Corrosion resistant copper alloy tube and fin-tube heat exchanger

The copper alloy tube disclosed here contains 0.05 to 1.5 wt. % of Mn and deoxidized copper containing oxygen concentration at 100 ppm or less. At least one element selected from a group of elements comprising P, B, Li, Pb and Sb can be added at the amount of 0.20 wt. % or less in total. At least one element selected from another group of elements comprising Cr, Ti, Zr, Al and Si also can be added at the amount of 0.50 wt. % or less in total. Further, at least one element selected from other group of elements comprising Mg, Fe, Co, Ag, In and As can be added at the amount of 1.0 wt. % or less in total. Furthermore, at least one element selected from a group of elements comprising Zn and Ni can be added at the amount 5.0 wt. % or less in total. Thereby, an corrosion resistant copper alloy tube having better corrosion resistant property against the ant-nest type corrosion which is specific problem for refrigerant tubes and tubes for the heat exchanger and also better brazing property can be provided.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to an corrosion resistant copper alloy tube
 which is used as a refrigerant copper alloy tube or a heat exchanger
 copper alloy tube and a fin-tube heat exchanger which is used for an
 air-conditioner, particularly relates to an corrosion resistant copper
 tube and a fin-tube heat exchanger having improved corrosion resistant
 property against an ant-nest type corrosion.
 2. Description of Prior Art
 A tube which was made of copper deoxidized by phosphorous has been widely
 used for the conventional refrigerant tube or the conventional heat
 exchanger tube generally due to its better bending and brazing properties.
 In these tubes, however, organic materials such as lubricant oil or process
 oil and organic solvents unavoidably remaining on the surface of the fins
 and tubes after the tubing and fabrication processes may decompose during
 the repeated deposit and evaporation of water due to a coolant and during
 the exposure to peculiar temperature/moisture and air-exchange environment
 created as a nature of its construction to form carboxylic acids which
 cause peculiar corrosion showing local ant-nest type corrosion on the
 surface of the tube.
 Thus, a large amount of lubricant oil has been used in the fabrication
 process of the heat exchanger, however considering recent environmental
 problems there is a trend to avoid the degreassing wash by organic
 solvents and rather to use volatile lubricant oil instead of such organic
 solvents. In this case, even though the base oil itself is volatile, such
 lubricant oil still contains some oil additives which may remain on the
 surface of the copper tube.
 Therefore, there is an increasing risk for the ant-nest type corrosion in
 future according to more usage of volatile lubricant oil, compared to the
 case the degrase wash was performed using organic solvents. Reflecting
 such circumstance, measurements for the ant-nest type corrosion are
 attracting the attention of the industry as one of serious problems.
 Further, increase of remaining organic materials on the surface of the
 copper alloy tube is creating another problem of poor conjunction of tube
 during the brazing which is used as a major method for the tube
 connection. Therefore, development of a copper alloy tube having superior
 corrosion resistant and brazing properties than the conventional
 phosphorous deoxidized copper tube is desired as a tube material for the
 refrigerant tube or the heat exchanger tube.
 Further, the fin-tube heat exchanger used for an air-conditioner is
 generally fabricated using aluminum or aluminum alloy plate fins provided
 with tube insertion holes and copper tubes. Inside the insertion hole, a
 tube-type fin collar is provided. Many of said fins are placed in parallel
 and the copper tube is inserted into said fin collar so as to connect each
 fin. Then, this tube extended and fixed on the fins. And the heating
 medium is allowed to flow through the inside of said tube and its heat is
 transmitted to and radiated from said fins. In this fin-tube heat
 exchanger, said plate fins are made from aluminum or aluminum alloy due to
 its thermal conductivity and cost, and, for said tube, the copper tube is
 widely used from the stand points of its thermal conductivity and
 corrosion resistant properties. For this copper tube, a pure copper called
 as phosphorous dioxided copper is mainly used.
 However, in these conventional fin-tube heat exchanger, organic materials
 such as lubricant oil and organic solvents used in the processes of
 blanking and extending of the tube unavoidably remain on the surface of
 the tubes, and these organic materials are affected by repeated deposit
 and evaporation of water during storage of fins and tubes or usage as the
 heat exchanger. These organic materials are also exposed to the peculiar
 temperature/humidity and air-exchange environment during usage of the heat
 exchanger. Under such conditions, these organic materials decomposed to
 form carboxylic acids which cause the peculiar local corrosion showing the
 ant-nest type corrosion, resulting in leakage of the tube frequently.
 In addition, as aforementioned, although a large amount of lubricant oil
 has been used during fabrication process of the fin-tube heat exchanger,
 considering recent environmental problems there is a trend to avoid the
 degreassing wash by organic solvents and rather to use volatile lubricant
 oil instead of such organic solvents. Even though the base oil itself is
 volatile, such lubricant oil still contains some oil additives which may
 remain on the surface of the copper tube. Therefore, the amount of organic
 materials remaining on the surface of raw materials is in trend towards
 increase compared to the case of degreassing wash by organic solvents and
 the risk for the ant-nest type corrosion is higher than the past.
 Under such circumstance, measurements for the ant-nest type corrosion of
 the fin-tube heat exchanger are attracting the attention of the industry
 as one of serious problems, and development of a fin-tube heat exchanger
 having superior corrosion resistant property against the ant-nest type
 corrosion is desired.
 SUMMARY OF THE INVENTION
 The object of the present invention is to provide an corrosion resistant
 copper alloy tube having better corrosion resistant property against the
 ant-nest type corrosion even though exposed to the phenomenon specific to
 the refrigerant tube or the heat exchanger tube; that is, repeated deposit
 and evaporation of water, and used under the peculiar environmental
 conditions of temperature/humidity and air-exchange, and having better
 brazing property so that capable of increasing its integrity and life span
 as the refrigerant tube or the heat exchanger tube.
 The another object of the present invention is to provide a fin-tube heat
 exchanger having better corrosion resistant property against the ant-nest
 type corrosion even though affected by the phenomenon specific to the
 fin-tube heat exchanger; that is, repeated deposit/evaporation of water,
 and used under the peculiar environmental conditions of
 temperature/humidity and air-exchange so that carboxylic acids are formed,
 and capable of increasing its integrity and life span.
 A corrosion resistant copper alloy tube according to the present invention
 consists essentially of 0.05 to 1.5 wt. % of Mn, 100 ppm or less of
 oxygen, and Cu and inevitable impurities.
 The corrosion resistant copper alloy tube according to the present
 invention shows better corrosion resistant property against the ant-nest
 type corrosion which specifically may occur in the conventional
 refrigerant tube or the heat exchanger tube made of phosphorous deoxidized
 copper; that is, the ant-nest type corrosion which may occur under the
 conditions of affecting repeated deposit and evaporation of water and
 peculiar environmental conditions of temperature/humidity and
 air-exchange, and shows better brazing property. Therefore, it is capable
 of increasing its integrity, applicability and life span as the
 refrigerant tube or the heat exchanger tube. Thus, the present invention
 is very useful.
 A corrosion resistant copper alloy tube for a heat exchanger according to
 the present invention, comprises a main tube body including a copper alloy
 tube and an oxide film formed on the surface of said main tube body in the
 thickness of from 30 to 3000 .ANG. by oxidizing the surface of the main
 tube body. Said copper alloy consist essentially of at least one additive
 element at 1.7 to 3.0 wt. % in total, the volume ratio of oxide thereof to
 Cu base metal (ratio of molecular volume of oxide to atomic volume of Cu
 base metal) being within 1.7 to 3.0, and Cu and inevitable impurities. The
 additive element or elements remaining in said copper alloy is solid
 solubilized into Cu base metal. The differential natural electric
 potential between said oxide film and phosphorous deoxidized copper in 0.1
 v. % of formic acid solution is within the range of from 0.2 V to -0.2 V.
 In the conventional heat exchanger copper tube made of phosphorous
 deoxidized copper, the corrosion resistant property was obtained by the
 oxide film on the surface thereof. However, under the environmental
 condition allowing to contact with corrosive media such as carboxylic
 acids having a strong oxidative effect, the oxide film on the surface of
 copper alloy tube is vigorously eroded so that the corrosion protection by
 the oxide film is destroyed. In order to improve the corrosion resistant
 property against the ant-nest type corrosion compared to the ordinary
 phosphorous deoxidized copper, it is necessary to form more finer and less
 defect oxide film on the surface of tube. The present inventors found that
 such oxide film can be obtained by adding certain additive elements to
 copper alloy and then oxidizing the surface of these copper alloy
 materials.
 The heat exchanger copper alloy tube according to the present invention has
 higher corrosion resistant property against the ant-nest type corrosion
 than the conventional phosphorous deoxidized copper tube being used for
 the heat exchanger and therefore very useful as a copper alloy tube for
 the heat exchanger used under the environment containing carboxylic acids
 easily causing the ant-nest type corrosion.
