ASTM E2338-22 PDF

SIGNIFICANCE AND USE 4.1 Conformable Eddy Current Sensors—Conformable, eddy current sensors can be used on both flat and curved surfaces, including fillets, cylindrical surfaces, etc. When used with models for predicting the sensor response and appropriate algorithms, these sensors can measure variations in physical properties, such as electrical conductivity or magnetic permeability, or both, as well as thickness of conductive coatings on any substrate and nonconductive coatings on conductive substrates or on a conducting coating. These property variations can be used to detect and characterize heterogeneous regions within the conductive coatings, for example, regions of locally higher porosity. 4.2 Sensors and Sensor Arrays—Depending on the application, either a single-sensing element sensor or a sensor array can be used for coating characterization. A sensor array provides a better capability to map spatial variations in coating thickness or conductivity, or both (reflecting, for example, porosity variations), and provides better throughput for scanning large areas. The size of the sensor footprint and the size and number of sensing elements within an array depend on the application requirements and constraints, and the nonconductive (for example, ceramic) coating thickness. 4.3 Coating Thickness Range—The conductive coating thickness range over which a sensor performs best depends on the difference between the electrical conductivity of the substrate and conductive coating and available frequency range. For example, a specific sensor geometry with a specific frequency range for impedance measurements may provide acceptable performance for an MCrAlY coating over a nickel-alloy substrate for a relatively wide range of conductive coating thickness, for example, from 75 to 400 μm (0.003 to 0.016 in.). Yet, for another conductive coating-substrate combination, this range may be 10 to 100 μm (0.0004 to 0.004 in.). The coating characterization performance may also depend on the thick... SCOPE 1.1 This practice covers the use of conformable eddy current sensors for nondestructive characterization of coatings without standardization on coated reference parts. It includes the following: (1) thickness measurement of a conductive coating on a conductive substrate, (2) detection and characterization of local regions of increased porosity of a conductive coating, and (3) measurement of thickness for nonconductive coatings on a conductive substrate or on a conductive coating. This practice includes only nonmagnetic coatings on either magnetic (μ ≠ μ0) or nonmagnetic (μ = μ0) substrates. In addition to discrete coatings on substrates, this practice can also be used to measure the effective thickness of a process-affected zone (for example, shot peened layer for aluminum alloys, alpha case for titanium alloys) and to assess the condition of other layered media such as joints (for example, lap joints and skin panels over structural supports). For specific types of coated parts, the user may need a more specific procedure tailored to a specific application. 1.2 Specific uses of conventional eddy current sensors are covered by Practices D7091 and E376 and the following test methods issued by ASTM: B244 and E1004. Guidance for the use of conformable eddy current sensor arrays is provided in Guide E2884. 1.3 Units—The values stated in SI units are to be regarded as standard. The values given in parentheses are mathematical conversions to inch-pound units that are provided for information only and are not considered standard. 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 appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.5 This international standard was developed in accordance with internationally recognized ...