Assessing the Corrosion Rate of Carbon Steel in Steam Cycle Chemistries Using X-Ray Computed Tomography and Electrochemical Methods

Corrosion management and mitigation from steam cycle contaminants are top priorities for power plant operators. As such, accurate estimation of corrosion rate dependencies on steam cycle chemistry contamination levels are of critical importance. While electrochemical methods can detect corrosion rate increases due to known corrosion agents, like chloride or sulfates, they often underrepresent the danger they present to power plant operations due to their inability to quantify localized corrosion values and the extent of under-deposit corrosion (UDC). High resolution X-ray computed tomography (CT) scans can bridge this gap and provide a means of measuring of localized corrosion rates to better inform the risks associated with specific steam cycle contaminants. If combined with conventional electrochemical monitoring, these methods provide a more comprehensive picture of the corrosion risk associated with particular steam cycle chemistry environments. Herein, we compare corrosion rates obtained from these methods for carbon steel samples exposed to steam cycle chemistries at 300 °C and 124 bar for 60 hours in a laboratory setting. Both linear sweep voltammetry (LSV) and linear polarization resistance (LPR) were used to estimate corrosion rate throughout the exposure test. After the exposure test, X-Ray CT scans were done at a resolution of 710 nm over a sample region of 1.4 mm to determine general and localized corrosion rates. The highest rates calculated for the localized corrosion were all an order of magnitude higher than the general corrosion values calculated from LSV and LPR. The largest discrepancy between the general and localized corrosion rate was observed for chloride contamination. For this case, general corrosion rates were between 0.21 and 0.57 mm y -1 , whereas localized corrosion rates were as large as 5.55 mm y -1 .