The Acceleration of Pitting Corrosion of AISI 304 Stainless Steel by Ultraviolet Light Illumination in Acidic Chloride Solution

Abstract

The influence of ultraviolet light (UV, λ = 254 nm) illumination on pitting of AISI 304 stainless steel was investigated using critical pitting chloride concentration (CPCC) measurement. In a H2SO4 solution with a gradually increased chloride ion concentration, the CPCC was measured for AISI 304 samples at 0.65 VSCE and 30 °C under different illumination conditions. Direct UV illumination significantly reduced the CPCC value from 0.286 ± 0.018 M (in the dark) to 0.087 ± 0.008 M. Both the passivation process in pure H2SO4 solution and pit growth in acidic chloride solution were affected by UV illumination. The passive film formed in 0.1 M H2SO4 solution with UV illumination (in which a smaller ratio of metal oxides to metal hydroxides was observed) had a lower corrosion resistance than that formed in the dark, indicating the decreased stability of passive film after UV illumination. In addition, UV illumination also accelerated the pit growth rate of 304 samples in acidic chloride solution. After the CPCC tests, lacy cover and rough edges were observed with pits formed in the dark, while no lacy cover was present for pits developed under UV illumination.