US 3490497 A
Description (OCR text may contain errors)
Jan. 20, I970 IT. KENNEDY, JR 3,490,497
PROTECTION FOR UNDERGROUND-PIPES I Filed Aug. 1, 1966 INVENTOR. TED KENNEDY, JR.
Miami; LM W ATTORNEYS United States Patent US. 'Cl. 138-144 Claims ABSTRACT OF THE DISCLOSURE Means for protecting an underground pipe against electrolytic corrosion as the result of exposure to ground moisture comprising a film wrapped around the pipe having perforations therein to admit cathodic protection current under the film.
The present invention relates to an improved covering for the protection of underground pipes, conduits and the like against deterioration by electrolytic corrosion. Corrosion of underground pipes is primarily electrolytic and occurs in the presence of moisture where current leaves the pipe. Accordingly, underground pipes are generally coated and/or wrapped so as to protect them physically from moisture, and in addition a cathodic protection system is provided in the vicinity of the pipe such that the flow of current will always be toward the pipe or conduit as a cathode, rather than in the reverse sense. If there is a holiday or break in the pipe covering, the current impressed upon the pipe through the holiday by the cathodic protection system will be in a direction toward the pipe and thereby will prevent corrosion.
It is an essential object of this invention to provide a pipe covering which is particularly well adapted, in conjunction with the cathodic protection system, to protect the pipe from electrolytic corrosion.
Another object is to provide a covering adapted to be wrapped around the pipe and having a plurality of perforations to admit cathodic protection current under the covering.
Another object is to provide a covering in the form of a film in which the perforations are spaced from one another a distance not greater than one-half the distance cathodic protection current can travel under the film.
Another object is to provide a perforated film over a re-applied coating and/or wrapping system for the pipe.
Another object is to provide a perforated film of poly ethylene or other suitable plastic over a pre-applied covering for the pipe which may comprise a heat softenable compound such as a bituminous coating and a wrapper such as asbestos felt, rag felt, or kraft paper.
Another object is to provide a covering for the pipe consisting of the perforated film wrapped over the bare pipe, said film to distribute the cathodic protection over the length of the pipe.
Another object is to provide the perforated film with an adhesive inner surface.
Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings, illustrating a preferred embodiment of the invention, wherein:
FIGURE 1 is a fragmentary plan view of a pipe provided with a cathodic protection system and with a covering, in accordance with my invention,
FIGURE 2 is a view in enlarged scale and in section along the line 2-2 of FIGURE 1.
FIGURE 3 is a sectional view taken on the line 33 of FIGURE 1.
FIGURE 4 is a fragmentary transverse sectional view showing a modification of the invention.
FIGURE 5 is similar to FIGURE 4 and shows a further modification.
In general, the protective covering applied to an underground pipe seals the surface of the pipe so as to exclude moisture and thereby prevent corrosion. However, in the event of a holiday or break in the pipe protection system exposing a surface portion of the pipe, cathodic protection means are provided adjacent the pipe, including the anodes 10 shown in FIGURE 1 as being installed in the ground adjacent to the pipe. The anodes 10 produce a current which will be carried to the pipe in the presence of moisture in the ground and should there be a holiday in the pipe covering the current will be impressed upon the pipe at the exposed point. The direction of current flow is toward the pipe so as to prevent corrosion, it being understood that corrosion takes place only where current leaves the pipe.
In each of the modifications disclosed, the protective covering for the pipe includes an outer plastic film 12 formed with a multiplicity of perforations 14. The perforations are small holes in the film which allow the current from the anodes to enter under the film 12. Thus the surface area of the pipe under the perforated fil-m will be protected from corrosion, whether or not the pipe has a pre-applied coating under the perforated film 12. Obviously, if the pipe has a pre-applied coating and/or Wrapping system under the film 12, the cathodic protection current would protect any surface area of the pipe where a holiday existed in the pre-applied system. In each of the embodiments to be described the spacing between the perforations is dependent upon the distance the current can flow under the film 12. Hence the distance between perforations will not be greater than one-half the distance the current can travel under the film 12 so that any point on the pipe can receive current from one of the two perforations on opposite sides thereof. While the perforations are shown in the drawing as being in uniform rows both transversely and longitudinally of the film and, while this is a convenient arrangement to insure proper spacing, obviuosly other arrangements can be provided.
