Corrosion Monitoring by Electrochemical Noise Probes in a Purified Terephthalic Acid Production Plant

Abstract An on-line electrochemical noise corrosion-monitoring program was commissioned in a Purified Terephthalic Acid (PTA) production plant. The program was initiated because of the necessity for monitoring the sporadic occurrences of insidious pitting corrosion of types 316L and 2205-Duplex stainless steels in the process vessels, piping, and nozzles in the plant. The pitting corrosion was aggravated by process upsets and the presence of aggressive contaminants. The electrochemical noise monitoring system was used for instantaneous detection of pitting corrosion and process upsets in the PTA plant to enable timely remedial measures to be taken. The instrument transmits current and voltage data from four channels in the plant to a control room were it is logged and automatically analyzed. The data are generated every second, processed, and presented in graphical formats depicting “pitting index” - a measure of the propagation of stable corrosion pits; and “instability index” - a measure of adverse conditions in the process stream that may lead to pitting corrosion. The system is configured to provide warning alerts corresponding to periods of high levels of pitting corrosion activity. The paper demonstrates how the corrosion monitoring data can be utilized for process optimization, maintenance planning, and materials selection for the PTA plant.