Electrochemical noise analysis of polyurethane coated steel subjected to erosion-corrosion

Puget, Y., Trethewey, K.R. and Wood, R.J.K. (1998) Electrochemical noise analysis of polyurethane coated steel subjected to erosion-corrosion. Wear, 233-235, 552-567. (doi:10.1016/S0043-1648(99)00226-4).

Abstract

This paper presents the degradation mechanisms of porous and non-porous PU coatings on steel subjected to slurry erosion–corrosion using a purpose-built apparatus. The samples were subjected to a slurry jet made of 3.5% wt. NaCl solution, containing 0–3% wt. sand particles (90° impact angle, jet velocity 4 m/s). Prior to testing the corrosion reactions present on the steel substrate were examined by Electrochemical Impedance Spectroscopy (EIS) and during the test by Electrochemical Noise Analysis (ENA) on the corrosion current. The non-porous coatings remained fully protective at least 10 months when exposed to a purely corrosive solution, and until total stripping by the sand particles when exposed to a corrosive slurry. In contrast, for the porous coatings, corrosion reactions were rapidly initiated on the substrate after solution transport, via defects in the coating, to the coating/metal interface. However, no synergism was detected between the erosion and the corrosion under these test conditions. Analysis of corrosion current fluctuations provided information on the coating degradation mechanisms. The mean and standard deviation were found to act as effective qualitative indicators of the extent of coating damage. The skewness, kurtosis and PSD slope indicated the initiation of the corrosion reactions on the substrate, i.e. the beginning of coating breakdown.

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