Behavior of Type 316 Steel in Acidic Sulfate Solutions at 300-350 Degree C

摘要

Most cation resin beds in service in CEGB power stations, and particularly those in AGR stations, are regenerated with sulfuric acid. Slippage results in trace levels of sulfate passing into the boilers. Previous work has shown that in once-through boilers, feedwater containing 2 mu g kg/sup -1/ of sulfate could concentrate at localized dry-out sites to form solutions having from 0.1 to 7 wt percent of solute. It has been shown also that if the sulfate was present in an acidic solution and it were to be in contact with Type 316 austentitic superheater steel, then intergranular corrosion and intergranular cracking could occur. Previous data, including some unreported results, are tabulated and discussed. The current work had two main objectives. The first was to extend the previous investigations to examine a wider range of acidic sulfate concentrations (as indicated by calculations on the concentration of solute in feedwater), the influence of environment pH, and the effect of sensitization of specimens. The second objective was primarily concerned with elucidating the causes of scatter in the results. This involved examining the influence of electrode potential, the aging characteristics of the environment, and the method of applying stress to the specimens. (ERA citation 13:046772)