US2021519A - Corrosion preventative - Google Patents

Description

Noy. 19, 1935. H, s. POLIN 2,021,519

CORROSION PREVENTATIVEV Filed Dec 12, 1933 4 h t h e 1 INVENTOR HIT/7551775. PflZ/A/ BY QM p LWA/-M ATTORNEYS Nov. 19, 1935. H. s. POLIN 2,021,519

I CORROSION PREVENTATIVE Filed Dec. 12, 1933 4 s t -s t, 2

'I f I I i r INVENTOR HERBERTS POL //v ATTORNEYS 4 Nov. 19,1935. HSPQUN 2,021,519

CORROSION PREVENTATIVE Filed Dec. 12, 1955 4 Sheets-Sheet 5 NOV. 19, 1 935. H, s, POLIN V I 2,021,519

QORROSION PREVENTATIVE Filed Dec. 12, 1953 4 heets-sheet 4 Patented Nov. 19, 1935' i vPAT,IZNT OFF-ICE ooanosron- PREVENTATIVE Herbert Spencer Polin,

Port 'Washington, N. Y.,

assignmto Polin, Inc., New York, N. Y., a cor-" poration of Delaware Application December 12, 1933, Serlal'No. 701,97

1 claim. (01. 204-25) The present invention relates to method'and apparatus for prevent ng corrosion of metallic. surfaces in contact with gaseous or. liquid fluids.

In accordance with accepted theory a nonc homogeneous metal in contact with an electrolytic or ionizable solution constitutes a multiplicity of simple shortcircuited'voltaic cells, where- I in electronic currents flow. withinthe metalfrom particles of the more reactive'to particles of the -10 nobl'er;

-verse is true, thatis, the'flow' of electronic cur- I metaLqHIhe consequenceis that-the more reac tive metal passes into solution with liberation of l5 hydrogen gasat the surfaces of'the nobler me-i' tallic particles. r

It has heretoforebeen proposed to overcome I corrosion thus produced by suspending in the solution metallic bars, webs, or the like, between 20' which and the metallic surface to be protected, a source of direct voltage is connected with its negative electrode joined to the protected metal.

The magnitude of the resulting electronic current flowing within the solution from the. pro- 25 tected metal to the suspended members is then' adjusted manually, according to the known practices, to equal or exceed the corroding electronic current, due to voltaic cell action, tending to flow into the more-reactive portions of the.pro-

30 tected' surfaces, in consequence of which themore reactive metal isfprevented from passing I ;thin as possible, and it has been found that theseinto solution and the protected surface maintained intact. v s f The dlillculty with known methods whereinthe 85 compensating current flow is manually adjusted to offset the effect of the corroding current, re-

sides in the fact that the latter vary in magnitude within wide limits and more or less continuously. due, for example, to temperature changes, fluc- 40 tuations'tin strength of the electrolytic solution, etc. It therefore the compensating current is manually adjusted to equal the corroding cur- 'rents'for a given instantaneous set :of conditions, subsequent unbalances of one polarity will per- 45 mit 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 50 will be found badly corroded.

. If, on the other hand, the"compensating cur- -rent is established of such large'magnitude as to more than counterbalance for all conditions the. flow of corroding current, the suspended it members will be completely consumed within metal. Within the solution the con-- rent is, from the noble) to the more; reactive such short intervals as to render this expedient impracticable.

The'present invention. eliminates the defects noted by making adjustment of the compensating. current electrically automatic and such that the 5. compensating current can be caused to just balance the corroding current for all fortuitous variations of the latter; or in the alternative the compensat ng current can be made to vary automatically in response to variations of the corroding current, but in such manner as always toexceed the corrodingcurrent bya 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 as desired. It will be appreciated that adjustment of the compensating current to more v 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. i

Although not, limited thereto, the invention is particularly applicable to the condensing apparatus used on li'ghter-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 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 exhaust gases, which in solution form acids, and, being in contact with the metallic condenser tubes, permit electrolytic action to take. place of 40 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 whichv 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 andgrld electron The cathode system of the tube is effectively grounded to the protected Sill":

1 face. Insulatedly suspended in the electrolytic 1 tainer c 'so long as the initial conditions remain solutionor inthe exhaust gases are a pair of conductive elements or screens, whlch may comprise concentric cylindrical mes hes. The susm nded elements are joined respectively to resistors interposed in'the grid and anode circuits of the tube. The connections andelectrical 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 I 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, al-

,though susceptible to fluctuations in magnitude.

cally to compensate for corrosion currents vary-1 ingfortuitouslyin both magnitude and polarity. Fig. 4 shows an arrangement employing a gas;

' eous or glow discharge tube for supplying relav tively large compensating current where required.

be concentric cylinders.

