Effect of aldehyde bisulfite compounds on corrosion of stainless steels in SO2-containing media

An effect of temperature t (25, 40, 60, and 80 degrees C) an the corrosion rate K of stainless steels (10X17H13M2T, 08X21H6M2T, 08X22H6T, and 10X18H10T) and CT3 in approximately 50 mM SO2 solution (a model of liquor in the production of sulfite cellulase) is studied. For stainless steels, the plots of K vs. t are nonmonotonic: K is high at 40 and 80 degrees C and low at 60 degrees C. When 57 mmol/l ethanal is added to this SO2 solution, approximately 40% SO2 is bound into a relatively stable aldehyde bisulfite compound (ABSC), i.e., into easily detachable SO2. Thereby, the solution's pH increases by unity, and K decreases at t = 40-60 degrees C. By contrast, when 114 mmol/l ethanal is added, unstable ABCS forms, which partially decomposes into starting substances at high t, and a plot of K vs. t again becomes similar to that described for pure 50 mM SO2 solution.