Cold-and hot-water supply copper-alloy pipe with inner-surface protective film, method for manufacturing same, and hot-water supply heat exchanger

A cold- and hot-water supply copper alloy pipe with an inner-surface protective film is provided. A pipe body is made of a copper alloy which consists essentially of at least one of Zn and Mn by 0.02 wt % or more as the total amount, Zn being restricted to 5 wt % or less and Mn being restricted to 3 wt % or less and balance being copper and inevitable impurities. A protective film is formed on the inner surface of the copper alloy pipe body and made of Sn and inevitable impurities. The protective film has an average thickness of 0.2 to 4 .mu.m in the pipe circumferential direction. The protective film can be made of Sn, an intermetallic compound of Sn and Cu, and inevitable impurities or made of an intermetallic compound of Sn an Cu and inevitable impurities. In any case, Cu.sub.3 Sn must not present on the surface of the protective film. This type of copper alloy pipe makes it possible to prevent an .epsilon. phase which causes pitting from forming on the surface of the protective film, prevent copper ions from being eluted, and improve the pitting resistance.

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 99180/1992). 
This method of applying electroless tin plating to the inner surface of a 
copper pipe has the advantages that the method decreases the manufacturing 
cost, and moreover it can be applied to a pipe with a length larger than 
its diameter and particularly, the method makes it possible to coat a 
coiled copper pipe. Therefore, the method is a very useful art. Moreover, 
the conventional electroless tin plating method shows corrosion resistance 
against the pitting which is a problem of a conventional Sn-coated copper 
pipe. 
However, when the conventional copper pipe to which the electroless tin 
plating is applied is used as a cold- and hot-water supply pipe, a problem 
occurs that the corrosion potential on the surface of the pipe slowly 
rises, then exceeds the corrosion potential of the base material, and 
finally causes the dangerousness of pitting to rise. 
The cause of the above problem is considered as shown below. That is, in 
the beginning of use of the pipe, the corrosion potential of the surface 
of the pipe does not exceed that of the base material because Sn is 
present on the surface of the pipe. However, as time passes, diffusion 
progresses between the Sn plating layer and the Cu base material of the 
pipe body, an .epsilon. phase (Cu.sub.3 Sn phase) of a Cu--Sn 
intermetallic compound grows, and the .epsilon. phase reaches up to the 
surface of the pipe. Because the .epsilon. phase forms an oxide film, the 
corrosion potential of which being higher than that of the base material, 
the base material may be pitted if a missing portion (e.g. pinhole or 
scratch) is present on the .epsilon. phase. This phenomenon becomes more 
remarkable as the operating temperature rises and may early occurs under a 
hot-water supply condition in which hot water close to 100.degree. C. is 
used. 
Moreover, even if a heat exchanger for a hot-water supply system is 
assembled by using the above prior arts and using a conventional copper 
pipe whose inner surface is plated with Sn, the Sn plating completely 
dissolves in the base material due to in-furnace brazing which may be 
formed in the assembling process. Therefore, Sn plating is not an 
effective means for preventing copper ion elution. 
It is an object of the present invention to provide a cold- and hot-water 
supply copper alloy pipe with an inner-surface protective film, wherein an 
.epsilon. phase which is the cause of the pitting corrosion is prevented 
from precipitating on the surface of the protective film, thereby 
preventing the elution of copper ion and improving the pitting corrosion 
resistance, also to provide a method for manufacturing the pipe, and a 
heat exchanger for a hot-water supply system. 
DISCLOSURE OF THE INVENTION 
The cold- and hot-water supply copper alloy pipe with an inner-surface 
protective film according to the present invention, comprises a pipe body 
made of a copper alloy which consisting essentially of at least one of Zn 
and Mn by 0.02 wt % or more as the total amount, Zn being restricted to 5 
wt % or less and Mn being restricted to 3 wt % or less, and balance being 
copper and an inevitable impurities; and a protective film which is formed 
on the inner surface of the copper alloy pipe body and made of Sn and 
inevitable impurities. 
