US3496079A - Corrosion prevention - Google Patents

Description

Feb. 17, 1970 J. F. NORTON CORROSION PREVENTION 2 Sheets-Sheet 1 Filed Sept. 19, 1968 FIG. 1

INVENTOR. W155 E IYOKTO/l %01'0 147' TOANE Y J. F. NORTON CORROSION PREVENTION Feb. 17, 1970 2 Sheets-Sheet 2 Filed Sept. 19, 1968 INVENTOR JAMES F. NORTON United States Patent O 3,496,079 CORROSION PREVENTION James F. Norton, 22327 89th Ave., Wodinville,\Vash. 98072 Continuation-impart of application Ser. No. 440,570, Mar. 17, 1965, which is a continuation-in-part of application Ser. No. 215,119, Aug. 6, 1962. This application Sept. 19, 1968, Ser. No. 760,917

Int. Cl. C23f 13/00 US. Cl. 204-147 6 Claims ABSTRACT OF THE DISCLOSURE Apparatus and method of preventing corrosion in equipment, pipes, and the like in which an anode made of interposed ferrous and non-ferrous metal segments in closely spaced array and connected in parallel to one pole of a source of electrical energy is immersed in an aqueous liquid, the source being externally connected to the equipment. The source characteristics and anode size result in the depositing of a protective coating on all equipment surfaces in contact with the liquid, including surfaces out of sight of the anode, and surfaces contacted by the vapor phase of the liquid.

CROSS REFERENCE TO RELATED APPLICATIONS The present application is a continuation-in-part of application Ser. No. 440,570, filed Mar. 17, 1965, now abandoned which was a continuation-in-part of application Ser. No, 215,119, filed Aug. 6, 1962.

BACKGROUND OF THE INVENTION The present invention provides superior corrosion protection to such equipment as boilers, pipe lines, paper making machines and the like. This is achieved through the use of an anode comprising interposed ferrous and non-ferrous segments and through the application of a hydrogen overvoltage.

It is recognized that corrosion arise from a flow of electric current, and that where metal parts are in circuit with each other through an internal circuit formed in part by an aqueous solution, and through an external circuit, current will flow. These parts together form a cell. A source of electric potential is required and such a source exists when a chemical or physical anomaly exists in the structure. A commonly found factor which causes an electric potential is the presence of dissimilar metals, copper and iron, for example. It will be recognized that in most water or liquid handling equipment dissimilar metals are used; hence the wide spread corrosion problem.

A major method of combatting corrosion is known as cathodic protection, in which there is established an electromotive cell having an artificial anode and external circuit. The cell may therefore be seen to comprise an internal circuit in which the metal of the equipment to be protected is the cathode, the aqueous medium, such as water, slurry, etc. is the electrolyte and the anode is a specially manufactured structure positioned in the liquid in the equipment. The external circuit is made up of the equipment, the anode, a SOurCe of potential and suitable conductors. Usually, the potential source is a direct current source. The cell functions so that in the internal circuit, current flows from the anode to the cathode, i.e., from the artificial anode to the equipment. Since that electrode from which current flows is the one which corrodes, the artificial anode corrodes, or is sacrificed, and the eqipment, which receives the current flow, is consequently a cathode, and is therefore protected.

In the patent literature, the basic concept of cathodic protection is disclosed as early as 1912, in Young Patent No. 1,032, 723. Many systems of cathodic protection have subsequently been proposed, with improvement of the systems as experience was acquired with them. However, certain deficiencies still exist in heretofore known systems, notably the failure of these systems to provide protection for those parts of the equipment which are out of sight of the anode, excessive corrosion as shown by an excessive loss of the metal of the equipment, and undesirably large electric energy requirements. By way of explanation of the first noted deficiency, i.e., failure to satisfactorily protect equipment out of the line of sight of the anode, it is noted by way of example that in a boiler in which tubes are surrounded by water and through which tubes pass heated products of combustion, the anode may be placed in the water above the uppermost of the horizontal tubes; while the upwardly facing peripheries of the tubes will receive reasonable protection, the downwardly facing peripheries of these tubes will not receive adequate protection, and consequently, with prior art protective systems, the underneath portions of the tubes which were out of the line of sight of the anode were found to corrode at an undesirably rapid rate, even though the upper surfaces of these tubes, in the line of sight of the anode, did receive adequate protection.

