JPS6234821B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a copper alloy pipe having excellent corrosion resistance (particularly pitting corrosion resistance) and Cu ion elution resistance as a piping material for water supply and hot water supply. [Prior Art] Deoxidized copper, which has excellent corrosion resistance and workability, is widely used as a piping material for water supply, hot water supply, etc. However, even with deoxidized copper, it cannot be said that it fully satisfies the required properties, and depending on the water quality, Cu ions may gradually elute, resulting in the problem of blue water formation.
In other words, when the amount of Cu ions eluted from pipes increases and exceeds the water quality standard value (Cu: 1.0ppm) for tap water, Cu
Problems arise when laundry, etc. is colored blue by ions. It is known that as the period of use passes, an oxide film is formed on the surface and the elution of Cu ions stops. However, it takes a long period of time, such as 1 to 2 years, for such a copper oxide film to be formed on the inner surface of water supply/hot water supply pipes, and the problem of Cu ion elution during that time cannot be avoided. On the other hand, under other conditions, a phenomenon in which pitting occurs locally due to corrosion may occur, and in this case, the pipe wall is penetrated within a short period of time, resulting in a water leakage accident. This pitting corrosion is commonly known as
There are two types: Type and Type. Type pitting occurs in cold water with hard water, while Type pitting corrosion occurs in warm water with soft water. Therefore, it is thought that the relationship between corrosion factors, especially water quality, shows different behavior. Various types of research are being carried out with the aim of improving the corrosion resistance of copper pipes, such as ``INFLUENCE OF MINOR ALLOYING''.
ADDITIONS ON CORROSION OF COPPER
TUBES IN DRINKING WATERS by Diene
DEVROEY and claude DEPOMMIER”
INTERNATIONAL COPPER RESEARCH
ASSOCIATION, INC. (September 1970) also proposed a technique to improve corrosion resistance by incorporating trace amounts of Al or Sn into deoxidized copper. On the other hand, type pitting corrosion is said to occur more easily in hot water where HCO ₃ ^- /SO ₄ ^2- is less than 1 and the residual chlorine concentration is high, but research into alloys that improve corrosion resistance against this type of pitting corrosion is underway. Not done. [Problems to be solved by the invention] Even alloys that are considered effective against TYPE pitting corrosion cannot be said to fully meet the requirements for TYPE pitting corrosion, and even when containing appropriate amounts of Al and Sn, corrosion resistance is poor. There are significant variations in performance, making it impossible to obtain a practical and stable corrosion resistance effect. The present invention aims to provide a technology that can stably and reliably prevent the elution of Cu ions and pitting corrosion regardless of the water quality. [Means for solving the problem] The structure of the corrosion-resistant copper alloy tube according to the present invention contains the following elements as essential components: Al: 0.01 to 1.5% Sn: 0.03 to 2.5%, provided that (Al+Sn)≧0.1 % One or more of P, Mg, B, Mn and Si:
Total amount: 0.005-0.5% Oxygen content is regulated to 100ppm or less, and the remainder is Cu
Another feature of the present invention is that a copper alloy containing unavoidable impurities is formed into a tube shape, and another structure of the present invention is to form a silicate layer with a thickness of 10 to 100,000 Å on the inner surface of a copper alloy tube that satisfies the above requirements. The gist is that it is formed by forming a film. [Function] Hereinafter, the reason for specifying the above requirements will be explained in detail, and the function of the present invention will be clarified. First, the reason for selecting Al and Sn as additive alloying elements will be explained. The first oxide film that forms on the inner surface of a copper tube in water, especially hot water, is Cu ₂ O. As long as this Cu ₂ O film is evenly formed on the inner surface, Cu ion elution and pitting corrosion will not occur. Hard to occur. However, in hot water with a high concentration of oxidizing agent (residual chlorine), Cu ₂ O is oxidized to CuO in a short period of time, and most of the oxide film is converted to CuO. The CuO film has a high self-potential that easily exceeds the pitting corrosion potential, leading to pitting corrosion. Therefore, in order to eliminate pitting corrosion, the inner surface of the copper tube should always be covered with a Cu ₂ O film, but as mentioned above, Cu ₂ O converts to CuO in a short period of time. Therefore, the components of the copper oxide film formed on the copper surface are calculated as follows: Cu ₂ O > CuO
We wondered if there was a way to maintain this state stably, and investigated the effects of addition using various alloying elements.
As a result, it was confirmed that by adding appropriate amounts of Al and Sn together, the components of the copper oxide film could be maintained in the state of Cu ₂ O>CuO. Moreover, in order to maintain the copper oxide film component formed on the copper surface in a state of [Cu ₂ O > CuO] without being affected by changes in water quality, it will be clarified in the examples later (particularly in Figure 1). The amount of Al and Sn added should be 0.01% or more.
It was confirmed that the content must be 0.03% or more, and the sum of both must be 0.1% or more. However, it has been found that even if the amounts of Al and Sn added are set strictly, sufficient pitting corrosion resistance cannot be obtained by itself, and that significant pitting corrosion phenomena may sometimes occur. As a result of searching for other causes of pitting corrosion, we found that pitting corrosion resistance significantly changes depending on the amount of oxygen contained in the copper alloy.
It was found that when the content exceeds 100 ppm, the above-mentioned effect of improving pitting corrosion resistance by Al and Sn is almost completely lost. This tendency can be seen in the examples described later (especially in Figure 2).
However, as is clear, in order to ensure a high level of corrosion resistance, appropriate amounts of Al and Sn must be added.
In addition to adding oxygen, it is essential to suppress the amount of oxygen to 100 ppm or less. However, if the amount of Al added is too large, the workability during pipe manufacturing will decrease, so the addition amount is 1.5%.