The protective film can be a film made of Sn, an intermetallic compound of 
Sn and Cu, and inevitable impurities. In this case, however, Cu.sub.3 Sn 
must not substantially be present on the surface of the protective film. 
Moreover, the protective film can be a film made of an intermetallic 
compound of Sn and Cu and inevitable impurities. Also in this case, 
Cu.sub.3 Sn must not substantially be present on the surface of the 
protective film. 
Furthermore, the copper alloy pipe body can contain at least one element 
selected from a group of elements P, B, Mg, and Si by 0.20 wt % or less as 
the total amount. 
Furthermore, the copper alloy pipe body can contain at least one element 
selected from a group of elements Al, Sn, and Ni by 2 wt % or less as the 
total amount. 
Furthermore, it is preferable that the average thickness of the protective 
film in the pipe circumferential direction ranges from 0.2 to 4 .mu.m. 
The method for manufacturing a cold- and hot-water supply copper alloy pipe 
with an inner-surface protective film according to the present invention, 
comprises the steps of forming a Sn plating layer on the inner surface of 
a pipe body made of a copper alloy which consists essentially of at least 
one of Zn and Mn by 0.02 wt % or more as the total amount, Zn being 
restricted to 5 wt % or less and Mn being restricted to 3 wt % or less, 
and the balance being copper and an inevitable impurities. 
In this case, Cu.sub.3 Sn is an .epsilon. phase and Cu.sub.6 Sn.sub.5 is an 
.eta. phase. 
Moreover, in the heat exchanger for a hot-water supply system according to 
the present invention, comprises a heat transfer fin and a heat transfer 
pipe, the heat transfer pipe being made of the copper alloy pipe with a 
protective film according to claims 1 to 6. 
BEST MODE FOR CARRYING OUT THE INVENTION 
The present inventors performed various experiments and researches to 
examine the cause of the pitting and as a result, the present inventors 
found that an .epsilon. (Cu.sub.3 Sn) phase of a Cu--Sn intermetallic 
compound grew at the boundary between the base material and the Sn-plating 
layer, because a heat exchanger pipe in a hot-water supply system was 
operated at a high temperature and thereby, diffusion was progressed 
between the base material and the Sn plating layer. Because the corrosion 
potential of the .epsilon. phase is higher than that of copper of a base 
material, the possibility of causing the pitting gets high when the 
corrosion potential of the surface of the pipe becomes higher than that of 
the base material of the pipe according to use of the pipe, even if Sn 
plating is applied to the heat exchanger for a hot-water supply system 
after it is assembled. 
Moreover, the present inventors performed various researches and found that 
there was no possibility of pitting even if an .eta. phase is formed on 
the surface of an Sn plating layer (inner surface of the copper pipe) 
unless the .epsilon. phase is formed on the surface. Furthermore, they 
found that, in order to restrain the formation of the .epsilon. phase, it 
was necessary to prevent Cu from diffusing in the Sn plating layer toward 
the surface of the layer and, in order to prevent the Cu diffusion, it was 
necessary to add Zn or Mn into the copper-alloy base material. Thereby, 
the possibility of pitting is dissolved even under a hot-water supply 
condition in which temperature rises during operation. 
The present invention is completed in accordance with the above knowledge. 
By plating the inner surface of a copper alloy pipe with Sn by the 
electroless plating method, an intermetallic compound of Cu and Sn is 
produced at the interface between the Sn plating protective layer and the 
copper alloy pipe body as time passes. Therefore, the protective layer 
formed by plating the inner surface of the copper alloy pipe body with Sn 
changes from a state in which only Sn is present to a state in which Sn, 
Cu.sub.3 Sn (.epsilon. phase), and Cu.sub.6 Sn.sub.5 (.eta. phase) are 
present. Therefore, even under the state in which the .epsilon. phase and 
.eta. phase are present in addition to Sn, there is the effect of 
preventing pitting. However, as described above, when the .epsilon. phase 
is formed on the surface of the protective film, pitting occurs. 
Therefore, it is necessary to prevent the .epsilon. phase from forming on 
the surface of the protective film.

Reasons of limiting constituents specified in the present invention are 
described below. 
