Optical corrosion monitoring and detection systems as well as methods to detect and monitor corrosion under process conditions and generally in real time using electromagnetic radiation, particularly light. The systems generally provide for incident light to be allowed to reflect from a coating which is exposed to the corroding action of the process stream. As the coating is corroded, the intensity, or other function, of the incident light is changed and this change is detected and used to extrapolate a level of corrosion.