If the amount of Sn added is too large, hot workability and crushing corrosion resistance will decrease.
Must be kept below 2.5%. In addition, in the present invention, in order to ensure a low level of oxygen concentration as described above, P, Mg, B, Mn and
It is necessary to contain one or more elements selected from the group consisting of Si as a deoxidizing agent. However, the fifth
The figure is a graph showing the results of investigating the relationship between residual P concentration and oxygen concentration at the completion stage of melting, and this trend was the same for Mg, B, Mn, and Si. That is, if the amount of these deoxidizing elements is less than 0.005%, the oxygen concentration in the copper alloy cannot be suppressed to 100 ppm or less, and satisfactory pitting corrosion resistance cannot be ensured. Moreover, by containing appropriate amounts of these deoxidizing elements, hydrogen embrittlement can be suppressed. In other words, it is known that oxygen-free copper, for example, is prone to embrittlement if it is heated with a torch in an oxidizing atmosphere and then heated in a reducing atmosphere during brazing work; During the process, oxygen diffuses into the copper,
It is believed that this oxygen reacts with hydrogen that enters when heated in a reducing atmosphere, causing hydrogen embrittlement. However, if a small amount of elements that have a strong bond with oxygen are included as mentioned above, these elements will combine with the oxygen that enters when heated in an oxidizing atmosphere, causing oxygen to penetrate deep into the body. It is thought that it is difficult for hydrogen to penetrate and, as a result, it becomes difficult to cause hydrogen embrittlement. However, if the amount of these deoxidizing elements is too large, processability will deteriorate, so at most
It should be kept below 0.5%, preferably below 0.1%. A copper alloy tube that satisfies the above-mentioned structural requirements has the above-mentioned effects, and exhibits superior pitting corrosion resistance compared to conventional corrosion-resistant copper alloy tubes. However, the copper oxide film in the initial stage of use (unless otherwise specified below)
It is undeniable that some amount of Cu ions will be eluted during the period when the formation of copper oxide film (Cu ₂ O > CuO) is incomplete. Therefore, in order to reduce the elution of Cu ions to a level that does not pose a practical problem from the beginning of use, it is recommended to form a silicate film of an appropriate thickness on the inner surface of the copper alloy tube. Specific examples of compounds that form a silicate film include lithium silicate, sodium silicate, potassium silicate, amine silicate, ethyl silicate, colloidal silica, etc., but the reason why silicate-based compounds were particularly selected in the present invention is as follows. . The coating does not deteriorate due to heating during brazing, etc., and no harmful gases are generated. When the film peels off during use, it elutes into extremely fine (100 μm or less) fragments, so there is no risk of clogging pipes, valves, etc., and it is completely harmless to the human body. Since the silicate film is hydrophilic and porous, a copper oxide film gradually grows under the film (ie, on the surface of the copper alloy material). Furthermore, the silicate film itself is soluble in water, and gradually dissolves into water as SiO ₂ , which is harmless to the human body. Since the formation of a corrosion-resistant copper oxide film has already been completed by the time the product is used, the elution of Cu ions can be reduced to a level that does not pose a practical problem from the beginning of use. In order to effectively exhibit the effects of the silicate film as described above, and to suppress the amount of Cu ion elution to less than 1 ppm, especially at the beginning of use, the film thickness must be 10 Å or more. There is no upper limit to the film thickness from the perspective of preventing the elution of Cu ions, but if it is too thick, the film is likely to crack or peel when an external force such as bending is applied to the pipe, so avoid such problems. In order to do so, it should be kept below 100,000 Å. The method for forming the silicate film is not particularly limited, but the most common method is to remove lubricating oil adhering to the inner surface of the copper alloy pipe during the pipe manufacturing process with a degreaser, and then add one or more of the silicate compounds to water. This method involves diluting the solution, applying it to the inner surface of the tube, and dehydrating it by heating it at 100 to 200°C for several minutes to several tens of minutes in a heating furnace or hot air drying oven. However, in the case of ordinary deoxidized copper pipes, even if a silicate film is formed using the method described above, it is not possible to firmly adhere the film, and about 50% of the film peels off after about 3 months of water flow. surface protection effect cannot be effectively exerted. However, as described above, when a copper alloy tube to which an appropriate amount of Al is added is used, the adhesion of the silicate film is dramatically improved, and the surface protection effect of the silicate film is maximized. The reason for this is thought to be that Al in the copper alloy and Si in the silicate film form a covalent bond at the bonding interface. That is, in the second invention disclosed in this specification (corrosion-resistant copper alloy tube with a silicate coating formed on the inner surface), Al mixed into the tube material stabilizes the composition of the copper oxide coating by coexisting with Sn as described above. In addition to (Cu ₂ O > CuO), it also performs the important function of improving the adhesion of the silicate film. [Example] Example 1 Using a copper alloy with the chemical composition shown in Table 1,
Copper alloy tubes of 22.2 mm × wall thickness of 0.81 mm were made, and a model hot water water flow test was conducted under the following conditions, and the pitting corrosion status of the inner surface of each copper alloy tube after one year was investigated. The results are shown in Table 1. <Experimental conditions> Water quality Water temperature...60℃ HCO ₃ ^{-Concentration} ...30ppm SO ₄ ^2- Concentration...50ppm Cl ^{-Concentration} ...10ppm ClO ^{-Concentration} ...1~3ppm PH...7.0 Flow rate: 2m/sec Test period: 1 year Pitting corrosion Occurrence status Number of pitting corrosion/dm ² Less than 1…◎ 1-5…〇5-20…△ More than 20…×