Zn and Mn Alloy Elements in Copper Alloy Base Material of Pipe Body 
It is necessary to contain Zn or Mn individually or both Zn and Mn by 0.02 
wt % or more as the total amount in a copper alloy. Thereby, an .epsilon. 
phase is restrained from growing. In this case, to obtain the 
.epsilon.-phase growth restraining effect, it is necessary to add Zn 
and/or Mn by 0.02 wt % or more as the total amount and it is more 
preferable to add Zn and/or Mn by 0.05 wt % as the total amount. 
However, when the content of Zn exceeds 5 wt %, the possibility of stress 
corrosion crack increases. When the content of Mn exceeds 3 wt %, the 
copper alloy cannot practically be used as a pipe material because the 
bending property is deteriorated. Therefore, it is necessary to set the 
content of Zn to 5 wt % or less and that of Mn to 3 wt % or less. 
At Least One Element Selected From a Group of Elements P, B, Mg, and Si 
Must be Contained in Copper-Alloy Base Material by 0.20 wt % or Less as 
the Total Amount 
It is possible to add P, B, Mg, and Si to the copper alloy as deoxidation 
materials or as elements for improving the strength. However, if the 
content of those elements exceeds 0.20 wt % as the total amount, it is 
necessary to add these components by 0.20 wt % or less as the total 
amount. 
At Least one Element Selected From a Group of Elements Al, Sn, and Ni Must 
be Contained in the Copper Alloy Base Material by 2.0 wt % or Less as the 
Total Amount 
It is possible to add Al, Sn, and Ni to a copper alloy pipe in order to 
increase the strength, heat resistance, and corrosion resistance of the 
pipe. However, if the copper alloy contains them by more than 2.0 wt %, 
those effects are saturated and moreover the manufacturing cost increases. 
Therefore, it is necessary to set the content of these elements to be 
added to 2.0 wt % or less as the total amount. 
An .epsilon. Phase Must Not be Formed on the Surface of a Protective Film 
When the .epsilon. phase appears on the surface of the film, it is oxidized 
by oxygen dissolved in supplied cold or hot water, the corrosion potential 
gets extremely high relative to the base material, and the possibility of 
pitting increases. Therefore, it is necessary to prevent the .epsilon. 
phase from forming on the surface of the protective film. 
The Thickness of the Protective Film Must be Kept Between 0.2 and 4 .mu.m 
When the thickness of the protective film comes to less than 0.2 .mu.m, 
eluted amount of copper ions suddenly increases and moreover, the 
protective film cannot withstand the physical peeling action. Moreover, 
when the thickness of the protective film exceeds 4 .mu.m, the 
protective-film forming cost increases. Therefore, it is preferable to 
keep the thickness of the protective film between 0.2 and 4 .mu.m. 
Then, embodiments of the present invention are described below in 
comparison with their comparative examples. A copper-ion elution test, 
.epsilon.-phase growth acceleration test, corrosion test, hot-working 
property test, bending property test, and stress corrosion cracking 
property test were performed by using the plating solutions shown in Table 
1 below and pipes having the compositions shown in Tables 2 and 3. Methods 
for evaluating the above characteristics are shown below. 
Hot-Working Property 
A drop-hammer testing specimen with a diameter of 15 mm and a length of 15 
mm is sampled out of each alloy casting ingot and a drop hammer test at a 
deformation rate of 50% at 850.degree. C. was applied to the specimen to 
check if the specimen was cracked. 
Bending Property 
Each alloy pipe (outside diameter of 15.88 mm and wall thickness of 0.71 
mm) was bent and a bending test at a bending pitch of 50 mm was applied to 
each pipe to check if the bent portion was creased or broken. 
Stress Corrosion Cracking Property 
A stress of 80% of proof stress was applied to each alloy pipe (outside 
diameter of 15.88 mm, wall thickness of 0.71 mm, and length of 100 mm) and 
the alloy pipe was set in a desiccator storing 12% aqueous ammonia by 
separating the pipe from the aqueous ammonia surface by 50 mm and exposed 
to ammonia gas at room temperature for 2 hr to check if the pipe was 
cracked. 
