US2221997A - Corrosion preventative - Google Patents

Description

Nov. 19, 1940." H. s. POLIN 2,221,997

SORROS ION PREVENTAT IVE Filed Nov. 13, 1935 3 Sheets-Sheet 1 INVENTOR Herberl S. P01 in ATTORNEYS Nov. 19, 1940. s PQLIN 2,221,997

CORROSION PREVENTAT IVE Filed Nov. 13, 1935 3 Sheets-Sheet 2 Q l s filhmfib W i w 1 I l I I I l i lNVENTOR ATTORNEYS Herberl 5.1 066 Nov. 19, 1940. H. s. POLIN 2,221,997

CORROSION PREVENTATIVE Filed Nov. 13, 1955 3 Sheets-Sheet 3 INVENTOR Herbeni Slolin M M ll ORNEYS Patented Nov. 19, 1940 PATENT OFFICE CORROSION PREVENTATIVE Herbert S. Polin, Sands Point, Long Island, N. Y., assignor of one-half to Harry A. F n-man,

Schenectady, N. Y.

Application November 13, 1935, Serial No; 49,500

Claims.

The present invention relates to method and apparatus for preventing corrosion of metallic surfaces in contact with gaseous or liquid fluids.

In this case I claim the method or process of g performing the invention set forth in my copending application Serial No. 701,976 for patent on Corrosion preventative filed December 12, 1933, which is now become Patent No. 2,021,519, dated November 19, 1935. The claim of said patent is limited to the apparatus for practicing the said invention.

In accordance with accepted theory a nonhomogeneous metal in contact with an electrolytic or ionizable solution constitutes a multiplicity of simple short circuited voltaic cells, wherein electronic currents flow within the metal from particles of the more reactive to particles of the nobler metal. Within the solution the converse is true, that is, the flow of electronic curgo rent is from the nobler to the more reactive metal. The consequence is that the more reactive metal passes into solution with liberation of hydrogen gas at the surfaces of the nobler metallic particles.

g; It has heretofore been proposed to overcome corrosion thus produced by suspending in the solution metallic bars, webs, or the like, between which and the metallic surface to be protected, a source of direct voltage is connected with its 30 negative electrode joined to the protected metal.

The magnitude of the resultingv electronic current flowing within the solution from the; protected metal to the suspended members is then adjusted manually, according to the known prac- 35 tices, to equal or exceed thecorrodingelectronic" current, due to voltaic cell action, tending to flow into the more reactive portions of the protected surfaces, in consequence of which the more reactive metal is prevented from passing into solution and the protected surface maintained intact.

The difilculty with known methods wherein the compensating current flow is manually adjusted to offset the effect of the corroding current, resides in the fact that the latter vary in magnitude within wide limits and more or less continuously due, for example, to temperature changes, fluctuations in strength of the electrolytic solution, etc. If therefore the com- 50 pensating current is manually adjusted to equal the corroding currents for a given instantaneous set of conditions, subsequent unbalances of one polarity will permit corrosion of the protected surface to proceed, while unbalances of the opposite polarity will entail consumption of the suspended bars or web members. Thus after a period both the protected surface as well as the suspended members will be found badly corroded.

If, on the other hand, the compensating current is-establishecl of such large magnitude as to more than counterbalance for all conditions the flow of corroding current, the suspended members will be completely consumed within such short intervals as to render this expedient impracticable. 1

The present invention eliminates the defects noted by making adjustment of the compensating current electrically automatic and such that the compensating current can be caused to just balance the corroding current for all fortuitous 15 variations of the latter; or in the alternative the compensating current can be made to vary automatically in response to variations of the corroding current, but in such manner as alwaysto exceed the corroding current by a substantially constant amount. Thus the present invention will assure complete and continuous protection of the metal to be preserved, while causing no consumption of the suspended members, or a consumption thereof which can be made as gradual 5 as, desired. It will be appreciated that adjustment of the compensating current to more than counter-balance the corroding current constitutes, in a sense, a factor of safety assuring the elimination of all corroding effects in the protected surface.

Although not limited thereto, the invention is particularly applicable to the condensing apparatus used on lighter-than-air craft, in which the moisture content of the exhaust gases from the motors, is condensed so as to prevent, as far as possible, the lightening of the ship as fuel is burned. Since in airships any excess weight is undesirable, the condensing pipes are made as thin as possible, and it has been found that these pipes are very rapidly corroded by the fuel exhaust gases condensed, necessitating frequent replacement of the pipes.

