Patent ID: 11965856
Assignee: NIPPON STEEL CORPORATION
Field: Measurement (Instruments)
Classification: CPC G  B | IPC B  G

Claim 3:
4. The method for detecting a metal residue present in an electric-resistance-welded steel pipe according to claim 1,
wherein the second step includes
an alternating-current application step of applying an alternating current having a predetermined frequency to the detecting coil,
a flaw detection step of detecting a flaw present in the electric-resistance-welded steel pipe on the basis of a signal component obtained by synchronous detection with the frequency of the alternating current, in the output signal of the detecting coil to which the alternating current is applied, and
a metal residue detection step of detecting the metal residue present in the electric-resistance-welded steel pipe on the basis of a signal component permeating a low pass filter having the frequency of the alternating current as a cutoff frequency, in the output signal of the detecting coil to which the alternating current is applied.