Pitting and crevice corrosion studies of nitrogen bearing stainless steels in bleach media

Traditionally, the pulp and paper industry has been worst hit by corrosion problems because of aggressive environments ranging from hot alkaline sulphide cooking liquors to acidic and highly oxidizing bleach solutions. Corrosion in bleach plant is very severe in stainless steel washer drums, piping, pumps and crevices under pulp deposits and welds in the chlorination stages. Electrochemical pitting and crevice corrosion behavior of type 316L stainless steels containing 0.068%, 0.14% and 0.16% of N was investigated in the washer stages I & II (2,500 ppm of Cl- for stage I and 5,500 ppm of Cl-. for stage II respectively), hydrogen peroxide and hypochlorite stages were studied. The higher breakdown and crevice corrosion potentials obtained indicate the better corrosion resistance of nitrogen bearing stainless steels even in this aggressive environment in comparison with. type 316L SS. ICP-AES studies. indicate a considerable amount of metal ions leached out in this harsh environment. The results of the present investigations revealed that the presence of nitrogen as an alloying element significantly affects the localized corrosion behavior in bleach media.