US3260661A

US3260661A - Sacrificial metal pipe coverings

Info

Publication number: US3260661A
Application number: US444662A
Authority: US
Inventors: Woodrow E Kemp; Robert C Kenan
Original assignee: Koppers Co Inc
Current assignee: Beazer East Inc
Priority date: 1965-04-01
Filing date: 1965-04-01
Publication date: 1966-07-12
Anticipated expiration: 1983-07-12

Description

July 12, 1966 w. E KEMP ETAL SACRIFICIAL METAL PIPE COVERINGS Filed April 1,, 1965 2 Sheets-Sheet l FIG. 2

FIG. 4

INVENTORS WO0DEOW E. KEMP FOBEET C. KENAN fie/r y 2, 1966 w. E. KEMP ETAL SACRIFICIAL METAL PIPE COVERINGS 2 Sheets-Sheet 2 Filed April 1, 1965 FIG. 5

INVENTOR. WOOD/20W E. KEMP ROBEPT C- KEN/IN BY 5 l/Ieir United States Patent 3,260,661 SACRIFICIAL METAL PIPE COVERINGS Woodrow E. Kemp, Pittsburgh, Pa., and Robert C. Kenan, Long Grove, Ill., assignors to Koppers Company, Inc., a corporation of Delaware Filed Apr. 1, 1965, Ser. No. 444,662 4 Claims. (Cl. 204148) This invention relates generally to electrolysis and more particularly to apparatus and method for providing cathodic protection to metallic structures, such as steel and iron pipe and the like and is a continuation-in-part of th invention described in application Serial No. 162,795, filed December 28, 1961, now abandoned.

Pipes or conduits that are installed underground are subjected to attack by such corrosive elements as moisture, water, oil, electrical current, bacteria, and other elements that may be present in the soil. Coal tar pitch and asphalt have long been used for the coating of gas,

' oil and water lines to give protection to such lines. Coal tar pitch is resistant to soil bacteria and soil corrosives as well as to water but when either coal tar pitch or asphalt has been used to coat underground pipelines, it has not been able to minimize or prevent the destructive effect of galvanic corrosion or stray current electrolysis on the buried pipe.

It has been necessary, heretofore, to provide cathodic protection by making the pipe electrically negative with respect to the surrounding soil or other structures. Conventionally, an electrical potential was impressed on the pipe by connecting it with an artificial supply of direct current at a properly controlled voltage or with a galvanic cell using a piece of zinc and the pipe as the electrodes and the soil as the electrolyte. These particular methods of cathodically protecting pipe are not satisfactory however, because the need of an electrical potential by using an artificial supply of direct current requires extra equipment and a continuing source of electrical current. The use of single pieces of zinc or other metals as electrodes requires extensive engineering study to determine the number of zinc electrodes that should be spaced along the pipe line to give the proper cathodic protection. This type of study can be very involved since oil and gas pipe lines, for example, stretch for hundreds of miles and this means that the pipe line will be, in soils of varying chemical and electrical makeup; thus it is difiicult to determine the proper amount of spacing of electrodes.

The heretofore known methods of providing cathodic protection to pipe included the application of the coal tar pitch and coal tar enamel coatings to outer surface of the pipe. It is necessary in such methods to heat the coal tar pitch to approximately 500 F. and the application of this hot pitch created handling problems and it is not conveniently practical to place a metal electrode in the tar coating to provide cathodic protection to the pipes.

In contrast to th foregoing cathodic protective methods, the present invention includes a method for providing cathodic protection to metallic structures such as steel pipe, structural members and the like comprising the steps of applying to the surface of the metallic structure a laminate structure comprised of a sacrificial anodic metallic foil selected from the group consisting of zinc, magnesium, and zinc-magnesium alloys, and a pressure sensitive adhesive for adhering one surface of the foil and to the metallic structure comprised of coal tar pitch in quantity amounting to between 40 and 60 percent by weight of the adhesive composition and having a Brookfield viscosity at 200 F. in the range of 100 to 400, a copolymer of acrylonitrile and butadiene in quantity amounting to between 0.5 and 3.0 percent by weight of the adhesive composition and having a Mooney viscosity 3,260,661 Patented July 12, 1966 "ice v in th range of 25 to 175, polyisobutylene in quantity amounting to between 30 and 50 percent by weight of the adhesive composition and having a molecular weight in the range of 7,000 to 15,000, and fibrous, hydrous magnesium silicate in quantity amounting to between Zero and 20 percent by weight of the adhesive composition and having a specific gravity of about 2.5, an oil absorption in the range of 34 to 44, and a particle size such that between 50 and 60 percent passes through a United States standard No. 140 screen, and electrically bonding said anodic lamina to said metallic structure.

