Patent GB-1509696-A (GB)
Title: Arrangement for the inspection of transverse weld seams of a large-diameter steel pipe
IPC: G01N27/82
Filed: 1976-08-16
Abstract: 1509696 Detecting flaws magnetically F FORSTER 16 Aug 1976 [10 Oct 1975] 34036/76 Heading G1N Transverse weld seams of a steel pipe-line are inspected by means of a flux leakage detecting probe including a continuous magnetic recording means, the probe being driven through the pipeline by a drive unit which is arranged to be stopped when the recording medium faces a weld. A weld seam 3 of pipe-line 1 is encompassed by an electrical conductor 11 enclosed by a plurality of U-shaped iron stirrups 15 connected by a strip 19 of electrically non-conductive material to form a closed magnetic circuit within the adjacent part of the pipe-line so that when conductor 11 is energized the weld seam 3 is magnetized in the longitudinal direction of the pipe-line. An inspection carriage 9 is driven through the pipe-line 1 by means of three pairs of wheels 39, 40 arranged at angles of 120 degrees relative to one another and by motor 45. The front end of housing 41 is provided with a hollow shaft 71 rotatably driven by motor 63 and the shaft 71 has fastened thereto a disc 83 having a spring 99 biased swivel arm 87 pivotably mounted thereto. Pivoted on the swivel arm 87 by journal 111 is a cylinder 109 of a storage body 89 covered by a flexible storage tape Fig. 2 (not shown) so that as the disc 83 rotates anti-clockwise the storage body and tape rolls in an anti-clockwise direction on the internal wall of the pipe 1. In operation the carriage 9 is moved in the direction of arrow 133 by energizing motor 45 at the same time as a solenoid 101, whose armature is connected to an extension 107 of the swivel arm 87, is energized so that the upper portion of the swivel arm carrying the storage body 89 is pulled away from the pipe wall. When a signal receiver 79 such as a magnetic probe mounted on a vertical counter weighted beam 75 rotatably secured to projection 73 of housing 41 comes into facing alignment with a signal transmitter 23 e.g. a magnet which locally magnetizes the pipe wall a signal is generated which via a signal processing circuit (not shown) changes over gear-box 47 of the motor 45 to slow speed. The slowly moving carriage 9 is then stopped by a second signal generated when the receiver 79 faces signal transmitter 25 and which is arranged at a distance from field unit 5 so that the unit 5 and storage unit 89 face one another. Stopping of the carriage 9 actuates the magnetizing unit and motor 63 which starts the rotation of disc 83 and hence the scanning of the weld by the storage body 89, solenoid 101 being deenergized so that the body 89 and brush 127 come into sliding contact with weld seam 3. Magnetic stray fluxes emerging at the defects are stored in the tape read by a read head and then erased by an erase head, Fig. 2 (not shown). The signals read out are fed to a chart recorded via cable 72. In order to relate the defect signals with the location of the defects on the circumference of the pipe a plurality of magnets 129, 131 are sunk in the rear face of a disc 83 rotated by motor 63, the magnets being equally angularly spaced around the disc so that a signal is generated at receiver 81 as they pass the latter. Magnet 129 is reverse poled to produce a different signal. A signal transmitter can be mounted on beam 75 and a plurality of receivers mounted on disc 83. A single transmitter and receiver may be employed.