.epsilon. Phase Growth Restraint 
A plating with a thickness of 1.5 .mu.m was formed on each alloy pipe 
(outside diameter of 15.88, wall thickness of 0.71 mm, and length of 100 
mm) by flowing the plating solution shown in the following Table 1 through 
the pipe and thereafter, the pipe was heated at 100.degree. C. for 900 hr 
to apply a .epsilon.-phase growth acceleration test to the pipe and 
measure the thickness of the .epsilon. phase by observing the cross 
section the pipe with a scanning electron microscope. 
Corrosion Test and Copper Ion Elution Test 
Plating was applied to each alloy pipe (outside diameter of 15.88 mm, wall 
thickness of 0.71 mm, and length of 500 mm) by flowing the plating 
solution shown in the following Table 1 and thereafter, the pipe was 
heated to control a protective film. Then the eluted amounts of copper 
ions were measured by the atomic absorption method after 24 hours passed 
from the time when the pipe was filled with tap water. Thereafter, it was 
checked if the pipe was pitted after flowing tap water through the pipe 
for one year (400 liter/day). 
TABLE 1 
______________________________________ 
No. Type of plating 
Composition of plating solution 
______________________________________ 
1 Substitutional 
Tin(II) chloride 
20 g/lit 
electroless Sodium cyanide 188 g/lit 
plating Sodium hydroxide 
25 g/lit 
solution 
2 Substitutional 
Tin(II) chloride 
5 g/lit 
electroless Thiourea 55 g/lit 
plating Tartaric acid 40 g/lit 
solution 
3 Reductive Sodium tartrate 3.0 mol/lit 
electroless EDTA 0.08 mol/lit 
plating Nitryl Sodium triacetate 
0.2 mol/lit 
solution Tin(II) chloride 
0.04 mol/lit 
4 Reductive Sodium tartrate 0.3 mol/lit 
electroless EDTA 0.1 mol/lit 
plating Tin (II) sulfate 
0.1 mol/lit 
solution Nitryl sodium triacetate) 
0.1 mol/lit 
Titanium sulfate 
0.05 mol/lit 
______________________________________ 
TABLE 2 
__________________________________________________________________________ 
Alloy 
No. Cu Zn Mn P B Mg Si Al Sn Ni 
__________________________________________________________________________ 
Examples 
1 bal. 
0.18 
2 bal. 0.12 
3 bal. 
3.21 0.03 
4 bal. 1.66 0.02 
5 bal. 
1.13 0.05 
6 bal. 2.54 0.02 
7 bal. 
0.22 
0.13 
8 bal. 
0.54 
1.12 
0.02 
9 bal. 0.33 0.01 
10 bal. 
0.03 0.01 0.01 
11 bal. 
4.86 0.03 
12 bal. 
2.44 1.44 
13 bal. 0.05 1.77 
14 bal. 
0.01 
0.05 0.30 
15 bal. 0.03 
0.02 0.10 
16 bal. 
0.04 0.009 
17 bal. 
0.06 0.006 0.03 
18 bal. 
0.11 0.08 
19 bal. 0.21 
0.008 0.005 
20 bal. 0.07 0.01 
__________________________________________________________________________ 
TABLE 3 
__________________________________________________________________________ 
Alloy 
No. Cu Zn Mn P B Mg Si Al Sn Ni 
__________________________________________________________________________ 
Comparative 
Examples 
21 bal. 
22 bal. 0.03 
23 bal. 
0.01 
24 bal. 0.016 0.31 
25 bal. 
0.009 0.04 0.20 
26 bal. 
0.007 
0.004 0.004 0.88 
27 bal. 
5.34 0.30 
28 bal. 
5.98 0.10 
29 bal. 3.33 
30 bal. 3.45 0.01 
0.20 
31 bal. 
6.00 
3.89 0.007 
32 bal. 