This corrosion is due partly to the presence of carbon monoxide and carbon dioxide in the ex- 4 haust gases, which in solution form acids, and,

. being in contact with the metallic condenser tubes, permits electrolytic action to take place of the character above described, which is intensifled at the high temperatures of operation. The corrosion is in this instance also due to the fact that some or all of the molecules composing the exhaust gases, are electrically charged, whereby in the condensing process small electric currents are set up which additionally corrode the walls of the tube.

The present invention which compensates and hence eliminates both types of corrosion, employs for maintaining the compensation electrically automatic, a space discharge device, such as an electronic tube having an anode, a cathode and grid electrodes. The cathode system of the tube is effectively grounded to the protected surface. Insulatedly suspended in the electrolytic solution or in the exhaust gases are a pair of conductive elements or screens, which may comprise concentric cylindrical meshes. The suspended elements are joined respectively to resistors interposed in the grid and anode circuits of the tube. The connections and electrical magnitudes are such that changes in conductivity or voltage developed within the fluid medium apply to the grid of the tube instantaneous potentials of proper magnitude and polarity to provide in its anode 'circuit the desired instantaneous value of compensation.

In the drawings: Fig. 1 shows diagrammatically a form of the invention adapted to eliminate corrosion where the corroding currents are of constant polarity, either plus or minus, although susceptible to fluctuations in magnitude.

Fig. 2 shows an adaptation of the Fig. 1 arrangement to an extensive conduit system to be protected.

Fig. 3 shows an arrangement employing a gaseous or glow discharge tube for supplying relatively large compensating current where required.

Referring to Fig. 1, there is shown in longitudinal section a fluid conduit or container C, containing either a gaseous medium interspersed by charged particles, such as the exhaust gases of motors, or an electrolytic medium, or both. Insulatedly mounted within the container, as by porcelain or ceramic supports 2, are a pair of conductive elements or screens S and D, here shown as longitudinally spaced but which may be concentric cylinders. Screen D is connected by means of a conductor 5 through an insulating plug 6, to the grid G of an electronic tube V.

The cathode K, of the tube is energized from battery B1, through a resistor R, variably tapped through leak resistor L to the grid G of tube V, for biasing the grid as desired. The anode circuit of the tube, energized by battery B2, contains a potentiometer P, the midpoint M of which is tapped by means of conductor 1 through an insulating plug 8 in the container, to screen S therein. The container C to be protected against corrosion, is variably tapped at T to potentiometer P by means of conductor I0 containing an ammeter l-I.

Assuming container C to be filled with an electrolytic solution E, batteries Bi and B2 will establish in grid resistor L, with the system as arranged in the drawings, an electronic current i1 flowing in the solution from screen D to the container C returning over conductor 5. This current will be so small, due to the large value of the grid resistor L, as to produce no appreciable effect on meter H. Concurrently the space current of tube V will, in traversing the potentiometer P, establish a potential drop between points T and M thereof, producing an electronic current i2 flowing from container C to screen S in the solution.

It will be observed that current i: is in the right direction to compensate or counterbalance the electronic current flowing into the more active metal portions of container C in consequence of the voltaic cell action described. For a. given set of conditions, conductivity of the solution, etc., current i2 can be so adjusted by variation of potentiometer tap T and by observation on meter I I, as to prevent corrosion of container C so long as the initial conditions remain unaltered.

Assume, however, that by some fortuitous circumstance the conductivity of solution l2 should increase, as by increase of temperature, increase of concentration, etc. The resulting increase in corrosive voltaic cell action established between the more and less active portions of the nonhomogeneous container C, immediately necessitates an increase in the compensatory current i2, which is the result automatically produced by the vacuum tube system as follows:

The increase in conductivity of solution E, decreases the total resistance in the path traversed by the grid current ii, in consequence of which current i1 increases thereby increasing the voltage drop across grid resistor L, and thus increasing in a positive sense the biasing potential applied to control grid G. This produces an increase of space or anode current in tube V, which in traversing the potentiometer P, increases the voltage between points T and M thereof, and hence increases the magnitude of current i2 from container C to screen S, which is the result desired.

If on the other hand the conductivity of solution E should decrease, the corroding currents would decrease and a smaller compensating current i2 would suflice. The system of the drawings automatically provides for this in a manner which is just the converse of that above described for an increase in conductivity of the solution. As the conductivity of the solution decreases, the grid current i1 likewise decreases, thereby decreasing in a positive sense or increasing in a negative sense the biasing potential applied to grid G. This decreases the space current of tube V, and hence the magnitude of the compensating current i2, which again is the result desired.

