Magnetic Particle Inspection
units allow the component to be magnetized in two directions,
longitudinally and circumferentially, in rapid succession. Therefore,
inspections are conducted without the need for a second shot.
In multidirectional units, the two fields are balanced so that
the field strengths are equal in both directions. These quickly
changing balanced fields produce a multidirectional field in the
component providing detection of defects lying in more than one
Just as in conventional wet-horizontal systems, the electrical
current used in multidirectional magnetization may be alternating,
half-wave direct, or full-wave. It is also possible to use a combination
of currents depending on the test applications. Multidirectional
magnetization can be used for a large number of production applications,
and high volume inspections.
To determine adequate field strength and balance of the rapidly
changing fields, technique development requires a little more
effort when multidirectional equipment is used. It is desirable
to develop the technique using a component with known defects
oriented in at least two directions, or a manufactured defect
standard. Quantitative Quality Indicators (QQI) are also often
used to verify the strength and direction of magnetic fields.