Measuring the atmospheric corrosion of Q235B and T91 steels using gray value, wavelet analysis and fuzzy Kolmogorov–Sinai entropy

Purpose This paper aims to quantify atmospheric corrosion by image analyses. The corrosion extent, form and distribution of corrosion product on Q235B and T91 steels exposed to a Zhoushan marine atmosphere over one year are characterized by image analysis. Design/methodology/approach Image analysis of corrosion images were achieved using the gray value, wavelet analysis and fuzzy Kolmogorov–Sinai (K–S) entropy. Findings As corrosion becomes extensive, the gray value of corrosion images decreases, and the energy value of nine subimages after wavelength decomposition decreases. Fuzzy K–S entropy increases as localized corrosion propagates but decreases as uniform corrosion spreads. Originality/value The methods proposed in this work open a new way for fast corrosion evaluation of metallic materials exposed to atmospheric conditions.