For a further understanding of the present invention and for further advantages and features thereof, reference may be made to the following description taken in conjunction with the accompanying drawings which show for the purpose of exemplification, embodiments of the invention.

In the drawings:

FIG. 1 is a schematic view of one embodiment of the laminate structure of the invention being applied in one manner to a length of pipe;

FIG. 2 is a schematic view of a preferred first embodiment of the laminate structure of the invention;

FIG. 3 is a schematic view of the laminate structure of the invention being applied in another manner to a length of pipe;

FIG. 4 is a schematic view of a second embodiment of the laminate structure of the present invention;

FIG. 5 is a schematic view of a third embodiment of the present invention being applied to a portion of a length I of pipe;

FIG. 6 is a schematic view of a fourth embodiment of the present invention being applied to a portion of a length of pipe;

FIG. 7 is a schematic view of a fifth embodiment of the present invention being applied to a portion of a length of pipe;

FIG. 8 is a sectional view along line VIII-NIH of FIG. 5; and

FIG. 9 is a sectional view along line IXIX of FIG. 3.

In FIG. 1, a length of pipe 10, which may either be steel or iron or other metal which is subject to corrosive attack, is being coated with a laminate 9 in' the form of a sleeve split lengthwise so as to embrace the pipe 10.

FIG. 2 illustrates a preferred first embodiment of the laminate 9 which comprises an outer environmental protective layer 7 applied to an adhesive coated sacrificial anodic metallic layer 6. The surfaces of the anodic metallic layer are coated with an adhesive 8 which is preferably a coal tar pitch, pressure-sensitive type adhesive. The exposed surface of the adhesive layer 3 is covered with a conventional type of silicone treated re lease paper layer 2. The sacrificial anodic metallic layer 6 is preferably either zinc or magnesium, or an alloy thereof.

The laminate 9 or adherend is comprised of materials which are flexible and readily conformable to the surface of another adherend, such as metal structures including pipes, structural members and the like. The laminate 9 is comprised of selected materials having the requisite characteristics for cathodically portecting underground meter of thickness.

or an alloy of these metals.

volts per millimeter of thickness permits the anodic metal lic layer 6 to be consumed rapidly, because the current loss resulting from the electrical resistance to current flow would be extremely high. A dielectric strength greater than 1,000 volts per millimeter of thickness has no practical advantage in the novel laminate of this invention since the electrical currents encountered are not expected to be high enough to Warrant use of such material.

The dielectric material layer 7 should be flexible. If the dielectric material can be bent on a 1 inch diameter mandrel, through an arc of 180 Without cracking it is suitable. The dielectric material should be moisture-resistant. If the material absorbs more than 8 percent of water, electrical currents would then be conducted directly to the pipeline and cause corrosion deterioration. The dielectric material, when used in thicknesses under 50 millimeters, should have a moisture vapor transfer rate of less than 1 perm, measured in accordance with specification ASTM No. E96-53T. Examples of some materials suitable for the dielectric layer are: polyethylene, polyvinylchloride, asphalt, and coal tar pitch.

The release paper layer 2 is a conventional material, such as silicone treated film or paper which readily adheres to the adhesive composition layer 8, but which may also be readily stripped off, leaving the adhesive composition with sufficient tackiness to form \an instantaneous strong bond to whatever surface it is thereafter applied.

