抄録
A study on pitting corrosion of carbon steel heat exchanger tubes was carried out to evaluate the effect of corrosion inhibitors and pretreatments of tube surface in several water qualities. The effect of inhibitors on the prevention of pitting corrosion tends to increase in the order: phosphonate based inhibitors<zinc-phosphonate based inhibitors<zinc-chromate based inhibitor. The distribution of pit depth varied with time. However, it was found that the maximum pit depths fit the extreme value distribution and the statistical analysis of extreme values is useful in evaluation of pitting corrosion. The scale parameters (α) were almost independent of the treatments, while the location parameters (λ) varied with the respective treatments. An addition of zinc ions and increasing the concentration of M-alkalinity decreased the pit depth, and consequently λ. Pretreatments of tube surface also influenced the pitting processes and λ. In comparison with no pretreatment and degreasing, pickling could markedly decrease the pitting tendency.
