Magnetic Testing

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 sub-surface 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.