Instant ecological pickling on stainless steel welds and innovative surface passivation

The aim of this work is to improve the innovative process for pickling and passivating stainless steel welds and surfaces in order to obtain complete removal of non-protective oxides and to restore the passivation. The treatment, based on an electrochemical principle, uses specific electrolytes and patented electrodes: the advantage is to increase the corrosion resistance, working speed (instant process) and surface appearance on stainless steel, avoiding the traditional pickling solutions (which usually contain high concentrations of strong and toxic acids). Different solutions were prepared using low concentrations of weak organic acids, e.g. citric, oxalic, sulphamic, gluconic and lactic, up to the new neutral (pH 7, acid free) solution used to gain high passivation on stainless steel surfaces. This aspect is very important to reduce the hazardousness of the solution compared to the pure phosphoric acid (standard solution) and moreover to the traditional pickling acids. The best solutions in terms of aesthetic result were tested in terms of corrosion resistance (free and accelerated) XPS analysis, on TIG and MIG samples. A S.E.M. analysis is used to show the influence of the carbon fiber effect depending on the technology used (transformer vs inverter) and electrolyte. A number of real field application is presented, both manual and custom/automation.