[Table] In Table 1, Nos. 1 to 19 are examples that meet the specified requirements of the present invention, and all have excellent pitting corrosion resistance. On the other hand, Nos. 20 to 26 are comparative examples that lack any of the requirements specified in the present invention as shown below.
Both have insufficient pitting corrosion resistance. No. 20, 21: Since the sum of Al and Sn is less than 0.1%, the corrosion resistance of the copper oxide film is insufficient. No.22, 23: Due to lack of either Al or Sn,
After all, sufficient pitting corrosion resistance cannot be obtained. No. 24, 25, 26: Pitting corrosion resistance is not improved because one or both of Al and Sn is not included. In addition, Figure 1 shows that the oxygen concentration was approximately 30 ppm and
This is a graph showing the influence of Al and Sn content on pitting corrosion resistance by extracting samples with a phosphorus content of approximately 0.025%. It is the same as the judgment criteria. As is clear from Figure 1, in order to ensure satisfactory pitting corrosion resistance, Al≧0.01%, Sn≧0.03% and [Al
+Sn〕≧0.1% Al and
The Sn content must be determined. Next, using a copper alloy with a basic composition of 0.1% Al content, 0.5% Sn content, and the remainder being substantially Cu, several types of copper alloy tubes differing only in oxygen concentration were manufactured in the same manner as above. The occurrence of pitting corrosion was investigated. The results are shown in Figure 2, and the oxygen concentration
When the oxygen concentration is below 100ppm, almost no pitting corrosion occurs, but when the oxygen concentration exceeds 100ppm, the number of pitting corrosions that occur increases rapidly, and the corrosion resistance improvement effect of Al and Sn is virtually lost. I know that there is. Example 2 22.2mm with a copper alloy having the chemical composition shown in Table 2
×0.81mm ^t ×1000mm test tube was manufactured, and model hot water of the same water quality as used in Example 1 (flow rate:
2m/sec) to measure Cu over time from the start of water flow.
Changes in the amount of ion elution were investigated. However, the amount of Cu ions eluted was determined by filling each test tube with model hot water during a predetermined measurement period, leaving it for 24 hours, and quantifying the Cu ions eluted into the hot water during this period.

