The a.c. corrosion of stainless steel—II. The polarization of ss304 and ss316 in acid sulfate solutions

Abstract

An experimental study has been made to examine the effect of alternating current on the corrosion of Types 304 and 316 Stainless Steels in acidic aqueous sulfate solutions. The polarization curves were measured with an alternating voltage (AV) modulation technique and the pitting behavior of the stainless steels was examined with a constant potentiostatic coulometry and SEM photomicrography. The experiments were made with sinusoidal, square and triangular AV over a range of AV frequencies from 60 to 1000 Hz and AV magnitudes from 0 to 1000 mV rms. The results indicate that AV increased the critical current density for passivity and decreased the passive potential regime by shifting the transpassive potential toward the active direction and increasing the current density in the passive regime. The effect was similar to the addition of chloride ions to the corrosion environment. AV enhanced the pitting of the stainless steels at both the passive and transpassive potentials. Passivity was destroyed regardless of the AV waveforms; triangular wave caused the severest destruction, followed by sinusoidal and square waves.