Therefore, irrespective of whether the conductivity of solution E increases or decreases from a given condition, the compensating current i: will automatically vary in the same direction along with it, that is current 1: always varies automatically in magnitude in the same direction as do the forces tending to produce corrosion.

Now from a. series of preliminary tests based on the character of electrolyte or charged gaseous fluid normally present in container C, the metallic structure of the container as well as screens S and D, etc., the optimum value of current i2 for minimizing corrosion of all metallic surfaces, can be ascertained for various conductivities of the fluid. With this information preliminarily available, the system can be so designed as automatically to maintain the current 1': at its optimum value throughout the range of fluid conductivities encountered in practice. Factors determinative of this design are the resistances of L and potentiometer P, the magnitude of batteries B1 and B2, characteristics of tube V, etc. By suitably proportioning these circuit components the current i2 can not only be made to vary automatically in the right direction but by just the proper amount to effect optimum compensation for each change in conductivity of the fluid.

Where, as in the case of condensation of exhaust gases from motors, charged particles of the gaseous medium tend, in discharging to the grounded pipe I, to set up a flow of corroding current to or from the pipe, optimum compensation may be effected by so adjusting the compensating current i2 th9,t. the meter deflection is zero, since for this adjustment the compensating current would be equal and opposite to the corroding current. It will be observed in this connection that if found necessary, the polarity of the compensating current i2 can be reversed in-sign as well as adjusted in magnitude by merely shifting the variabletap T to one side or the other of the mid- E I .ffIl'iefinvention is not limited to a single tube V for providing the automatically regulated compensating current or voltage. It may be advisable in"certain' cases to arrange additional tubes in tandem with tube V, in which event the potentigmeter P would be interposed in the anode circhit of ag'subsaquent tube, tube V merely serving to continuously detect the requisite electrical characteristic of fluid E, and to control in accordance therewith the voltage applied to a subsequent tube, which in turn would provide the proper compensating voltage or current.

In this connection the employment of a plurality of tubes in tandem provides a means alternative to the mid-tap M of potentiometer P for reversing the polarity of the compensating voltage. Thus the midtap M could conveniently be shifted to the lower terminal of the potentiometer.

In the case of a large ship, complex relationships, electro-potentially, between the various pipes, the hull, the sea water and stray electrical currents leaking from the electrical conduits, may impart to the metallic structure a multiplicity of currents varying in sign, potential and magnitude at any moment. 'Ijhe system herein described provides for the installation of a detecting and distribution panel identified with an electrical network throughout the ship, and with a central power supply located at the distribution panel so introduced into each circuit as to effectively neutralize the many and variable currents flowing at those points located as major potential difference sources. The area of efiectiveness of each neutralizing circuit may be determined by the metallurgical bulk of this branch, by the areaof the source of potential difference, and by the proximity of the neutralizing system to each source.

Fig. 2 shows the manner of adapting the invention to a continuous conduit system traversed by a fluid medium of corrosive character. The conduit system, which may represent the sea water damage control mains of a battleship, etc., comprises pipe sections C1, C2, Ca, etc. At appropriate intervals, as best determined by tests on the particular system under consideration, are

insulatedly positioned in the fluid medium, the screens S1. S2, S3, connected to potentiometers P1, P2, P3, etc., arranged in the anode circuits of tubes V1, V2, V3, etc. in the manner of Fig. l. Concentric with screens S1, S2, Sc, etc., respectively, or appropriately spaced therefrom, are the detector screens D1, D2, D3, etc., joined to the grids of tubes V1, V2, V3 respectively. All of the tubes are energized from the common filament and space current supply sources B1 and B2, as shown. In the operation of the system the variable arms of the potentiometers P are individually adjusted to eliminate corrosion in the particular pipe section containing the associated screens S and D.

The circuit of Fig. 3 is ideally adapted to prevent corrosion in extensive conduit systems, such as the sea water ballast pipe lines of battleships, wherein the total current required for purposes of compensating the corroding currents, is relatively large, and may be considerably in excess of that which can be conveniently supplied by the space current of an electronic tube- Under such circumstances resort may be had to gaseous or glow discharge tubes, such for example as that known as the Thyratron, for providing the compensating current.

In the circuit of Fig. 3 the corroding potentials are detected thermionically by means of the electronic tube V1 having its grid G1 connected, through short circuiting contacts of a switch 25 to the conduit C, and its cathode connected to detector screen D positioned in the fiuid medium E within the conduit.

