Sensor based corrosion condition monitoring of coating substrate system informed by fracture mechanics, electrochemistry and heat transfer concepts.

Abstract

This research investigates delamination and blistering as coating failure mechanisms due to corrosive diffusing species, residual and thermal stresses. Several mathematical models to include environmental variables as temperature, humidity ratio and atmospheric constituents have been developed and reported. During this study various coating failures have been analysed through a combination of electrochemistry, fracture mechanics and heat transfer concepts. This approach enabled the development of comprehensive mathematical models for the prediction and prognoses of coating failures applied to high value assets. The formation of blister and its propagation due to diffusion of corrosive species was investigated. Fracture mechanics concepts were utilised to study the initiation and propagation of a circular blister as an interfacial crack under the coupling affects of compressive and diffusion induced stresses along with heat transfer due to pressure gradient at the interface of coating substrate system. The direction of blister propagation was defined through a mathematical model with blister radius r and radial angle θ as initial defining parameters. Experimental work was conducted to assess the influence of varying temperatures, humidity ratios and environmental pollutants as SO2 and salt particles to investigate corrosion failures. Live condition monitoring techniques were developed to assess corrosion rate with respect to large vehicles operation frequencies to study the effects of changing environments. Three years of real time data consisted of 150K data points was acquired for investigating corrosion failures with or without coatings. Both experimental and simulation data was compared to predictive and prognostics models. There is excellent agreement between experimental and simulation results to be applied for live corrosion condition monitoring of large high value assets. A sensor based corrosion condition monitoring methodology, informed by experimental and simulation results has been developed and is presented.