Referring to Fig. 1, there is shown in longitudinal section a. fluid conduit or container C, con taining'either a gaseous medium interspersed by charged particles, such as the exhaust gases of motors, or anmel'ectrolytic 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 ID, here shown as longitudinally spaced but which may Screen D is connected by means of a conductor 5 throughan insulating plug 6, tothe grid G of an electronic tube V.

The cathodeK, of the tube is energized from battery Bi; througha resistor R, variably tapped through leak resistor L to the grid G oi tube V, iorxbiasing the grid ,as desired. The anodecircult of the tube, energized by battery B2, contains a potentiometer P', the midpoint M of. which is tapped by meansof conductor 1 through an insulating plug 8 in the container, to screen 8' therein. The container Q to be protected against .sistor L, as to produce no ap'preciableeflect on meter H. Concurrentiy the space current oicorrosion, is variably tapped at T to potentioin eter P by meansoi conductor" ill containing an ammeter ll. 1 a I v Assuming container C. to be fllledwith an elec- I trolytic solution E, batteries B1 and B: will establish in grid resistor L, with the system as arranged tube- V will, in traversing thepotentiometer P,

establish a potential drop betweenpoints 'I and M thereof, producing an electronic current i:

flowing from container 0 to screen S in the'solution.

It will be observed that current izis 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 actie'n described. For a given set -of -conditions,fconductivity oi the .solution,.etc.,; current i: can be's6 adjusted by variation of potentiometer tap T and by observationon meter I I, as to prevent corrosion of conunaltered.

Assume, however, that by some. fortuitous circuinstance the conductivity of solution I2 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 0,, immediately necessi.

tates an increase in the compensatory current i2, which is the result automatically produced by the vacuum tube system as follows: I

The increasein conductivity of solution E, decreases thetotal resistancein the path traversed by the grid current .11, in consequence of which current i1 increases thereby increasing the volt- A age drop across g'rid 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, in-

creases the voltage. between points T. and M thereof, and hence increases the magnitude of current i: from container C to 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- wouldsufiice. The system of the drawing 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 11 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 curfent is, which again is the result desired.

- tion as do the forces tending to produce corrosion. i

Now .i'rom a series of preliminary tests based on the character or electrolyte or charged gaseous fluidnormally present in container C,i the metallic' structure of the container astwelh as screens 8 and D, etc., 'the optimumvalue of current i: for minimizing corrosion of. all me- ;tallic surfaces, can .be ascertained for various conductivities of the fluid. With this -ini'ormascreen S, which tion preliminarily available, the system can be so designed as automatically to maintain the cur: ,rent. 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 oi' batteries B1 and Bzcharacteristics' of tube V, etc. By suitably proportioning these circuit components the current i1 can not only be made to vary automatically iri the right'direc tion but by just the proper amount to effect optimum compensation for each change in con'du'c-Y tivity of the fluid.

Where, as in the case oiv condensation or ex- ,haust gases'i'rom motors/charged particles of thegaseous medium tend, in dischafging to the grounded pipe I,'to set up a flow oi corroding current to or from the'pipe, optimum compensav v I 2,021,519 zero, since for. this. adjustment the compensating current woulld be equal and opposite to the corroding' current. connection that'if found necessary, the polarity of the compensating current 2': can be reversed in sign as well as adjusted in magnitude by mere 1y shifting the variable tap T to one side orthe other of the midtap M.

' The invention is not. limited to a single tube V for providing the automatically regulated compensating current or voltage. It may be advis able in certain cases to arrange additional tubes in tandem with tube V, in which event the potentiometer P would-be interposed in the anode circuit of a subsequent tube, tube V merely serving to continuously detect the requisite electrical 1 characteristic of fluid E, and to control in accordance therewith the voltage applied to a subships, electro-potentially, between.the various a fluid'medium of corrosive character.

duit system, which may represent the sea water' pipes, the hull, the seawater and stray electrical currents leaking from the electrical conduits, may im'partto the metallic structure a multiplicity of currents varying in sign, potential and magnitude at any moment. The 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 efiectively 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 bedetermined by the metallurgical bulk of this branch, by the area of the source of potential difierence, 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 The coninsulatedly positioned in the fluid medium, the

screens S1, S2, 8:, connected to potentiometers P1, P1, P3, etc., arranged in-the anode circuits of tubes V V2, V3, etc. in the manner of Fig. 1.

Concentric with screens S1, S2, S3, etc., respectively, or appropriately spaced therefrom, are the detector screens D1, D2, D3, etc., joined to the grids of tubes V1, V2, V: 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.

