Cold-and hot-water supply copper-alloy pipe with inner-surface p

Details Cold-and hot-water supply copper-alloy pipe with inner-surface p Cold-and hot-water supply copper-alloy pipe with inner-surface p

1997-02-10

1998-06-23

Scherbel, David

Pipes and tubular conduits

Distinct layers

Bonded to each other

138 38, 138146, F16L 914

Patent

active

057691290

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a copper-alloy pipe whose inner surface is plated with Sn as an inner-surface protective film and which is used for a cold- and hot-water supply pipe, a method for manufacturing the pipe, and a heat exchanger using the copper-alloy pipe and used for a business- or home-use hot-water supply system in which copper ions are prevented from being eluted and the pitting resistance is improved.


BACKGROUND ART

A copper pipe, a galvanized steel pipe, a vinyl chloride pipe, a stainless steel pipe, or a vinyl-chloride-lining steel pipe is used as a conventional cold- and hot-water supply pipe. Among these types of pipes, the copper pipe is particularly superior in the practicedness and corrosion resistance and has an advantage that even a long copper pipe can be easily transported, because the copper tube can be coiled. Therefore, the copper pipe is widely used as a cold- and hot-water supply pipe.
A phosphorus deoxidation copper (JIS H3300C1220T) pipe is mainly used as a heat-transfer pipe for heat exchanger incorporated into a conventional hot-water supply system. The phosphorus deoxidation copper pipe is superior in the heat transfer characteristic and corrosion resistance and widely used as this type of the heat transfer pipe.
In a heat exchanger using a phosphorus deoxidation pipe, however, copper ions are eluted from the pipe wall and the copper ion concentration of clean water may exceed 1 ppm which is the criterion of the quality of clean water with a legally-specified copper ion concentration for a certain type of water such as water with a low pH or water with a lot of free carbon dioxide. Even if the copper ion concentration is 1 ppm or lower, a white cloth may be blued. Therefore, it is preferable to decrease the elution of copper ions into water. As means for preventing the copper ion elution, chemicals have been added to supplied water, a copper-ion elution preventive alloy has been developed, or the inner surface of a pipe has been coated so far. Though addition of chemicals to supplied water is effective to prevent copper ions from being eluted, it is not practical because the pipe manufacturing cost increases.
As for the problem of copper ion elution, it is proposed to use a Cu--Mg or Cu--Ca type copper-ion-elution preventive alloy (Japanese Patent No. 964347) for a cold- and hot-water supply pipe, and therefore it is considered to use the alloy as the material of a heat exchanger in a hot-water supply system. However, the alloy is not practical because the alloy is not only difficult to cast the ingot but also the alloy does not have a high copper-ion elution preventive effect.
Moreover, an art for plating the inner surface of a copper pipe with Sn has generally been known as a means for preventing copper ion elution (H. H. UHLIG (transliterated), "Corrosion and Corrosion Control--Theory and Application", SANGYO TOSHO (transliterated)(1968), p. 275) and many Sn coating methods are proposed.
That is, the following methods are generally known as methods for manufacturing a pipe whose inner surface is coated: a method having a step of applying metallic powder with a low melting point and flux to the inner surface of the copper pipe and a step of heating it (Japanese Patent Laid-Open Nos. 200954/1985, 200975/1985, 61717/1987, and 61718/1987), a method having a step of forming a Cu--Sn alloy film on the inner surface of the copper pipe (Japanese Patent Laid-Open No. 221359/1986), and a method having a step of hot-dipping on the inner surface of the copper pipe (Japanese Patent Laid-Open No. 61716/1986). However, these methods cannot be applied to a pipe with a length larger than its diameter though it can be applied to a pipe with a length smaller than its diameter.
Therefore, to solve these problems of a conventional method for coating a protective film on an inner-surface of a pipe, a pipe inner-surface coating method is proposed which applies electroless tin plating to the inner surface of a copper pipe (Japanese Patent Laid-Open Nos. 45282/1992 and

REFERENCES:
patent: 4217886 (1980-08-01), McLaughlin
patent: 4337793 (1982-07-01), Sato et al.

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