(Keynote) Sensor Design, Construction and Validation for in-Situ Water Layer Thickness Determination during Accelerated Corrosion Testing

Abstract

The design, construction, validation, and application of a sensor to determine water layer (WL) thickness in the range of 0 to 5 mm in salt spray testing using finite element modeling (FEM) and experimental methods is presented. The sensor determines WL thickness based on electrical resistivity, which is a function of the width of the sensor, distance between the electrodes, and solution conductivity. Sensor design, and validation under known WL thicknesses, was informed by FEM results. The utility of the sensor was shown by measuring WL thickness in a continuous salt spray test similar to ASTM B117 (3.5 wt % NaCl at 35 ˚C) and the range of specifications allowed within the standard were explored. Within the realms of accelerated corrosion testing, the angle of exposure played the largest role in WL thickness. Furthermore, it was found that above an angle of 20˚ from vertical the WL experiences semi-periodic run-off events causing a transient decrease in the WL by up to 80%. Finally, the angle of sample exposure in salt spray environments determines if thin film conditions are achieved, influencing the rate of corrosion. The large allowances for sample angle present in most standards for laboratory corrosion chamber testing pose a large source of test-to-test and chamber-to-chamber variability. Acknowledgements SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. This document is SAND2020-5133 A