Reliability of magnetic particle inspection
Reliability of magnetic particle inspection
(OP)
I have a cold forging supplier whose parts were detected of having cracks. The parts are cold extruded, machined, carburise hardened and supplied. Right now root cause analysis is going on to find out where crack happens - during extrusion or at HT. To run production, we have asked supplier to do 100% Magnetic Particle Inspection of parts. My question is
1. How reliable is MPI?What is the min. width and depth of the crack it can detect?
2. What is the Repeatability & Reproducibility of MPI checking? i.e. will once accepted part be rejected when inspected again by different person/equipment?
Thank you in advance for the clarifications.
1. How reliable is MPI?What is the min. width and depth of the crack it can detect?
2. What is the Repeatability & Reproducibility of MPI checking? i.e. will once accepted part be rejected when inspected again by different person/equipment?
Thank you in advance for the clarifications.





RE: Reliability of magnetic particle inspection
RE: Reliability of magnetic particle inspection
Type of electrical current- AC, DC, Pulse DC, if AC the frequency (skin effect)
Direct methods - prod, head/tail stock etc. or indirect/induced methods yokes, coils
Dry or wet mganitic particle
Visible or fluorescent particles
2. Because MPI requires a lot of human attention, one technician may find something that the other did not.
RE: Reliability of magnetic particle inspection
I have to qualify these statements by saying it takes a good testing procedure and a qualified technician to get the maximum benefit from MT testing, in fact any NDT testing. You should have a eminently qualified person, a ASNT level III MT or equivalent, setup the inspection procedure with the proper controls and the testing be accomplished by a qualified technician, an ASNT level II or equivalent.
The procedure will be setup according to what type defect and the location that you are looking for. If the defect is known to occur in the same location on each part this makes for a simple inspection. If the defects have random locations this brings the inspection procedure and technician into play big time.
I have to say again that having a qualified person oversee the inspection process will pay big dividends both for you and the part supplier.
RE: Reliability of magnetic particle inspection
RE: Reliability of magnetic particle inspection