The Magnetic Particle method can be used only
on ferromagnetic materials to reveal surface discontinuities and to a limited
degree, those located below the surface. The sensitivity of this method
decreases rapidly with depths below the surface being examined and
therefore, it is used primarily to examine for surface discontinuities. Ned
Marine offers large, stationary in-house test units for high volume inspection
and a full range of portable units designed for reliable, efficient testing in
the field.
Scientific Principles
A magnetic field is applied to a
component made from ferromagnetic material. The magnetic lines of
force travel through the material, and exit and re-enter the material at the
poles. Defects such as crack or voids cannot support as much flux, and force
some of the flux outside of the part. Magnetic particles distributed over
the component will be attracted by the areas of flow leakage and will give a
visible indication.
Main Uses
Used to inspect ferromagnetic materials (those
that can be magnetized) for defects that result in a transition in the magnetic
permeability of a material. Magnetic particle inspection can detect surface and
near surface defects.
Main Advantages
- large
surface areas of complex parts can be inspected rapidly;
- can
detect surface and subsurface flaws;
- surface
preparation is less critical than it is in penetrating inspection;
- magnetic
particle indications are produced directly on the surface of the part and form
an image of the discontinuity;
- equipment
costs are relatively low.
Disadvantages
- only
ferromagnetic materials can be inspected;
- proper
alignment of magnetic field and defect is critical;
- large
currents are needed for very large parts;
- requires relatively smooth surface;
- paint
or other nonmagnetic coverings adversely affect sensitivity;
- demagnetization
and post cleaning is usually necessary.
Please
contact us here if you require any more information or a
quote.