The magnetic force of attraction pulls the magnet assemblies into contact with the inside of the pipe wall. As a result, the dynamic performance of a tool traveling down a pipeline is quite complex. For tools with brushes, the brushes not only couple the magnetic field into the pipe, but they also act as an integral part of the mechanical dynamics of the magnetization system. Brushes help absorb the shock that can result at internal penetrations such as weld roots, restrictions, and dents in the pipeline. For tools with solid magnetic shoes, the dynamic performance is not as smooth, but the magnetic coupling is better. Spring mounting systems are used to attach the magnets to the body of the tool. These systems help center the tool in the pipe, and they absorb and damp vibrations.

Permanent magnet tools have a discrete number of magnet assemblies spaced around the circumference. Ideally, the magnet assemblies should be close together in order to produce a uniform magnetic field in the pipe wall. Practical pipeline operating conditions require the magnet bars to collapse to ride over obstructions, dents, and other diameter reductions as shown in the figure. Therefore, in normal operating positions, there are gaps between magnet assemblies. These necessary gaps can lead to differences in the applied magnetic field strength, which affects inspection performance.

Sometimes more than one magnetizing system is used; that is, the entire magnetizing system (and sensor assemblies) is duplicated at two locations along the tool. Multiple magnet systems along a tool's length can allow a more complete inspection coverage. On systems with two magnetizing and sensor systems, gaps that may exist between the first set of sensors can be covered by the second set of sensors.