ASTM B499 – Standard Test Method for Measurement of Coating Thicknesses by the Magnetic Method: Nonmagnetic Coatings on Magnetic Basis Metals
Significance and Use
5.1 The thickness of a coating is often critical to its performance. For most nonferrous coatings on steel, the magnetic method is reliable for measuring coating thickness nondestructively and is suitable for specification acceptance testing and SPC/SQC applications.
5.2 This test method should not be used to determine the thickness of electrodeposited nickel coatings on steel. Test Method B530 is suitable for that determination.
1.1 This test method covers the use of magnetic instruments for the nondestructive measurement of the thickness of nonmagnetic coatings over ferrous or other magnetic base metals. It is intended to supplement manufacturers’ instructions for the operation of the instruments and is not intended to replace them.
NOTE 1: Autocatalytically deposited nickel-phosphorus alloys containing more than 8 % phosphorus are sufficiently nonmagnetic to be measured by this test method, as long as the measurement is made prior to any heat treatment.
1.2 These instruments measure either the magnetic attraction between a magnet and the basis metal, as influenced by the presence of the coating (categorized as “magnetic pull-off”), or the change in magnetic-flux density within the probe (categorized as “electronic”). These instruments cannot distinguish the thickness of individual layers. They can only measure the cumulative thickness of all layers beneath the probe down to the base metal.
1.3 Measurements made in accordance with this test method will be in compliance with the requirements of ISO International Standard 2178.
1.4 Units—The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.