A pre-wound coil of few turns is used to create longitudinal field in the part when placed
within it. The field direction is parallel to the axis of the coil itself favouring the detection of
flaws basically in a direction transverse to the axis of the coil Figure 7.3. The effective area of
inspection by coil magnatization is approx. 6 inch to 9 inch (15 to 23 cm) on either side from the
centre of the solenoid or coil. The current requirements for inducing a longitudinal field into a
part are often calculated by the following relations.