Field testing of stainless steels in paper machine environment

At the wet ends of paper machines and especially at splash zones, pitting and crevice corrosion of stainless steels caused by chloride (C[Symbol Not Transcribed]) and thiosulphate (S[Symbol Not Transcribed]O[Symbol Not Transcribed]) ions is a common phenomenon. Chloride ions originate from wood floated in sea water, supplied water and chemicals added to the pulp mix. Mechanical pulp brightened with dithionite (S[Symbol Not Transcribed]O[Symbol Not Transcribed]) is the main source of thiosulphate ions (f.1). Thiosulphate pitting is known to occur within a narrow voltage potential range (f.2) and molar ratio [Equation Not Transcribed] (f.3). The most sensitive region for thiosulphate pitting is in the potential range of 0 to -400 mV[Symbol Not Transcribed] (f.4) and molar ratios of 10 to 30 (f.3). To initiate thiosulphate pitting corrosion on type 316L stainless steel the molar ratio [C[Symbol Not Transcribed]]/[SO[Symbol Not Transcribed]] should be [Symbol Not Transcribed]1 (f.3).