METHOD FOR INVESTIGATING DAMAGE POSITION OF ANTICORROSION COAT OF BURIED METALLIC PIPE AND APPARATUS THEREFOR

摘要

PROBLEM TO BE SOLVED: To provide a method and an apparatus by a magnetic field analysis which can investigate a damage position of anticorrosion coats of buried metallic pipes in a simple constitution with a high sensitivity. ;SOLUTION: An a.c. signal current is sent by a transmitter 5 to a buried metallic pipe 1, thereby generating a magnetic field by a current i1 flowing in and out to an anticorrosion coat damage position 2 of the buried metallic pipe 1. At the same time, two coils inclined by 45° to a ground surface within a vertical plane along an axis of the metallic pipe and disposed with respective axes being kept parallel to each other are scanned along the pipe axis, thereby continuously detecting an intensity of the magnetic field. A correlation of detection signals is obtained or a sum of the detection signals is synthesized. The damage position is investigated from a square sum of the correlation output signal or a position of a maximum value of an amplitude output of the synthesized signal. Alternatively, a difference of the detection signals is synthesized and, the damage position is investigated from a position of a minimum value of an amplitude output of the synthesized signal.;COPYRIGHT: (C)2000,JPO