Electrochemical Sensors for Continuous Measurement of Corrosion and Coating System Performance in Outdoor and Accelerated Atmospheric Tests

Abstract

Organic coatings are the primary means of protecting structures from atmospheric corrosion in harsh environments. Environmental compliance and a desire for increased performance continue to drive the development of new coatings; however, this process may take many years. Corrosion tests for coatings development, qualification, and selection often provide poor correlation to service performance. Conventional tests and characterization procedures may not assess the most relevant degradation mechanisms of loss of barrier properties, localized corrosion, and galvanic attack. Furthermore, these tests do not yield information on interactions between specific environmental parameters and material degradation or the kinetics of failure. To improve coating evaluations, electrochemical sensors and data acquisition systems have been developed to measure coating performance and corrosion continuously during atmospheric tests. The sensing elements are incorporated in multisensor test panels that can be cleaned, coated, and scribed like conventional coating test panels. The multisensor panels support measurement of coating barrier properties, free corrosion, and galvanic corrosion. The barrier properties and free corrosion are measured using impedance-based methods, and galvanic corrosion is quantified using a zero resistance ammeter. Local measurements of panel surface temperature, air temperature, and relative humidity are used to correlate degradation rates and barrier properties to environmental conditions. The simultaneous environmental measurements also provide records that can be used to ensure the validity of performance comparisons between separate tests and within a single test. A description of the sensors, electrochemical measurements, and methods for coating testing are reported.

Variable selection for Gaussian process regression through a sparse projection

“…The ten selected variables are regarded as important factors influencing environmental corrosion. Temperature and relative humidity have been identified as major drivers of corrosion in many existing works (Friedersdorf et al 2019, Zheng et al 2009).…”

“…Ozone is a strong oxidizer that can lead to significant corrosion and material degradation at a high exposure level, and the impedance can be correlated to the amount of pollutants on the surface of a metal specimen (Friedersdorf et al 2019). The effect of rain on the corrosion behavior of aluminum is more complicated because it can both reduce corrosion by washing inorganic pollutants off the surface as well as increase corrosion by scrubbing gases out of the air, becoming acid rain.…”