Degradation Modeling and Lifetime Evaluation for Organic Anti-Corrosion Coatings Using a Three-Stage Electrochemical Statistical Model

Evaluating the status and lifetime of organic coatings has great significance in structural safety. However, it is quite difficult to evaluate the lifetime of coatings priorly based on conventional visible indicators because they cannot measure the internal changes of coatings. In this paper, a new and effective composite indicator, i.e., circuit-resistance-impedance (CRI), is used to characterize the multi-source uncertainty of the performance degradation of coatings, and a three-stage electrochemical statistical model is proposed to evaluate the service life of organic coatings. Particularly, the Box-Cox transformation is first utilized to improve the normality of the distribution of corrosion rate. Then, a constrained maximum likelihood estimation algorithm considering failure mechanism equivalence is presented to estimate the unknown model parameters. Next, a time-varying reliability model is constructed based on proposed CRI failure criterion and the reliable lifetime of coatings is further evaluated. Finally, a rapid discrimination method of coating status is proposed through measuring the asynchrony of degradation using the coefficient of variation. A corrosion test for epoxy coatings is designed and conducted to demonstrate the effectiveness of the proposed models. Results indicate that they can significantly improve the rationality and validity of coatings lifetime evaluation.