 A fin-tube heat exchanger according to the present invention comprises: a
 main tube body including said copper alloy tube according to claim 1 or 2
 and a plurality of plate type fins of aluminum or aluminum alloy placed in
 parallel each other on the outer surface of the main tube body. In this
 case, said copper alloy main tube body is preferably to be an internally
 grooved tube having a plurality of grooves provided in parallel each other
 on the inner surface thereof, the outer diameter of said copper alloy main
 tube is 4 to 25.4 mm, the ratio h/Di of the depth h of the groove to the
 inner diameter Di of the tube defined by the crest part between the
 grooves is 0.01.ltoreq.h/Di.ltoreq.0.05, and the helix angle .gamma. is
 0.degree..ltoreq..gamma..ltoreq.30.degree..
 Compared to the conventional heat exchanger using phosphorous deoxidized
 copper tube, the fin-tube heat exchanger according to the present
 invention is superior in the corrosion resistant property against the
 ant-nest type corrosion which easily occurred when affected by repeated
 deposit and evaporation of water and exposed to the peculiar environmental
 conditions of temperature/humidity and air-exchange, therefore it is very
 useful as the heat exchanger used under such environmental conditions.
 Further, the fin-tube heat exchanger according to the present invention is
 different from the conventional phosphorous refined copper tube; since the
 copper tube containing elements inferior in the electric potential to Cu
 is used, the potential difference between the tubes and the fins (made of
 aluminum or aluminum alloy) can be reduced. Therefore, since the electric
 corrosion of the fins can be reduced, decrease of the thermal conductivity
 can be minimized during its use and the initial thermal conductivity can
 be maintained for a longer period.
 A corrosion resistant copper alloy tube according to the present invention
 comprises; a main tube body containing at least one additive element
 having the standard enthalpy of -169 kJ for formation of an oxide at the
 amount within the range shown by the equation 1 below, and an oxide film
 formed on the surface of said main tube body in the thickness from 40 to
 2000 .ANG. by the heat treatment of the main tube body. The ratio Ix/Icu
 of the main peak intensity Ix of said additive element to the main peak
 intensity of Cu obtained by X-ray Electron Spectroscopy on the surface of
 said oxide film is 0.10 or greater.
EQU 0.04.ltoreq..SIGMA.[Ax.multidot.ln(.DELTA.H.sup.0 f(x)/(-169))].ltoreq.4.2
 (1)
 where, Ax is the content (atom %) of additive element x.
 ln is natural logarithm.
 .DELTA.H.sup.0 f(x) is the standard enthalpy (kJ/mol) for formation of
 oxide of additive element x.
 .SIGMA. is the sum of Ax.multidot.ln(.DELTA.H.sup.0 f(x)/(-169)) for each
 additive element.
 The corrosion resistant copper alloy tube according to the present
 invention, because the oxide film containing the pre-determined amount of
 certain additive elements is formed on the surface of main tube body,
 shows a superior corrosion resistant property against the ant-nest type
 corrosion which specifically occurs in the ordinary refrigerant tube or
 the heat exchanger tube consisting of phosphorous deoxidized copper tube;
 that is, the ant-nest type corrosion which may occur when affected by
 repeated deposit and evaporation of water and exposed to the peculiar
 environmental conditions of temperature/humidity and air-exchange, and
 capable of increasing its integrity and life span as the refrigerant tube
 or the heat exchanger tube, therefore the present invention is very
 useful.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 As a result of having conducted a series of diligent research to develop a
 copper alloy tube resistant to the ant-nest type corrosion, the present
 inventors found the followings.
 That is, in the copper alloy containing the pre-determined amount of Mn and
 maintaining the oxygen content at the pre-determined level or less as
 described in the present invention, the corrosion resistant property is
 extremely improved compared to the conventional phosphorous deoxidized
 copper. Further, when at least one element from P or B is added to said
 copper alloy at the pre-determined amount, the brazing property is
 significantly improved compared to the conventional phosphorous deoxidized
 copper. The present invention was made based on these experimental
 results.
 Then, the reason for addition of each component and for restriction of the
 composition will be fully explained.
 Mn
 The corrosion resistant property against the ant-nest type corrosion is
 improved by adding Mn. However, in case the Mn content is less than 0.05
 wt. %, sufficient improvement effect of corrosion resistant property
 against the ant-nest type corrosion can not be achieved. The Mn content of
 0.1 wt. % or more is preferable and by these contents further improvement
 can be observed. Meantime, if the Mn content exceeds 1.5 wt. %, resulting
 tube is not practically suitable because its resistance strength becomes
 higher so that bending property as tube decreases. Therefore, the Mn
 content should be within the range from 0.05 wt. % to 1.5 wt. %.
 Oxygen Content
 During the melting process of the copper alloy, inclusion of oxygen at
 certain level is unavoidable, but if oxygen exists in the base copper
 metal at the level exceeding 10 ppm, the hydrogen embrittlement may occur
 during the brazing process widely used for connecting of the copper tubes
 and resulting product is not yet strong enough for practical use.
 Therefore, the oxygen content is restricted to 100 ppm or less.
 First Group Elements (P, B, Li, Pb, Sb)
 All of P, B, Li, Pb and Sb are allowed to add as the deoxidation agent or
 as elements to improve the strength, but if total amount of these elements
 exceed 0.20 wt. %, the corrosion resistant improvement effect of Mn
 against the ant-nest type corrosion may decrease and the hot working
 property of the tube may decrease. Therefore, the amount to be added of
 each element belonging to the first group should be restricted to 0.20 wt.
 % or less in total.
 Second Group Elements (Cr, Ti, Zr, Al, Si)
 Cr, Ti, Zr, Al and Si are allowed to add in order to improve the strength
 and the heat resistance of the copper tube. However, if the content of
 these elements exceeds 0.50 wt. % in total, the brazing property may
 decrease, the bending property as tube may decrease due to increase of the
 proof stress and decrease of the expendability, and the corrosion
 resistant improvement effect of Mn against the ant-nest type corrosion may
 also decrease. Therefore, total amount to be added of each element
 belonging to the second group should be restricted to 0.50 wt. % or less.
 Third Group Elements (Mg, Fe, Co, Ag, In, As)
 Mg, Fe, Co, Ag, In and As can be added in order to improve the strength and
 the heat resistance of the copper tube, but if the content of these
 elements exceeds 1.0 wt. % in total, the bending property as tube may
 decrease due to increase of the proof stress and decrease of the
 expendability. Therefore, total amount to be added of each element
 belonging to the third group should be restricted to 1.0 wt. % or less.
 Fourth Group Elements (Zn, Ni)
 Zn and Ni are added in order to improve the strength and the corrosion
 resistant property of the copper tube, but if the amount to be added of
 these elements exceeds 5.0 wt. %, the bending property as tube may
 decrease due to increase of the proof stress and decrease of the
 expendability. Therefore, the amount to be added of each element belonging
 to the fourth group should be restricted to 5.0 wt. % or less.
 P
 P is usually added as a deoxidation agent during copper refining process or
 as the element to improve the strength of the copper alloy tube, but if P
 is added together with Mn, the brazing property of the copper alloy is
 improved further compared to the conventional phosphorous deoxidized
 copper.
 At the heated state (at 700-900.degree. C.) during the brazing process, P
 reduces Cu and Mn oxides so that P is effective to improve the brazing
 property. However, in the conventional phosphorous deoxidized copper, P on
 the copper surface is lost by sublimation due to high temperature during
 the brazing process and can not give sufficient reduction effect. However,
 in the copper alloy containing P and Mn, P concentrated on the copper
 surface forms reaction products with Mn added together which inhibit
 sublimation of P, resulting in sufficient exhibition of the reduction
 effect during the brazing process.
 However, if the P content is less than 0.002 wt. %, sufficient improvement
 of the brazing property can not be achieved. Preferably, the P content is
 0.005 wt. % or more so that further improvement of the brazing can be
 observed. On the other hand, if the P content exceeds 0.15 wt. %, the
 corrosion resistant property against the ant-nest type corrosion may
 decrease. Therefore, the P content should be restricted to the range from
 0.002 wt. % to 0.15 wt. %. Further, if the Mn/P ratio is less than 2, the
 amount of P added is higher than the amount of Mn added and sufficient
 improvement effect against the ant-nest type corrosion can not be
 obtained. On the other hand, if the Mn/P ratio exceeds 100, the amount of
 P added is too lower than the amount of Mn added to obtain the improvement
 effect by Mn-phosphate compounds. Therefore, the Mn/P ratio should be
 restricted to the range from 2 to 100.
