US2491225A - Method of protecting subterranean metallic structures - Google Patents

Description

Patented Dec. 13, 1949 UNIT ED STATES v. PA-T-El`1'l`f OFFICE METHODmOFgPROSIECTING SUBTERR'ANEAN- i METALLIC STRUCTURES' Y Dick E.V Stearns; Shreveport, La.v

Application Octoberxl, 1944,- Serial hlm-558,924

5 Claims.' (Cl. 204-147) This invention .relatesto `method and. means, of protecting subterranean or. buried metallic. structures from electrolysis and corrosiondue. to local action.

It is common.practicettoprevent such electrolysis andv corrosion-.oisubsurface structures such as pipe lines or thelike vby .applyingto .the structure adirectcur-rent `volt'age'oi suchpolarity as to'causev the currenttolowin a direction to make deposit on the pipeline rather than to take material` from thepipe lineY or, other. structure. Such structuresV are usually:Ak coated. .with an insulating material but suchinsulationeither has or develops weakA spots .at which, .accelerated corrosion or electrolysistakes place `andthe electrical protection justy referred to tends .tcstopor atleast eife'ctively inhibit.thedeterioration otthe pipe line or other ,structureat such defective spotsin the insulation.

In applying. sucha voltage to a subterranean structure, theA present custom is, to.. install an anode yat a substantialdistance.away fromv the pipe line .so .thatdirect .current .induced tolow from.. the anode Yto ythepipe line willbe spread over asubstantial length of. the pipeline. Because of the relative nearness of the conventional anode-tothe pipeline-as compared to the extent of the pipe line over which protection from corrosion is desired,v there isV substantial wastage of electrical energy between the two extremities (of 0 the pipe linesectionunder Iprotection) receiving i the critical amount of potential required for protection. Efforts haveabeen-pmade'with a degree of success towards increasing over-all efficiency byV using several smaller units'over a given extent of pipe line rather thanr'having only one lunit therefor. At best, howeverythefprotection units with the present system-must ine-placed every-few miles along apipe-line lor similar structurein order to give the'necessary prOtection and even then the protection afforded is not uniform and is unreliable.

lAs 'an example 'of `one ofthe vproblems encountered'with the Apresently used system, there is a result known as interferenceiwhich occurs where two structures, one. of whichisprotected by the usual method,... approachA onerosa-each other. Someoffthe current from..v the buried anode williowto anadacent. portion o the other structure, thence along that structure to the point ci nearest approach of the two structures, and then across to the structure being protected. This does not hurt the structure being protected, but will quickly eat away or cori-ode the other structure and destroy it.

The present. invention. has for .its principal and general objectthe provision of fully adequate and reliable protection for a pipeline or similar struct ture buried in the earth or .otherwise made subject to corrosiondue to electrolysisand local electro? chemical action..

More specically itis an object of the present invention to provide more yadequate .protection for such a structure with a smaller number oi units than now necessaryandto make it. possible to place such units at the most convenient points on the structure., Another object Voftheloresent invention isV to provide a means for more adequatelycontrolling the current flow by which the protection is' secured, as` compared with. inadequate current control of the methods heretofore used..

Another object is to avoid the interference above described...

Other objects and advantages of this invention 'willbecome apparent from the followingdescription taken in connection with" the accompanying drawing wherein is set forth b'y way of illustration and example Vone embodiment of this invention.

In the drawing;

Fig. 1 is a view partly in. elevation Yand partly in longitudinal cross section through a pipe line, illustratingY the apparatus employed and the method of carrying jout'the present invention.

Fig. 2is atransverse crosssection'taken along the line '2"-2'of Fig; l. Y

Fig. 3 isa diagrammatic illustration showing the. applicationof the protective voltage to a pipe or similar object 'to be protected in. accordance with this invention.

Referring more in detail to the drawing, the numeral l illustrates. a pipeline which in this particular instance is' the structure to be. protected.' This pipeline .isprovidedwith an insulating coating 2 'which' may generallyv speaking be of the type presently.4 employed on suchlstruc'- tures such asy enamels or coatings having a coaltar base oranyother suitablecoating material.

V,Such acoating k2 manif. desired,.be wrapped'inV a manner .suchlas now employed with a suitable brous insulating wrapper such. as indicated at 3. It. willbe .understood that `upto this point. the 'practice described is thesame. as that.. employed in connection vwith `the. present protection of buried pipe lines'.