〔Effect of the invention〕

The present invention is constructed as described above, but the key point is to obtain a copper alloy tube that exhibits excellent corrosion resistance by containing appropriate amounts of Al and Sn in the copper alloy and by significantly limiting the amount of oxygen. was completed. Furthermore, by forming a silicate film on the inner surface of this copper alloy pipe, the amount of Cu ions eluted during the initial stage of water flow can be significantly reduced, greatly extending the life of the transport piping, and reducing the amount of leaching of the piping material. This made it possible to reliably prevent water quality deterioration.

[Brief explanation of the drawing]

Figures 1 to 5 are graphs showing the experimental results. Figure 1 is the interaction between the amount of Al and Sn on pitting corrosion resistance, and Figure 2 is the relationship between the oxygen concentration in the copper alloy and the number of pitting corrosion. , Figure 3 shows the relationship between the water flow period and the amount of Cu ions eluted, Figure 4 shows the relationship between the thickness of the silicate film and the amount of Cu ions eluted, and Figure 5 shows the relationship between the amount of residual P in the melt and the oxygen concentration. .

Claims (1)

[Scope of Claims] 1 In addition to containing the following elements as essential components, Al: 0.01 to 1.5% (weight %: the same below) Sn: 0.03 to 2.5%, provided that (Al+Sn) ≧0.1% P, Mg, B, Mn , and one or more types of Si: 0.005 to 0.5% in total. Oxygen content is regulated to 100 ppm or less, and the remainder is Cu.
A corrosion-resistant copper alloy tube, characterized in that it is formed by forming a copper alloy containing unavoidable impurities into a tube shape. 2 In addition to containing the following elements as essential components, Al: 0.01-1.5% Sn: 0.03-2.5% However, (Al+Sn) ≧0.1% One or more of P, Mg, B, Mn, and Si: total amount 0.005~0.5% Oxygen content is regulated to 100ppm or less, and the remainder is Cu.
A corrosion-resistant copper alloy tube characterized in that a silicate film with a thickness of 10 to 100,000 Å is formed on the inner surface of the copper alloy tube consisting of unavoidable impurities.