METHOD OF ELECTROMAGNETIC FLAW DETECTION FOR CASING PIPES IN WELL AND ELECTROMAGNETIC FLAW DETECTOR FOR IMPLEMENTATION OF METHOD Russian patent published in 2008 - IPC G01N27/82 

FIELD: electromagnetic flaw detection.

SUBSTANCE: several couples of search coils connected differentially register alternate electromagnetic field generated by an exciter coil; simultaneously in the exciter coil generating alternate electromagnetic field a periodic sequence of rectangular current pulse is transmitted at such recurrence rate that the width of skin layer for the first harmonic surpasses the width of metal pipe wall. First harmonic is separated at the search coils, active and reactive components of the given tension are measured, then amplitude and phase shift of the given tension against exciter coil current are defined. Tension curves with phase shift in the 0 to 360 degrees range with 5-10 degrees pitch are calculated for each measurement point, a curve with fewer aberrations caused by electromagnetic pipe heterogeneity, then local tension abnormalities corresponding to the pipe flaws are separated at the chosen curve. The result is achieved by separation of abnormalities of local flaws of casing pipes against the background abnormalities caused by electromagnetic heterogeneities of casing pipe steel.

EFFECT: improves information capacity and simplifies interpretation of flaw detection results, allows defining the form and orientation against the pipe axis of the flaws detected.

8 cl, 3 dwg