In accordance with the present invention, there is added to the coatings on the structure to be protected, a sheathing or wrapping of sheet metal or metal foil 4. This sheet metal or metal foil may be of any suitable material but is preferably of some very light and thin material such as aluminum foil and is preferably of such a nature as to cover the entire or substantially the entire surface of the exterior of the insulated structure. With a pipe line or other structure coated or wrapped as just described, it is put in place in the ground or in such other position as would subject it to electrolysis and local action, and the negative pole of a direct current Voltage is applied to the structure to be protected the same as in the present system of protecting such structures. However, instead of connecting the other pole to an electrode buried at a substantial distance from the structure to be protected, the other pole is connected directly to the sheathing 4 which covers substantially the entire surface of the insulation over the structure to be protected.

Inasmuch as the sheathing 4 is made of metal, and preferably of a metal which has a very low electrical resistance, it will assume substantially the same potential throughout its extent, because unless there are holes in the insulating coating underneath this sheathing, there will be substantially no flow of current. Even if there is a considerable iiow of current, the extent of the metal sheathing provides a substantial path for the flow of current and hence would tend to minimize any voltage drop due to such ow.

Inasmuch as the protective voltage is applied substantially uniformly over the entire surface of the structure to be protected, and at a position closely adjacent such structure, the protection afforded Will be uniform and the voltage for providing such protection may be substantially lower than that which has heretofore been employed. Furthermore, due to the excellent path provided for current flow and the fact that the anode extends along, substantially parallel to and in close proximity to the structure to be protected,

only a relatively few points of application of the voltage will be necessary and these may be located more nearly where they may be conveniently tended. Also since the sheath which forms the anode is close to the structure protected at all points and is between that structure and any adjacent structure, there will be no possibility of interference such as above described.

Although the method and means for protecting subterranean structures has been described as applied to buried pipe lines or the like, it will be appreciated that it may also be applied to other structures such as buried tanks, cables and in fact any structure which is in such a location that it is subjected to corrosion due to electrolysis and local action.

It will also be appreciated that by the apparatus and method just described there has been provided a means for carrying out and accomplishing all of the objects and advantages sought by this invention.

Having described my invention, I claim:

1. The method of protecting buried metallic structures from corrosion due to electrolysis and local action, which comprises coating the same the positive and negative poles of a source of di- 4 rect current electric voltage to said sheath and metallic structure respectively.

2. The method of protecting buried metallic structures from corrosion due to electrolysis and local action, which comprises coating the same with an electrical insulator, sheathing the insulated coating of such structure with an electrically conductive sheath of sheet metal of foil thickness in close relation thereto, and applying the positive and negative poles of a source of direct current electric voltage to said sheath and metallic structure respectively.

3. The method of protecting buried metallic structures from corrosion due to electrolysis and local action, which comprises coating the same with an electrical insulator, wrapping the coated structure with a thin metallic sheathing of foil thickness applied spirally over substantially the entire exterior surface of the structure in close relation thereto, and applying the positive and negative poles of a source of direct current electric voltage to said wrapping and said metallic structure respectively. v

4. The method of protecting a pipe line of electrically conducting material to be buried in the ground from corrosion due to electrolysis and local action comprising the steps of coating the pipe line exteriorally with insulating material, applying a thin sheet of metal surrounding the insulating material in close relation thereto and applying the positive and negative poles of a source of direct current electric voltage to the sheet and pipe line, respectively.

5. The method of protecting a pipe line of electrlcally conducting material to be buried in the ground from corrosion due to electrolysis and local action comprising the steps of coating the pipe line exteriorally with insulating plastic material, then wrapping the coated pipe line spirally with a fibrous wrapper, then wrapping the thus coated pipe line with a metal wrapper of foil thickness in close relation with the fibrous wrapper and then applying the positive and negative poles of a source of direct current electric voltage to the metallic wrapping and pipe line, respectively.

DICK E. STEARNS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 843,357 Partee et al. Feb. 5, 1907 1,096,177 Marino May 12, 1914 1,867,984 Pistor July 19, 1932 1,871,125 McGary et al Aug. 9, 1932 FOREIGN PATENTS Number Country Date 249,714 vItaly Aug. 7, 1926 408,799 Germany Jan. 30, 1925 OTHER REFERENCES Transactions of the Electrochemical Society, vol. 64 (1933), pages 115 to 123.

Technologic Papers of the Bureau of Stand ards, No. 52, Dec. 27, 1915, pages 33 to A37.

Images