US2744863A - Cathodic protection of metal in vapor space - Google Patents

Description

o. E. ANDRUS 2,744,863

CATHODIC PROTECTION OF METAL IN VAPOR SPACE May 8, 1956 Filed Oct. 25 1951 INVENToR. Orrm E Andrus BY @mq/WAV ATTORNEYS.

nited States Patent CATIv-GDIC'PROTECTIGNOF METAL 1N VAPQR'.f

SPACE Orrin E. Andrns, Milwaukee, Wis;,'assignor to A. O. Smith Corporation, Milwaukee, Wis.,a corporation of New York- Applicationctoberf25, 1951, Serial No. 253,060 4 Claims. .(Cl. 21M- 196) electrolyteor the surface was in contact with a substance,

such as earth or soil, bearing an electrolyte. Surfaces in contact with vapors have not been protected cathodically in a commercial manner.

The .'present invention is directed to ameans o f cathodically protecting metal-surfaces which are in contact with a vaporous mediumfthatis capable of conducting an electric current whencondensed. To carryout the invention, the metal surface to be protected is 'initially coated withan absorbent material such as felt, asbestos fiber, or the like.I An expendable perforated metal liner isapplied* to the coated 'surface' with the `intermediate labsorbent coating Vserving to separate-one metal surface from Thecorrosive-,condensate in the Vapor-region-passes between -the linen-plates and is absorbed -inl the insulating" coatingjto-formv an electrolyte therein;A

Corrosion of the expendable liner maythen be pro moted--by eitherapplying a--lowl-voltage current -tothe unit withthe liner-'being madeY the anode and the surface to be protected-,the cathode,- or secondly, by employing a metal which-isanodic tothe -surfacef-to-be protected as the liner and providing-electrical-contact-between-saidsurface-andthe linen-such asby a number-of4 retaining studs-- One object of the present-invention is' tovprovide an -Y effective means of-cathodically protectinga'metal-surface in contact with a Vaporous--medium which-is Icapable ofv conducting arr electrical current when condensed.

Anotherobject of the invention is-A to provide an elec-- tzrolyte-inr the `vapor-or sprayfregiont. which establishes` electrical-1contact ibetweenthe -1netal1surface-Ltol be protected-4 and :a second-expendable metal, surface'.-

Still another objectissto provide .a simple .and inerty pensive :methQd-Jof protecting;metalisurfaces.exposed-xto- 'r1 corrosive?condensatelirr. the vaporIV region-pwherebyr ythe condeuatefis absorbed .in an insulating material and functions as, an electrolyte.

In the drawingsgtx,

taininghjthe present invention;

Figfllis an enlarged fragmentary sectional-.view showing the attachment of the invention to the tank surfaces;

FigJ-S-is a second embodiment of-the invention showing a sideelevationpartially-insection-of a tank containfing the inventiongiand w1' Fi g.1.'=4 :is an; enlarged `fragmentaryi sectional `View showa ing .the :.a-.ttacli.menty 1of` the embodiment, l.of Figrto; the

taule-surface..

'ice

Referring to the drawings, there is.shown.in.Figures. 1... and 2 an embodiment -of the present invention. as applied. to a .tank..1 .Whichis-.to be protected cathodically. from corrosive vapors..

Tank 1 is Vadapted to contain Water or any other liquidv 2 which will evaporate andsaturate the .air abovel the liquid level with vaporwhich in itself is capabley of con,

ducting an electrical current when condensed. Tank .1,

comprises a generally cylindrical.body section 3 havingv the upper end thereof enclosed by a roof member 4 and the bottom thereof enclosed by a floor 5.

Roof member 4 and floorl 5 are secured. to body sectiony 3 by welding to provide an integralleak-tight container. Tank 1 is constructed. of' steel or any high-strength Imetal and is designed with a..thicl 'ness to withstand the force.

ofthe internal pressure exerted by the contained water or liquid.

As shownin the first embodiment of the invention the inner surface of tank 1.`is.covered with a protective'coating 6,N such as glass, plastic, enamel or the like. Coating 6, as applied, may contain"v minute imperfections,

cracks or discontinuities. The-vapor. contained. within tank. 1 may condense at the tank surface and penetrate into.. these imperfections `causing..intensified corrosion of the tank at the p ointof penetration.

To protect the tank from this'corrosion, a porous .ab-L sorbent insulating material-7,1such as felt,.asbestos ber; f

glass wool or the like is applied to the 'inner rsurfaces of tank 1' which are to be exposed'to the condensed' vapor.V y

A metal linerV 8 is disposed against theinsulatingmate.- rial 7 to conne the same, and the materia1;7 serves kto separate .and insulatethe metal tank. 1 from the metal Liner -8 may consist-'of largeor small areasv of scrap steel-or other metal,v `or it may consist of sections of perforated metal'plate,--'as shown-in the drawings. Since Y' the liner-8 is not intended togivey physical'strengthitothe -tank or to prevent loss of lluid therefrom; it is con- I venient and -practical-to'butt the edges of the liner plates' without joining orsealing the same.

