| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a method for detecting the damage position of the coating film of embedded piping, enabling stable measurement and capable of certainly detecting the damage place of the coating film. SOLUTION: Voltage is applied across an embedded steel pipe 11 and a ground electrode 14 from an AC power supply 12 through a power amplifier 3 to allow a current to pass through the steel pipe. In this state, a survey instrument 16 is moved on the surface of the earth along the pipe axial direction of the embedded steel pipe 11. A magnetic sensor 17 is provided in the survey instrument 16 to detect the magnetic field in the vicinity of the surface of the earth. The output thereof is detected by a magnetic field detector 19 through a filter 18. When there is a damage part in the coating film of the embedded steel pipe 11, a current flows in the coating film from the damage part 15 corresponding to the applied voltage and a magnetic field is generated in the vicinity of the surface of the earth by the current flowing through the earth at this time to be detected by the magnetic sensor 17.</p> |
