The magnetizing assemblies in all currently available tools are oriented with their backing bars along the pipe axis. So, the flux lines that are produced are parallel to the axis of the pipe. The open area between the poles allows a convenient place for sensors to detect the flux leakage from metal-loss defects. By using magnet and sensor assemblies around the pipe circumference, this practical orientation enables the full (100 percent) monitoring of the flux leakage at the inside pipe surface.

An axial magnet orientation is not sensitive to longitudinal defects, such as axial stress corrosion cracking, seam weld cracks, and seam corrosion. These longitudinal abnormalities are parallel to the magnetic flux lines and do not cause a significant amount of flux to leak into the air. Circumferential defects, such as lack of fusion or root bead cracking at a girth weld, are potentially detectable with current magnet systems ^[Holden97].