FIG. 4 illustrates a second embodiment of the laminate in the form of a tape 9a, and the sacrificial anodic metallic layer 6 is in the form. of a foil mesh such as wire mesh. The foil mesh material is preferably zinc or magnesium The general construction of the laminate 9a is the same as the laminate 9 except for the form of the sacrificial anodic metallic layer 6.

FIG. 5 illustrates a third embodiment of the laminate, in the form of a tape 9b, and the sacrificial anodic metallic layer 6 in this instance is the outermost layer. The dielectric layer 7, in this embodiment, is interposed between the anodic layer 6 and the surface of the pipe 10. The layers 6 and 7 are maintained in spaced apart relation and are adhesively secured to each other and to the pipe by the adhesive layers 8, interposed in the manner shown. The release paper layer 2 in these cases is shown partially removed.

It is desirable and necessary to electrically connect the anodic metallic layer 6 to the pipe 10. This may be accomplished in any suitable manner. One such way is to insert a U-shaped clip 12 of copper foil or other electrically conductive material, into the tape 9b so that the copper foil 12 contacts both the anodic metallic layer 6 and the pipe 10. FIG. 8 shows one such copper foil 12 inserted in the tape 9b to electrically connect the metallic foil 6 and the surface of the pipe 10.

FIG. 6 illustrates a fourth embodiment of the laminate in the form of a tape 90 comprised of a sacrificial anodic metallic layer 6, which is the outermost layer in this instance, an adhesive layer 8 and a conventional silicone treated release paper layer 2 that is partially removed. It will be noted also that the anodic metallic layer 6 is likewise electrically connected to the metallic pipe 10 by one of the U-shaped copper foil clips. 12. In most instances the U-shva-ped copper clips may be inserted into the adhesive 8 at the interface between it and the metallic foil 6. The clip may be easily folded over the lower suface of the adhesive layer 8, as shown in FIGS. 8 and 9 whereby a,

satisfactory electrical conductive path is established between the an-odic layer 6 and the metal pipe 10.

FIG. 7 illustrates a fifth embodiment of the laminate, in the form of a tape 9d, comprised of the usual sacrificial anodic metallic layer 6, forming the outer layer, superposed on a layer 11 of coal tar pitch which is adhesively secured to an adhesive layer 8. When applied to the pipe 10, the conventional release paper layer 2 is removed, as shown, and one of the U-shaped copper foil clips 12 is inserted to provide an electric connection between the anodic layer 6 and the surface of the pipe 10.

FIG. 3 illustrates the copper foil clip 12 installed at the end of one length of the present laminate tape 13 and adjacent the beginning of another length of laminate 130. It is desirable and convenient to insert the COPPEI foil clips 12 adjacent the end of one length of tape or at the commencement of another length of tape. However, the U-shaped copper foil clips 12 may be inserted along a length of tape whenever desirable or necessary.

It is important that the several embodiments of the laminate 9 be prepared in such a manner that the anodic metallic foil or mesh is never contiguous with the pipe to be protected. This for the reason that, if a small puncture or hole is made in the laminate, water can seep through the laminate and reach the pipe surface. Corrosive activity will result and there will then be a continuous deposition of corrosive products at the interface of the laminate and the pipe.

FIG. 1 illustrates one method for cathodically protecting a length of pipe using the laminate of the present invention. The method comprises the steps of: (1) cutting a strip of laminate 9, preferably in the form of a tape having a Width substantially equal to the circumference of the pipe 10 and a length substantially equal to the length of the pipe; (2) removing the release paper layer 2; (3) placing the strip of laminate lengthwise on the pipe with the adhesive layer 8 against the outer pipe surface; (4) Wrapping the laminate around the pipe so that the longitudinal edges of the laminate either abut or slightly overlap and form a single lengthwise seam; and then (5) heat sealing the longitudinal seam by means known in the art.

