Magnetically detectable plastic pipe

Abstract

A magnetically detectable plastic, e.g., polyethylene, polyvinyl, etc., pipe for underground use comprises a hollow tubular plastic pipe having particles of magnetic material embedded in plastic and secured integrally with the wall of the pipe. The magnetic particles are of iron oxide or barium ferrite and of a size, shape, distribution and proportion such that the plastic pipe may be easily detected by magnetic detection apparatus on the surface when the plastic pipe is buried at a selected depth under the ground. The magnetic particles are uniformly distributed throughout the thickness and uniformly distributed around the entire circumference of the plastic pipe or the magnetic particles may be distributed in discrete portions of the plastic pipe, as for example, a uniform outer layer of the pipe or in stripes or strips extending along the pipe. The particles may be extruded with the plastic in forming the pipe, whether uniformly dispersed or in discrete regions or the pipe may be formed of plastic free of the magnetic particles and the magnetic particles provided in a separately applied strip which may be coextruded or fused or adhered to the wall of the pipe. The magnetic strips or magnetic portions of the plastic pipe may have selective areas or portions magnetized to encode information readable from the surface of the ground above the buried pipe or in inventorying pipe on the surface.

I claim: 
     
       1. A method of producing magnetically detectable plastic pipe for underground use, comprising; providing an organic plastic .Iadd.consisting essentially of polyethylene or polyvinyl resin .Iaddend.for extrusion,   providing particles of magnetic material comprising electrically-nonconductive, highly-magnetizable iron oxide or barium ferrite,   mixing said particles of electrically-nonconductive, highly-magnetizable iron oxide or barium ferrite uniformly with said organic plastic, .Iadd.at a concentration of about 8% by weight of the plastic which concentration does not substantially decrease the tensile strength of the pipe produced, .Iaddend.   heating and extruding said mixture of organic plastic and electrically-nonconductive, highly-magnetizable iron oxide or barium ferrite and highly magnetizing said particles.Iadd., after extrusion, .Iaddend.to produce a hollow tubular pipe having said highly magnetized particles distributed and proportioned such that the .Iadd.magnetized .Iaddend.plastic pipe may be easily detected by magnetic detection apparatus on the surface when the plastic pipe is buried at three to five feet or more under the ground.   
     
     
       2. A method according to claim 1 in which said electrically-nonconductive, highly-magnetizable iron oxide or barium ferrite particles are selectively magnetized .[.after formation of said pipe.]. to encode data therein readable from the surface after the pipe is buried three to five feet or more under the ground.   
     
     
       3. A method according to claim 1 in which said mixture of organic plastic and magnetic particles is extruded to produce a hollow tubular plastic pipe which,   said electrically-nonconductive, highly-magnetizable iron oxide or barium ferrite particles are uniformly distributed throughout the thickness of the wall of said plastic pipe, and   uniformly distributed around the entire circumference of said plastic pipe.   
     
     
       4. A method according to claim 1 including providing an additional quantity of said organic plastic free of said magnetic particles, and   extruding said organic plastic free of said magnetic particles and said mixture of organic plastic and electrically-nonconductive, highly-magnetizable iron oxide or barium ferrite particles together to produce a hollow tubular plastic pipe having said electrically-nonconductive, highly-magnetizable iron oxide or barium ferrite particles distributed and proportioned in separate discrete regions of the plastic pipe such that the plastic pipe may be easily detected by magnetic detection apparatus on the surface when the plastic pipe is buried at three to five feet or more under the ground or otherwise at a substantial distance from the plastic pipe.   
     
     
       5. A method according to claim 1 including providing an additional quantity of said organic plastic free of said magnetic particles, and   extruding said organic plastic free of said magnetic particles and said mixture of organic plastic and electrically-nonconductive, highly-magnetizable iron oxide or barium ferrite particles together to produce a hollow tubular plastic pipe having said electrically-nonconductive, highly-magnetizable iron oxide or barium ferrite particles distributed and proportioned in a separate discrete region of the plastic pipe comprising an outer layer integral with the plastic pipe such that the plastic pipe may be easily detected by magnetic detection apparatus on the surface when the plastic pipe is buried at three to five feet or more under the ground or otherwise at a substantial distance from the plastic pipe.   
     