 B
 Similar to P as aforementioned, also B is generally used as a deoxidation
 agent or as an additive to improve the strength, but the brazing property
 may be improved by adding together with Mn. The effect of B in improvement
 of the brazing property is similar to the effect of P, B concentrated on
 the surface reacts with Mn to form borites so that sublimation of B may be
 inhibited and sufficient reduction effect of B may be obtained under high
 temperature during the brazing process.
 However, if the B content is less than 0.002 wt. %, sufficient improvement
 effect of the brazing property can not be obtained. To obtain sufficient
 improvement effect of the brazing property the B content is preferably
 0.005 wt. %. If the B content exceeds 0.15 wt. %, the corrosion resistant
 property against the ant-nest type corrosion may decrease. Therefore, the
 B content should be restricted to the range from 0.002 wt. % to 0.1 wt. %.
 Meantime, the Mn/B ratio is less than 2, the amount of B added is too high
 compared to the amount of Mn added to obtain sufficient effect of the
 corrosion resistant property against the ant-nest type corrosion. If the
 Mn/B ratio exceeds 100, the amount of B added is too low compared to the
 amount of Mn added to obtain sufficient improvement effect of the brazing.
 Therefore, the Mn/B ratio is restricted to the range from 2 to 100.
 P and B
 As aforementioned in the sections for P and B, P and B have similar effect
 against the brazing property and, if P and B are added together,
 improvement effect of the brazing property can be obtained. In this case,
 the ratio of Mn and P plus B; that is, Mn/(P+B) is preferably restricted
 to the range from 2 to 100.
 Inevitable Impurities
 In the present invention, Sn is an inevitable impurity. During the
 manufacturing process of the copper alloy tube, inclusion of Sn is
 unavoidable. If Sn exists in the copper alloy at the level of 0.01 wt. %
 or more, improvement in the corrosion resistant property of copper alloy
 tube by addition of Mn is deteriorated. Therefore, the inevitable impurity
 Sn is restricted to less than 0.01 wt. %.
 As mentioned above, in the present invention, the copper alloy tube for the
 refrigerant tube or the heat exchanger having better corrosion resistant
 property against the ant-nest type corrosion than the conventional
 phosphorous deoxidized copper and further more practical and having better
 brazing, hot working and bending properties as tube can be obtained by
 adding Mn at the amount of said range and at the same time by controlling
 the oxygen content within said range and by restricting the content of
 each element shown in the first, second, third and fourth groups as well
 as the composition ratio of Mn and P and/or B within said range.
 Then, the properties of the copper alloy according to the embodiment of the
 present invention will be fully explained comparing to the reference
 alloy.
 The tube materials (O materials; 9.5 mm in outer diameter; 0.3 mm thick)
 listed in Tables 1 and 2 below were prepared by melt casting, hot
 extrusion, cold forging, and heat treatment processes, and the corrosion
 resistant against the ant-nest type corrosion, brazing, hair-pin bending,
 hot working and hydrogen embrittlement were evaluated.
 The method used for evaluation of each property is shown below.
 Corrosion Resistant Against the Ant-Nest Type Corrosion
 Test pieces were exposed to the environment of formic acid and acetic acid
 as typical carboxylic acids, and the maximum corrosion depth was
 determined after corrosion. The test conditions ware as follows:
 Corrosion medium:
 100 ml of 1% aqueous solution of formic acid or 1% solution of acetic acid.
 Exposure condition:
 the test piece (100 mm long) was dipped into deionized water in a beaker
 which was placed in a one liter container containing said corrosion
 medium, then the container was sealed.
 Temperature and Testing Period:
 maintained at 40.degree. C. for 20 days.
 Brazing Property
 Pre-determined amount of the phosphorous copper brazing filler metal
 (BCuP-2, 1.6 mm in diameter, 10 mm long) was placed on each test piece
 (half cut of the tube) and these test pieces were maintained at
 850.degree. C. under nitrogen stream for 10 minutes, then the length of
 diffused brazing filler metal was determined. The piece was a half cut of
 the tube with 300 mm long.
 Hair-Pin Bending Property
 The 180.degree. bending test was carried out using a mandrel with 8.7 mm in
 diameter at the pitch of 25.4 mm, and the presence of wrinkling and
 broken-out in the bending part was observed.
 Hot Working
 Using test sample, 15 mm in diameter and 15 mm long, selected from the
 ingots, the drop hammer test with the deformation rate of 50% was carried
 out at 850.degree. C., and the presence of cracks was determined.
 Hydrogen Embrittlement
 The test pieces were subjected to heat treatment at 850.degree. C. under
 hydrogen stream for 30 minutes and then the cross section was observed for
 cracks by hydrogen embrittlement.
 TABLE 1 (1)
 Maximum
 Corrosion
 Compostion Oxygen Length
 Hair-pin
 (Weight %) Content (mm)
 Brazing Bending Hot
 Mn P Others (ppm) Formic Acid Acetic Acid
 Property Property Working
 Example A1 0.08 .ltoreq.0.001 .ltoreq.0.001 82 0.03
 0.01 .smallcircle. .smallcircle. .smallcircle.
 A2 0.12 .ltoreq.0.001 .ltoreq.0.001 70 0.02
 0.01 .smallcircle. .smallcircle. .smallcircle.
 A3 0.27 .ltoreq.0.001 .ltoreq.0.001 63 0.01 --
 .smallcircle. .smallcircle. .smallcircle.
 A4 1.02 .ltoreq.0.001 .ltoreq.0.001 55 -- --
 .smallcircle. .smallcircle. .smallcircle.
 A5 2.05 .ltoreq.0.001 .ltoreq.0.001 45 -- --
 .smallcircle. .smallcircle. .smallcircle.
 A6 1.05 0.12 .ltoreq.0.001 35 0.01 --
 .smallcircle. .smallcircle. .smallcircle.
 A7 0.97 0.023 B:0.10 30 -- --
 .smallcircle. .smallcircle. .smallcircle.
 A8 0.95 0.026 Li:0.11 32 0.01 --
 .smallcircle. .smallcircle. .smallcircle.
 A9 1.08 0.025 Pb:0.13 45 0.01 --
 .smallcircle. .smallcircle. .smallcircle.
 A10 1.10 0.027 Sb:0.12 48 0.01 --
 .smallcircle. .smallcircle. .smallcircle.
 A11 1.05 0.024 Cr:0.40 45 -- --
 .smallcircle. .smallcircle. .smallcircle.
 A12 1.00 0.024 Ti:0.36 40 0.01 --
 .smallcircle. .smallcircle. .smallcircle.
 A13 1.03 0.022 Zr:0.36 41 0.01 --
 .smallcircle. .smallcircle. .smallcircle.
 A14 1.05 0.023 Al:0.37 40 0.01 --
 .smallcircle. .smallcircle. .smallcircle.
 A15 0.98 0.025 Si:0.41 45 -- --
 .smallcircle. .smallcircle. .smallcircle.
 A16 1.01 0.027 Mg:0.76 43 0.01 --
 .smallcircle. .smallcircle. .smallcircle.
 A17 0.95 0.027 Fe:0.72 40 -- --
 .smallcircle. .smallcircle. .smallcircle.
 A18 0.97 0.026 Co:0.70 42 -- --
 .smallcircle. .smallcircle. .smallcircle.
 A19 1.02 0.023 Sn:0.75 45 0.01 --
 .smallcircle. .smallcircle. .smallcircle.
 A20 0.99 0.023 Ag:0.74 44 -- --
 .smallcircle. .smallcircle. .smallcircle.
 A21 1.03 0.025 In:0.72 46 0.01 --
 .smallcircle. .smallcircle. .smallcircle.
 A22 1.01 0.024 As:0.68 50 0.01 --
 .smallcircle. .smallcircle. .smallcircle.
 A23 1.05 0.022 Zn:3.05 45 -- --
 .smallcircle. .smallcircle. .smallcircle.
 A24 0.98 0.028 Ni:3.02 42 -- --
 .smallcircle. .smallcircle. .smallcircle.
 A25 1.03 0.11 Al:0.35 35 0.01 --
 .smallcircle. .smallcircle. .smallcircle.
 Sn:0.75
 Zn:2.53
 A26 1.05 .ltoreq.0.001 B:0.10 30 -- --
 .smallcircle. .smallcircle. .smallcircle.
 Cr:0.30
 Ni:3.05
 A27 1.00 .ltoreq.0.001 Li:0.12 38 -- --
 .smallcircle. .smallcircle. .smallcircle.
 Zr:0.35
 Ag:0.72
 A28 1.02 0.025 Pb:0.10 45 0.01 --
 .smallcircle. .smallcircle. .smallcircle.
 Fe:0.73
 In:0.70
 A29 0.98 0.023 Si:0.37 48 0.01 --
 .smallcircle. .smallcircle. .smallcircle.
