JPS61221378A - Method for preventing dissolution of copper - Google Patents

Abstract

PURPOSE:To remarkably reduce the leaching of copper from a copper piping system by feeding an oxidizing treating soln. into the piping system to form a slightly water-soluble copper oxide film on the inside of the piping system. CONSTITUTION:An oxidizing treating soln. is fed into a copper piping system, especially a copper piping system as a hot water path. A soln. contg. a strong alkali as the principal component and one or more kinds of compounds selected among hypochlorites, perchlorates, persulfates and permanganates as an oxidizing agent is used as the oxidizing treating soln. A slightly water-soluble copper oxide film of 0.01-10mum thickness is formed on the inside of the copper piping system.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a treatment method for reducing copper dissolution from hot water supply copper piping systems.

[Prior art and its problems] A variety of materials are used as pipe materials for tap water and hot water supply, including copper, steel, stainless steel, synthetic resins, plated steel pipes, and synthetic resin-coated steel pipes. Steel pipes are widely used because of their good workability and good corrosion resistance against water and hot water.In particular, steel pipes are widely used for hot water piping in buildings because of their stability and workability. has been done. However, in special water quality environments, the surface of the steel pipe may dissolve, and the copper concentration in the water may exceed the Ministry of Health and Welfare's water quality standards (1 ppm <ml g/l).

Further, even if the degree of ri4S is less than 1 pDm, when sanitary equipment or the like is used for a long period of time, this copper may precipitate as a copper salt, causing a problem of coloration blue.

Measures to reduce this copper dissolution have conventionally been taken by easing the water quality, that is, the corrosive environment, changing the material, etc., but these have caused the following problems. Measures to alleviate water quality and corrosive environments have mainly been taken by introducing chemicals into the water. For example, alkaline caustic soda, sodium bicarbonate, etc. were injected into acidic feed water, and small amounts of sodium silicate, sodium phosphate, etc. were injected into water where scale as a protective film was difficult to form. However, this method requires the replenishment of used chemicals and the installation and maintenance of new chemical injection equipment. Furthermore, these tasks are generally outsourced to specialized contractors and are not suitable for private residences.

As countermeasures by changing the material, there have been examples of using alloys with strong corrosion resistance, such as stainless steel, and resin-coated pipes that are stable for water and hot water supply. However, these materials cannot be joined by simple brazing as with steel pipes, and it is difficult to treat the ends of joints, especially in cladding pipes, and there may still be problems with corrosion resistance. Other measures to prevent copper dissolution include metal plating, but similar to the previous example, there were problems such as difficulty in terminal treatment and the effects of contact corrosion between different metals.

[Summary of the Invention] In view of the above points, the present invention is aimed at dissolving copper by treating the inner surface of the piping system in a copper piping system with an oxidizing treatment liquid and forming a water-insoluble copper oxide film. This is a decrease in

[Example] Examples will be described below.

In the hot water piping system shown in FIG. 1, a hot water boiler 4 connected to the water supply and a hot water faucet 3 in a kitchen, washroom, bathroom, etc. are connected by two types of conduits 1 and 2 with different outer diameters. There is.

In such a piping system, the upstream side of the hot water boiler 4,
An oxidation treatment liquid tank 6 and a pump 7 are connected to the hot water tap 3 at the end via a circulation vibrator 10, and the oxidation treatment liquid 9 heated and kept warm by a heater 8 circulates through the piping system, and its inner surface can be oxidized. The tank 6, pump 7, and ring vibrator 10 can be removed as appropriate after the fact.

In the configuration shown, the outer diameter is 22.22 m + the wall thickness is 0.
．． 81 am+, length 5 m copper pipe 1, outer diameter 15°88 sub, wall thickness 0.71 JI11 length 5 TrL, using sodium hydroxide 100 ar/f as the oxidation treatment liquid.
, an aqueous solution containing sodium hypochlorite 15 (7/f) is prepared, and after heating and keeping this solution at 90°C in tank 6 and supplying and circulating it to the hot water system for 10 minutes, the system is filled with tap water 5 Washing water was passed for 30 minutes.

After this piping system was returned to its normal operating condition, the hot water supply temperature was once raised to 70°C, the hot water supply was stopped, and the system was allowed to stagnate and cool for 24 hours. After that, the water was sampled and the dissolved copper concentration was measured.

The water quality of tap water is as shown in Table 2. The copper eluted from the piping system before oxidation treatment was 0.851) pm, while that from the piping system after oxidation treatment was 0.851) pm. O, o6
ppm, and the effect of preventing copper dissolution by oxidation treatment was confirmed.

Oxidation treatment experiment After degreasing the inner surface of a copper tube with an outer diameter of 15.88 m and a wall thickness of 0.71 m, oxidation treatment was performed using the recipe shown below (all in aqueous solution).
.

Prescription 1 Caustic soda: 100qr/j! .

Potassium chlorite: 15g/f.

Processing temperature: 95°C.

Processing time = 1-5 minutes.

Prescription 2 Caustic soda: 50gr/1 Potassium persulfate: 10o/J.

Processing temperature: 95-100°C.

Processing time: 21-10 minutes.

Prescription 3 Copper sulfate: 120g/i.

Potassium chlorate: 50g/f.

Processing temperature: 260-80°C.

Processing time: 21-10 minutes.

Prescription 4 Copper sulfate: 120Q/f.

Carini permanganate 15Q/1 Processing temperature = 80-95°C.

Processing time: 1-10 minutes.

Dissolution test Steel pipes treated with the above four types of formulations and untreated steel pipes,
Distilled water, tap water (weakly corrosive) and artificial water (strongly corrosive,
Adjusted P)-1) @:, Seal each tightly, 7
After holding at 0°C for 24 hours, the degree of copper S in the water was measured.

The measurement results of copper concentration are shown in Table 1, and the tap water quality is shown in Table 2.

water v, 1
Table 2 As is clear from Table 1, when the formulation and the thickness of the oxide film differ, the dissolution rate of copper also changes, and the thickness is 0.01 μmL.
J, the effect of preventing dissolution becomes remarkable.

[Effects of the Invention] Since the present invention forms a water-insoluble copper oxide film on the inner surface of copper piping, no maintenance is required, unlike water treatment methods that add rust preventives.

Furthermore, the piping material is exactly the same as the conventional one, so it can be implemented only in systems where the problem of coloring due to copper dissolution occurs. Therefore, it is also possible to avoid using expensive corrosion-resistant materials throughout areas where staining problems are previously anticipated.

[Brief explanation of drawings]

The figure is an explanatory diagram showing an example of the method according to the present invention. 1.2...Copper piping, 3...Hot water tap, 4...Hot water boiler. 6...Tank, 7...Circulation pump, 8...Heater. 9... Oxidation treatment liquid, 10... Circulation pipe.

Claims (4)

[Claims] (1) A method for preventing copper dissolution, which comprises supplying an oxidizing treatment liquid into a copper piping system to form a copper oxide film that is sparingly soluble in water on the inner surface of the copper piping system. (2) The method according to item 1 above, wherein the copper piping is a hot water passage. (3) The method according to item 1 or 2, wherein the copper oxide film has a thickness of 0.01 to 10 μm. (4) The main component of the oxidizing treatment liquid is a strong alkali,
The method according to item 1, item 2, or item 3, wherein the oxidizing agent contains at least one of hypochlorite-11 perchlorate, persulfate, and permanganate.