In comparative tests with systems disclosed in the prior art (Smith No. 1,984,899) and with conventional systems, i.e., systems which differ from the present inventive system and method by the characteristics of the anode, equipment weight loss was reduced by at least /s, while at the same time power requirements were reduced by over 50%.

SUMMARY OF THE INVENTION The present invention provides a cathodic protection system and method in which there is provided an anode having a series of spaced segments of ferrous metal and another series of spaced segments of non-ferrous metal, with the segments of the two series being interposed and connected in parallel. The electric energy supplied to the apparatus is sufficiently large and the anode is sufficiently large that hydrogen is generated at the surfaces of the equipment being protected below liquid level. This invention provides a greater than neutralizing counter electro-chemical action in the presence of metal surfaces at which nascent hydrogen is generated so actively and thoroughly that the deterioration of these surfaces is avoided altogether, or is greatly diminished in comparison with known cathodic protection systems and apparatus. In addition, this invention significantly provides cathodic protection above liquid levels coextensively with the below liquid level protection, As a result of the present invention apparatus and method, there is electrochemically produced some or all of the following: magnesium oxide, sodium aluminate, calcium oxide and calcium carbonate, which are carried by liquid vapors into vapor zones bounded by exposed metal surfaces of the equipment being protected, where they adhere to the metal surfaces of the equipment to thereby provide a protective film on these surfaces, which otherwise are exposed to corrosive vapors.

Both of the above liquid level protection and below liquid level protection are maintained on substantially all of the metal surfaces which serve as a cathode in the circuitry forming and constituting a part of the cathodic protection system of the present invention.

Such complete metal surface protection is relatively economically maintained. The anode costs are favorable in comparison with conventional anode cost, and electric power requirements are not materially higher than in known systems; indeed, power requirements with the present invention system are significantly reduced.

The improved results achieved with the present invention include the protection of not only those surfaces which are in the line of sight from the anode of the present invention system, but in addition provides for the protection of surfaces which are out of the line of sight of the anode. Another important advantage of the present invention system is that there is less corrosion than with known systems, using known anodes. Yet another significant advantage to the present invention system is the requirement for significantly less electrical energy.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross section of a boiler with the protective system of the present invention applied thereto.

FIG. 2 shows a pipe line installation protected by the present invention.

FIG. 3 shows a heating tank protected by the present invention.

FIG. 4 discloses irregular heating vessels protected by the present inventive cathodic system.

DESCRIPTION OF PREFERRED EMBODIMENT Referring now to the drawings, FIG. 1 schematically illustrates a typical environment being protected by the present invention. Within a boiler mounted on supports 11 attached to a power plant building floor 12 or ship deck 12, are located multiple spaced boiler tubes 13, a bafiie 14, and a liquid 15 shown reaching a level 16 and leaving a vapor space 17. A composite anode 18 composed for ferrous metal segments 19 and non-ferrous metal segments 20 is located within boiler 10' below liquid level 16 and an electrical wire lead 21 is attached to anode 18 and extended outside boiler 10 through insulated packing fitting 22 for attachment to a terminal 23 of an electrical power source 24. The other terminal 25 of source 24 receives an electrical wire lead 26 which is electrically and physically connected to boiler 10 with fitting 27. Other boiler system equipment is not pertinent and not shown.

During the complete operation of boiler 10 and continued utilization of both the method described and the representative illustrated apparatus, all metal surfaces otherwise subject to liquid or vapor contact, are protected from corrosion and scale formation. No shadow effects will occur. The voltage applied to the composite anode and the balance of the electrical system maintains the generation of nascent hydrogen gas known as hydrogen overvoltage, adjacent all surfaces otherwise exposed to the liquids. Both sides of the bathe 14 are protected. The entire surfaces of tubes 13 both in line of sight of the anode and hidden, and all the below liquid line 16 boiler surfaces are protected. In addition the voltage applied to the composite anode and the balance of the electrical system electro-chemically produces magnesium oxide, sodium aiuminate, calcium oxide and/ or calcium carbonate for transport by the liquid vapors and subsequent deposit on the otherwise exposed above liquid level metal surfaces in the vapor space 17.

