Remote field eddy current flaw detector for metal pipes having a pair of receiver coils providing a differential offset amplitude signal
US5210492A · kind A · utility
Assignees
Inventors
Key dates
| Filing date | Aug 5, 1991 |
| Grant date | May 11, 1993 |
| Priority date | — |
| Expiry date | Aug 5, 2011 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01N27/9046
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
The present invention relates to a flaw detector for metal material for maintaining and managing pipelines using a remote field eddy current sensor. An AC signal having a constant level and shifted by predetermined phase angle is added to signals received in receiving coils of the remote field eddy current sensor to obtain accurate phase detection in a normal, nonflawed portion of the pipeline to be tested (e.g. uniform thickness, no holes, etc.). By preventing generation of abnormal flaw data, precise diagnosis of the pipeline can be performed. An AGC circuit may be used to maintain at a constant level of received signal. Two sets of spaced apart receiving coils are spaced from an exciting coil a distance greater than a predetermined distance (about two times the pipeline diameter). The set of receiving coils closest to the exciting coil has a greater number of coil turns than the other set. This coil configuration generates sensed coil differential signals having sufficient signal amplitude to permit stabilized and accurate phase detection and comparison for nonflawed and gradually flawed regions in the pipe.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.