EXPRESS: Corrosion measurement of Q355C steel based on laser induced breakdown spectroscopy.

Q355C steel is a critical structural material widely used in offshore wind power facilities, including steel piles and tower cylinders, corrosion caused by marine salt spray poses a serious threat to long term structural integrity. In this study, laser-induced breakdown spectroscopy (LIBS) was employed to assess the corroded characteristics of Q355C steel. A field-deployable LIBS system based on two-dimensional scanning was developed for surface analysis. A quantitative calibration curve was established between the surface salt density of uncorroded Q355C steel and the sodium spectral intensity, achieving a high coefficient of determination (R2=0.94). Subsequently, LIBS measurements were performed on simulated corrosion specimens, revealing variations in elemental distribution within the corrosion zone with depth. Since surface corrosion products primarily consist of iron oxide whose thickness varies with corrosion severity, the ratio of manganese to iron spectral intensities (IMn/IFe) was identified as a potential indicator for distinguishing corrosion severity. By exploiting the spectral differences between genuine corrosion areas and pseudo-corrosion areas (areas covered by flow rust), accurate differentiation between the two was achieved. The accuracy of the LIBS binarization method was approximately 24% higher than that of traditional visual methods.