This report evaluates materials for cooling systems that use aerated, treated geothermal or other high-chloride water, such as the Raft River 5 MW(e) geothermal power plant. The tests were originally run to find a replacement tube material for the Raft River 5 MW(e) Pilot Power Plant's isobutane carbon steel condenser, and also gave a preliminary evaluation of alternative materials for other high-saline, aerated cooling water systems.
Overall the report favours highly-alloyed ferritic stainless steels such as 29-4 (29%Cr) and the proprietary alloy Sea-Cure. Throughout its sections, though, Ferralium® 255 is noted as providing equivalent performance to either of these alloys.
Test results at high chloride
The ferritic stainless steels examined at 100,000 ppm chloride were SEA-CURE, 29-4, 29-4-2 and 29-4-C. SEA-CURE and 29-4 were the only alloys to show any weight loss. SEA-CURE corroded at 0.05 mdd (0.01 mpy) after four weeks of exposure - roughly 1/20th of the rate seen at 50,000 ppm. The 29-4 alloy showed greater general corrosion at 100,000 ppm than at 50,000 ppm, and also exhibited crevice corrosion. None of the ferritic stainless steels pitted at 100,000 ppm chloride. Corrosion of Ferralium® 255 was similar to that of 29-4.