Referring to Fig. l', with a given setting or variable tap T, automatic compensation will' be efiected i'or corroding currents of but one polarity. An arbitrary reversal oi the corroding polarity will necessitate shifting tap 'T from one side to the other of the midtap M. The system of Fig. 3,

It will be observed in this .The detector tubeV1 has its'grid G1 grounded 5 to container C over lead 20, and its cathode connected over lead 2| to adetector screen}? positioned'in contact with the fluid E of container C. Thespace current of tube'V1 traverses a potentiometer P1 variably tapped at T- and Te and connected by means oi conductors 22 and 23, in opposite polarity between grid and cathode oftubes Va and V: respectively. The anode current of tube V: traverses a potentiometer Pa,'the positive terminal of which is 15 connected to a screen S1 in contact with the fluid. with the variable tap T: grounded to container C. Similarly the anode current of tube V: traverses a potentiometer P1, which, in this case, has its positive terminal grounded to container 20 C and its variable tap T3 joined. to screen S: within the container.

In the operation of this system, with, now!- roding voltage applied between screen D and the detector tube grid, tubes V2 and V: are biased 25 to cutofl' by adjustment of the grid taps to resistors R2 and R3, respectively. Assume now that the fluid medium establishes a corroding voltage such as to make the screens negative with respect to thecontainer, therebyestablishing a COI'I'Oding electronic current flow from the fluid. to the container. In order to compensate for the corroding current thus established, tubev V3, which tends to establish a current flow from conduit C to screen S1, as indicated by arrow a, should -become activated. -I I That this is the result effected is apparent from the fact that the corroding-voltage having the polarity assumed, increases in a positive sense the potential of grid G1 of the detectortube 40 cutofl, thereby establishing a flow: of, thefd'esired compensating current from container C in screen S1.

Meantime tube V; remains inactive, because the increased current flow in potentiometer Pi, increasesin a negative sense the potential applied to grid G; of tube Va. Since, tube V: is initially biased to cutoff, the increasingly negative potential of its grid produces no flow'otspace current.

If the corroding voltage is such as increase' in a negative sense the potential'ot the detector grid G1, tube'Vz is maintained inactive, while.

tube Va is rendered increasingly active to establish a flow of compensating current from screen S3 to conduit P.

The circuit of Fig. 4 is ideally adapted to prevent corrosion in extensive conduit, systems, such as the sea water ballast pipe lines oi! battle ships, wherein the total current required for purposes oi 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 electronictube. Under"- f 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. 4 the corroding potentials are detected thermionically by means or the electronlc tube V1 having its grid G1 connected,

through short circuiting contacts of a switch 2 5 to the conduit C, and its. cathode connected to detector screen D positioned in within-the conduit.

, If the fiuid 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 Vi automatic regulation of a grid controlled, glow discharge tube -V2, such that a compensating current is caused to flow between trolled gaseous discharge tubes necessitates pericharge devices, metallic screen's individual thereodically interruptingthe fiow'of space current in order to maintain operationoi the device un-- der control of its grid. To this end tube Vais.

energizedfrom an alternating current source 21 I connected to a transformer 28 having secondary cathode K2, and the other for applying an alternating potential between the cathode K: and

;. the anode A1. V

The magnitude of tube V is regulated under control or tube V1 by connecting its gridGa through the variable, re-'- sistanc'e consisting o1 potentiometer P1 in shunt the fluid medium E windings 30 and II, the one iorfenergizing the space current supplied by the space path resistance of tube V1 in response to variations in its grid potential, produces a plied between grid and cathode of tube V: with respect to that applied between its anode and cathode such as to varyin the manner required relative shift in phase of, alternating current ap for automatic compensation the average "space currentof --tube V2.

Connected in the anode circuit of tube V2 is a low pass filter 32 the output of which termipotentiometer connected to conduit C.

The rectified pulsating current flowing be.-

tween anode and cathode ofv tube V5 is thus converted by the filter 32 into a non-pulsating direct current traversing potentiometer P2, thereby providing the requisite fiow of compensating curren between Iscreen S and conduit C. I

:I claim: i

Means preventing corrosion o! a metallic surface subjected to corrosive action 01 a fiuid comprising, a'plurality 01 grid controlled space disto insulatedly positioned in said fluid, means responsive to the space current of a first said tube. for passing between its associated screen and the metallic surface a compensating current of one polarity, means'similarly responsive to the space. current of a second said tube for passing between its associated screen and the metallic surface acompensating vcurremt i' the opposite polarity, means whereby a third tube detects the potential difference between itsassociate'd screen and the metallic surface tending to produce-corrosion, and means whereby said thirdtube selec-, tively regulates the flow of space current in said .first and second tubes automatically to compensate ior corroding currents varying fortuitously in magnitude and polarity.

i 40 HERBERQI', SPENCER .IPOI'JIZIT.

Images