US 3053511 A
Description (OCR text may contain errors)
p 1962 J. w GODFREY 3,053,511
cum ALLOY METAL FOR CORROSION RESISTANCE AND HEAT EXCHANGER MADE THEREFROM Filed Nov. 15, 1957 IN VENT OR.
HTTORNEY ire Sttes This invention relates to clad alloy metal for corrosion resistance and more particularly to cladding of coppernickel alloy material for inhibiting corrosion of the base alloy.
The prevention of corrosion has always been a major problem in the metal fabricating industries. Reasonably effective protection has been achieved in the past by applying surface coatings of such nature as to obtain physical protection by reason of the covering of the base metal. The measure of protection afforded by such covering layers is of course limited since fabricating and usage conditions frequently expose the base metal thereby making it subject to attack. The most effective protection has been found to be that which affords not only the physical protection of covering the base metal but also protects the base metal by electrolytic action. Such protection has been achieved by covering the base metal with such metals as aluminum, aluminum alloys and zinc.
Copper-nickel alloys have been used in the past for fabrication of metal articles which are subjected to sea water exposure in normal usage. It has been found that such alloy materials may be efifectively protected from corrosion by applying zinc coatings or by using a zinc protective or sacrificial anode which has electrical connection to the base alloy and is preferentially corroded with regard to the base alloy. However, it has been known that the protection afforded by such means is unsatisfactory for the reason that the rate of zinc corrosion is extremely rapid. The thickness of the coating or the quantity of sacrificial anode must therefore be extremely large in order to meet life-test requirements. These factors are of extreme importance in the fabrication of sea water heat exchangers such as are in common use in water vehicles since economy, maintenance and weight factors require that the heat exchanger design be such as to resist corrosion over long periods of time in order to minimize operational delays for tear down and maintenance while at the same time achieving economy of space and weight.
It is therefore an object of my invention to provide corrosion resistant clad copper-nickel alloy which will provide corrosion protection over extended periods of time; it is a further object of my invention to provide a corrosion resistant clad copper-nickel alloy in which the cladding material contains substantially the same constituents as that of the base alloy. It is a further object of my invention to provide a heat exchanger wherein the surfaces are protected from corrosion by means of a copper-nickel alloy coating containing substantially the same constituents as' those of the base metal. It is a still further object of my invention to provide a brazed heat exchanger adapted for salt water exposure wherein the copper-nickel base alloy is protected from corrosion by means of a copper-nickel alloy coating containing different percentages of the constituent materials contained in the base alloy.
These and other objects of my invention are attained by providing the base copper-nickel alloy with a coppernickel alloy coating containing different weight percentages of the same constituents contained in the base material.
The nature of my invention will be apparent to those 3,053,511 l Patented Sept- 1,
skilled in the art from the following description as read in connection with the drawing in which:
FIGURE 1 discloses a broken out portion of a heat exchanger embodying the principles of my invention in plan view and in which FIGURE 2 shows an enlarged cross-sectional view of a typical heat exchanger tube taken on line 2-2 of FIG- URE 1.
Having reference now to FIGURE 1 of the drawing, there is shown a portion of a heat exchanger embodying the principles of my invention in which a plurality of tubes '1 extend between and interconnect an inlet header 3 and an outlet header 5 in order to permit one medium of the heat exchange system to flow through the tubes for heat exchange contact with another medium flowing over the tubes.
The heat exchanger shown on the drawing is particularly adapted for applications involving exposure to sea water, the base material of the heat exchanger elements being formed of a copper-nickel alloy well known in the art for such purposes. As is shown more clearly in FIGURE 2, the individual tubes 1 are formed by interconnecting two half-tube sections 7 and 9 having their side edges 11 and 13 formed so as to over-lap one another to create a tubular member 1. The half-tube sections are interconnected at the overlapping edges 11 and 13 by means of any suitable method such as brazing or welding in order to create a fluid-tight seal. The interconnection .15 shown on the drawing is preferably attained by brazing with copper foil. A cladding layer 17, more particularly described hereinafter, is provided on the outer surface of the tubes 1 to inhibit corrosion of the base metal.
The material most commonly used in applications involving sea water exposure are those compositions commonly known in the art as 70-30 and 90-10 copper-nickel alloy. The chemical composition of each of these alloys as hereinafter referred to in the specification and claims is shown in Table I below in terms of weight percentage:
Table I Copper (min.) 64. 85.0 Nickel 29.0-32; 0 9 011.0 Zinc (113m)." 1.0 1.00 on 0 40-0. 70 1 001. Lead (max.) 0.0 0.05 Manganese (max.) 1. 00 0.75 Copper plus sum of named elements (min.) 99. 50 99. 50
The remaining 0.50% may be trace elements such as carbon, titanium, silicon, aluminum, tin, sulfur and others.