 As:0.68
 A30 1.02 0.022 Ti:0.34 55 -- --
 .smallcircle. .smallcircle. .smallcircle.
 Co:0.75
 A31 0.98 0.027 Sb:0.10 53 0.01 --
 .smallcircle. .smallcircle. .smallcircle.
 Mg:0.70
 Compara- A32 &lt;0.001 0.025 .ltoreq.0.001 60 0.20 0.08
 .smallcircle. .smallcircle. .smallcircle.
 tive A33 0.025 0.024 .ltoreq.0.001 56 0.18 0.07
 .smallcircle. .smallcircle. .smallcircle.
 Example A34 1.72 .ltoreq.0.001 .ltoreq.0.001 40 -- --
 .DELTA. .DELTA. .smallcircle.
 A35 0.12 0.001 .ltoreq.0.001 125 0.05 0.02
 X .smallcircle. .smallcircle.
 A36 0.10 0.26 .ltoreq.0.001 30 0.10 0.04
 .smallcircle. .smallcircle. X
 A37 0.09 .ltoreq.0.001 B:0.28 32 0.08 0.03
 .smallcircle. .DELTA. X
 A38 0.12 0.001 Li:0.24 43 0.08 0.03
 .smallcircle. .smallcircle. X
 A39 0.08 0.025 Pb:0.27 50 0.10 0.04
 .smallcircle. .smallcircle. X
 A40 0.11 0.023 Sb:0.25 52 0.09 0.03
 .smallcircle. .smallcircle. X
 A41 0.10 0.024 Cr:0.68 45 0.03 0.01
 .DELTA. X .smallcircle.
 A42 0.11 0.026 Ti:0.65 50 0.05 0.02
 .DELTA. X .smallcircle.
 A43 0.11 0.025 Zr:0.70 55 0.05 0.02
 .DELTA. X .smallcircle.
 A44 0.12 0.022 Al:0.70 58 0.07 0.03
 .DELTA. .DELTA. .smallcircle.
 A45 0.10 0.021 Si:0.65 52 0.06 0.02
 .DELTA. X .smallcircle.
 A46 0.09 0.025 Mg:1.25 51 0.05 0.02
 .smallcircle. .DELTA. .smallcircle.
 A47 0.10 0.023 Fe:1.28 48 0.10 0.03
 .smallcircle. X .smallcircle.
 A48 0.11 0.024 Co:1.24 45 0.08 0.03
 .smallcircle. X .smallcircle.
 A49 0.11 0.027 Sn:1.22 55 0.12 0.04
 .smallcircle. .DELTA. .smallcircle.
 A50 0.10 0.028 Ag:1.20 50 0.03 0.01
 .smallcircle. .DELTA. .smallcircle.
 A51 0.12 0.020 In:1.23 53 0.08 0.03
 .smallcircle. .DELTA. .smallcircle.
 A52 0.12 0.026 As:1.27 47 0.06 0.02
 .smallcircle. X .DELTA.
 A53 0.13 0.023 Zn:7.52 49 0.02 0.01
 .smallcircle. .DELTA. .smallcircle.
 A54 0.10 0.025 Ni:7.05 50 0.02 0.01
 .smallcircle. .DELTA. .smallcircle.
 TABLE 2
 Maxinum
 Oxygen Corrosion Length
 of Hair-pin
 Compostion Ratio Content Length Wetted
 Area Bending Hydrogen
 Mn P B Mn/(P + B) (ppm) (mm) (mm)
 Property Embrittlement
 Example A55 0.06 0.005 &lt;0.001 12 76 0.06 120
 .smallcircle. .smallcircle.
 A56 0.10 0.025 &lt;0.001 4.0 32 0.05 130
 .smallcircle. .smallcircle.
 A57 0.30 0.004 &lt;0.001 75 70 0.02 110
 .smallcircle. .smallcircle.
 A58 0.33 0.015 &lt;0.001 22 55 0.03 120
 .smallcircle. .smallcircle.
 A59 0.32 0.040 &lt;0.001 8.0 25 0.04 140
 .smallcircle. .smallcircle.
 A60 0.96 0.012 &lt;0.001 80 46 -- 100
 .smallcircle. .smallcircle.
 A61 1.05 0.030 &lt;0.001 35 30 -- 110
 .smallcircle. .smallcircle.
 A62 1.21 0.120 &lt;0.001 10 16 0.03 130
 .smallcircle. .smallcircle.
 A63 0.032 &lt;0.001 0.005 64 60 0.01 110
 .smallcircle. .smallcircle.
 A64 0.31 &lt;0.001 0.020 16 40 0.02 130
 .smallcircle. .smallcircle.
 A65 0.28 &lt;0.001 0.050 5.6 30 0.03 150
 .smallcircle. .smallcircle.
 A66 0.30 0.005 0.005 30 56 0.02
 120 .smallcircle. .smallcircle.
 A67 0.32 0.020 0.020 8.0 28 0.03
 140 .smallcircle. .smallcircle.
 Comparative A68 &lt;0.001 0.025 &lt;0.001 -- 45 0.20 100
 .smallcircle. .smallcircle.
 Example A69 0.02 0.005 &lt;0.001 4.0 80 0.15 100
 .smallcircle. .smallcircle.
 A70 2.04 0.040 &lt;0.001 51 23 0.01 60
 X .smallcircle.
 A71 2.04 0.040 &lt;0.001 80 85 0.04 80
 .smallcircle. .smallcircle.
 A72 1.08 0.205 &lt;0.001 5.3 15 0.14 130
 .DELTA. .smallcircle.
 A73 0.10 0.100 &lt;0.001 1.0 33 0.25 130
 .smallcircle. .smallcircle.
 A74 1.00 0.005 &lt;0.001 200 42 -- 50
 .smallcircle. .smallcircle.
 A75 &lt;0.001 &lt;0.001 0.020 -- 48 0.18 100
 .smallcircle. .smallcircle.
 A76 0.06 &lt;0.001 0.001 60 90 0.05 80
 .smallcircle. .smallcircle.
 A77 1.05 &lt;0.001 0.182 5.8 20 0.16 130
 .DELTA. .smallcircle.
 A78 0.10 &lt;0.001 0.090 1.1 38 0.23 130
 .smallcircle. .smallcircle.
 A79 0.96 &lt;0.001 0.006 160 47 -- 60
 .smallcircle. .smallcircle.
 A80 0.12 0.060 0.035 1.3 31 0.24
 120 .smallcircle. .smallcircle.
 A81 1.02 0.005 0.003 130 44 -- 70
 .smallcircle. .smallcircle.
 A82 0.30 0.015 &lt;0.001 20 150 0.03 130
 .smallcircle. X
 In Table 1, ".sup.-- " under the heading of "maximum corrosion length"
 stands for "no corrosion". Under the heading of "brazing property",
 ".largecircle." stands for "good wettability of brazing filler metal",
 ".DELTA." for "poor wettability of brazing filler metal", "X" for
 "presence of hydrogen embrittlement". Under the heading of "hair-pin
 bending property", ".largecircle." stands for "good bending", ".DELTA."
 for "presence of wrinkling" and "X" for "presence of broken-out". Under
 the heading of "hot working", ".largecircle." stands for "good" and "X"
 for "presence of cracks".
 As obvious from Table 1, all examples No.A1 through No. A31 of the present
 invention have better corrosion resistant property against the ant-nest
 type corrosion than the phosphorous deoxidized copper tube (comparative
 example No. A32); the example No.A1 (Mn:0.08 wt. %) showed the maximum
 corrosion depth equivalent to about 1/7 of that of the phosphorous
 deoxidized copper tube, and no evidence of corrosion was observed in the
 example No.A4 (Mn: 1.02 wt. %); the corrosion resistant property was
 further improved according to increase of the Mn content.
 Furthermore, the examples No.A6 through No.A31 containing the
 pre-determined amount of the element(s) listed in either first, second,
 third or fourth group showed better corrosion resistant property
 equivalent to those not containing any element listed in the first,
 second, third and fourth groups and any practical problem could be seen
 since all brazing, hair-pin bending and hot working properties were good.
 On the other hand, the comparative example No.A33, since the Mn content is
 lower, showed insufficient corrosion resistant improvement effect against
 the ant-nest type corrosion. On the contrary, the comparative example No.
 A34, since the Mn content is too high, showed sufficient corrosion
 resistant property against the ant-nest type corrosion but poor brazing
 and hair-pin bending properties so that may not practically useful.
 Further, the comparative example No. A35 also is not suitable for
 practical use because the corrosion resistant improvement effect of added
 Mn against the ant-nest type corrosion decreased and the hydrogen
 embrittlement occurred due to high oxygen level.
