Multitechnique corrosion monitoring in flue gas desulfurization systems: Phase 1, Interim report

Advanced electrochemical corrosion monitoring equipment has been used to investigate the effect of short term changes in process conditions in FGD systems. Laminar flush mounted electrochemical probes, fabricated from Type 316L stainless steel were exposed in the flue gas environment of a model scrubber at the LaQue Center for Corrosion Technology, Inc. (LCCT) and an operating dual alkali scrubber system at the R.M. Schahfer Generating Station. The monitoring system employed a combination of electrochemical impedance, zero resistance ammetry, electrochemical potential noise and coupling current noise to identify the degree of corrosivity of the outlet duct environment and pit initiation and propagation characteristics of the stainless steel. Monitored trends of corrosion were confirmed by coupon exposure and visual inspection but the electrochemical methods were able to identify that short term variations in process conditions were responsible for the corrosion damage. The pitting type corrosion was linked to the deposit of salts in conjunction with the absorption of moisture. Thus, cycling of parts of the system through a wet/dry condition is largely responsible for the corrosion. A fall in temperature of less than 10/sup 0/F (5/sup 0/C) is sufficient to cause a humidity rise which stimulates the corrosion under the deposits. 10more » refs., 88 figs., 6 tabs.« less