Some of the localized attack and SCC appeared to be related to weld heat affected zone regions. This may be corrected with post weld annealing to remove carbide precipitation and to re-solution the major alloying elements. No data in this survey specifically referenced the use of cobalt base alloys or their corrosion behavior. In some cases, cobalt base alloys can give better performance than nickel base alloys particularly for high temperature oxidation or hot corrosion. This is usually because there materials have generally lower levels of Cr and Mo and nickel base alloys specifically designed for high resistance to hot chloride containing solutions.
Titanium alloys have excellent resistance to hot chloride containing aqueous environments.
However, they can have problems and may not be suitable for use at high temperatures due to creep problems. Nonetheless, Ti Grade 7 was tested in a very acidic condition up to 500 C in one case survey. No attack and excellent corrosion resistance was observed for this alloy. Ceramics were tested only in SCWO conditions and did not resist that harsh environment. At high pH 12, alumina, silicon carbide, silicon nitride and zirconia dissolved .