 Furthermore, the comparative examples No.A36 through No.A54 contains the
 pre-determined amount of single element listed in the first, second, third
 and fourth groups. However, the comparative examples No.A36 through No.A40
 are not suitable for practical use mainly due to poor performance in the
 hot working. The comparative examples No.A41 through No.A45 are not
 practical mainly due to decrease of brazing property. The comparative
 examples No.A46 through No.A52, No.A53 and No.A54 are not suitable for
 practical use mainly because the hair-pin bending property became poor due
 to increase of the proof stress and decrease of the expendability.
 In Table 2, ".sup.-- " under the heading of "maximum corrosion length"
 stands for "no corrosion". Under the heading of "hair-pin bending",
 ".largecircle." stands for "good bending", ".DELTA." for presence of
 wrinkling" and "X" for "presence of broken-out". Under the heading of
 "hydrogen embrittlement", ".largecircle." stands for "good" and "X" for
 "presence of cracks".
 As obvious from Table 2, the examples No.A55 through No.A67 showed superior
 corrosion resistant property against the ant-nest type corrosion to the
 comparative examples No.A68 of phosphorous deoxidized copper tube.
 Further, the example No.A55 showed the maximum corrosion depth equivalent
 to about 1/3 of that of the phosphorous refined copper tube and no
 evidence of corrosion could be seen in the examples No.A60 and No.A61,
 indicating that the corrosion resistant property is improved according to
 increase of the Mn content. Furthermore, the examples No.A55 through
 No.A67 showed improvement in the length of the area wetted by the brazing
 filler metal compared to the comparative example No.A14 of phosphorous
 deoxided copper tube, indicating that these are all epoch-making materials
 capable of improving both corrosion resistant property against the
 ant-nest type corrosion and brazing property at same time. Further, these
 examples No.A1 through No.A31 and No.A55 through No.A67 are all good in
 the hair-pin bending and hydrogen embrittlement and have no problem in
 practical use.
 On the other hand, the comparative example No.A69 is not suitable for
 practical use because the corrosion resistant improvement effect of Mn is
 not sufficient due to low content of Mn, and the comparative example
 alloys are not suitable for practical use because the Mn content is too
 high so that, even though the corrosion resistant property is sufficient,
 but both diffusion of the brazing filler metal and the hair-pin bending
 properties are not satisfactory. Also, the comparative examples No.A71 and
 No.A76 showed only limited diffusion of the brazing filler metal due to
 lower content of B or P, and the comparative examples No.A72 and No.A77
 showed lower corrosion resistant property against the ant-nest type
 corrosion due to higher content of P or B.
 Further, the comparative examples No.A73, A78 and A80 showed lower
 corrosion resistant property due to lower Mn/(P+B) ratio, and the
 comparative examples No. A74, A79 and A81 showed lower wettability of the
 brazing filler metal due to higher Mn/(P+B) ratio. Furthermore, the
 comparative example No.A82 is not suitable for practical use because the
 hydrogen embrittlement occurred due to excess oxygen content.
 Next, a corrosion resistant copper alloy tube for the heat exchanger
 according to another embodiment will be fully described, particularly
 focusing on the rationale for restriction of the values of the volume
 ratio of the oxide of added element to the base metal, the amount of
 element to be added, the thickness of the oxide film and the electric
 potential of the oxide film.
 Volume Ratio of Oxide
 The micro-structure of oxide film varies by the volume ratio .phi. of oxide
 formed on the surface thereof to Cu base metal (ratio of the molecular
 volume of the oxide to atomic volume of Cu base metal), which affects on
 the corrosion resistant property.
 Said volume ratio of oxide can be expressed by the following equation (2).
EQU .phi.=Md/nmD (2)
 where, M is the molecular weight of oxide, D is the specific gravity of
 oxide, m is the molecular weight of base metal, d is the specific gravity
 of base metal, n is number of metal atoms contained in one molecule of
 oxide.
 If this volume ratio is 1.0 or less, since the volume of oxide is lower
 than that of base metal, an oxide film formed on the surface of base metal
 becomes porous which allows the corrosion medium to contact with the
 surface of base metal so that the corrosion resistant property decreases.
 In case of the conventional phosphorous deoxidized copper, the volume
 ratio of oxide film (Cu.sub.2 O) formed on the surface is about 1.7. In
 order to prevent the ant-nest type corrosion, the volume ratio of oxide
 film on the surface of copper alloy is to be 1.7 or more. If the volume
 ratio exceeds 3.0, difference between the molecular volume of oxide film
 and the atomic volume of base metal becomes too large which may create
 some distortion of the oxide film and consequently defects such as cracks
 may occur. In this case, the corrosion resistant property may decrease as
 the case of porous oxide film. Therefore, the volume ratio of oxide should
 be restricted to the range from 1.7 to 3.0. The elements such as Mn, Fe,
 Co and Cr can be used to form such oxides.
 Amount to be Added
 If the amount of additive element to be added to the copper alloy is less
 than 0.05 wt. %, the volume ratio of Cu oxide from the base metal against
 the oxide of additive element in the oxide film becomes significantly
 high, resulting in decrease of the corrosion resistant property. On the
 other hand, if the added amount of additive element exceeds 3 wt. %, the
 probability of poor wettability of the brazing filler metal becomes high
 due to strong oxide formed from the additive element during the brazing
 process as one of fabrication processes of the heat exchanger, therefore
 there is a danger of generating leakage in the brazed part during the
 pressure test. Therefore, the amount of additive element to be added into
 the copper alloy should be restricted to the range from 0.05 to 3 wt. %.
 Thickness of Oxide Film
 If the thickness of oxide film formed on the surface of tube is less than
 30 .ANG., Cu erosion by carboxylic acids may occur through the Cu oxide
 film and the corrosion medium easily contacts with the surface of base
 metal, resulting in decrease of the corrosion resistant property. If the
 thickness of said oxide film exceeds 3000 .ANG., the brazing filler metal
 may poorly wet or spread out on the brazing part, therefore there is a
 danger of generating leakage in the brazed part. Therefore, the thickness
 of oxide film should be restricted to the range from 30 to 3000 .ANG..
 Electric Potential of Oxide Film
 If the potential difference between the main body of tube and the oxide
 film is large and there is a defect in the oxide film, the potential
 difference between the oxide of additive element and Cu oxide existing in
 the oxide film or between these oxides and the main body of tube may
 create the cell reaction, and consequently the corrosion may be enhanced.
 The corrosion may also be enhanced if the additive element has already
 deposited in the Cu base metal. In order to reduce the corrosion by the
 cell reaction as aforementioned, the natural electric potential of the
 oxide film is to be within the range of from 0.2 V to -0.2 V against the
 phosphorous deoxidized copper having oxide film of the same thickness (30
 to 3000 .ANG.). In this case, the natural electric potential of the oxide
 film is determined after a tube provided with the oxide film was dipped
 into formic acid solution of 0.1 v. % at room temperature (20 to
 30.degree. C.) for 24 hours, for example. If the natural electric
 potential of the oxide film is less than -0.2 V against the phosphorous
 deoxidized copper, the oxide formed from the additive element may easily
 dissolve into carboxylic acids. On the contrary, the natural electric
 potential of the oxide film exceeds +0.2 V against the phosphorous
 deoxidized copper, the corrosion resistant property of the Cu base metal
 in the copper alloy is deteriorated. Therefore, the differential of
 natural electric potential between the oxide film and the phosphorous
 deoxidized copper in said formic acid solution should be restricted to the
 range of from 0.2 V to -0.2 V.
 Further, addition of P as the deoxidation agent into said copper alloy does
 not affect on the aforementioned effects. Addition of Pb into said copper
 alloy also does not affect on the aforementioned effects.
 Then, various copper alloy tubes for the heat exchanger according to the
 examples of the present invention were actually manufactured and their
 corrosion resistant property was compared to the comparative examples as
 follows.
 The copper alloy tubes containing the additive element at the amount listed
 in Table 3 below and balanced with Cu and other unavoidable impurities
 were manufactured. The dimensions of each tube were as follows: 9.52 mm in
 outer diameter and 0.36 mm thick. The comparative example B12 was the
 ordinary phosphorous deoxidized copper tube.
 These tubes were subjected to the heat treatment under N.sub.2 atmosphere
 containing 100 ppm of O.sub.2 and 5% of H.sub.2 to form the oxide film of
 30 to 3000 .ANG. thick on the surface thereof. The volume ratio of the
 oxide of additive element (PbO) in the comparative example B15 was 1.40,
 that of the oxide of the additive element (SnO) in the comparative example
 B16 was 1.31, that of the oxide of the additive element (MgO) in the
 comparative example B17 was 0.85, and that of oxide of the additive
 element in each of the examples B1 through B9, and the comparative
 examples B13 and B14 was established in the range from 1.7 to 3.0.