5.99 
3.50 
0.24 
__________________________________________________________________________ 
TABLE 4 
______________________________________ 
Stress 
Hot- corrosion .epsilon. phase 
Alloy working Bending cracking 
Type of 
thickness 
No. property 
property 
property 
plating 
(.mu.m) 
______________________________________ 
examples 
1 .largecircle. 
.largecircle. 
.largecircle. 
1 0.20 
2 .largecircle. 
.largecircle. 
.largecircle. 
1 0.25 
3 .largecircle. 
.largecircle. 
.largecircle. 
1 0.25 
4 .largecircle. 
.largecircle. 
.largecircle. 
1 0.25 
5 .largecircle. 
.largecircle. 
.largecircle. 
1 0.25 
6 .largecircle. 
.largecircle. 
.largecircle. 
2 0.20 
7 .largecircle. 
.largecircle. 
.largecircle. 
2 0.20 
8 .largecircle. 
.largecircle. 
.largecircle. 
2 0.25 
9 .largecircle. 
.largecircle. 
.largecircle. 
2 0.25 
10 .largecircle. 
.largecircle. 
.largecircle. 
2 0.50 
11 .largecircle. 
.largecircle. 
.largecircle. 
3 0.20 
12 .largecircle. 
.largecircle. 
.largecircle. 
3 0.25 
13 .largecircle. 
.largecircle. 
.largecircle. 
3 0.30 
14 .largecircle. 
.largecircle. 
.largecircle. 
3 0.25 
15 .largecircle. 
.largecircle. 
.largecircle. 
3 0.55 
16 .largecircle. 
.largecircle. 
.largecircle. 
4 0.40 
17 .largecircle. 
.largecircle. 
.largecircle. 
4 0.25 
18 .largecircle. 
.largecircle. 
.largecircle. 
4 0.20 
19 .largecircle. 
.largecircle. 
.largecircle. 
4 0.25 
20 .largecircle. 
.largecircle. 
.largecircle. 
4 0.30 
Comparative 
21 .largecircle. 
.largecircle. 
.largecircle. 
1 1.55 
examples 
22 .largecircle. 
.largecircle. 
.largecircle. 
1 1.50 
23 .largecircle. 
.largecircle. 
.largecircle. 
1 1.20 
24 X .largecircle. 
.largecircle. 
1 1.05 
25 .largecircle. 
.largecircle. 
.largecircle. 
2 1.35 
26 .largecircle. 
.largecircle. 
.largecircle. 
2 1.35 
27 X .largecircle. 
X 2 0.25 
28 .largecircle. 
.largecircle. 
X 3 0.25 
29 .largecircle. 
.DELTA. 
.largecircle. 
3 0.20 
30 .largecircle. 
X .largecircle. 
4 0.25 
31 .largecircle. 
X X 4 0.25 
32 X X X 4 0.25 
______________________________________ 
TABLE 5 
______________________________________ 
Protective 
Protective 
Alloy 
Type of Heat film film 
No. plating treatment forming phase 
thickness (.mu.m) 
______________________________________ 
1 1 no heat Sn 1.05 
treatment 
2 1 100.degree. C. .times. 
10 hr .eta. 0.95 
3 1 100 24 .eta. 1.35 
4 1 140 3 Sn + .eta. 
1.20 
5 2 140 3 .eta. + .epsilon. 
0.45 
11 3 140 48 .eta. + .epsilon. 
1.85 
12 3 160 0.5 Sn + .eta. 
2.45 
14 3 100 1 .eta. 0.30 
18 4 160 3 .eta. + .epsilon. 
0.50 
20 4 no heat Sn 0.35 
treatment 
1 1 100.degree. C. .times. 
0.5 hr 
.eta. 0.15 
2 1 140 5 .epsilon. 
0.30 
3 1 160 7 .epsilon. 
0.50 
4 1 no heat Sn 0.10 
treatment 
8 2 160 3 .epsilon. 
