Review of pH and reference electrodes for monitoring corrosion in HPHT extreme environments

Due to different degradation mechanisms, the oil and gas industry uses a wide range of non-destructive testing techniques to monitor corrosion. While these methods can be used to reveal corrosion problems once they have reached a certain point, they often cannot be used for continuous in-situ measurements of corrosion and environmental parameters, such as corrosion rates and solution pH, respectively, which can be used to predict the corrosion hazard before it happens. Thus, accurate and efficient realtime monitoring methods are needed that can supply corrosion rate data over an extended period of time and would be able to differentiate between different forms of corrosion. To address this very challenging technological gap and to take advantage of the electrochemical nature of metal corrosion, electrochemical sensors are often employed. The sensor set should be able to measure real-time corrosion rate effectively, efficiently, and objectively during service. Also, pH-sensitive, conductivity, and redox probes can be included in the sensor set. This paper reviews previous experiences and provides recommendations on sensor design and analysis for of monitoring the corrosion process in elevated temperatures, pressures and salinity. Also, recent results related to electrochemical sensors development are presented.