DE2520679

In the representative embodiment of the present invention disclosed herein, new and improved pipe-inspection apparatus for examining oilfield piping includes, along with other flaw-inspection devices, a flux-leakage inspection device uniquely arranged for detecting minute magnetic-flux anomalies which are indicative of metal defects such as cracks, pits, holes and the like. In contrast, however, to the prior-art high-intensity electromagnetizers typically having cores of minimum magnetic reluctance, the unique pipe-inspection apparatus of the present invention instead employs an electromagnetizer having a core of a substantial length and minimum cross-sectional area to specifically make its reluctance relatively large in relation to the combined magnetic reluctances of the magnetized piping wall and the annular clearances between the piping wall and the magnetizer pole pieces. In this manner, changes in either the surface conditions of the piping wall or in the internal diameter of the well bore piping will have little or no influence on the resulting flux-leakage measurements. Moreover, as a further significant aspect of the present invention, since the magnetic field produced by the magnetizer is relatively weak, other flaw-detection measurements provided by this new and improved inspection apparatus will be relatively unaffected.