Types of Magnetic Particle Inspection (MPI)

Wet Method (Wet Fluorescent or Visible

The Wet Method is the most commonly used MPI technique, where the magnetic particles are suspended in a liquid medium (water or oil-based). This method can be further divided into two types: fluorescent and visible.

Direct Current (DC) Method

In the DC Method, a direct current is passed through the component being tested, which creates a magnetic field. This technique is particularly effective for detecting surface defects, especially in larger components with thicker materials. It can also detect very fine cracks and other defects that could affect the component’s structural integrity.

• Simple to apply and very effective for surface defect detection.
• Can be used for components of various sizes and geometries.

Alternating Current (AC) Method

The AC Method uses alternating current to magnetize the component. This technique is highly effective for detecting both surface and near-surface defects, as the alternating current creates a magnetic field that induces surface leakage fields at discontinuities. It’s typically used for thinner materials and components that need to be inspected for both surface and subsurface flaws.

Combination of AC and DC Methods (Hybrid)

The Hybrid Method involves combining both direct current (DC) and alternating current (AC) techniques to enhance defect detection. This approach helps to identify both surface and subsurface flaws by applying different magnetic fields at different stages of the inspection process.