If the fluid E comprises an electrically charged gaseous medium, a. potential will be established on grid G1 determined by the polarity and magnitude of the charge existing between screen D and the conduit C. If on the other hand the fluid is an ionized liquid, switch 25 may be operated to connect the battery 26 in the grid circuit, in order to establish a current flow in the resistor L1, the voltage drop across which will depend upon the conductivity of the electrolyte.

In any event the corroding forces thus detected establish, by variation in the space path resistance of tube V1 automatic regulation of a grid controlled, glow discharge tube V2, such that a compensating current is caused to flow between screen S and conduit C which varies in conformity with the corroding forces.

As is well known, the operation of grid controlled gaseous discharge tubes necessitates periodically interrupting the flow of space current in orderto maintain operation of the device under control of its grid. To this end tube V2 is energized from an alternating current source 21 connected to a transformer 28 having secondary windings 30 and 3|, the one for energizing the cathode K2, and the other for applying an alternating potential between the cathode K2 and the anode A2.

The magnitude of space current supplied-by tube V2 is regulated under control of tube V1 by connecting its grid G2 through the variable resistance consisting of potentiometer P1 in shunt to the space path resistance of tube V1, and thence to cathode K2 through a secondary winding 29 of transformer 28. An inductance 33 is connected between grid G2 and anode A2. With the elements properly proportioned, variation in the space path resistance of tube V1 inresponse to variations in its grid potential, produces a relative shift in phase of alternating current applied between grid and cathode of tube V2 with respect to that applied between its anode and cathode such as to vary in the manner required for automatic compensation the average space current of tube V2.

Connected in the anode circuit of tube V2 is a low pass filter 32 the output of which terminates in a potentiometer P2 variably tapped at T2 to screen S, with the positive terminal of potentiometer connected to conduit C.

The rectified pulsating current flowing between anode and cathode of tube V2 is thus converted by the filter 32 into a non-pulsating direct current traversing potentiometer P2, thereby providing the requisite flow of compensating current between screen S and conduit 0.

What I claim is:

l. The method of preventing corrosion of a metal subjected to electrolytic action of the fluid which comprises, continuously detecting the potential difference between the metal and the fluid, utilizing the detected potential difference for controlling and varying a spacedischarge current, causing said space discharge current to apply a compensating voltage between the metal and the fluid in opposition to the detected potential difference, whereby the potential difference tending to produce corroding currents is continuously counterbalanced by the compensating voltage.

2. Means preventing corrosion of a metal surface subjected to electrolytic action of the fluid comprising, a pair of metallic members insulatedly positioned in said fluid, a space discharge device having an anode, a cathode and a control electrode, means responsive to space current of said tube and including one said metallic member for passing through said surface a compensating current of opposite polarity to the current causing corrosion, and means including the second said metallic member and said control electrode for automatically varying the compensating current to continuously counterbalance variations of the corroding current.

3. Means preventing corrosion of a metallic surface subjected to electrolytic action of a fluid comprising, a pair of metallic members insulatedly positioned in said fluid, a space discharge device having an anode, a cathode and a control electrode, means responsive to space current of said tube for applying between the metallic surface and one said metallic member a compensating voltage in opposition to the voltage tending to cause corrosion, and means including the second said metallic member and said control electrode for automatically so varying the compensating voltage as to continuously counterbalance the voltage tending to cause corrosion.

4. Means preventing corrosion of a metallic surface subjected to electrolytic action of a fluid comprising, a pair of metallic screens insulatedly positioned in said fluid, a thermionic tube having an anode, a cathode and a grid electrode, an energizing connection between said anode and cathode, potentiometric means interposed in said connection for impressing between the metallic surface and one said screen a compensating voltage of opposite polarity to the voltage tending to cause corrosion, and means including a resistance between said grid and cathode and a connection therefrom to said second screen for automatically so varying the compensating voltage as continuously to counterbalance the voltage tending to cause corrosion.

5. Means preventing corrosion of a metallic surface subjected to electrolytic action of a fluid comprising, a pair of metallic screens insulatedly positioned in said fluid, a thermionic tube having an anode, a cathode and a grid electrode, an energizing connection between said anode and cathode, potentiometric means interposed in said connection for passing between the metallic surface and one said screen a compensating current of opposite polarity to the current causing corrosion, and means including a resistance between said grid and cathode and a connection therefrom to said second screen for automatically so varying the compensating current as continuously to counterbalance the currents causing corrosion.

HERBERT S. POLIN. V

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