Effect of Time on Corrosion Rates in Sulfuric Acid Predicted from Electrochemical Data

Effect of time on the cathodic polarization behavior of Ni, Cr, Ti, Al, and six Ni-Cr-Al and Ni-Cr-Ti alloys was determined in hydrogen saturated, 1N sulfuric acid at 22 C (71 F). Corrosion current densities (i_corr) obtained for these specimens, using the beta-extrapolation technique, were generally found to be strongly time dependent. Corrosion current densities for Ni, Cr, and the six ternary alloys decreased with time and approached steady state values after about 72 hours exposure to the electrolyte. Corrosion current density for Al decreased markedly during the initial 24-hour period; further exposure did not appreciably affect the corrosion current density. The corrosion current density for titanium decreased only slightly as the exposure time was increased. All materials exhibited steady state corrosion current densities after sufficient exposure to the acid. Corrosion rates predicted using the steady state corrosion current densities correlated well with rates obtained from long time, weight loss tests. It was established that accurate corrosion rates can be predicted from electrochemical data only after steady state corrosion current densities have been obtained.