Abstract
The effects of cathodic polarisation switch-off on the passivation of AISI 304L stainless steel in air and its crevice corrosion susceptibility in 3.5 wt.% NaCl aqueous electrolyte were investigated. Scanning Kelvin probe (SKP) data showed that the oxide film is significantly destabilised and the rate of steel passivation in air is slowed down. Thermal desorption analysis (TDA) highlighted that hydrogen absorption is proportional to the applied cathodic current density. A special crevice corrosion set-up was designed to realise simultaneous reproducible monitoring of potential and galvanic current to study the impact of prior cathodic polarisation on crevice corrosion onset.
Highlights
The technique of impressed current cathodic protection (ICCP) was introduced in 1928 for the protection of steel gas pipelines in the United States, and it is widely used for many industrial applications [1]
Cathodic polarisation leads to thermodynamic non-stability of water molecules, creating atomic hydrogen at the surface of the cathode (Equation (1)), where H(ads) is adsorbed hydrogen
It is well known that hydrogen induced by cathodic polarisation can modify the oxide film composition by reducing the Fe3+ to Fe2+ [31] and by the reaction of H+ ions with O2−
Summary
The technique of impressed current cathodic protection (ICCP) was introduced in 1928 for the protection of steel gas pipelines in the United States, and it is widely used for many industrial applications [1]. Hydrogen absorbed in the steels and the passive films during cathodic polarisation may affect the stability of the passive layer and, the susceptibility of steel against corrosion. As suggested in the study of Cui et al [21], an increase in metallic iron indicates that the passive film becomes thinner compared to uncharged AISI 304 due to the destabilisation caused by hydrogen. The investigation of AISI 316 (UNS S31603) by Ningshen et al showed an increase in the passive current, accompanied by a decrease in the pitting potential after hydrogen pre-charging in 0.1 N NaOH + 250 ppm As2 O3 [14]. To investigate the impact of cathodic polarisation switch-off on the initiation of crevice corrosion, simultaneous monitoring of potential and galvanic current was carried out in a specially designed crevice assembly cell. Was carried out to quantify the total hydrogen content and to analyse its evolution after various desorption times
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