Surface qualification of AISI 316L bioprocessing tanks applying on-sitelectrochemical measurements

Abstract

The passivation level of AISI 316L bioprocessing tanks of roughness average of 0.8 μm mechanically polished was assessed. The on-site inspections were performed after tanks manufacturing and in distinct surface conditions: (i) after 12 months of industrial operation, (ii) with biofilm adhesion, (iii) after chemical passivation treatment. The PassivityScan inspection instrument was used in on-site measurements of passivation level applying the open circuit potential and cyclic potentiodynamic polarization techniques. The results showed that the tank inner surface in as-built condition obtained a relative low passivation level (Eprot –Ecorr < 150 mV(Ag|AgCl|KCl 3 mol/L) and high corrosion kinetic. The passivation level and durability of the surface were reduced after 12 months of operation. A worst-case scenario was noted with biofilm adhesion given that the surface was not able to repassivate. It worth to emphasize that the passivation treatment increased the passivation level to 520 mV(Ag|AgCl|KCl 3 mol/L) and reduced the passivation current density from 20 to 0.7 μA cm–2. It was concluded that a passivated AISI 316L tank reach a better operational reliability, and also the chemical passivation treatment should be done every 12 months in order to restorage the passive film resistance.