Factors controlling pitting of stainless steels under wet deposits in splash zones in chlorine dioxide bleaching

Oxidizing power of chlorine dioxide: In some preliminary tests, different methods of adding chlorine dioxide to the "deposit" were tested, Fig. 2. In the case of Curve A, 2 mL of chlorine dioxide solution (7 g/L) were added onto the wet pulp deposit at the start of the experiment (27 min), and 1 ml of the same solution was added at a later stage (110 min). In cases B (single dose) and C (continuous flow), a similar chlorine dioxide solution was added only into the beaker and not onto the pulp deposit. On the basis of these results, continuous pumping of chlorine dioxide solution was chosen for the experiments.

The test results for steel S31726 at 70 [Symbol Not Transcribed]C are summarized in Fig. 5, and those for steel S31254 at 70 [Symbol Not Transcribed]C and 85 [Symbol Not Transcribed]C in Fig. 6. The accumulation of chloride ions during the tests was estimated as described above. For tests where no indication of pitting was observed within the first hour or so, an open triangle denotes the composition of the solution when the potential has reached the value of 700 mV. The start of eventual pitting is denoted by filled "diamonds", and the end of tests without pitting by open squares. Trend lines for the lowest chloride content.