Abstract: An apparatus is disclosed for manipulation by an operator or user for detecting magnetically detectable plastic pipe and other sources of magnetic fields from a distance having a horizontally oriented support member with a handle extending at an acute angle therefrom. A magnetic field gradiometer comprising a hollow non-magnetic tube with two flux-gate magnetometers therein is supported at the distal end of the support member a substantial distance ahead of the operator in a substantially vertical position. A microprocessor is supported on the support member operatively connected through a differential amplifier to the gradiometer for processing signals therefrom. An electronic read-out module is supported on the handle spaced from the gradiometer and operable to receive signals from the microprocessor and convert them into an audible or visual display to be sensed by the operator or user.

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.

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.