FIG. 3 illustrates another method for cathodically pro- I tecting a length of pipe by spirally wrapping it with the protective laminate 9 in the form of tapes 13, 13a. The laminate 13, 13a may of course have any suitable widths. The tapes 13, 13a also may have any one of the structures shown and described hereinbefore, and be wrapped around pipe spirally in such a manner that the edges of adjacent convolutions abut or slightly overlap. Of course, before the tape is wrapped on the pipe, the release paper layer 2 is removed. The adhesive quality of the particular coal tar pitch adhesive layer 8 provides satisfactory effective adhesion not only to the pipe surface, but also with the adjacent abutting spiral convolution. Thus, when adjacent convolutions are pressed against one another during the application of the tape, the abutting adhesive layers 8 tend to cold flow together and form a single homogeneous adhesive layer. There is no need to heat seal the outer layer or any part of the laminate tape unless such action is preferred.

The cathodic protective characteristics of the laminate tape may in some instances, be further improved by placing the anodic metallic foil or mesh 6 on the exterior of the laminate as shown in FIGS. 5-7. The metal foil or mesh 6 is made of a suitable metal which is anodic to the material of the object to be protected. Generally, the anodic metal foil or mesh will be either Zinc or magnesium, or a zinc-magnesium alloy and the metal to be protected will be steel. Such sacrificial anodic foil or mesh materials have excellent electrical conducting characteristics and stray electrical currents will not cause galvanic or electrolytic corrosion of the pipe. Moveover, in the unlikely event that moisture would reach the pipe through a hole or a puncture in the protective coating, corrosion of the metal pipe would not take place, because, at selected strategic locations along the length of pipe the copper foils 12 are connected between the metal pipe and the anodic metal foil layer 6.

Several samples of the laminate of this invention were prepared and coated onto steel pipe. For each sample, the position of the zinc anode was varied and the type of dielectric material used was also varied. Each of these coated pipes consisted of 2 /2" diameter by 1 long mild specifically described in Table I which is set out below,-

the adhesive material used was prepared according to the description given as follows.

EXAMPLE I 40 parts of heavy creosote oil are added to 30 parts of coal tar pitch. The temperature of this mixture is raised to 350 F. (1 hr.) and 30 parts of pulverized coal added. The mixture is then placed in an agitated still and heated to a temperature of 600 F. and held at this temperature for 1 hour or until the coal dissolves. The mixture is then cooled for 2 to 3 hours to 300 F. and 5 parts of a medium molecular weight copolymer of butadiene and acrylonitrile (75:25 ratio), and 30 parts of heavy creosote oil are added. The mixture is then maintained at 300 F. for four hours. Thereafter, 35 parts of ball clay are added and mixed for three hours.

The resulting composition is a black, thick, creamy material having a viscosity at 250 F., using a Brookfield viscometer, model LVF spindle number 4, 12 r.p.m., of between 20,000 and 40,000 centipoises, and a penetration of 100-140 mm. at 77 F. (50 gms.; 5 seconds) ASTM D5 and a ring and ball softening point of 45 C. to 55 C.

The composition, as prepared in this example, was applied to a steel I-beam of the type used in construction. Subsequently, the thus-coated I-beam was further encapsulated in concrete. The composition adhered completely to both the metal beam and to the concrete cover, preventing any deterioration or corrosion of the metal beam by the action of the corrosive agents present in concrete. The composition of this example can be similarly applied to other metal construction materials which are to be coated with concrete, such as aluminum.

TABLE I.LAMINATE COMPOSITION IN THE ORDER OF MATERIAL LOCATION TO THE PIPE SUBSTRATE The above samples were removed from the sea water after 4 months exposure. The samples were then checked for corrosion in the areas adjacent to the deliberate punctures. No corrosion was observed. Each of the puncture areas was covered with a white deposite which consisted of a cathodically deposited calcareous coating resulting from sea water decomposition and from some anodic zinc corrosion product. The pipes were completely free of corrosion and the coating compositions showed no damage.

Another adhesive composition of the pressure-sensitive type, which has been found to be exceptionally effective for the purpose of adhering the sacrificial anodic metallic lamina to a metallic surface subject to corrosive attack, comprises a mixture of coal tar pitch, a copolymer of acrylontrile and butadiene, polyisobutylene and fibrous hydrous magnesium silicate.