 These copper alloy tubes of the examples or the comparative examples were
 exposed to the atmosphere affected by 1 v. % of formic acid solution or
 acetic acid solution for 20 days, then the maximum corrosion depth was
 determined to evaluate the corrosion resistant property. Exposure to
 formic acid or acetic acid was used because the ant-nest type corrosion
 can be readily reproduced by formic acid and acetic acid.
 Further, each copper alloy tube was dipped into 0.1 v. % of formic acid
 solution at 256, 36.degree. C. for 24 hours, then the natural electric
 potential of the oxide film on the surface of the copper alloy tube was
 determined. From this value and the natural electric potential of the
 phosphorous deoxided copper determined under similar conditions, the
 differential potential was calculated.
 Furthermore, using each tube of the examples and the comparative examples,
 the finned coil was fabricated, the return-bending part was brazed, then
 the brazing property of each tube of the examples and the comparative
 examples was evaluated. The brazing was carried out using BCuP-2 as the
 brazing filler metal, at 850 .degree. C. for 30 seconds. The air-tightness
 test was carried out at the air pressure of 2.94 MPa for each tube after
 brazing to evaluate the brazing property based on presence or absence of
 leakage. These results are shown all together in Table 3. Under the
 heading of "brazing property", ".largecircle." stands for "no leakage" and
 "X" for "presence of leakage".
 TABLE 3

Electrical
 Additive Maximum Corrossion Length
 Potential
 P content Elements (mm) Brazing
 Difference
 (wt %) (wt %) 1% Formic Acid 1% Acetic Acid Property
 (V)
 Example B1 0.023 Mn:0.08 0.01 --
 .smallcircle. -0.01
 B2 0.025 Mn:0.12 0.01 --
 .smallcircle. -0.02
 B3 0.021 Mn:1.31 -- -- .smallcircle.
 -0.02
 B4 0.031 Mn:2.60 -- -- .smallcircle.
 -0.05
 B5 0.024 Mn:1.75 -- -- .smallcircle.
 0.10
 Fe:1.20
 B6 0.031 Mn:0.72 -- -- .smallcircle.
 -0.12
 Pb:2.42
 B7 0.035 Co:0.75 0.01 --
 .smallcircle. -0.05
 B8 0.027 Cr:0.91 0.01 --
 .smallcircle. -0.09
 B9 0.028 Fe:0.52 0.01 --
 .smallcircle. -0.11
 B10 -- Mn:0.32 0.01 -- .smallcircle.
 -0.02
 B11 -- Mn:2.00 -- -- .smallcircle. -0.03
 Comparative B12 0.022 -- 0.26 0.17
 .smallcircle. 0
 Example B13 0.024 Mn:0.02 0.15 0.08 X
 -0.01
 B14 0.019 Mn:3.14 -- -- .smallcircle.
 -0.13
 B15 0.021 Pb:0.02 0.17 0.12
 .smallcircle. -0.20
 B16 0.026 Sn:1.76 0.14 0.11
 .smallcircle. -0.31
 B17 0.030 Mg:0.06 0.24 0.16
 .smallcircle. -0.02
 As obvious from Table 3, in case 1 v. % formic acid solution was used as
 the corrosion medium, only corrosion with about 0.01 mm depth was observed
 in the examples B1 through B11, indicating better corrosion resistant
 property. In these examples B1 through B11, the brazing property was also
 good. On the other hand, the conventional phosphorous deoxidized copper of
 the comparative example B12, the comparative example B13 which contains
 only small amount of the additive element, and comparative examples B15,
 B16 and B17 which have small volume ratio of the oxide were all inferior
 to the examples in the corrosion resistant property. The comparative
 example B14 which has large amount of the additive element showed poor
 brazing property.
 Next, a fin-tube heat exchanger according to another embodiment will be
 explained. In the fin-tube heat exchanger according to the present
 embodiment, a plurality of plate type fins of aluminum or aluminum alloy
 are placed in parallel each other on the outer surface of the main tube
 body of claim 1 or 2.
 An internally grooved tube is preferred as the copper alloy tube used for
 the fin-tube heat exchanger according to the present invention. This
 internally grooved tube, 4 to 25.4 mm in outer diameter, having a
 plurality of internal grooves parallel each other, is constructed so as to
 satisfy the following relationships:
EQU 0.01.ltoreq.h/Di.ltoreq.0.05 and 0.degree..ltoreq..gamma..ltoreq.30.degree.
 where, h is the depth of groove, Di is minimum internal diameter
 (determined at the crest part), and is helix angle toward the tube axis.
 Thereby, the heat transfer capacity can be significantly improved.
 If the outer diameter of the internally grooved tube is less than 4 mm, the
 pressure loss of the thermal medium may increase and sufficient heat
 transfer capacity can not be obtained. On the other hand, if the outer
 diameter exceeds 25.4 mm, the heat exchanger becomes large size and
 uneconomical as the fin-tube heat exchanger. Therefore, the outer diameter
 of tube should be restricted to the range from 4 to 25.4 mm.
 If the ratio h/Di is less than 0.01, improvement of heat transfer capacity
 is not sufficient. On the contrary, if the ratio h/Di exceeds 0.05, the
 pressure loss increases so that the heat transfer capacity may decrease.
 Further, if the helix angle .gamma. toward the tube axis exceeds
 30.degree., the pressure loss increases and sufficient heat transfer
 capacity can not be obtained. Therefore, the ratio h/Di is preferably
 within the range from 0.01.ltoreq.h/Di .ltoreq. to 0.05, and the helix
 angle .gamma. within the range from 0.degree. to 30.degree..
 When the internally grooved tube having internally formed grooves with such
 construction is used as the tube, the fin-tube heat exchanger having
 better corrosion resistant property against the ant-nest type corrosion
 and further having better heat transfer capacity as the heat exchanger can
 be obtained.
 Further, the copper alloy tube constituting the tube according to the
 present invention may contain unavoidable impurities such as P and B which
 are usually used as deoxidation agents in addition to Zn, Mn and Mg, but
 existence of such impurities does not cause any problem for improvement of
 the corrosion resistant property.
 Then, the examples of the present invention will be explained comparing to
 the comparative examples. The fin-tube heat exchanger shown in FIG. 4 were
 prepared using the tubes (annealed) having the composition listed in Table
 4 below, the corrosion resistant property, the heat transfer capacity, the
 essential characteristics such as working and brazing properties required
 for manufacturing were evaluated. FIG. 2 is a view of this fin-tube heat
 exchanger sectioned toward the tube axis, FIG. 3 is a sectional view of
 the tube, and FIG. 4 is a partially enlarged view of the tube. Each fin 1
 is substantially a plate having a plurality of tube insertion holes formed
 in between the top and the bottom thereof, and to the surrounding edge of
 each insertion hole is provided with a tube type fin collar 5 in the way
 that the axis direction thereof is orthogonal to the fin 1. All plate type
 fins 1 are placed in parallel each other, and a tube 2 is inserted into
 the fin collar 5 of each fin 1. This tube 2 is formed in U-shape with a
 hair-pin bending part 3 to connect each tube into one line of tube; that
 is, each tube 2 is inserted into the fin collar 5 and fixed to the fin 1
 by expanding the tube 2, then both ends of the tube 2 are connected to the
 end of neighboring tubes 2 through a semi-circular tube 4 by brazing.
 Each tube 2 is provided with a plurality of grooves 7 on the internal
 surface thereof, and these grooves 7 spirally extends inside the tube 2.
 The internal diameter Di of the tube 2 is defined as the distance between
 a crest 6 of the groove 7 and the opposed crest 6, representing the
 minimum internal diameter.
 The internally grooved tube used in the fin-tube heat exchanger of the
 present example has the following dimensions: the outer diameter=7 mm, the
 inner diameter (Di)=6.14 mm , 50 grooves at the sectioned surface
 orthogonally to the tube axis, the groove depth (h)=0.18 mm, the bottom
 thickness (t)=0.25 mm, the bottom width of groove (W)=0.23 mm, and the
 helix angle .gamma. of groove against the tube axis=18.degree.. The
 composition of copper alloy for each tube 2 is shown in Table 4 below.
 Volatile lubricant oil was used in each step of blanking of the fin,
 hair-pin bending and expansion of the tube during manufacturing of the
 fin-tube heat exchanger, but subsequent degreassing step by solvent was
 eliminated. The brazing of the tube was carried out using the phosphorous
 copper brazing filler metal (BCuP-2; the species defined by JIS-Z3264 and
 containing 6.8-7.5% of P, 0.2% of other elements and the remaining is
 mainly Cu) by the burner brazing. Results of evaluation of each
 characteristic are shown in Table 5 below. The heat transfer calorie shown
 in Table 5 was obtained under air blowing at 1.0 m/sec.
