What can sensors tell us about corrosion processes?

Sensors that give an output as a response to corrosive conditions have application for the monitoring of structures, particularly where sensors are exposed to the extremes of wet and dry conditions. These corrosivity sensors are sought to provide information to asset owners (i.e. transport and civil infrastructure) to assist in maintenance planning, with overall savings achieved through a reduction of labour costs. However, like the majority of approaches to corrosion sensing, corrosivity sensors provide an indirect measure of the corrosion rate and ultimately it is desired that their outputs be calibrated against the corrosion performance of bulk metals. In addition to these calibrations, corrosion sensors have proved to be a valuable tool for gaining greater knowledge of fundamental corrosion mechanisms. This article presents corrosion sensor data during wetting, immersion and drying cycles. The magnitude and rate of change of sensor outputs are analysed in terms of the surface state of the sensor and level of salt contamination. The trends implied by the sensors are discussed in the context of the accumulation of corrosion damage by common metals when exposed to both atmospheric conditions and accelerated testing procedures.