Numerical analysis of industrial electrolytic pickling for cold-rolled flat stainless steel using secondary current distribution

Electrolytic neutral pickling (ENP) is a process to remove undesired surface oxides formed during the annealing of cold-rolled flat stainless steel products. It is a key production step that ensures the corrosion resistance of the material. However, the process suffers from poor current and energy efficiency, which causes it to be the bottleneck step in the production of a wide range of grades. In this article, a finite element model is implemented and validated using data collected during typical operation in a real industrial cell configuration. While the cell voltage is, in general, overestimated by the model, the slope of the polarization curve is predicted by the model with a relative error of 4%. The by-pass current and the voltage efficiency are evaluated numerically for different values of the cell current. The strip current efficiency (i.e. the relative strip current) is found to be above 90% for a typical cell configuration under typical operating conditions. This value is much larger than most reported values in the literature, and suggests that by-pass current is not the limiting factor in industrial ENP cells. The voltage efficiency, found to be under 20%, and the competition with oxygen evolution, seem to be more concerning points. The low voltage efficiency is mainly due to the high ohmic overpotentials, which account between 50% and 60% of the total cell voltage.