0.10 
10 None no plating -- -- 
______________________________________ 
TABLE 6 
______________________________________ 
Maximum Copper ion 
Alloy corrosion elution test 
No. depth(mm) (ppm) 
______________________________________ 
1 -- &lt;0.01 
2 -- &lt;0.01 
3 -- &lt;0.01 
4 -- &lt;0.01 
5 -- &lt;0.01 
11 -- &lt;0.01 
18 -- &lt;0.01 
20 -- &lt;0.01 
22 -- &lt;0.01 
1 -- 0.24 
2 0.23 &lt;0.01 
4 -- 0.33 
8 0.25 0.39 
10 -- 0.85 
______________________________________ 
Test results of the specimens are shown in Table 4. In Table 4, symbol "o" 
in the column for hot-working property represents a preferable case and 
symbol "x" represents a case in which a crack occurs. Moreover, symbol "o" 
in the column for bending property represents a preferable case, symbol 
".DELTA." represents a case in which a crease occurs, and symbol "x" 
represents a case in which a break occurs. Furthermore, symbol "o" in the 
column for stress corrosion cracking property represents a preferable case 
and symbol "x" represents a case in which a crack occurs. Furthermore, in 
Table 5, symbols in the column for type of plating in Table 5 correspond 
to the plating solutions shown in Table 1 respectively. 
From Table 4, it is found that .epsilon. phases of the alloys of examples 
Nos. 1 to 20 containing a predetermined amount of Zn and/or Mn are 
securely restrained in .epsilon.-phase growth. Moreover, the examples 
containing a predetermined amount of elements such as P and Al are same as 
those which do not contain these elements in .epsilon.-phase growth 
restraint effect and superior in hot-working, bending, and 
stress-corrosion cracking properties. Therefore, the alloys can 
practically be used. 
However, the comparative-examples of alloy Nos. 21 to 26 are not restrained 
in .epsilon. phase growth because they contain a small amount of or no Zn 
and/or Mn. However, the comparative-example alloy Nos. 24, 27, and 32 
containing elements including P by more than 0.2 wt % as the total amount 
are inferior in hot-working property and the comparative-example alloy 
Nos. 29 to 32 containing Mn by more than 3 wt % are inferior in bending 
property. Moreover, the comparative-example alloy Nos. 27, 28, 31, and 32 
containing Zn by more than 5 wt % cannot practically be used because a 
stress corrosion crack occurs in them. 
Table 5 shows types of phases forming protective films and thicknesses of 
protective films when forming an Sn layer on the alloys having the 
composition shown in Table 2 by using the plating solutions shown in Table 
1 and heat-treating them under the conditions shown in the column for heat 
treatment in Table 5. Moreover, Table 6 shows the maximum corrosion depth 
and the eluted amount of copper ions obtained from a corrosion test as the 
result of applying the corrosion test and a copper-ion elution test to the 
specimens. 
From Table 6, it is found that pitting occurs in specimens having an 
.epsilon. phase on the surface and the eluted amount of copper ions 
increases for those with a protective-film thickness of 0.2 .mu.m or less. 
Therefore, they cannot practically be used. 
Then, the heat exchanger shown in Table 7 are assembled to perform a copper 
ion elution test and a corrosion test. The method for evaluating each 
characteristic is shown below. 
Corrosion Test 
It is checked if pitting occurs by using the heat exchanger shown in Table 
7 and performing a corrosion test under the conditions below. 
Heat-exchanger pipes used have an outside diameter of 12.7 mm, a wall 
thickness of 0.6 mm, and a length of 1 m. 
Test Water Quality! 
pH=6.8 to 7.0 
HCO.sub.3.sup.- /SO.sub.4.sup.2- =0.6 
R-Cl (Residual chlorine)=3 ppm 
SiO.sub.2 =20 ppm 
Water Supply Conditions! 
Heating: Combustion gas by a propane-gas burner 
Water flow rate: 2 liter/min 
Supplied water temperature 
Incoming side of heat exchanger: Room temperature 
Outgoing side of heat exchanger: 95.degree. to 100.degree. C. 
Water supply time: 1 hr.times.4 times/day 
Out of water supply time: Leaving at room temperature 
Water Supply Period! 