     
       6. A method according to claim 1 including providing an additional quantity of said organic plastic free of said magnetic particles, and   extruding said organic plastic free of said magnetic particles and said mixture of organic plastic and electrically-nonconductive, highly-magnetizable iron oxide or barium ferrite particles together to produce a hollow tubular plastic pipe having said electrically-nonconductive, highly-magnetizable iron oxide or barium ferrite particles distributed and proportioned in separate discrete regions of the plastic pipe comprising stripes of magnetic material extending longitudinally of the plastic pipe such that the plastic pipe may be easily detected by magnetic detection apparatus on the surface when the plastic pipe is buried at three to five feet or more under the ground or otherwise at a substantial distance from the plastic pipe.   
     
     
       7. A method according to claim 6 in which said electrically-nonconductive, highly-magnetizable iron oxide or barium ferrite particles are magnetized in the course of forming said pipe. .[.8. A method according to claim 6 in which   said electrically-nonconductive, highly-magnetizable iron oxide or barium   
     
     
        ferrite particles are magnetized after formation of said pipe..]. .[.9.  A method according to claim 6 in which said electrically-nonconductive, highly-magnetizable iron oxide or barium ferrite particles are selectively magnetized after formation of said pipe to encode data therein readable from the surface after the pipe is buried   
     
     
        or otherwise at a distance from the plastic pipe..]. 10. A method of producing magnetically detectable polymeric pipe for underground use, comprising: providing a hollow tubular pipe of organic polymer,   providing a strip of organic plastic containing particles of electrically-nonconductive, highly-magnetized iron oxide or barium ferrite, .Iadd.in a ratio of about one part by weight of said particles to three parts by weight of said plastic material, .Iaddend.   affixing at least one said strip of organic polymer containing particles of electrically-nonconductive, highly-magnetized iron oxide or barium ferrite to said plastic pipe to produce a composite pipe having said electrically-nonconductive, highly-magnetized iron oxide or barium ferrite particles positioned and proportioned such that the plastic pipe may be easily detected by magnetic detection apparatus on the surface when the plastic pipe is buried at a selected depth under the ground or otherwise   
     
     
        at a distance from the plastic pipe. 11. A method according to claim 10 in which said strip of magnetized-particle-carrying polymeric material.Iadd., in a ratio of about one part by weight of said particles to three parts by weight of said polymeric material, .Iaddend.is extruded and subsequently   
     
     
        fused to the surface of the wall of said plastic pipe. 12. A method according to claim 10 in which said strip of magnetized-particle-carrying polymeric material.Iadd., in a ratio of about one part by weight of said particles to three parts by weight of said polymeric material, .Iaddend.is adhered to the surface of   
     
     
        the wall of said plastic pipe. 13. A method according to claim 10 in which said strip of magnetized-particle-carrying polymeric material.Iadd., in a ratio of about one part by weight of said particles to three parts by weight of said plastic material, .Iaddend.is coextruded with said plastic 
     
     
        pipe. 14. A method according to claim 10 in which said particles are magnetized in the course of forming said strip. .[.15. A method according to claim 10 in which said particles are selectively magnetized after formation of said pipe to encode data therein readable from the surface after the pipe is buried or   
     
     
        otherwise at a distance from the plastic pipe..]. .[.16.  A method according to claim 10 in which said particles are magnetized after formation of said strip..]. .[.17. A method according to claim 16 in which   said magnetic particles are selectively magnetized after formation of said pipe to encode data therein readable from the surface after the pipe is buried. .]. .Iadd.18. A method according to claim 1 in which,   said highly magnetized particles are platelets of barium ferrite and magnetized across the thickness of said platelets. .Iaddend. .Iadd.19. A method according to claim 1 in which,   said highly magnetized particles are needles of gamma iron oxide and magnetized across the length of said needles. .Iaddend. .Iadd.20. A method according to claim 1 in which,   said particles have a remenance of up to about 1000 gammas. .Iaddend.