NDT ScienceLocation:Home > NDT Science
Magnetic Memory Testing Methods
Release Time:08/09/2015

What is magnetic memory testing method?

The Metal magnetic memory(MMT) testing - is a non-destructive testing method which applies the basic principle with recording and analyzing its self-magnetic leakage fields distribution in the stress-concentration areas of the workpieces and the equipment. In this case, the self-magnetic leakage field reflects the irreversible change of the magnetization toward the direction of the main stress of the working load put on, the heredity of the metal structure and the manufacturing process of the part and the weld after they are manufactured and cooled in the earth's magnetic environment. The Metal magnetic memory methods make use of the natural magnetization and the metal parts and the equipment’s deformation effect shown in the metal magnetic memory in terms of the actual metal deformation and the metal structure deformation.

The physical basis of the metal magnetic memory method

- Magneto-elastic and Magneto Mechanical Effects

- Locking Effect of Magnetic Domain Boundary on Dislocation Wall in Stress Concentration Region

- Leakage field effect caused by inhomogeneous microstructure and mechanical strength of metal with the natural magnetization

The magnetic parameters used in the metal magnetic memory testing

- the normal component of the self-magnetization field leakage Hp

- the gradient value of the magnetic field in the direction of length x

Metal magnetic memory methods detect the situation of objects in metals and welds

- The state of stress and deformation as well as the inhomogeneity of the metal structure according to the magnetic parameters

- Stress concentration zone - the main source of damage development

- Metallic tissue damage in stress concentration area

- non-metallic density (macro defects)

Advantages of metal magnetic memory method

- It does not require any preparation in terms of the test (surface cleaning, etc.)

- It does not require artificial magnetization, because it uses the natural magnetization formed during the manufacture and the usage of the workpiece

- Metal magnetic memory not only detects equipment that is working, but also detects the equipment in reparations;

- Metal magnetic memory method - the only method that can determine the stress concentration area of equipment with 1mm accuracy.

- Metal magnetic memory testing using portable instruments, separate power supply units, recording devices, microprocessors and 4MB of memory

- Mechanical manufacturing of parts, metal magnetic memory method to ensure 100% quality inspection and online production sorting

- Improved the detection efficiency and accuracy with integration of the traditional non-destructive testing methods

The difference from traditional non-destructive testing methods 

- The methods of metal fatigue damage and on the verge of damage are different

- Metal magnetic memory method is the only answer to "where do metal sampling? "Methods when evaluating the life of equipment.

- The second non-active detection method following acoustic emission. MMT method makes use of the information in the transmit on its own structure. Meanwhile the metal magnetic memory method can provide the actual stress-deformation state and the reason for the development failure besides the early detection of defects.

- Metal magnetic memory method measures the self-leakage magnetic field parameter generated by dislocation accumulation in the stress concentration area. The other known magnetic methods measure the leakage magnetic field of the artificial magnetic field.

Application scope of magnetic memory testing

- The machinery manufacturer checks the quality of parts and welds;

- Pipes, containers, equipment, any structure and fittings (ferromagnetic material metal) manufactured, repaired and used by all industrial sectors;

- Lifting and rotating machinery;

- Research of the mechanical properties of metals in the laboratory.

Copyright Rights © The Chinese Society Of Nondestructive Testing Reserved 沪ICP备12028500号