected to the steps of extrusion → rolling → drawing to have an outer diameter of 15 mm × wall thickness 1 mm × length 5 m. Finished with tube dimensions of At this time, a die and a plug were selected at the time of the final drawing, and the average surface roughness of the inner surface of the tube was changed. Using these tubes, Sn plating of various plating thicknesses was applied to the inner surfaces of the tubes in an electroless plating process described below to obtain test materials. <Electroless plating process> Degreasing → washing with water → pickling → washing with water → plating → washing with water → drying Degreasing: flowing an alkaline degreasing solution through the tube. Rinsing: Tap water is distributed in the pipe. Pickling: Dilute acid is passed through the tube. Plating: An electroless Sn plating solution (Enplate TIN-421 Special, manufactured by Meltex Co., Ltd.) is passed through the tube. Drying: Normal temperature air is passed through the tube.

[0013] From each end of the tube of this test material 50c
m was cut out and divided in half, and the Sn plating film thickness and the center line average roughness of the inner surface were measured. In addition, the Sn plating film thickness is measured by a fluorescent X-ray film thickness measuring device (manufactured by Seiko Electronics Industries,
Using SFT-156A), the center line average roughness of the inner surface was measured using Talysurf 6 (manufactured by Rank Taylor Bobson), and a total of 20 points were measured at any 10 points on both ends,
The average value was defined as the Sn plating film thickness of the test material and the center line average roughness of the inner surface. Table 1 shows the results.

[0014]

[Table 1]

The remaining 4 m of each test material is 1 m × 4.
It was cut into a book and subjected to a corrosion test of four levels for a period in the steam environment shown below. <Steam corrosion test> Electric conductivity is 4 to 6 μS / cm, pH
Heat the deionized water of 6.5 to 7.5 to a temperature of 180
A steam was generated at a flow rate of 4000 liters / hour at a flow rate of 4000 liters / hour at a temperature of 1000 ° C. for 3 months, 6 months, 1 year, 2 years, and a corrosion test was conducted. A schematic diagram of the corrosion test is shown in FIG. 1 (ion-exchanged water is heated in a heating furnace 1 to generate steam, and the steam is distributed to each test tube S through a header 2 and exhausted to the atmosphere via a valve 3). .

In the evaluation, the test tube through which steam was circulated for a predetermined time was halved, the state of the coating layer was visually observed, and the maximum corrosion depth was measured. Table 2 shows the results.

[0017]

[Table 2]

As apparent from Table 2, the base material contains a predetermined amount of Zn, P is regulated to a predetermined amount or less, has a predetermined plating thickness, and has a predetermined inner surface center line average roughness. In all of Examples 1 to 10 having a degree, no peeling was observed at all in the two-year corrosion test, and no corrosion was observed at all.

On the other hand, Comparative Example 11 containing no Zn,
In No. 12, even if P is 0.04% or less and has a predetermined plating thickness and an inner surface center line average roughness, peeling and corrosion of the film are progressing. Further, even if Zn is contained, 0.01
% In Comparative Example 13 and Comparative Example 14 in which the plating thickness is less than 0.1 μm, although no peeling of the film was observed in 3 months, peeling and corrosion of the film were observed in 6 months. become. Furthermore, predetermined Zn and P contents,
The inner surface center line average roughness is 1.
In the case of the comparative material 15 exceeding 2 μm, peeling and corrosion of the film are observed. Even though the Zn content, the plating thickness, and the inner surface center line average roughness are predetermined, the specimen 16 having a P content exceeding 0.04% exhibits peeling and corrosion of the coating. In the test material 17 having no coating layer, corrosion has occurred.

[0020]

According to the present invention, a predetermined Sn or / and Cu-Sn alloy coating is applied to the inner surface of a Zn-containing copper alloy tube, and the center line average roughness of the inner surface is defined, whereby steam or water is introduced into the tube. And / or as a steam pipe through which the drain water passes, the corrosion resistance is remarkably improved, and the life and reliability thereof can be greatly increased.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a corrosion test.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating furnace 2 Header 3 Valve S Test tube

Claims (1)

[Claims] 1. The method according to claim 1, wherein Zn is contained in an amount of 0.01 to 10 wt%.
A copper alloy tube having a content of 0.04% or less, a protective coating layer of 0.1 to 3 μm of Sn or / and Cu—Sn alloy layer on the inner surface, and a center line of the inner surface. A copper alloy pipe for steam piping, wherein the average roughness (Ra) is 1.2 μm or less.