AThe-corrosive condensate-inA the vapor region oftank 1 may thus reach the absorbent-insulating material -7-and be absorbed therein. --Liner--S functions -as-v anV expendable anode, as will-be hereinafter-described.-

Liner-S--isJ secured-to tank l-by a pluralityl'of stud's 9 which are -welded to the inner-surface of the tank.

Studs I9 project inwardly through coating-6, insulating material 7,- and extend through suitable-openings in liner 8. --A sleeve-10 cennposedof an insulatingmaterialfis disposed around each stud 9 and the annularflang'e '11 of sleeve- 10 bears against'the outer surface/'ofliner -8.=

Sleeves-10 serve to-maintain studs i9 o`t of contact=with=-" linerI-S-an'd preventelectrical conduction-bymetallie con` t tact therebetween. --The outer-threadedlendof each stud 9 receives a-Ametal washer-12 andisengaged by a-'nut 13. A portionofl the lvapor-forming at the-liquidlevel in tank l-rtends---to penetrate behind lirierfsheetsS and condense on the inner surfacei'of tank 1H and'wet insu-' lating material 7.. This condensed vaporwhich is absorbed' in the insulating material functions as an electrolyte' and provides; electricalcontact through defects in coating between tank surfaces 1 and liner.8.

A sourceof low-voltage current, such as a rectier ,or

generatorlt; may-be employed to apply direct current to the tank land liner 8. A lead lconnects-the generator or other ,source of current to'a .suitableterminal `on the tank- 1.-.

Patented. May 8, 195.6.

A second `lead-16 extends from generatorl .w throughnan insulatedopening, in tank --1 ,and coating ,6r y. and-.is connected-to:aterminalfon liner.8.-\ As tank 1i .isf the surface,which-iis. to be-y cathodically :protected against corrosion, it is made the cathode, and liner 8 is made the anode.

The insulating material 7 and liner 8 is applied to all the tank surfaces 1 which are apt to be continually or intermittently exposed to the contained vapor through the defects in coating 6. lf the liquid in tank l is to be maintained at a constant level, the insulating material need only extend upwardly from a point slightly below the fixed liquid level in order to embrace the tank surfaces exposed to the vapor. In this case the tank surfaces below theliquid level may be cathodically protected by commonly known means. However, if the liquid level in tank l is apt to fluctuate or if the tank is periodically emptied and filled, the entire internal surface of tank 1 will, at one time or another, be exposed to the vapor and thus should be coated with the insulating material 7 and liner tl.

A second embodiment of the present invention is shown in Figs. 3 and 4 as applied to a tank 17 bearing no protective coating, such as glass or plastic but otherwise corresponding to tank 1 in the previous embodiment.

An absorbent insulating material i8, such as glass fiber` felt or the like, is applied to the inner surface of tank 17.

An expendable metal liner 19, similar to liner S previously described, is disposed against insulating material 18 and secured to tank 17 by a plurality of studs 26.

Studs 2t) are welded to the inner surface of tank 17 and provide electrical contact between tank i7 and liner 19. Studs extend inwardly through insulating material 1S and through suitable openings in liner 19. The outer end of each stud 20 is engaged by a retaining nut 2l or is otherwise secured.

Liner 19 may consist of separate pieces of aluminum, magnesium, zinc or any metal which is anodic to the metal of the tank 17, or liner 19 may consist of a number of perforated plates of the aforementioned class of metals. The condensed vapor which is absorbed in material 18 functions as an electrolyte and is capable of conducting an electrical current. Thus the anodic metal liner 19 is corroded by galvanic action and the tank i7 is protected from corrosion until the liner 19 is expended.

To promote corrosion of the expendable liner 19, it may be preferred to insulate liner 19 from tank i7 instead of providing electrical contact therebetween through studs 20 and to apply a low voltage current to the system, as described in the first embodiment, with the liner being made the anode and the tank the cathode.

Conversely, in the first embodiment, electrical contact between tank l and liner 8 may be provided through uninsulated studs and a dissimilar anodic metal used as the anode to promote corrosion of the expendable liner.

The present invention may be employed to protect metal surfaces from any type of vapor which will conduct an electric current when condensed, such as water, salts, acids or the like.

The metal surfaces to be protected may include such articles as pier piles or dredge boats and equipment which are intermittently subjected to water spray and varying water levels due to tides, or to any type of metal tanks, such as petroleum storage tanks which are to be protected from hydrogen sulfide and water vapor.

Various embodiments may be employed within the scope of the following claims.

l claim:

l. A cathodically protected metal article, which comprises a first metallic member having a surface subject to corrosion when exposed to a liquid capable of conducting an eectric current, a second metallic member extending substantially coextensively with said first member and in spaced relation thereto and having a plurality of openings therein, a plurality of spaced metal means extending from one member to the other said member to support the members in fixed spaced relation and provide a clearance between the members into which the openings in the second member communicate for passage of said liquid, electrically insulating absorbent material confined within the clearance between the members and adapted to absorb said liquid with the absorbed liquid functioning as an electrolyte to provide an electrical connection between the members through said electrolyte, and means electrically connecting said first and second members other than said electrolyte to provide a second electrical connection between the members and to complete the electric circuit between said members, the said first member being the cathode and the second member the anode in said circuit to thereby promote corrosion of the second member and inhibit corrosion of the first member.

