Monitoring of a military vehicle coating under Prohesion exposure by embedded sensors

Two-layered organic coatings protect metallic structures against corrosion by reducing the transport of water, ions, and oxygen from the environment to the substrate and storing species that provide corrosion inhibition. The topcoat and the primer provide the former and latter, respectively, with the primer also providing adhesion between the topcoat and the substrate. A standard testing method for coatings is the ASTM G85 Prohesion® test. This test involves alternating between a wet exposure of 1-h salt spray at 25 °C and a dry exposure of 1-h air at 35 °C. Apart from visual inspection, conventional monitoring of coating properties is achieved by ex situ electrochemical tests under immersion in a suitable electrolyte. In situ monitoring during a Prohesion® test was performed for a military vehicle coating system using embedded sensors located between the topcoat and primer. In situ results associated with the dry and wet exposures are presented from electrochemical impedance spectroscopy and electrochemical noise measurements. In situ single-frequency impedance measurements were used to monitor the water uptake/loss associated with the exposures of the test conditions. Ex situ monitoring was also performed for comparison with the in situ embedded sensor monitoring.