Laboratory‐scale simulation of industrial neutral electrolytic pickling as a bipolar system—Parameters affecting indirect polarization pickling of annealed stainless steel

Abstract

As the production of stainless steel increases, environmental concerns due to an increasing demand of production capacity, require an efficient use of energy and materials. Efficient removal of otherwise slow-to-dissolve chromium oxide layer can be achieved with electrochemical pre-pickling before final mixed acid pickling. Neutral electrolytic pickling can be used to rapidly dissolve chromium oxides but suffers from low current efficiency of both the reaction and the system. In order to study the effect of critical parameters for the current efficiency of the system, a pickling device was assembled. A system current efficiency factorial analysis of bipolar neutral electrolytic pickling was conducted for temperature, electrolyte concentration, cell potential, and electrode-to-sample distance. Lowering the concentration of electrolytes shows potential to increase current efficiency significantly as conductivity can be used to reduce electrode-to-electrode short-circuiting, which is the biggest cause of decreased efficiency in neutral electrolytic pickling. Increasing the temperature has a positive effect on efficiency, despite increased conductivity, possibly from increasing reaction kinetics. K E Y W O R D S bipolar electrode, current efficiency, factorial analysis, neutral electrochemical pickling, stainless steel This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Finite Modeling and Simulation of the Effects of Neutral Electrolytic Pickling Process Parameters on EN 1.4404 Steel Strips

“…When the applied external voltage was 5-15 V, it was calculated that only 40-50% of the steel strip's surface was sufficiently polarized. This value is within the range of previous studies, which indicated 40% from direct measurements of the current [32] and 60-65% calculated by mathematical modeling [39]. The loss of potential was mainly due to the electrolyte's resistance.…”

“…Figure 10 shows that, even though the electrolyte's properties did not affect the polarization behavior of the electrodes (as shown in Figure 7), a significant part of the polarizing power was lost to the electrolyte's resistance. Nevertheless, the calculated current densities were within the industrial levels of 500-3500 A m −2 reported in numerous studies [31,32,40].…”

“…Furthermore, of the current supplied to a pickling cell, only 20-30% is used in the polarization of stainless steel. If we consider the side reactions on the steel's surface, the current efficiency of oxide scale removal can be less than 10% [32].…”