Atmospheric corrosion sensors of two types were tested over a period of time at two locations in Baton Rouge, Louisiana. The fmt type was a commercially available sensor based on the principles of galvanic corrosion. The second type of sensors utilizes thin film electrodes of selected metals and the measurements are performed by LPR and Tafel slope methods. The performance and applicability of both types of these sensors are considered and explained.
Atmospheric corrosion is an important cause of the degradation of structural materials, particularly in contaminated zones such as coastal and industrial areas. The prerequisite for atmospheric corrosion is the presence of thin films of condensed water on the metal surface, which provides a medium for corrosion-electrochemical reactions to occur. Factors that accelerate atmospheric corrosion are contaminants in the air, such as chlorides, sulfur-containing compounds (H,S, SO,) and others. The contaminants dissolve in the surface condensate and increase the overall corrosivity, e.g., by affecting its conductivity and pH. Hence the necessity of means for on-site monitoring of these and other environmental parameters has been repeatedly emphasized.
There are at least two approaches to obtaining information about atmospheric corrosion by electrochemical means. One method employs the principle of galvanic corrosion and the corresponding sensors may involve two dissimilar metallic electrodes connected to a current-measuring instrument. Once moisture condenses on the surface of such a sensor, it completes the electric circuit and enables the passage of galvanic corrosion current. This approach is realized in some cases, e.g., in a commercially available corrosion monitoring unit (CMU).? The CMU is a microprocessor-based measuring and recording system. This kind of sensors is usually considered as time-of-wetness monitors? proposed by Sereda? and subsequently studied by several authors. Recently, a CMU has been in service for over a year at a location on the campus of Southern University in Baton Rouge, Louisiana.
The other method involves creating a complete electrochemical cell on the sensor: which would provide the possibility of measuring parameters such as corrosion potential, Tafel slopes, polarization resistance, and corrosion current density. In addition, other elements might be incorporated in the sensor complex to measure atmospheric variables such as relative humidity, temperature, and levels of contaminants. This approach is being pursued with the purpose of creating a multipurpose total atmospheric corrosion sensor (TACS).5 This paper describes some preliminary results obtained from testing this kind of sensors at two locations in Baton Rouge over the past several months.
The purpose of this work was to follow the trends of the climate in Baton Rouge (LA) over the period studied and to evaluate the behavior of the two types of sensors with respect to their comparative usability and prospects for future work.
