Online environmental monitoring of pitting corrosion in brine using potential noise method with pipe-type electrodes under residual stress

Stainless steel SUS316L are generally used in salt manufacturing plants exposed to high-temperature and high-concentration brine, however, pitting corrosion can still occur. Online environmental monitoring to prevent pitting corrosion is required for safe operation. In this research, online environmental monitoring system was developed using a pipe-type electrode with a residual tensile stress of 250 MPa and a titanium pipe electrode as the reference electrode. These electrodes were installed in circulation test apparatus, and 10 wt% NaCl solution was flowed at 1.8 m/s. The potential was measured at 50 °C to 80 °C during the test. Numerous pits were observed on the inner surface of the pipe-type electrode after test. RD (Rapid Drop)-type potential noise was detected during the test. The event frequency was increasing from 0.41 h −1 at 50 °C to 1.73 h −1 at 80 °C. Linear relationship between cumulative event count and time was confirmed. As a result, the event frequency is a reliable indicator of environmental corrosivity. The developed method demonstrated the feasibility of online environmental monitoring for pitting corrosion and could be extended to monitor crevice corrosion and stress-corrosion cracking.