“Say what you do and do what you say.” That’s a quick way of describing how quality systems work. Processes are documented in procedures (Say what you do), and regular audits verify that those procedures are being followed (Do what you say).
For Nadcap-accredited suppliers doing magnetic particle inspection (MPI), the second part can be the most difficult. Over the past year, the #1 non-conformance found by Nadcap auditors was demonstrating that parts were properly magnetized in accordance with the procedure or technique sheet. To demonstrate proper magnetization, first you need to know what’s in the procedure.
Written procedures for magnetic particle inspection must refer to the governing standard and must be approved by the responsible Level III. There are a lot of details required to spec out the full process, including part identification, materials used, process control checks, pre- and post-processing, and marking of parts after examination.
The technique sheet for a specific part must include the following information
- Equipment used to magnetize the parts
- Type of magnetizing current: AC, HWDC, FWDC, 3-phase, etc.
- Magnetic field directions and the order they are applied
- Method for magnetizing the part: head shot, coil shot, cable wrap, etc.
- Shot duration and number of shots required
- Demagnetizing requirements between shots
- Amperage or amp-turns of each shot
- Method for balancing fields if multidirectional magnetization is used
- Magnetic particle application method: continuous or residual