Effects of Fluoride and Chloride Ions on Corrosion of Titanium Grade 7 in Concentrated Groundwaters

Titanium Grade 7 (Ti-7) was tested for both general and local corrosion in environments consisting of fluoride and chloride salts added to simulated groundwaters. Tests were conducted on both U-bends and disks in order to determine the extent of corrosion under stressed and unstressed conditions. The experiments were run over a broad range of temperatures and pH values for periods of up to 164 days. It was found that Ti-7 is susceptible to intergranular attack in some of the test solutions at moderately elevated temperatures, leading to conspicuous localized corrosion. Pitting was detected within 14 days, with pit depths on the order of 0.1 mm. Surface defects appeared to promote the initiation of pitting. The same environment caused stress corrosion cracking failure in a statically stressed U-bend.