2. A cathodically protected storage structure comprising, a metallic container having an inner surface exposed to corrosive condensate in a vapor region, a metallic liner disposed within the container and extending generally coextensive with said inner container surface and being spaced from said surface to provide` a clearance therebetween, said liner having a series of discontinuities ex tending therethrough and communicating with said clearance, means for attaching said liner in spaced relation to said container, a layer of fibrous absorbent electrically insulating material confined within said clearance and adapted to absorb condensed vapors with the condensate serving as an electrolyte therein, and means for electrically connecting said liner and said container to complete an electric circuit through said container and liner and electrolyte, with said container being disposed as the cathode in the circuit and the said liner the anode in the circuit to thereby inhibit corrosion of said container and promote corrosion of said liner.

3. A cathodically protected metal article, which comprises a first metallic member having a surface subject to corrosion when exposed to a liquid capable of conducting an electric current, a second metallic member extending substantially coextensively with said first member and in spaced relation thereto and having a plurality of openings therein, a plurality of spaced metal means extending between each of said members and secured thereto to support the members in spaced relation and provide a clearance between the members into which the openings in the second member communicate for passage of said liquid, said spaced metal means providing an electrical connection between the members, and electrically insulating absorbent material confined Within the clearance between the members and adapted to absorb said liquid with the absorbed liquid functioning as an electrolyte to provide an electrical connection between the members through the electrolyte and to complete the electrical circuit between the members, the said first member being of a metal cathodic to the second member to thereby promote corrosion of the second member and inhibit corrosion of the first member.

4. A cathodically protected metal article, which com- V prises a first metallic member having a surface subject to corrosion when exposed to a liquid capable of conducting an electric current, a second metallic member extending substantially coextensively with said rst member and in spaced relation thereto and having a plurality of openings therein, a plurality of spaced metal means extending between each of said members to support the members in spaced relation and provide a clearance between the members into which the openings in the second member communicate for passage of said liquid, electrically insulating absorbent material confined within the clearance between the members and adapted to absorb said liquid with the absorbed liquid functioning as an electrolyte to provide an electrical connection between the members through said electrolyte, means electrically connecting said first and second members to complete theelectric circuit between the members and the electrolyte, and a source of low Voltage current connected to said `connecting means to provide a current to said connecting means with the first member being the cathode and the second member the anode in said circuit to 5 6 thereby promote corrosion of the second member and 2,020,844 Magos et al. NOV. 12, 1935 inhibit corrosion of the rst member. 2,267,361 Andrus Dec. 23, 1941 2,273,897 Scott Feb. 24, 1942 References Cited in the le of this patent 2,485,276 Gerbes Oct. 18, 1949 5 2,491,225 Stearns Dec. 13, 1949 UNITED STATES PATENTS 1,512,557 Mills Oct. 21, 1924

Claims (1)

1. A CATHODICALLY PROTECTED METAL ARTICLE, WHICH COMPRISES A FIRST METALLIC MEMBER HAVING A SURFACE SUBJECT TO CORROSION WHEN EXPOSED TO A LIQUID CAPABLE OF CONDUCTING AN ELECTRIC CURRENT, A SECOND METALLIC MEMBER EXTENDING SUBSTANTIALLY COEXTENSIVELY WITH SAID FIRST MEMBER AND IN SPACED RELATION THERETO AND HAVING A PLURALITY OF OPENINGS THEREIN, A PLURALITY OF SPACED METAL MEANS EXTENDING FROM ONE MEMBER TO THE OTHER SAID MEMBER TO SUPPORT THE MEMBERS IN FIXED SPACED RELATION AND PROVIDE A CLEARANCE BETWEEN THE MEMBERS INTO WHICH THE OPENINGS IN THE SECOND MEMBER COMMUNICATE FOR PASSAGE OF SAID LIQUID, ELECTRICALLY INSULATING ABSORBENT MATERIAL CONFINED WITHIN THE CLEARANCE BETWEEN THE MEMBERS AND ADAPTED TO ABSORB SAID LIQUID WITH THE ABSORBED LIQUID FUNCTIONING AS AN ELECTROLYTE TO PROVIDE AN ELECTRICAL CONNECTION BETWEEN THE MEMBERS THROUGH SAID ELECTROLYTE, AND MEANS ELECTRICALLY CONNECTING SAID FIRST AND SECOND MEMBERS OTHER THAN SAID ELECTROLYTE TO PROVIDE A SECOND ELECTRICAL CONNECTION BETWEEN THE MEMBERS AND TO COMPLETE THE ELECTRIC CIRCUIT BETWEEN SAID MEMBERS, THE SAID FIRST MEMBER BEING THE CATHODE AND THE SECOND MEMBER THE ANODE IN SAID CIRCUIT TO THEREBY PROMOTE CORROSION OF THE SECOND MEMBER AND INHIBIT CORROSION OF THE FIRST MEMBER.

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