Regulations to Comply with When Using Instruments
1. Characteristics of the base metal
For magnetic methods, the magnetic properties and surface roughness of the base metal of the standard piece should be similar to those of the base metal of the specimen.
For the eddy current method, the electrical properties of the standard substrate metal should be similar to those of the specimen substrate metal.
2. Base metal thickness
Check if the thickness of the base metal exceeds the critical thickness. If not, one of the methods in 3.3 can be used for calibration.
3. Edge effect
Measurements should not be taken at sudden changes close to the specimen, such as edges, holes, and internal corners.
4. Curvature
It should not be measured on the curved surface of the specimen.
5. Surface cleanliness
Before measurement, any attached substances on the surface, such as dust, grease, and corrosion products, should be removed, but no covering material should be removed
Magnetic thickness measurement is affected by changes in the magnetic properties of the base metal (in practical applications, changes in the magnetic properties of low carbon steel can be considered slight). To avoid the influence of heat treatment and cold working factors, standard plates with the same properties as the base metal of the specimen should be used to calibrate the instrument; Calibration can also be performed using the test piece to be coated.
6. Number of readings
Usually, due to the fact that each reading of the instrument is not exactly the same, several readings must be taken within each measurement area. The local differences in the thickness of the covering layer also require multiple measurements within any given area, especially during surface roughening.
