Real-time corrosion mapping of steel surfaces using an optoelectronic instrument based on lightwave scattering

The application of an optoelectronic-sensor-based virtual instrument designed by the authors, for visualising and estimating the degree of corrosion of steel surfaces exposed to different concentrations of sulphuric acid, is reported. The optoelectronic sensor consisting of a light-emitting diode (LED) and a pair of photo detectors was fixed very close to the sample placed on a stepper motor-driven moving platform so that the sample surface may be scanned by a thin light beam from the LED. The reflected and scattered light signals from each point in the scanned area were acquired separately by the two detectors in the sensor module. A parameter incorporating the relative value of these signals proved to be a fairly reliable measure of the degree of corrosion. The corrosion factor values were computed by a personal computer and presented in the form of a three-dimensional graph. The average values of the corrosion factor for different steel samples were plotted against the concentration levels of the corroding agent. The variation of the corrosion factor was found to obey a bilogarithmic law, which was in conformity with the previous results.