US2273897A - Method of and means for electrically protecting against corrosion partially submerged linear metallic structures - Google Patents

Description

Fb. 24, 1942. OTT 7 2,273,897

G. N. SC METHOD OF AND MEANS FOR ELECTRICALLY PROTECTING AGAINST CORROSION- PARTIALLY SUBMERGED LINEAR METALLIC STRUCTURES Filed NOV. 10, 1937 a "II- $3 r 'INVENTOR 8" 3 u 1|; g. Gordon N. 50072 BY f I I ATTORNEY "UNITED STATES PATENT OFFICE METHOD OF AND MEANS'FOR ELECTRICAL- LY PROTECTING AGAIN ST CORROSION PARTIALLY SUBMERGED LINEAR METAL- LIC STRUCTURES Gordon NhScott, Los Angeles, Calif.

Application November 10, 1937, Serial No. 173,864

3 Claims.

This invention relates to methods of electrically protecting against corrosion pipe lines, piles and other metallic structures which pass from water to air and is particularlyapplicable where the surface elevation of the water is subjected to tidal variations;

The use of electrical energy for maintaining metallic structures buried in soil free from corcured by depressing the potential of the metallic structure to be protected a predetermined amount below that of the immediate electrolytic environment of the structure.

I have found that bare steel even when completely submerged in water can be protected against corrosion by means of cathodic protection. In the case of piles and other structures which emerge from water to air,,the protective influence of the electric current is effective only on the submerged portion. The exposed metal is then subjected to severe atmospheric corrosive influences which are not corrected by cathodic protection.

Above the water line, being always in air, the

structure may be readily painted, or otherwise coated, and thus protected against atmospheric corrosion. Below the water line the structure may be placed under cathodic protection, and when so protected, willsufier no deterioration from corrosion. On the other hand, the metal in that portion of the structure which, depending upon the tide, is neither submerged nor exposed to air at all times, which will be referred to hereinafter as the water line region, is subros'ion' is a process that has recently become well :trolytically conductive during ebb tide.

jected' to the severest type of corrosion since the surface of the metal is kept moist by the ,spattering of the water as by wind or waves, and

isreadily accessible to the oxygen of the air. Also through the mechanical action ofthe waves and driftwood beating against the structure, any coating thereon is subjected to considerable physical damage." l

' It is for the protection of the metal in the water and in the water line region that my invention has particular application. 'During the period of submergence the structure in the water line region receives the benefitsof cathodic protection. During this period, there is deposited. upon the metal as a result of the passage of the current, a protective film of hydrogen gas which while being replenished as long as the current flows is dissipated when the cathodic currents cease. Further, during the cathodic reaction which may be indicated drogen gas, there is simultaneously formed hydroxide ion which, when concentrated, deposits on the surface of the metal desirable protective precipitates, calcium and magnesium hydroxides. During the post submergence period the protective gas is dissipated and the accumulation of hydroxide is lost due to the washing action of the waves. A very corrosive condition results from the evaporation of the sea water which causes. a concentration of salts on the surface of the metal, which together with the oxygen of the air, react on the'metal.

One application of my invention embodies the interposing between the pipe and its environment of an electrolytically conducting medium, which during the entire ebb tide period will remain conducting and thus provide the metal contained therein the benefits of cathodic protection at all times. One means of accomplishing this result-is to encompass the pipe in the water line region completely in heavy cordage, or other materia1 easily saturated by sea water. The cordage is applied within the entire water line region and extending below it to an extent that the wick-like action of the cordage will always be effective.

The cordage accomplishes many desirable things. During flood tide the cordage becomes saturated with salt water, thus remaining elecnatural bulk of the cordage prevents the rapid evaporation of moisture during ebb tide and tends to retainabout thepipe the desirable protective hydrogen film, together with the hydroxides of calcium and magnesium which accumulate. The inward diflusion of oxygen, which is a hydrogen depolarizer and therefore an accelerprevented.

It is evident that a further advantage of the invention is the economy of application and the ease of replacement of the conductive medium when deteroriated. Another advantage of my invention is that theconductive medium serves to protect the surface of the metal against mechanicalabrasion, 'as from driftwood, etc.

My invention has many other objects, advantages, and features. some of which, with the fore- 0ing,wi11-be set forth at length in the following by the evolution of hy- The description where I shall outline certain forms of the invention, which I have selected for illustration in the drawing accompanying and forming a part of the present specification. In the said drawing, I have shown certain forms of my invention, but it is to be understood that I do not limit myself to such forms, since the invention, as expressed in the claims, may be embodied in a large plurality of forms.

Referring to the drawing:

Figure 1 is a perspective view of an embodiment of my invention as applied to the protection of bare submerged pipe and of pipe in the water line region.

Figure 2 is an enlarged view of the conducting medium as applied to pipe or piling in the water line region.

Figure 3 is a perspetcive view of an embodiment of my invention asapplied to piling.