I have found the -10 alloy to be difiicult to fabricate where such techniques as brazing and welding are utilized since the melting point of this composition is relatively low and is about 21100" F. The brazing of sheets formed therefrom is diflicult to control and results in frequent burning through of the material at the brazing points. Compositions of the 70-30 type are preferred for the base tube material since the melting point is appreci- I have discovered that very effective corrosion resistance is achieved by providing the 70-30 base material with a clad or coating of 90-10 copper-nickel alloy. It has been found that this cladding alloy is anodic to the base alloy and therefore will protect it through galvanic action. That is, if corrosion attack occurs, it will concentrate on the relatively thin layer of the cladding material, and the basic alloy material will not be attacked as long as the cladding material is present. This is, in essence, the well known principle of galvanic corrosion, but is controlled and applied to achieve the useful purpose described. It has been found that the potential of the 70-30 base coppernickel alloy is about 0.25 volt with reference to a saturated Calomel half cell whereas that of the 90-10 coppernickel alloy cladding is about 0.27 volt. It is thus obvious that while the cladding alloy is anodic to the base alloy, their potentials are so close that the rate of galvanic corrosion of the cladding material is extremely slow with the result that heat exchangers utilizing extremely thin cladding layers may be utilized without fear of corrosion of the base alloy over long periods of operation.
I have found that a heat exchanger using tubes formed of my clad sheet material having a total thickness of about 0.021 with the thickness of the cladding being about one-sixth to one-third of the total thickness or 0.0035" to 0.007" results in a unit having extremely long life cycle characteristics. A further advantage resulting from the use of 90-10 copper-nickel alloy as cladding for a 70-30 copper-nickel base alloy is that appreciable savings in the use of nickel, a strategic material, are achieved. Also, it has been found that the 90-10 alloy inhibits fouling of the heat exchanger due to the growth of sea water animal life on the metal surfaces.
I have found that a heat exchanger formed of 70-30 copper-nickel base alloy of about 0.014" thickness of the following composition in terms of weight percent:
copper 69.0 nickel 29.3 zinc 0.3
iron 0.6 lead 0.03
and having a cladding of 90-10 copper-nickel alloy of resulted in a successful life-test of more than two years in duration under sea water exposure conditions. It was unnecessary to tear down the exchanger for repair and/ or replacement of parts during this entire period.
It is apparent from the foregoing description that I have provided a clad alloy material having high resistance to corrosion and being adapted to be formed into sheets for the fabrication of such devices as sea water heat exchangers. The cladding may be applied to the base material in either sheet form or ingot form, the cladding becoming alloyed with the base material during the hot working and subsequent fabricating operations. The cladding may be applied in other ways well known to the art, such as by dipping or spraying, the cladding operation forming no part of my invention.
While I have described my invention with particular reference to salt water heat exchangers, it should be recognized that this corrosion inhibiting clad alloy may be used in other devices and that the cladding may be applied to more than a single surface of the base alloy material. These and other embodiments of my invention will be apparent to those skilled in the art from the foregoing description and such embodiments are to be considered as within the intended scope of the claims which follow.
1. A corrosion resistant metal alloy material consisting of a base copper-nickel alloy metal having metallurgically bonded thereto as cladding a layer of copper-nickel alloy metal having substantially the same constituents as the base metal but in differing amount by weight so that the potential of the cladding is more negative than but close to that of the base metal, said base metal being formed of -30 copper-nickel alloy and said cladding being formed of -10 copper-nickel alloy.
2. A corrosion resistant metal alloy material consisting of a base copper-nickel alloy metal having metallurgically bonded thereto as cladding a layer of copper-nickel alloy metal having substantially the same constituents as the base metal but in differing amount by weight so that the potential of the cladding is more negative than but close to that of the base metal, said base metal being formed of copper 69%, nickel 29.3%, iron 0.6%, manganese 0.4%, zinc 0.3% and lead 0.03%, and said cladding being formed of copper 88.7%, nickel 9.1%, iron 1.2%, manganese 0.3%, Zinc 0.3% and lead 0.04%.
3. In a heat exchanger adapted to withstand the corrosive effects of salt water and comprising inlet and outlet headers and heat transfer tubes interconnecting said headers, said heat transfer tubes being formed of a corrosion resistant metal alloy material consisting of a base 70-30 copper-nickel alloy metal having metallurgically bonded thereto as cladding a layer of 90-10 copper-nickel alloy, the potential of the cladding being more negative than but close to that of the base metal, the thickness of the cladding being at least about one-sixth the total thickness of the tube material.
4. In a heat exchanger adapted to withstand the corrosive effects of salt water and comprising inlet and outlet headers and heat transfer tubes interconnecting said headers, said heat transfer tubes being formed of a corrosion resistant metal alloy material consisting of a base copper-nickel alloy metal having metallurgically bonded thereto as cladding a layer of copper-nickel alloy, the potential of the cladding being more negative than but close to that of the base metal, the thickness of the cladding being at least about one-sixth the thickness of the tube material, said base metal being formed of copper 69%, nickel 29.3%, iron 0.6%, manganese 0.4%, zinc 0.3%, and lead 0.03% and said cladding being formed of copper 88.7%, nickel 9.1%, iron 1.2%, manganese 0.3%, zinc 0.3%, and lead 0.04%.
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