Development and Evaluation of Respirometric in Situ Corrosion Monitoring System

Abstract

There is a growing need for a system to be used for real-time in-situ monitoring of corrosion rates. This system/method allows the determination of real-time corrosion rates under realistic exposure conditions and is capable of following changing exposure conditions in situ. This is realized by a combination of optical Oxygen sensor measurements with either gravimetric volume sensitive techniques or pressure sensor based techniques in a closed chamber. This study was therefore aimed at developing and evaluating a low-cost, real-time corrosion monitoring system, using copper (Cu) as a test sample. Materials used were sourced locally, the circuitry was designed and used to develop the system with incorporation of sensors that can monitor temperature, humidity and pressure within an airtight glass bottle and placed in a housing which was fabricated. The developed system was then evaluated using a piece of Cu exposed to 5% Sodium Chloride (NaCl). Hydrogen evolution reaction (HER) and Oxygen Reduction Reaction (ORR) within the closed chamber were monitored; and thus Ideal gas and Henry laws were adopted to calculate the amount of gas molecules, and convert them to cathodic reactions. The methods were carried out in accordance with existing literature and standard procedure. Results of evaluation of the system showed that, the more Oxygen is being consumed, the higher the corrosion. Mass loss validation measurements carried out at the end of exposure showed a good correlation with the total recorded cathodic charge. Immersion corrosion kinetics can be monitored non-destructively and in real-time. Manometric approach showed that HER leads to a pressure increase while ORR leads to a decrease in pressure. ORR monitoring is possible based on the amount of consumed O2 by manometric and sensor-based approaches; sensitive, non-destructive corrosion rate measurements are possible on Cu and could be monitored remotely.