It was found that the major materials problems are occurring with outlet ducts and stack linings. Outlet ducts and stacks are critical components in that failures may require complete boiler shutdown and loss of generating capacity for lengthy periods due to the lack of standby components or bypass capability. Accordingly, EPRI funded a study by Battelle on the performance of candidate materials in the outlet ducts of FGD systems at two utility plants. Because of the impact of materials failures on FGD system reliability, EPRI is currently funding a study by Battelle on the causes of these failures. This study involves site visits for field evaluations of the failures, laboratory analyses of samples collected in the field, and analysis of the data to establish the causes of the failures. Information on outlet ducts is presented in this paper.