 TABLE 4
 Composition
 (wt %)
 Zn Mn Mg P Cu
 Example
 C1 0.5 -- -- -- balance
 C2 5.0 -- -- -- balance
 C3 -- 0.5 -- -- balance
 C4 -- 2.0 -- -- balance
 C5 -- -- 0.5 -- balance
 C6 -- -- 2.0 -- balance
 C7 5.0 1.0 1.0 -- balance
 Comparative
 Example
 C8 -- -- -- 0.03 balance
 C9 15 -- -- -- balance
 C10 -- 10 -- -- balance
 C11 -- -- 10 -- balance
 TABLE 5
 Corrosion
 Resistant
 Property
 Maximum Heat Transfer Capacity Working Brazing
 Corrosion Heat Transfer Calorie Wrinkling by Property
 Depth (kcal/h) Hair-pin Broken-out
 (mm) Evaporation Condensation Bending Part
 Valuation
 Example 1 0.03 1300 2200 small tube
 .smallcircle.
 2 0.02 1298 2196
 .smallcircle.
 3 0.02 1299 2198
 .smallcircle.
 4 0.01 1294 2190
 .smallcircle.
 5 0.03 1299 2198
 .smallcircle.
 6 0.02 1296 2192
 .smallcircle.
 7 0.01 1290 2182
 .smallcircle.
 Comparative 8 0.20 1300 2200 small tube
 .DELTA.
 9 0.01 1270 2153 large brazed
 part X
 10 0.01 1275 2156
 X
 11 0.10 1272 2154
 X
 Each characteristic listed in Table 5 was evaluated according to the
 following method.
 Corrosion Resistant Property Against the Ant-Nest Type Corrosion
 The fin-tube heat exchanger used each tube having composition listed in
 Table 4 was operated inside room under the following conditions and then
 the maximum corrosion depth by the ant-nest type corrosion was determined.
 Operation Environment:
 'temperature 30.degree. C., relative humidity 80%
 Operation Conditions:
 5-minute cooling and 10-minute air blowing,
 repeated for 6 months.
 Heat Transfer Capacity
 Using a wind tunnel test apparatus, the heat transfer calorie (evaporation
 and condensation) as the heat exchanger was determined.
 R-22 (Fleon HCFC-22: molecular formula CHClF.sub.2) was used as a
 refrigerant, and measurement conditions were as follows.
 Evaporation Test
 Air: Dry-bulb/wet-bulb temperature 27.0.degree. C./19.0.degree. C.
 Refrigerant: Out-put pressure from heat exchanger 5.4 kgf/cm.sup.2
 Overheating: 5.0 deg
 Condensation Test
 Air: Dry-bulb/wet-bulb temperature 20.0.degree. C./15.0.degree. C.
 Refrigerant: Out-put pressure from heat exchanger 18.8 kgf/cm.sup.2
 Undercooling: 5.0 deg
 Characteristics Required for Production
 Working (hair-pin bending: 10.5 mm in diameter):
 observed for incidence of wrinkling inside the bending part.
 Brazing Property:
 the breaking test was carried out under adding internal pressure to the
 tube of heat exchanger and then broken-out part was observed.
 As obvious from Table 5, the examples C1 to C7 of the present invention all
 showed better corrosion resistant property against the ant-nest type
 corrosion than the comparative example C8 using the conventional
 phosphorous deoxidized copper and other characteristics such as the heat
 transfer capacity required as the heat exchanger and the working and
 brazing properties required for manufacturing were good and almost equal
 to the comparative example C8 using the conventional phosphorous
 deoxidized copper.
 On the other hand, the comparative examples C9 to C11 were not suitable for
 practical use because heat transfer capacity as well as the working and
 brazing properties decreased due to use of the tubes containing large
 amount of Zn, Mn and Mg. The comparative example C11 showed inferior
 corrosion resistant property, probably due to deposit of Mg since the Mg
 content was too high and exceeded its solid soluble volume against Cu.
 Next, a corrosion resistant copper alloy tubes according to another
 embodiment will be described.
 As a result of having conducted a series of diligent research to improve
 the corrosion resistant property of copper alloy tube, the present
 inventors found that the corrosion resistant property against the ant-nest
 type corrosion can be significantly improved by providing on the surface
 of the main body of tube a oxide film containing oxide of an element
 having smaller standard enthalpy for formation of the oxide than that
 (-169 kj/mol at 298.15 K Kelvin temperature) for Cu oxide (Cu.sub.2 O).
 Such oxide film can be formed by annealing the main body of tube consisted
 of one or two additive elements having standard enthalpy -169 kJ/mol or
 less for formation of the oxide, Cu and unavoidable impurities in the
 inactive atmosphere or in the atmosphere containing small amount of
 oxygen, for example.
 In this case, if the thickness of oxide film is less than 40 .ANG.,
 sufficient improvement effect of the corrosion resistant property can not
 be obtained. On the other hand, if the thickness of said oxide film
 exceeds 2000 .ANG., further increase of effect can not be expected due to
 saturation of improvement effect of the corrosion resistant property and
 also the brazing property may decrease. Therefore, the thickness of oxide
 film should be restricted to the range from 40 to 2000 .ANG..
 Among said additive elements, elements having smaller standard enthalpy for
 formation of oxide have larger improvement effect of the corrosion
 resistant property. For said additive elements, the corrosion resistant
 property increases by increasing the content. However, if the content of
 said additive element exceeds certain level, the working property of
 copper alloy tube may significantly decrease. Therefore, the lower limit
 of content for the additive element should be restricted based on the
 corrosion resistant property and the upper limit should be restricted
 based on the working property. As a result of a series of diligent
 research, the present inventors found that the oxide film having better
 corrosion resistant property against the ant-nest type corrosion can be
 obtained by restricting the amount of additive element to the range
 expressed by the following equation (3).
EQU 0.04.ltoreq..SIGMA.[Ax.multidot.ln (.DELTA.H.sup.0 f(x)/(-169))].ltoreq.4.2
 (3)
 where, Ax is the content of additive element x in atomic %.
 ln is natural logarithm.
 .DELTA.H.sup.0 f(x) is standard enthalpy for formation of oxide of additive
 element in kJ/mol.
 .SIGMA. is sum of Ax.multidot.ln (.DELTA.H.sup.0 f(x)/(-169)) for each
 additive element.
 That is, the corrosion resistant property created by the oxide film relates
 to both standard enthalpy for formation of oxide and the content of
 additive element, and the value obtained from the following equation 4 can
 be used as the index for the corrosion resistant property.
EQU [Ax.multidot.ln (.DELTA.H.sup.0 f(x)/(-169))] (4)
 So, if the copper alloy tube contains the element having larger oxygen
 affinity than that of Cu (that is, the element having smaller standard
 enthalpy for formation of oxide), the oxide film on the surface of copper
 alloy tube mainly contains the oxide of that additive element. In general,
 there exists absorbed water on the surface of oxide as hydroxide radical,
 and there is a trend toward that the oxide having smaller standard
 enthalpy for formation contains larger amount of absorbed water.
 Therefore, if the standard enthalpy for formation of oxide of additive
 element is expressed by .DELTA.H.sup.0 f(x), it can be said that the alloy
 containing the element having larger ratio [.DELTA.H.sup.0 f(x)/(-169)]
 for the standard enthalpy for formation of oxide against the standard
 enthalpy (-169 kJ/mol) for formation of Cu oxide (Cu.sub.2 O) is covered
 on its surface by larger amount of hydroxide radical than pure copper. In
 the alloy covered on its surface by larger amount of hydroxide radical,
 even if dew drops formed on its surface, they diffuses to form water film
 so that its surface is maintained in uniform sate and the ant-nest type
 corrosion is hardly formed. That is, the value of the aforementioned
 equation (4) can be used as the index for the corrosion resistant property
 against the ant-nest type corrosion. Furthermore, if the content of these
 additive elements is increased, its effect becomes more remarkable, but
 the present inventors found that there is a relationship between the
 content Ax and [.DELTA.H.sup.0 f(x)/(-169)] and that improvement effect of
 the corrosion resistant property can be evaluated by the product of the
 natural logarithm of [.DELTA.H.sup.0 f(x)/-169] by Ax; that is,
 Ax.multidot.ln (.DELTA.H.sup.0 f(x)/(-169)) and further that the value of
 Ax.multidot.ln (.DELTA.H.sup.0 f(x)/(-169)) is additive property in case
 of the alloy containing two or more additive elements.
 Therefore, in case of the alloy containing a plurality of elements, the
 value obtained for each element from the equation (4) should be summed.
 That is, the following equation (5) can be applied.
