Abstract: A method of and apparatus for non-destructive investigation of the surface properties of a body of ferromagnetic material such as a pipeline in which a non-saturating source of magnetic flux is placed adjacent to said surface to create a magnetic circuit having a substantial proportion in non-ferromagnetic material and a sensor is used to measure the magnetic flux in said circuit, an indication of the surface properties of the body being derived from a plurality of such measurements.

Abstract: A pig for monitoring the internal surface profile of a pipeline carries a plurality of sensors to trace the surface as the pig traverses the pipeline. Output signals from the sensors are compared with an expected value and a reference signal generated when they differ by more than a predetermined amount. The sensor signals are recorded simultaneously with the reference signal.

Abstract: A particle analyzing device in which a suspension of particles in a fluid medium is passed through an aperture in a strip of plastic material, and the change in the conductivity of the suspension across the aperture, each time a particle flows through the aperture, is detected so that the number and volume of particles for a given quantity of the suspension can be determined. The strip can be provided with a plurality of scanning apertures and be selectively moved across the flow path to bring a new aperture into an operative position in the flow path, such as when an aperture becomes clogged by debris.