On-line corrosion monitoring at the High Sulfur Test Center. Final report

The corrosion performance of alloys used in flue gas desulfurization (FGD) outlet ducting and stacks was assessed over two years period in a 4MW pilot wet FGD system. Twelve sensor assemblies were installed in the post-absorber duct section, one sensor for each material tested. Candidate materials included austenitic stainless steels, nickel alloys and titanium alloys. In the first of the tests, the sensor assemblies were exposed under the same environmental conditions as the adjacent duct wall. In subsequent tests, other FGD operating conditions were simulated, including changes in degree of reheat and cycling of the gas temperature. Finally, the sensors were exposed when chemical additive tests were in progress in the absorber. Results showed that Alloy C276, Alloy C22, titanium grades 2 and 7 were the most corrosion-resistant alloys tested, though less expensive austenitic stainless steel could provide adequate service in FGD environments subjected to continuous condensation. Scrubber additives, such as thiosulfate, could adversely affect the corrosion rate of certain alloys. Other work has demonstrated that unlined carbon steel can be made to operate satisfactorily provided that the environment within the outlet duct is controlled within target parameters. It was concluded that opportunities exist for cost reductions and improved cost-effectivenessmore » of materials selection in many new and existing FGD installations.« less