A Numerical and Experimental Sensitivity Analysis on Electrochemical Neutral Pickling for Stainless Steel Using Secondary Current Distribution

Abstract

Electrochemical neutral pickling (ENP) is an extended process used in the stainless steel industry to remove the oxide surface layer formed during the annealing process. The absence of strong acids such as nitric acid results in a minimum loss of base material, improve operators working conditions, and reduces the pickling environmental impact, while keeping relatively low operation and maintenance costs. However, despite its multiple benefits, ENP may become the bottleneck for integrated annealing and pickling line, especially when processing thin austenitic and duplex steels. Fortunately, there is room for improvement as the total Faradaic efficiency of the process in typical operation is in general low (around 20 – 30 % for austenitic materials) [1]–[3], while estimations of the energy efficiency are as low as to 1 - 2 % [4].This work provides guidelines to the design and operation of ENP cells to increase the oxide removal rate. We focus on the effect of the geometry and some operational parameters, using secondary current distribution. The simulations are validated against experimental, and a sensitivity analysis of the oxide removal rate with respect to the geometry and some key operational parameters is performed. The electrode-to-strip and the inter-electrode distances were found to have a determining effect on the total cell resistance and on its so-called geometric efficiency (relative current reaching the strip). Moreover, an optimal range for the ratio of these distances is proposed. In addition, the strip thickness and width were found to significantly affect the cell performance, especially for the thinnest gauges.