The protection resulting from this properly regulated cathodic protection method and apparatus is complete. The hydrogen overvoltage maintained at a level, for example, of two and one-half times the level associated with hydrogen film rust preventive system such as described in Thomson No. 2,176,514, coupled with the economical operational benefits of a composite anode, for example, arranged in segments of non-ferrous and ferrous metals, keeps the metal equipment surfaces with little corrosion and uniform. There is no need for other protection steps to be undertaken such as: the addition of chemical inhibitors to change the chemical properties of the fluids; the use of more passive metals to corrosion attack (which metals are often more expensive substantially increasing the equipment costs), and/or the use of coatings of various types.

Moreover, this active or nascent hydrogen gas cathodic protection method and apparatus is readily installed in equipment already in use. The scale build up of such used equipment is lifted and removed upon the genera tion of the nascent gas when the substantial hydrogen overvoltage is maintained by the composite anode and the balance of the electrical system.

A proper relationship of the size of one or more composite anodes with the electrical voltage and power is readily established with respect to any given total exposed metal surface area to be protected. The thorough generation of the active or nascent gas must be maintained. The total composite anode size must be sutficient to sustain such generation with an applied electrical power at a hydrogen overvoltage. The additional size of one or more of such composite anodes will be governed by service life requirements.

Generally the composite anode, if made of non-ferrous and ferrous metals, such as aluminum and cast iron, respectively, is large enough so no replacements of sacrificial metal will be needed for at least a year. When cast iron and aluminum are alternately arranged in such a composite anode, aluminum appears to have about a minimum life of one year and cast iron appears to have a minimum life of five years. This life variance controls design of the composite anode which is arranged so segmented replacements may be conveniently made.

Although cast iron and aluminum are known by experiment to serve well in this composite anode, other combinations now appear to provide the beneficial protection wanted. In regard to such combinations, mild steel segments have been provided in lieu of cast iron in reference to ferrous segments. Moreover, segments from the general group of light metals consisting of aluminum, magnesium and zinc have been provided with both cast iron and mild steel. In addition, non-ferrous segments composed of copper and of lead have been provided, observations of these various composite anodes indicate that beneficial protection is obtained.

Illustrated in FIG. 2 is an anode 18 in accordance with the present invention installed in a tank 30 having pipe lines 31 and 32 connected with it. The protection achieved by the present invention system extends not only to the walls of the tank 30, but also protects the pipes 31 and 32 a significant distance therealong from tank 30.

In FIG. 3 there is shown an anode 18 in accordance with the present invention installed in a heating tank 35 which may be seen to comprise a heating element 36 and a baffie 37. Pipes 3'8 and 39' are provided to conduct a liquid into and out of the tank 35, and as before protection extends not only to the interior surfaces to the tank 35 which are in the line of sight of the anode 1'8, but also into the pipes 38 and 39 a significant distance, and to hidden surfaces in the tank 35.

In FIG. 4 there is shown an anode 18 in accordance with the present invention located in a tank 41 forming a part of a system of irregular heating vessels including the additional tanks 42 and 43 which are connected by the various pipes 44, 45, 46 and into which systems of heating vessels there extend pipes 47, 48, and 49. As before, cathodic protection is extended to surfaces which are out of the line of sight of the anode 18.

The above equipment structures are illustrative of additional equipment structures which may be protected effectively by the present invention system, and it is not to be construed that the equipment structures disclosed are the only ones which are capable of protection, as will be understood by those skilled in the art.

In order to demonstrate the superior results achieved with the present invention cathodic protection system, comparative tests were conducted. A test unit comprised a tank of non-metallic material in which was placed a test coupon in the form of a steel plate. The test coupon was placed at one end of the tank, and at the other end there was placed an anode, with one fiat side of the coupon plate facing the anode. Conventional exterior circuitry including a potential source was provided. The tank contained five millimeters of sulfuric acid in 2,000 millimeters of ordinary tap water. Voltage measuring equipment included a high sensitivity voltmeter and copper-copper sulfate electrode. A milliammeter for measuring current was also used. In a first tank, Tank No. 1, a conventional cast iron anode was used: in Tank No. 2, an anode as described herein and as illustrated in FIG. 1 was used: in Tank No. 3, an anode made as disclosed in Smith No. 1,984, 899 was used. Other than the diflerences in the anodes, the three test units were without significant or intended difference.

