Induction Time Studies of Fe18Cr and 430 SS under Open Circuit Conditions in Chloride-Containing Sulfuric Acid

Abstract

Abstract In order to promote the effective and efficient application of corrosion resistant metals and alloys in mineral processing environments, the Bureau of Mines, U.S. Department of the Interior, has characterized the effect of aggressive ions on the corrosion and passive behavior of two stainless steels, Fe18Cr and AISI 430 SS. Samples prepassivated in oxygen saturated 1 N H2SO4 at 0.6 V NHE and then released to open circuit and aged for times ranging from 10 min to 80,000 min (55 days), were subsequently exposed to chloride ion concentrations ranging from 5 to 44 parts per thousand (ppt). Susceptibility to chloride ion attack was determined as a function of time in solution (film aging time), chloride ion concentration [Cl−], and open circuit potentials (E) at the time chloride was added by measuring the amount of time (induction time, t) required for a sample to begin corroding after adding the chloride ion. The experimentally determined induction times were fitted to an equation of the form: 1/t=K Em[Cl−]n where K, m, and n are empirically determined constants. Results obtained for short (<100 min) aging times were different from those for long (100 to 80,000 min) aging times. For Fe18Cr exposed for short film aging times prior to addition of the chloride, larger [Cl−] resulted in shorter induction times, and higher values of E resulted in longer induction times. For 430 SS exposed for short film aging times, and for 430 SS and Fe18Cr exposed for longer film aging times prior to addition of chloride ions, both larger [Cl−] and higher values of E resulted in shorter induction times.