ASTM B244-09(R2021) pdf free download

ASTM B244-09(R2021) pdf free download.Standard Test Method for Measurement of Thickness of Anodic Coatings on Aluminum and of Other Nonconductive Coatings on Nonmagnetic Basis Metals with Eddy-Current Instruments
1.1 This test method covers the use of eddy-current instru- ments for the nondestructive measurement of the thickness of a nonconductive coating on a nonmagnetic basis metal. It is intended to supplement manufacturers’ instructions for the operation of the instruments and is not intended to replace them.
1.2 This test method is particularly useful for measuring the thickness of an anodic coating on aluminum alloys. Chemical conversion coatings are too thin to be measured by this test method.
1.3 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro- priate safety, health, and environmental practices and deter- mine the applicability ofregulatory limitations prior to use.
1.5 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
3.1.1 accuracy, n—the measure of the magnitude of error between the result of a measurement and the true thickness of the item being measured.
3.1.2 adjustment, n—the physical act of aligning a instru- ment’s thickness readings to match those of a known thickness sample (removal of bias), in order to improve the accuracy of the instrument on a specific surface or within a specific portion of its measurement range. An adjustment will affect the outcome of subsequent readings.
3.1.3 calibration, n—the high-level, controlled and docu- mented process of obtaining measurements on traceable cali- bration standards over the full operating range of the instrument, then making the necessary instrument adjustments (as required) to correct any out-of-tolerance conditions.
3.1.3.1 Discussion—Calibration of coating thickness instru- ments is performed by the equipment manufacturer, an autho- rized agent, or by an authorized, trained calibration laboratory in a controlled environment using a documented process. The outcome of the calibration process is to restore/realign the instrument to meet/exceed the manufacturer’s stated accuracy.
3.1.4 reference standard, n—a specimen ofknown thickness used to verify the accuracy of a coating thickness measuring instrument.
3.1.5 verification of accuracy, n—obtaining measurements on a reference standard prior to instrument use for the purpose ofdetermining the ability ofthe coating thickness instrument to produce reliable values, compared to the combined instrument manufacturer’s stated accuracy and the stated accuracy of the reference standard.
4. Summary of Test Method
4.1 Instruments complying with this test method measure coating thickness by the use ofeddy currents. Aprobe is placed directly on the coated surface in a perpendicular position and electronic circuitry is used to convert a reference signal into a coating thickness measurement.
4.2 The instrument probe coil is energized by alternating current that induces eddy currents in the metal substrate. The eddy currents in turn create a secondary magnetic field within the substrate. The characteristics of this secondary field are dependent upon the distance between the probe and the basis metal. This distance (gap) is measured by the instrument probe and shown on the instrument display as the thickness (microns or mils) of the intervening coating.
7.5 The basis metal thickness for the test and the calibration adjustment shall be the same ifthe critical thickness, defined in 8.3, is not exceeded. When possible, back up the basis metal of the standard or of the test specimen with a sufficient thickness of similar material to make the readings independent of the basis metal thickness. A way to determine if the basis metal thickness exceeds the critical thickness is to make measure- ments before and after backing up the basis metal with similar metal at least 3 mm (120 mils) thick. If there is no difference between the readings, the critical thickness is exceeded.