Coating thickness measurement is one of the most common quality assessments made during industrial coating applications. SSPC-PA 2, Procedure for Determining Conformance to Dry Coating Thickness Requirements is frequently referenced in coating specifications. As SSPC-PA 2 has evolved over the past four decades, a number of procedures and measurement frequencies are referenced in both the mandatory portions of the standard and in the non-mandatory appendices. While the measurement frequencies were never intended to be a statistical process, it is helpful to understand the statistical implications of the measurement process. And it is helpful to know what coating thickness variability is reasonable. This brief article explores how scanning probe technology can help to acquire a larger number of measurements (in a relatively short period of time) to better assess the consistency of the applied coating thickness, particularly on larger, more complex structures.
There are two industry standards that are widely specified for measurement of coating thickness. These include ASTM D7091, Standard Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic, Nonconductive Coatings Applied to Non-Ferrous Metals and SSPC-PA 2, Procedure for Determining Conformance to Dry Coating Thickness Requirements. The ASTM standard focuses on gage use, while the SSPC standard focuses on the frequency and acceptability of coating thickness measurements. The standards are designed to be used in conjunction with one another. In 2012, all references to measurement frequency were removed from the ASTM standard so that it did not conflict with SSPC-PA 2.
Read the full article at KTA University.
Scanning Illustration, courtesy of Elcometer Ltd.
