Quantitative performance assessment of corrosion protection systems for offshore wind power transmission platforms

The paper reports about the assessment of deteriorated protective coatings and exposed steel surfaces on offshore wind power platforms in the North Sea and the Baltic Sea. A simple procedure for the assessment of coating deterioration and metal loss on exposed steel surfaces is developed. The procedure delivers a protection number NPNC + NS, whereby the term NC characterizes coating deterioration, and the term NS characterizes metal loss at exposed surfaces. For NP = 0, the structure is fully protected, and for NP = 2, the capacity of the corrosion protection system (protective coating combined with corrosion allowance) is completely exhausted. This number is linked to maintenance procedures. A total of 750 inspection results are reviewed and categorized. The majority of coating damages can be attributed to unsuitable constructive design and to mechanical loading. Design specifications and testing scenarios for coating assessment may be updated in order to account for special stresses in addition to corrosive stresses. Color-based digital image processing is applied for the quantitative recording and rating of coating deterioration processes and for the estimation of NC-values. Preliminary investigations reveal that color-based digital image processing opens the opportunity to evaluate fouling, top coat color changes, and early iron corrosion products.

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