Developed potential measurement corrosion monitoring

The most common method of corrosion monitoring is the direct weight loss method, via small metal coupons. In addition, there are a number of electrical methods, including developed potential measurement,... 

A conventional weather station approach has often been used to monitor atmospheric variables regsuxitng atmospheric corrosion [7]. Temperature and relative humidity may be recorded continuously, and these data are used to produce average temperatures for periods of time such as days, weeks, or months. Electrical monitoring sensors have been developed to measure when wetness exists on the surface by means of detecting a potential difference between dissimilar metals [8]. A standard device is shown in ASTM G 84, Practice for Measurement of Time of Wetness on Surfaces Exposed to Wetting Conditions as in Atmospheric Corrosion Testing. The information on time of wetness is usually reduced to a percentage or fraction of time a surface is wet in a month or in a year. 

The criteria used for the control of a CP system also provide a direct method to monitor the efficiency of that system and determine how well a structure supposedly under CP is actually protected against corrosion. Potential measurements are used most commonly as a criterion of protection. The basis for this is that if current is flowing onto a protected structure, there must be a change in the potential of the structure with respect to the environment. This is because the current flow causes a potential change, which is a combination of the voltage drop across the resistance between the protected structure and the environment, and the polarization potential developed at the structure surface. 

The linear polarization technique requires us to polarize the steel whth an electric current and monitor its effect on the half cell potential. It is carried out with a sophisticated development of the half cell incorporating an auxiliary electrode and a variable low voltage DC power supply. The half cell potential is measured and then a small current is passed from the auxiliary electrode to the reinforcement. The change in the half cell potential is simply related to the corrosion current by the equation ... 

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