Principle and characteristics of magnetic particle testing

With the deepening and development of the reform and opening up, China’s magnetic particle detection technology has developed rapidly, and the standardization work has made important progress. With the development of digital technology, magnetic powder and permeation detection technologies begin to enter the era of semi-automation/automation and visualization.

Magnetic particle testing (abbreviated as MT), also known as magnetic particle detection, is one of the five general methods of nondestructive testing.Workpiece magnetized ferromagnetic material,but because of the discontinuity, the magnetic field lines on the surface of the workpiece surface and near local distortion and a leakage magnetic field is generated, adsorption on the surface of the magnetic powder and magnetic visible under the light of appropriate form visual mark, which shows the position of the discontinuity, size, shape and extent.

Magnetic particle testing for large diameter elbow welds

Magnetic particle testing for large diameter elbow welds

Magnetic particle detection can only be used to detect the defects on the surface or near surface of ferromagnetic materials. As the discontinuous magnetic traces are piled on the detected surface, the discontinuous shape, position and size can be intuitively displayed, and their properties can be roughly determined.

The sensitivity of magnetic particle detection can detect the discontinuous width up to 0.1μm. With a variety of magnetization methods, the magnetic particle detection is almost unaffected by the size and geometry of the workpiece, and can detect the defects in all directions of the workpiece.

Magnetic powder display is called magnetic powder inspection,because it shows intuitive, simple operation, people are willing to use, so it is one of the most commonly used methods.No magnetic powder display, used to be called magnetic leakage inspection,it often by induction coil,magnetic sensitive tube, hall element to reflect defects, it is more sanitary than magnetic powder inspection,but not as intuitive as the former.At present,magnetic inspection mainly USES magnetic powder to display defects.