ASTM D1186:01 pdf free download – Standard Test Methods for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to a Ferrous Base.
6. Test Specimens
6.1 When this test method is used in the field, the specimen is the coated structure or article on which the thickness is to be evaluated.
6.2 For laboratory use, apply the material to be tested to panels of similar roughness. shape, thickness, composition and magnetic properties on which it is desired to determine the thickness.
Note I—Applicable test panel description and surface preparation methods are given in Practice D609.
Note 2—Coatings should be applied in accordance with Practices D 823 or as agreed upon between the contracting parties.
7. Verification of Calibration of Apparatus
7.1 Different gage manufacwrers follow different methods of calibration adjustment. Verify calibration according to manufacturer’s instructions.
7.2 The section of the type of standards used to verify calibration should be predicated upon which type provides the best and most appropnate calibration considering: type of gage, sample surface geometry. and contract requirements. Appendix Xl provides information helpful to making an informed selection of standards.
7.3 Following the manufacturer’s operating instructions, measure the thickness of a series of calibration standards covering the expected range of coating thickness. To guard against measuring with an inaccurate gage, recheck the gage at regular intervals. That interval should be set by agreement between Contracting parties and maintained throughout the control process.
Note 3—Generally ‘Dial-typc” instruments can be used in any position, while “pencil-type” instruments may be used in the vertical position only unless they have separate indicators for the horizontal and vertical positions. Follow the manufacturer! s recommendations.
8. Procedure
8.1 Use the instrument only after calibration has been verified in accordance with Section 7.
8.2 Ensure that the coating is dry prior to use of the instrument.
8.3 Inspect the probe tip and surface to be measured to ensure that they are clean. Adherent magnetic filings or other surface contaminants will affect gage readings.
8.4 Take readings in locations free of electrical or magnetic fields. The location should also be free of vibration when using mechanical magnetic pull-off instruments.
8.5 The accuracy of the measurement can he influenced when made within 25 mm (1 in.) of the edge or right angle in the sample.
8.6 Measure the coating, following the manufacturer’s instructions.
8.7 Verify calibration periodically to ensure that the instrument continues to read properly. If the instrument is found to be out of adjustment, rerneasure the thicknesses taken since the last satisfactory calibration check was made.
8.8 Take a suflicient number of readings to characterize the surface.