In the drawing, the numeral It! indicates a pipe line which is provided with insulating flanges l I at both sides of the channel. The negative terminal l2 of a direct current source i4 is connected to the channel side of the pipe as at I5 by means of a-wire l6. The positive terminal ll of the direct current source' [4 is connected to an anode l8 by means of a wire Ill. The anode I8 is composed of several lengths of scrap pipe connected together and is buried or submerged at a convenient location approximately one hundred pipe diameters from the closest point of the protected surface.

As shown in detail in Figure 2, cordage 20, approximately one-half to one inch in diameter, was tightly spiraled about the pipe l0 from a point from one to two feet below the lowest ebb tide level 2| and carried well above the highest flood tide level 22. The cordage was entirely encased in canvas 23 which was tightly sewn or laced along a longitudinal seam. The canvas casing 23 held the cordage in place and afforded a finished appearance to the structure. It also serves to minimize evaporation, thus aiding in maintaining the medium conducting.

Additional benefits are derived by painting the canvas as with aluminum paint to reflect the heat rays of the sun, thus further reducing evaporation by maintaining a lower temperature in the cordage.

I have found that the best-results were ob tained with a current density of approximately ten to twenty-five milliamperes per square foot of protected bare surface but that satisfactory results can be obtained by the use of less current.

In another embodiment of my invention, I have found it advantageous to cover the metal suitably to be protected with an underlyingmaterial such as bitumen applied hot, certain paints and the like, where such an application is feasible, as in new construction. The use of such an underlying material in conjunction with cordage and duck effects a saving in electric power cost when cathodic protection is applied. While complete .coverage will not be secured by the bitumen, the amount of current which is necessary for the cordage to carry to the bare or exposed areas is materially reduced. In existing structures where a coating may conveniently be applied at ebb tide to within a few feet above the ebb tide level such coating applications can also be used to advantage even though complete coverage cannot be secured thereby. When'an underlying material such as hot bitumen is also used, the current conducting properties of the cordage and easing are negligibly taxed in carrying the electric current to the bare pipeat the abraded 1 or discontinuous places in the coating which has been applied within the water line region. This small amount of .bare area will require a small amount of current to protect it and hence a low voltage will suffice to drive the current through the conducting medium.

An embodiment of my invention in which a pier is protected against corrosion is shown in Figure 3, in which a pier 30 issupported by usual tubular steel piles 3|. The piles 3| were first coated in the water line region with bitumen applied hot. The piles 3| are connected together by means of wiring 32, one end of which is connected to the negative terminal 33 of a source of direct current 34. The positive terminal 35 of the direct current source 34 is connected to an anode 36 which is composed of several lengths of scrap pipe and which is buried or submerged in a convenient location approximately one hundred times the diameter of the steel piles 3| from the closest point of the protected structure. Cordage 20 similar to that used on the pipe 10 was then wound around the piles 3! in the water line regionand the cordage was then entirely encased in canvas 23.

Instead of using cordage, other means of providing an electrolytic conducting medium about the partially submerged structure may be used. For example, the canvas may be stuffed with asbestos, cotton, or other materials which would tend to retain moisture therein.

I have also obtained satisfactory results by the use of cordage alone, but for the reasons stated above, prefer to encase the cordage in canvas or some other suitable material.

From the foregoing description taken in connection with the accompanying drawing, the method of operation and the advantages of the construction will be readily understood by those skilled in the art to which the invention appertains, and while I have described the principle of operation, together with the forms which I now consider to be the best embodiment thereof, I desire to have it understood that the articles shown are merely illustrative, and that the invention is not to be limited to the details disclosed herein, but is to be accorded the full scope of the appended claims.

I claim:.

1. A method of protecting against corrosion a linear metallic structure partially submerged in water, in which the water line is variable and in which a layer of water is always in contact with the water-line region of said structure, which comprises encasing said structure in an envelope saturable by Water in the water line region, said envelope becoming electrolytically conducting when said envelope is partially submerged in water, an artificially placed anode adjacent said structure and discharging current from an external source from said anode through said Water in which said structure is partially submerged, said metallic structure being the cathode of said electric circuit.

2. A means of protecting against corrosionlinear metallic structures partially submerged in water in which the water line is variable and in which a layer of water the water-line region of said structure, which comprises a pervious encasement of material having a wick-like action about said structure in the water line region, an artificially placed anode at a distance from said structures and an interposed direct current source which is adapted to is always in contact with discharge current from said anode through the structure, which comprises a pervious encasement water in which the structure is submerged to about said structure in the water line region, said the structure which forms the cathode of the encasement containing material saturable by electric circuit. water, said material becoming electrolytically 3. A means of cathodically protecting against 5 conducting when said material is partially subcorrosion a linear metallic structure partially merged in water, an artificially placed anode'at a submerged in water in which the water line is distance from said structure and an interposed variable and in which a layer of water is always direct current source.

in contact with the water-line region of said GORDON N. SCOTT.

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