A Technique for Characterizing Crevice Corrosion Under Hydrothermal Conditions

Abstract

A technique was developed to monitor crevice corrosion of Grade-12 titanium In a high magnesium synthetic brine under hydrothermal conditions. The current between the cathode and anode, and the potential of the whole crevice assembly, provide information on th-ious stages of corrosion. Occasionally, the decoupled poten «,f the cathode and anode are measured to give supporting information about the crevice conditions. A parallel test is run on a specimen which has small wells to collect crevice solution whose pH is determined at room temperature. The current/potential results show that the crevice corrosion incubation period for a Grade-12 titanium crevice formed between two Teflon plates is approximately two days at 150°C. Optical and SEM observations show that the corrosion starts as isolated pitting which spreads along the surface as shallow pits. The corrosion conditions change significantly as the T102 corrosion product fills the crevice, and the rate of corrosion may be greatly reduced after several days. The rate of crevice corrosion of commercial purity (Grade-2) titanium under similar conditions is approximately three orders of magnitude higher. In this case, active dissolution of metal starts during the initial heating of the autoclave and the incubation period is negligible.

Risk assessment of uniform and localized corrosion of alloy 22

“…Evidence in some alloys indicates stifling of localized corrosion under the open circuit conditions. [18,19] In addition, the aqueous corrosion conditions in thin water films are generally known to be less conservative. For example, the separation of anode and cathode and reduced aqueous conductivity may promote stifling of localized corrosion as well.…”

“…The fast corrosion rates were varied from 10 Ϫ4 to 10 Ϫ2 cm/year; the fast corrosion times were varied from 1.19 ϫ 10 Ϫ4 to 1. 19 year. The fast corrosion rate was obtained from the current transient of Figure 4.…”

“…The fast corrosion rates would have to be at a rate of 10 Ϫ3 cm/year for 1. 19 year to decrease the WP lifetime to less than 10,000 years. Similar WP lifetimes less than 10,000 years would be obtained at a rate of 10 Ϫ2 cm/year for 0.119 years.…”