ASTM B567-98(R2021) pdf free download

ASTM B567-98(R2021) pdf free download.Standard Test Method for Measurement of Coating Thickness by the Beta Backscatter Method
1. Scope
1.1 This test method covers the beta backscatter gages for the nondestructive measurement of metallic and nonmetallic coatings on both metallic and nonmetallic substrate materials. 1.2 The test method measures the mass of coating per unit area, which can also be expressed in linear thickness units provided that the density of the coating is known. 1.3 The test method is applicable only ifthe atomic numbers or equivalent atomic numbers of the coating and substrate differ by an appropriate amount (see 6.2). 1.4 Beta backscatter instruments employ a number of dif- ferent radioactive isotopes. Although the activities of these isotopes are normally very low, they can present a hazard if handled incorrectly. This standard does not purport to address the safety issues and the proper handling of radioactive materials. It is the responsibility of the user to comply with applicable State and Federal regulations concerning the han- dling and use of radioactive material. Some States require licensing and registration of the radioactive isotopes. 1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.6 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. 1.7 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. Summary of Test Method
3.1 When beta particles impinge upon a material, a certain portion of them is backscattered. This backscatter is essentially a function of the atomic number of the material. 3.2 If the body has a surface coating and if the atomic numbers of the substrate and of the coating material are sufficiently different, the intensity of the backscatter will be between two limits: the backscatter intensity of the substrate and that of the coating. Thus, with proper instrumentation and if suitably displayed, the intensity of the backscatter can be used for the measurement of mass per unit area of the coating, which, if the density remains the same, is directly proportional to the thickness. 3.3 The curve expressing coating thickness (mass per unit area) versus beta backscatter intensity is continuous and can be subdivided into three distinct regions, as shown in Fig. 1. The normalized count rate, x n , is plotted on the X-axis, and the logarithm of the coating thickness, on the Y-axis. In the range 0 ≤ x n ≤ 0.35, the relationship is essentially linear. In the range 0.35 ≤x n ≤ 0.85, the curve is nearly logarithmic; this means that, when drawn on semilogarithmic graph paper, as in Fig. 1, the curve approximates a straight line. In the range 0.85 ≤ x n ≤1, the relationship is nearly hyperbolic. 3.4 Radiation other than the beta rays are emitted or backscattered by the coating or substrate, and may be included in the backscatter measurements. Whenever the term backscat- ter is used in this method, it is to be assumed that reference is made to the total radiation measured.
5. Instrumentation
5.1 In general, a beta backscatter instrument will comprise: (1) a radiation source (isotope) emitting primarily beta particles having energies appropriate to the coating thickness to be measured (see Appendix X2), (2) a probe or measuring system with a range ofapertures that limit the beta particles to the area of the test specimen on which the coating thickness is to be measured, and containing a detector capable of counting the number of backscattered particles (for example, a Geiger- Müller counter (or tube)), and (3) a readout instrument where the intensity of the backscatter is displayed. The display, in the form of a meter reading or a digital readout can be: (a) proportional to the count, (b) the normalized count, or (c) the coating thickness expressed either in thickness or mass per unit area units.