Referring now more particularly to the drawing, and especially to FIGURES 13, the reference numeral 16 generally designates a pipe or conduit of metal which is installed in the ground and which is protected from corrosion by the covering over the pipe designated in its entirety by the reference numeral 18.
The covering 18 may consist of a primary pre-applied covering including a suitable corrosion resistant vaporproof compound 20 applied to the pipe, and which may be one of the well known bituminous or petroleum wax coating. The primary pre-applied covering also may include the spirally applied and marginally overlapped tape 22 wound over the coating, which tape may, for example, be formed of asbestos felt, rag felt, or kraft paper. The coating 20 is applied hot, is overwrapped with the tape 22 and upon cooling sets in a firm condition.
This primary covering is overwrapped with the perforated plastic film 12 which preferably is made of polyethylene, although other plastics such as polyvinyl chloride, polyester, polyurethane or polyvinylidene chloride may be employed. The film 12 is spirally wrapped over the coated and wrapped pipe in overlapped turns as seen in FIGURES l and 2. Preferably, the thin film 12 is wrapped over the pre-coated pipe (or over bare pipe as may be seen in another embodiment to be described) at the point of installation in the ground. The film 12 may be merely wrapped loosely over the pre-coated and wrapped pipe or it may have an adhesive coating on its inner surface so as to be secured to the tape 22.
FIGURE 4 illustrates a modification in which the primary covering consists of a tape 24 of plastic material which is spirally wrapped about the pipe in overlapping tape 24, in the same manner as it is applied in the embodiment of FIGURES 13. Again, the perforated film 12 in FIGURE 4 may be applied loosely over the primary covering or it may be provided with an adhesive inner surface by means of which it will be secured to the primary covering tape 24.
FIGURE 5 shows a further modification of the invention in which the perforated film 12 is spirally wrapped in overlapping turns about the bare pipe. The perforated film 12 may be wrapped loosely about the pipe or it may be provided with an adhesive coating on its inner surface by means of which it is secured to the pipe surface. As in the other embodiments, the covering for the pipe in FIGURE 5 permits the cathodic protection current to be applied through the perforations 14 to all surfaces of the pipe so that the flow of current is in a direction toward the pipe, preventing corrosion. The spacing of the perforations, as already noted, is such that all surface areas of the pipe will be subjected to the protection of the cathodic protection current.
What I claim as my invention is:
1. In combination, a metal underground pipe, means for protecting said pipe against electrolytic corrosion as the result of exposure to ground moisture comprising a primary coating applied over said pipe, a plastic film wrapped around said pipe in contact with said primary coating spirally in overlapping turns and having a plurality of perforations therein, said perforations being adapted to admit cathodic protection current under said film, and cathodic protection means adjacent said pipe.
2. The combination defined in claim 1, wherein said perforations are spaced from one another a distance not greater than one-half the distance cathodic protection current can travel under said film.
3. The combination defined in claim 1, wherein said film has adhesive on the inner side to secure the same to said primary coating.
4. The combination defined in claim 1, wherein said film is polyethylene and said coating is a bituminous coating.
5. In combination, a metal underground pipe, means for protecting said pipe against electrolytic corrosion as the result of exposure to ground moisture comprising a primary coating applied over said pipe, a plastic film wrapped around said pipe in contact with said primary coating and having a plurality of perforations therein, said perforations being adapted to admit cathodic protection current under said film, and cathodic protection means for generating said current.
References Cited UNITED STATES PATENTS 3,163,183 12/1964 Sagara 138-444 3,359,822 12/1967 Hurlo'w 138-144 X 3,369,426 2/1968 Matz 138-144 X PATRICK D. LAWSON, Primary Examiner U.S. Cl. X.R.