Abstract: A pipeline pig is equipped with a gauging plate which consists of a flexible disc having strain gauges secured thereto so as to be subject to deformation when the disc makes contact with an obstruction or deformation in the pipe wall. The strain gauges are connected in a bridge circuit which goes out of balance when the disc is deformed. The output of the bridge circuit is connected to means for producing an output signal when the disc is bent rapidly but not when it is bent slowly so as not to respond to slow deformation due to build-up of debris in front of the pig.

Abstract: A magnetically detectable attachment for a pipeline pig comprises a wheel formed from two discs of magnetic material which serve as pole pieces for a permanent magnet mounted therebetween. The wheel is arranged, in use, to run along the top of the inside of the pipeline so as to magnetize a narrow longitudinal strip of the pipeline wall as the pig passes therealong.

Abstract: A pipeline pig for locating constrictions or irregularities on the inner surface of a pipeline consists of a fluid-filled envelope, such as a rubber or rubberlike spherical or toroidal ball, arranged to be a close fit within the pipeline, and means for sensing pressure variations within the envelope. The distance travelled along the pipeline by the pig may be measured by means of a contact wheel running on the pipeline surface and provided with a revolution counter.