Magnetic Particle Inspection (MPI or MT) is a relatively cost effective method of performing NDT on ferromagnetic material. Magnetism has been used for hundreds of years to check for surface defects in materials as it is a fairly simple process. This concept is a process of looking for leakages in magnetic flux.
This process involves magnetising the sample with a fairly powerful magnet. Once it is magnetised, it becomes polarized (North pole where the magnetic force exits and the south pole where it enters). This phenomenon will give the impression of something leaking out of the material (which is a clear indicator of the presence of a defect (this is called a magnetic flux leakage). Specific consumables are used in order to visually see this phenomenon which consists of an applicator and an emulsion of iron powder which will react with the magnetised sample.
Although the process of Magnetic particle inspection is relatively straight forward, surface preparation of the test sample is the first important step which includes cleaning the surface and descaling (if this is not done a false positive may result). Next a magnetic field must be introduced and once this is in place small ferromagnetic particles (as stated above) such as iron powder are added. The excess is carefully removed, i.e. by blowing with air, after which the inspection process may begin. It is noted that Any area where the ferro magnetic material remains will indicate a defect. Finally the sample must be rotated 90° and the process must be repeated as defects which lie parallel to the magnetic flux will not be visually identified.
The advantage of the MT method is its relatively low cost and high speed of evaluation.
It is noted that Metallurgical Testing Labs was the first lab in South Africa to achieve an ISO 17025:2017 (SANAS Accreditation) for this non-destructive testing method and as such are considered to be at the forefront of quality of testing when it comes to this method. Standards which we are accredited against include:
- ASME V, ASME VIII, ASME IX
- API 1104, API 650
- AWS D1.1, AWS D1.6
- BS EN ISO 17638, 23278, 12952, 13480