Magnetic particle testing is used to inspect the defects on surface or very near to the surface of ferromagnetic materials. The principle of this type testing explains that when a magnetic flux is applied to a material, the surface imperfections promote the formation of ‘Leakage Fields’. These leakage fields tends to attract magnetic particles towards themselves thus making an investigation of surface imperfections. By using special pigments, a contrast is formed among substrate and magnetic particles. The procedure is only applied to ferromagnetic materials over a wide range of temperature.
What is MPE?
MPE stands for Magnetic Particle Examination, new name for magnetic particle testing. It is defined as the investigation of surface or near surface imperfections by using basic magnetic principles. Simple magnetism and magnetic field phenomenon is applied that are not only easy to operate but also helps in certain ways. Following are the key points that make magnetic particle testing an exceptional technique.
1. Ferromagnetic Materials
Type of non-destructive testing that is used in inspection of surface defects only in ferromagnetic materials.
2. Easy to operate
Less level of skills are expected from the operator and easy in manipulation. A personal need less duration of time for training. There are many institutes in worldwide that offer training programs for MPE.
3. Cost effectiveness
The testing equipment and apparatus are cost effective and produce highly optimal results for a very low expenditure as compared to other non-destructive inspection techniques.
4. Swift Inspection
Time saving Inspection technique that provides expeditious results. Investigation of surface imperfections can be made swiftly but in efficient manner. Cracks are appeared directly on surface by background contrast.
The technique shows strong sensitivity towards minor defects of surface and quickly detects them. This behavior is only observed in ferromagnetic materials. Also the cracks which are close to surface (within 3mm) can be detected by MPI.
6. Less Surface Preparation
No hard conditions are required for surface preparation before magnetic particle inspection. Normally less level of surface preparation is required because surface pollutants may not hinder the inspection as happen in other inspection techniques. Also the post cleaning is normally not required after inspection.
Magnetic Particle Inspection can easily be carried out during manufacturing and repair works of pressure equipment and structural constructions. Portable equipments are also available in market for the examination of small sections and components.
Magnetic particle examination is a safe process because materials and equipment are non-hazardous. Less level of risk is expected for injuries and accidents. No poisonous and combustible materials are used during examination.
9. Direct Visibility
Surface imperfections are made directly visible on surface by using pigmented materials. Magnetic particles which are used for investigation are available either in wet (suspension in liquid) or in dried form. A contrast is made between the imperfection and background. Sometimes magnetic particles are made visible and sometimes background is made white by coating.
Cheap Non-destructive Examination Technique with safe materials, used for examination of surface discontinuities in ferromagnetic materials only. Although nothing is without limitations. Same with MPI, there are some disadvantages that hinder its use in certain applications.