Such adhesive composition is described in a copending application Serial No. 442,073, filed March 23, 1965. Generally, the adhesive is formulated in the following manner:

(a) Heating to 275 F. a quantity of coal tar pitch amounting to between 40 and 60 percent by weight of the adhesive composition and having a Brookfield viscosity at 200 F. in the range of -400;

(b) Adding to and mixing with said coal tar pitch at 275 F. a quantity of a copolymer of acrylonitrile and butadiene amounting to between 0.5 and 3.0 percent by weight of the adhesive composition and having a Mooney viscosity in the range of 25-175, until said copolymer is dispersed or dissolved and the mixture is homogeneous and free of lumps;

(c) Adding to said mixture and mixing therewith a quantity of polyisobutylene amounting to between 30 and 50 percent by weight of the adhesive composition and having a molecular weight in the range of 10,000-12,000, until the mixture is smooth again; and

(d) Adding to the mixture and thoroughly mixing therewith a quantity of fibrous hydrous magnesium silicate amounting to between Zero and 20 percent by weight of the adhesive composition and having a specific gravity of about 2.5, an absorption in the range of 34-44 pounds of oil per one hundred pounds of pigment, and a particle size such that between 50 and 60 percent thereof passes through a United States standard No. screen, until a smooth thixotropic product is produced.

It is generally desirable to cover the exposed surface of the adhesive with a silicone treated release paper layer 2 until it is ready for application. When ready for use the silicone treated release paper of course is removed. Such release papers are conventional and prevent the several configurations of the tape, when made and stored, from sticking together.

In contrast to known methods and apparatus to cathodically protect metallic structures such as pipe, the applicants have provided a novel laminar structure which can be simply and easily applied to a pipe. It is only necessary to remove the release paper layer and then wrap the tape around the object to be protected, inserting from time to time the copper foils 12. Such a structure is both simple to use and highly effective in service.

If the cathode is a length of pipe, for example, the preferred manner of applying the cathodic protective laminate is to spirally wind the tape on the pipe making sure that adjacent convolutions are edge abutting or slightly overlap. If the cathode is a structural member, such as an I-beam, channel, angle and the like, the preferred manner of applying the cathodic protective laminate is to apply lengths of the tape to the surface of the structural member making sure that adjacent lengths are edge abutting or slightly overlapping. The entire surface of the cathode in the area subject to corrosive attack should be protected with the laminate.

From the foregoing it should be apparent that the cathodic protective laminate of the present invention has many features and advantages not heretofore available, such as, continuity of protection, ease of application, effectiveness and simplicity.

We claim:

1. The method to cathodically protect a metallic structure comprising the steps of:

(a) providing a laminate structure comprised of (l) a sacrificial anodic metallic foil lamina selected from the groupconsisting of zinc, magnesium, and zinc-magnesium alloys;

(2) pressure sensitive adhesive laminae applied to opposed surfaces of said foil lamina, one of said adhesive lamina adhering the anodic foil lamina to and maintaining said foil in spaced apart relation to the surface of said metallic structure, said adhesive being comprised of (a) coal tar pitch in quantity amounting to between 40 and 60 percent by weight of the adhesive composition and having a Brook- 'field viscosity at 200 F. in the range of 100 to 400; (b) a copolymer of acrylonitrile and butadiene in quantity amounting to between 0.5-

and 3.0 percent by weight of the adhesive composition and having a Mooney viscosity in the range of 25 to 175;

(c) polyisobutylene in quantity amounting to between 30 and 50 percent by weight of the adhesive composition and having a molecular weight in the range of 7,000 to 15,000; and

(d) fibrous, hydrous magnesium silicate in quantity amounting to between zero and percent by weight of the adhesive composition and having a specific gravity of about 2.5, an oil absorption in the range of 34 to 44 pounds of oil per one hundred pounds of pigment, and a particle size such that between 50 and 60 percent passes through a United States standard No. 140 screen;

(3) an outermost flexible environmental protective dielectric lamina applied to and adhering to the other adhesive lamina on said anodic toil lamina;

(b) applying said laminate structure to the metallic structure so that the pressure sensitive adhesive lamina adheres to the surface of the metallic structure; and

(c) electrically connecting said anodic lamina to said metallic structure.