Six months 
Potential Measurement 
After the above corrosion test terminates, heat exchanger are disassembled, 
heat-exchanger pipes are cut by 10 cm in the longitudinal direction, 
halved pipes of the heat-exchanger pipes are sampled, and the edge and 
outside of the halved pipes are sealed with silicon resin to measure the 
potential of the halved pipes in tap water. 
Copper Ion Elution Test 
While performing the above corrosion test, the heat exchanger are filled 
with tap water to measure the eluted amount of copper ions by the atomic 
absorption method after 24 hr passed from filling the tap water, at the 
time, before supplying water, one month after starting the corrosion test, 
three months after starting the corrosion test, and when the corrosion 
test terminates. 
Measurement of Sn Plating Thickness 
The Sn plating thickness is measured by an fluorescent X-ray film-thickness 
measuring instrument by setting a dummy pipe with the same composition as 
a heat transfer pipe at the front end of an assembled heat exchanger, 
circulating an electroless Sn plating solution through the dummy pipe to 
plate it with Sn, and then removing and halving the dummy pipe. 
TABLE 7 
______________________________________ 
Heat Sn plating 
exchanger Heat transfer pipe composition (wt %) 
thickness 
No. Cu Zn Mn P Sn Ni (.mu.m) 
______________________________________ 
Examples 
1 bal. 0.21 -- 0.02 -- -- 0.23 
2 bal. -- 0.66 0.01 -- -- 0.79 
3 bal. 0.43 0.35 -- 0.14 -- 1.50 
4 bal. -- 1.73 0.03 -- -- 2.78 
5 bal. 3.45 -- -- -- 0.29 0.30 
Com 6 bal. -- 0.32 -- -- -- 0.07 
7 bal. -- -- 0.02 -- -- 0.05 
8 bal. -- -- 0.03 -- -- 1.02 
9 bal. 0.005 
-- -- -- -- 1.43 
______________________________________ 
TABLE 8 
______________________________________ 
Maximum corrosion 
Cu.sup.2+ elution test (ppm) 
corrosion potential 
Heat after 
depth as 
after 
ex- Before One Three ter- the result 
termination 
changer 
water month months 
mina- 
of corrosion 
of test 
No. supply later later tion test (mm) 
(mV SCE) 
______________________________________ 
1 &lt;0.01 &lt;0.01 &lt;0.01 &lt;0.01 
-- -150 
2 &lt;0.01 &lt;0.01 &lt;0.01 &lt;0.01 
-- -160 
3 &lt;0.01 &lt;0.01 &lt;0.01 &lt;0.01 
-- -150 
4 &lt;0.01 &lt;0.01 &lt;0.01 &lt;0.01 
-- -160 
5 &lt;0.01 &lt;0.01 &lt;0.01 &lt;0.01 
-- -160 
6 0.21 0.34 0.1I 0.10 -- -160 
7 0.33 0.47 0.13 0.15 0.24 +140 
8 &lt;0.01 &lt;0.01 &lt;0.01 &lt;0.01 
0.27 +130 
9 &lt;0.01 &lt;0.01 &lt;0.01 &lt;0.01 
0.10 +70 
______________________________________ 
In the corrosion test, symbol "-" represents a case in which no pitting 
occurs. 
From Table 8, it is found that a heat exchanger using a heat transfer pipe 
containing a predetermined amount of Zn and Mn is securely restrained in 
pitting. However, because comparative-example heat exchanger Nos. 7, 8, 
and 9 do not contain Zn and Mn or contain a small amount of Zn or Mn, 
pitting occurs in them and the corrosion potential of them after the test 
becomes extremely high. 
Moreover, for a plating thickness of less than 0.1 .mu.m, copper ions are 
eluted. For a plating thickness of 0.1 .mu.m or more, however, no copper 
ion is eluted even after time passes. 
Industrial Applicability 
The cold- and hot-water supply copper alloy pipe with a protective film 
according to the present invention is very useful as a copper alloy pipe 
used for a cold- and hot-water supply pipe in the architectural field 
because not only the pipe is superior in the copper ion elution preventive 
effect but also it does not cause pitting even under a high temperature 
and makes it possible to greatly improve the reliability and service life 
of a hot-water supply system.