EQU .SIGMA. [Ax.multidot.ln(.DELTA.H.sup.0 f(x)/(-169))] (5)
 If the value obtained from this equation (5) is less than 0.04, sufficient
 improvement effect can not be created by the oxide film. And, if the value
 obtained from the equation (5) exceeds 4.2, further improvement of the
 corrosion resistant property can not be expected due to saturation of
 improvement effect of the corrosion resistant property and the working
 property of the copper alloy tube is decreased by the additive element.
 Therefore, the content of additive element should be restricted to the
 range shown by the aforementioned equation (3).
 Further, the characteristics of the oxide film formed on the surface of
 tube can be readily judged based on intensity of the main peak from the
 X-ray electron spectroscopy (XPS) analysis. That is, when the ratio Ix/ICu
 of said main peak intensity Ix of said additive element to the main peak
 intensity ICu of Cu is 0.10 or grater, significant improvement effect of
 the corrosion resistant property against the ant-nest type corrosion can
 be obtained. Then, the ratio of the main peak intensity Ix for the
 additive element to the main peak intensity ICu of Cu will be explained in
 more detail.
 It is well known that the corrosion resistant property of the copper alloy
 largely depends not only on its alloy composition also on the film formed
 on the surface. In the present invention, better corrosion resistant
 property can be obtained by restricting not only the thickness of the
 oxide film formed on the surface also restricting the element constructing
 the oxide film. In order to increase the effect further of the alloy
 containing the element having small standard enthalpy for formation of
 oxide, the oxide film formed on the surface thereof should contain the
 additive element concentrated at higher level than the alloy composition
 ratio of the main body of tube, and in order to obtain that index the XPS
 analysis is most practical from technical and economical point of view. As
 a result of a series of diligent research on the relationship between said
 ratio Ix/ICu and the corrosion resistant property, the present inventors
 found that if the ratio Ix/ICu is 0.10 or more, improvement effect of the
 corrosion resistant property significantly increases. The main peak ratio
 Ix/ICu can be established at 0.10 or more, for example, by controlling the
 composition rate of reduction gas such as oxygen, CO and the like in the
 atmosphere in the annealing process for treating the copper alloy tube
 mild, but not restricted thereto.
 Then, comparing to the comparative examples, the examples of the present
 invention will be explained.
 First, the tube materials (O materials: 9.5 mm in outer diameter: 0.3 mm
 thick) having composition shown in Table 6 below were prepared by the melt
 casting, the hot extrusion, the cold forging and the heat treatment. The
 figures shown under the heading of "the symbol of an element" indicates
 the standard enthalpy in kJ/mol for formation of oxide of that element at
 the temperature of 298.15 K. The value calculated from the equation 5
 (under the heading of .SIGMA.[ ]) for each copper alloy tube or copper
 tube of these examples and the comparative examples, the thickness of the
 oxide film and the main peak intensity ratio Ix/ICu are also shown in
 Table 6. The thickness of the oxide film was obtained from the etching
 time by Auger Electron Spectroscopy (AES) analysis. The main peak
 intensity by the XPS analysis was determined using X-ray (K.alpha.)
 derived from Mg under the following conditions: output power 300 W
 (voltage 15 kV, current 20 mA), analyzed area 1000 .mu.m.sup.2.
 The corrosion resistant property against the ant-nest type corrosion,
 brazing and hot working properties of these examples and the comparative
 examples were evaluated by the following methods.
 Corrosion Resistant Against the Ant-Nest Type Corrosion
 Test pieces were exposed to the environment of formic acid as one of
 typical carboxylic, and the maximum corrosion depth was determined after
 corrosion. The test conditions were as follows:
 Corrosion Medium:
 100 ml of 1% aqueous solution of formic acid.
 Exposure Condition:
 the test piece (100 mm long) was dipped into deionized water in a beaker
 which was placed in a one liter container containing said corrosion
 medium, then the container was sealed.
 Temperature and Testing Period:
 maintained at 40.degree. C. for 20 days.
 Brazing Property
 The finned coil was fabricated and the return bending part was brazed. The
 brazing property was evaluated by presence or absence of leakage. The
 conditions of brazing were as follows; brazing filler metal: BCuP-2,
 temperature: 850.degree. C., brazing time:30 seconds. The air-tight test
 was carried out under air pressure of 2.94 MPa.
 Hot Working
 Using test sample, 15 mm in diameter and 15 mm long, selected from the
 ingots, the drop hammer test with the deformation rate of 50% was carried
 out at 850.degree. C., and the presence of cracks was determined.
 Results of these tests are shown in Table 7 below. Under the heading of
 "brazing property", "X" stands for presence of leakage and ".largecircle."
 for no leakage. Under heading of "hot-working property", "X" stands for
 presence of cracks and "C" for no crack.
 TABLE 6
 Composition (atomic %) Thickness of
 Cu Zn Mn Sn Co Ag Oxide
 Film
 -169 -348 -520 -581 -238 -31 .SIGMA. [ ]
 (.ANG.) Ix/ICu
 Example D1 balance 0.42 -- -- -- -- 0.30 800 0.35
 D2 1.10 0.19 -- -- -- 1.01 1300 0.44
 D3 0.33 -- 0.41 -- -- 0.74 1100 0.22
 D4 -- 0.04 2.60 -- -- 3.25 1500 0.90
 D5 1.21 -- -- 0.71 -- 1.12 600 0.31
 D6 -- -- 1.30 -- -- 1.61 400 0.18
 D7 -- 0.20 -- -- -- 0.22 400 0.20
 D8 -- 0.04 -- 0.08 -- 0.07 1200 0.28
 D9 1.13 0.41 1.97 -- -- 3.71 500
 0.77
 D10 -- -- 1.44 1.11 -- 2.16 300 1.10
 D11 1.07 0.22 -- 0.03 -- 1.03 900
 0.56
 D12 -- -- -- 0.55 -- 0.19 200 0.16
 Comparative 13 balance -- -- -- -- 0.31 0 400 0
 Example 14 -- -- -- 0.06 -- -0.52 500 0.15
 15 -- -- -- -- -- 0.02 400 0.20
 16 -- 1.21 1.03 -- -- 2.63 2500 1.60
 17 1.10 0.23 -- -- -- 1.05 200 0.05
 18 2.12 2.57 -- -- -- 4.42 1500 0.97
 19 -- 0.11 0.03 -- -- 0.16 30 0.07
 20 0.01 -- -- 0.02 -- 0.01 3000 0.11
 21 1.90 -- 2.89 -- -- 4.94 100 0.33
 22 -- -- 1.33 -- -- 1.64 30 0.05
 23 1.49 0.88 2.43 -- -- 5.07 2500 0.88
 24 -- 0.01 -- 0.03 -- 0.02 500 0.02
 TABLE 7
 Corrosion Depth
 (mm) Brazing Test Hot Working Test
 Example
 D1 0.02 .largecircle. .largecircle.
 D2 -- .largecircle. .largecircle.
 D3 0.01 .largecircle. .largecircle.
 D4 -- .largecircle. .largecircle.
 D5 -- .largecircle. .largecircle.
 D6 -- .largecircle. .largecircle.
 D7 0.02 .largecircle. .largecircle.
 D8 0.03 .largecircle. .largecircle.
 D9 -- .largecircle. .largecircle.
 D10 -- .largecircle. .largecircle.
 D11 -- .largecircle. .largecircle.
 D12 0.02 .largecircle. .largecircle.
 Comparative
 Example
 D13 0.24 .largecircle. .largecircle.
 D14 0.27 .largecircle. .largecircle.
 D15 0.19 .largecircle. .largecircle.
 D16 -- X .largecircle.
 D17 0.16 .largecircle. .largecircle.
 D18 -- .largecircle. X
 D19 0.16 .largecircle. .largecircle.
 D20 0.20 X .largecircle.
 D21 -- .largecircle. X
 D22 0.15 .largecircle. .largecircle.
 D23 -- X X
 D24 0.22 .largecircle. .largecircle.
 As obvious from Table 7, in the examples D1 through D12, the corrosion
 depth was very thin and 0.03 mm or less, the brazing and hot working
 properties were also good. On the other hand, the comparative examples
 D13, D14, D15, D20 and D24 showed small value for the equation (5) (0.02
 or less) as shown under the heading of [ ] but rated with high value of
 0.19 mm or more for the corrosion depth. The comparative examples D18, D21
 and D23 showed high value of 4.42 or more for the equation (5) and also
 poor hot working property. The comparative examples D16, D20 and D23
 having thick oxide film of 2500 .ANG. or more showed poor brazing
 property. The comparative examples D13, D17, D19, D22 and D24 having lower
 value of the peak intensity ratio Ix/ICu (0.07 or less) showed
 unsatisfactory corrosion resistant property.