2. The method to cathodically protect a metallic structure comprising the steps of;

(a) providing a laminate structure comprised of:

( 1) an outer sacrificial anodic metallic foil lamina selected from the group consisting of zinc, magnesium, and zinc-magnesium alloys;

(2) a next adjacent intermediary lamina comprised of coal tar pitch adhering to said foil lamina;

(3) a next adjacent innermost lamina comprised of a pressure sensitive adhesive for adhering the outer laminates to said metallic structure and being comprised of (a) coal tar pitch in quantity amounting to between 40 and 60 percent by weight of the adhesive composition and having a Brook- -fie1d viscosity at 200 F. in the range of 100 to 400;

(b) a copolymer of acrylonitrile and butadiene in quantity amounting to between 0.5 and 3.0 percent by Weight of the adhesive composition and having a Mooney viscosity in the range of to 175;

' (c) polyisobutylene in quantity amounting to between and 50 percent by weight of the adhesive composition and having a molecular weight in the range of 7,000 to 15,000; and

(d) fibrous, hydrous magnesium silicate in quantity amounting to between zero and 20 percent by weight of the adhesive composition and having a specific gravity of about 2.5, an oil absorption in the range of 34 to 44 pounds of oil per one hundred pounds of pigment, and a particle size such that between 50 and 60 percent passes through a United States standard No. 140 screen;

'(b) applying said laminate structure to the metallic structure so that the pressure sensitive adhesive lamina adheres to the surface of the metallic structure; and

(c) electrically connecting said anodic lamina to said metallic structure.-

3. The method to cathodically protect a metallic structure comprising the steps of:

(a) providing a laminate structure comprised of 1) an outermost flexible environmental protective dielectric lamina;

(2) a sacrificial anodic metallic foil mesh lamina selected from the group consisting of zinc, magnesium, and zinc-magnesium alloys interposed in spaced apart relation to said dielectric lamina and said metallic structure;

(3) a first adhesive lamina coating said anodic metallic mesh lamina and adhering the same to said dielectric lamina;

(4) a second adhesive lamina coating said anodic metallic mesh lamina and adhering the same to and maintaining the same in spaced apart relation to said metallic structure, said adhesive laminae being comprised of (a) coal tar pitch in quantity amounting to between 40 and 60 percent by weight of the adhesive composition and having a Brookfield viscosity at 200 F. in the range of to 400;

(b) a copolymer of acrylonitrile and butadiene in quantity amounting to between 0.5 and 3.0 percent by weight of the adhesive composition and having a Mooney viscosity in the range of 25 to 175;

(c) polyisobutylene in quantity amounting to between 30 and 50 percent by weight of the adhesive composition and having a molecular weight in the range of 7,000 and 15,000; and

(d) fibrous, hydrous magnesium silicate in quantity amounting to between zero and 20 percent by weight of the adhesive composition and having a specific gravity of about 2.5, an oil absorption in the range of 34 to 44 pounds of oil per one hundred pounds of pigment, and a particle size such that between 50 and 60 percent passes through a United States standard No. screen;

(c) electrically connecting said anodic lamina to said metallic structure.

4. The method to cathodically protect a metallic structure comprising the steps of:

(a) providing a laminate structure comprised of (1) an outer sacrificial anodic metallic foil lamina selected from the group consisting of zinc, magnesium, and zinc-magnesium alloys;

(2) a flexible dielectric lamina interposed in spaced apart relation to said anodic metallic foil lamina and said metallic structure;

(3) a first adhesive lamina adhering said dielectric lamina to said anodic metallic foil lamina; and

(4) a second adhesive lamina coating said dielectric lamina and adhering the same to and maint-aini-ng-the outer laminae in spaced apart relation to said metallic structure, said adhesive laminae being comprised of (a) coal tar pitch in quantity amounting to between 40 and 60 percent by weight of the adhesive composition and having a Brookfield viscosity at 200 F. in the range of 100 to 400;

(b) a copolymer of acrylonitrile and butadiene in quantity amounting to between 0.5 and 3.0 percent by weight of the adhesive composition and having a Mooney viscosity in the range of 25 to (c) polyisobutylene in quantity amounting to between 30 and 50 percent by Weight of the adhesive composition and having a molecular weight in the range of 7,000 to 15,000; and

(c) electrically connecting said anodic lamina to said metallic structure.

