SIGNAL SHAPES

Now you know how to look at flux leakage fields, but what do they mean? As you might have guessed, the signal characteristics are related to defect characteristics. For metal-loss, amplitude is related to depth; duration (or length) is related to length; and width is related to width. Here are some examples:

At right is a simple, round defect and its MFL signal. The signal has a single well-defined positive peak. The peak is the red-purple spot toward the top of the plot. There are two negative peaks: the dark blue areas before and after the positive signal. The negative peaks aren't as clearly defined. The signal gradient (color gradiation) is much more gradual.

In addition, the signal shape is not the same as the defect shape. The defect is round and the positive signal is oval. It's spread out in the circumferential direction.