What are the anti-corrosion effects of titanium in seawater applications
Seawater- general corrosion
Titanium resists corrosion from seawater at temperature up to 600oF(360oC). Titanium tubes exposed to contaminated seawater for 16 years in a condenser surface has showed slight discoloration but no signs of corrosion. Titanium has provided more than 30 years of free-troubled seawater services to the chemical,refining and desalination industries. Exposure of titanium to depths more than 1 mile below ocean’s surface over the years has not produced measurable corrosion. Even with the formation of marine sediments, pitting and crevice corrosion are completely absent. The presence of sulfides does not affect the corrosion resistance of titanium. Exposure of titanium to marine astomspheres or splash or tidal zones can not cause corrosion.
Erosion
Titanium has the ability to resist high-speed seawater erosion. Seawater at speeds up to 120 ft/sec only results in minimal increases in erosion rates. The presence of abrasive particles such as sand is extremely detrimental to copper and aluminum-based alloys, but has little effect on the corrosion resistance of titanium. Titanium is considered one of the best cavitation resistant materials available for seawater service.
Stress corrosion cracking
Grades 1 and 2 are largely immune to stress corrosion cracking (SCC) in seawater. Other unalloyed titanium grades with an oxygen content greater than 0.25% may be susceptible to SCC under certain conditions. Some titanium alloys may be susceptible to SCC in seawater if high-stress, pre-existing cracks are present. Grade 5 ELI (low oxygen content) is considered one of the best high strength titanium based alloys for seawater service.
Corrosion fatigue
Unlike many other materials, titanium does not suffer a significant loss of fatigue properties in seawater.
Biofouling
Titanium does not have any toxicity to marine life. Biofouling can occur on surfaces submerged in seawater. Titanium has been reported to produce massive biofouling after 800 hours of immersion in shallow seawater. However, the integrity of the corrosion-resistant oxide film was fully maintained under the marine sediments, and no pitting or crevice corrosion was observed. It has been pointed out that marine contamination of titanium heat exchanger surfaces can be minimized by maintaining water velocities in excess of 2 m/s. Chlorination is recommended to protect titanium heat exchanger surfaces from biofouling with seawater flow velocity less than 2 m/s
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