Relative to the amount of corrosion which occurred to the test coupons, measured after a test extending over a period of about five weeks, and determining weight loss of each coupon by weighing the coupon immediately prior to test, and after the test and after the deposits had been removed and the coupon cleaned to bare metal, it was found that the conventional anode protected coupon had lost approximately 18% of its original weight, that the coupon protected by the anode of Smith No. 1,984,899 had lost approximately 14% of its original weight and that a coupon protected by an anode in accordance with the present invention had lost only approximately 8.4% of its original weight. Hence, the weight loss sustained by the coupon protected by the present invention system and anode had only 60% of the corrosion of the next best anode protective system. And the present invention anode permitted corrosin of only 47% of that permitted by a conventional anode.

Relative to comparative power requirements, the above noted electrodes were utilized to determine the negative potential in front of and in back of each test coupon as related to the anode with which it was associated. In accordance with recognized procedures, 1.3 negative volts for the front electrode was chosen as optimum, and as the testing progressed, the current was changed once each day to bring the potential of the front electrode to that value, from which it had drifted from the previous days setting.

Some four and a half weeks after the initiation of testing, it was found that upon averaging the front and back negative potentials determined by the front and back electrodes, for each test tank setup, and multiplying that negative voltage by the current in milliamperes the power consumption in milli-amp-volts was found to be 650 for Tank No. 1, conventional anode; 11.8 for Tank N0. 2 (invention anode system); 292 for Tank No. 3 (anode of Smith No. 1,984,899). Consequently, it will be seen that after a sufficient period of time for the systems to achieve equilibrium, the power requirements of the present system was approximately l/25 of the power requirements of the next closest protective system.

There has been provided a superior cathodic protection system which is usable to protect both line of sight and hidden or shadow surfaces of various kinds and arrangements of metal esuipment having an aqeous body therein, such as boilers, tanks, pipelines, etc. In addition, the present invention is applicable to such other installations as the digesters of paper mills. Not only is there protection of hidden surfaces or shadow surfaces in such equipment, but the amount of corrosion which results with the utilization of the present invention system is significantly less than that which results when other systems are used. Significant also is the fact that the power consumption for corrosion protection with the present system is greatly reduced in comparison to power consumption of other systems.

What is claimed is:

1. Apparatus for preventing metal corrosion in a vessel having a confining space for liquid comprising an external source of electrical energy and an anode positioned beneath the level of a liquid, said anode comprising a first series of spaced apart segments of ferrous metal and a second series of spaced apart segments of non-ferrous metal, each segment of one series being in alternating relationship with a segment of the other series and each segment being spaced from but closely adjacent to the next adjacent segment, said vessel having at least one surface out of the line of sight of said anode, means electrically connecting said segments in parallel to the positive pole of said source, and means connecting the negative pole of said source to said metal vessel, said external source of electrical energy being sufficiently large and the anode being of sufficient size that hydrogen is generated on all said internal liquid-covered vessel surfaces.

2. The apparatus of claim 1, said ferrous segments being selected from the group consisting of cast iron and steel.

3. The apparatus of claim 1, said non-ferrous segments being selected from the group consisting of aluminum, magnesium, zinc, copper and lead.

4. The apparatus of claim 1, said ferrous segment being cast iron and said non-ferrous segment being aluminum.

5. The method of preventing scale formation on and corrosion of interior surfaces of metal vessels containing liquid comprising the steps of disposing first and second series of ferrous and non-ferrous anode segments in closely spaced relation within said vessel below the level of the liquid therein with each segment of one series alternating with a segment of the other series, providing an electrical power source outside said metal vessel, electrically connecting each of said segments in parallel to the positive pole of said source, connecting the negative pole of said source to said vessel, heating the liquid in said vessel and regulating the electrical power source to maintain a hydrogen overvoltage to effect substantially continuous liberation of hydrogen gas from the decomposition of said liquid in the metal vessel at a location immediately adjacent the metal vessel surfaces to provide protection against scale formation and corrosion of the interior vessel surfaces.

6. The method of claim 5, said liquid being an aqueous liquid.

References Cited UNITED STATES PATENTS 669,922 3/1901 Gottlob 204-196 1,984,899 12/1934 Smith 204147 2,903,405 9/1959 Sabins 204196 3,146,182 8/1964 Sabins 204197 T. TUNG, Primary Examiner U.S. Cl. X.R. 204196, 292.

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