References Cited by the Examiner UNITED STATES PATENTS 12/1941 Andrus 204-197 12/1949 Stearns 204-196 9/1956 P-reiser 204-197 8/1957 Phillipsen 161-167 4/1964 Lane et a1. 117-127 5/1965 Sheehan 156-190 8/ 1965 Canevari 204-148 FOREIGN PATENTS 7/ 1957 France. 9/ 1939 Germany.

15 JOHN H. MACK, Primary Examiner.

HOWARD S. WILLIAMS, Examiner.

T. TUNG, Assistant Examiner.

Claims

1. THE METHOD TO CATHODICALLY PROTECT A METALLIC STRUCTURE COMPRISING THE STEPS OF: (A) PROVIDING A LAMINATE STRUCTURE COMPRISED OF (1) A SACRIFICAL ANODIC METALLIC FOIL LAMINA SELECTED FROM THE GROUP CONSISTING OF ZINC, MAGNESIUM, AND ZINC-MAGNESIUM ALLOYS; (2) PRESSURE SENSITIVE ADHESIVE LAMINAE APPLIED TO OPPOSED SURFACE OF SAID FOIL LAMINA, ONE OF SAID ADHESIVE LAMINA ADHERING THE ANODIC FOIL LAMINA TO AND MAINTAINING SAID FOIL IN SPACED APART RELATION TO THE SURFACE OF SAID METALLIC STRUCTURE, SAID ADHESIVE BEING COMPRISES OF (A) COAL TAR PITCH IN QUANTITY AMOUNTING TO BETWEEN 40 AND 60 PERCENT BY WEIGHT OF THE ADHESIVE COMPOSITION AND HAVING A BROOKFIELD VISCOSITY AT 200*F. IN THE RANGE OF 100 TO 400; (B) A COPOLYMER OF ACRYLONITRILE AND BUTADIENE IN QUANTITY AMOUNTING TO BETWEEN 0.5 AND 3.0 PERCENT BY WEIGHT OF THE ADHESIVE COMPOSITION AND HAVING A MOONEY VISCOSITY IN THE RANGE OF 25 TO 175; (C) POLYISOBUTYLENE IN QUANTITY AMOUNTING TO BETWEEN 30 AND 50 PERCENT BY WEIGHT OF THE ADHESIVE COMPOSITION AND HAVING A MOLECULAR WEIGHT IN THE RANGE OF 7,000 TO 15,00; AND (D) FIBROUS, HYDROUS MAGNESIUM SILICATE IN QUANTITY AMOUNTING TO BETWEEN ZERO AND 20 PERCENT BY WEIGHT OF THE ADHESIVE COMPOSITION AND HAVING A SPECIFIC GRAVITY OF ABOUT 2.5, AN OIL ABSORPTION IN THE RANGE OF 34 TO 44 POUNDS OF OIL PER ONE HUNDRED POUNDS OF PIGMENT, AND A PARTICLE SIZE SUCH THAT BETWEEN 50 AND 60 PERCENT PASSES THROUGH A UNITED STATES STANDARD NO, 140 SCREEN; (3) AN OUTERMOST FLEXIBLE ENVIRONMENTAL PROTECTIVE DIELECTRIC LAMINA APPLIED TO AND ADHERING TO THE OTHER ADHESIVE LAMINA ON SAID ANODIC FOIL LAINA; (B) APPLYING SAID LAMINATE STRUCTURE TO THE METALLIC STRUCTURE SO THAT THE PRESSURE SENSITIVE ADHESIVE LAMINA ADHERES TO THE SURFACE OF THE METALLIC STRUCTURE; AND (C) ELETRICALLY CONNECTING SAID ANODIC LAMINA TO SAID METALLIC STRUCTURE.