Titanium Metals Corporation
Corrosion Resistance of Titanium
STRESS CORROSION CRACKING
TIMETAL 35A and 50A are essentially immune to stress-corrosion cracking (SCC) in seawater. This has been confirmed many times as reviewed by Blackburn et al (1973)^(16). Other unalloyed titanium grades with oxygen levels greater than 0.2% may be susceptible to SCC under some conditions. Some titanium alloys may be susceptible to SCC in seawater if highly-stressed, pre- existing cracks are present. TIMETAL 6-4 ELI (low oxygen content) is considered one of the best of the high strength titanium-base alloys for seawater service.^(17)

CORROSION FATIGUE
Titanium, unlike many other materials, does not suffer a significant loss of fatigue properties in seawater.^(11,18,19) This is illustrated by the data in Table 9.

BIOFOULING
Titanium does not display any toxicity toward marine organisms. Biofouling can occur on surfaces immersed in seawater. Cotton et al (1957) reported extensive biofouling on titanium after 800 hours immersion in shallow seawater.^(11) The integrity of the corrosion resistant oxide film, however, is fully maintained under marine deposits and no pitting or crevice corrosion has been observed.

It has been pointed out that marine fouling of titanium heat exchanger surfaces can be minimized by maintaining water velocities in excess of 2 m/sec.^(20) Chlorination is recommended for protection of titanium heat exchanger surfaces from biofouling where seawater velocities less than 2 m/sec are anticipated.

MICROBIOLOGICALLY INFLUENCED CORROSION
Titanium, uniquely among the common engineering metals, appears to be immune to MIC. Laboratory studies confirm that titanium is resistant to the most aggressive aerobic and anaerobic organisms.^(55) Also, there has never been a reported case of MIC attack on titanium.

CREVICE CORROSION
Localized pitting or crevice corrosion is a possibility on unalloyed titanium in seawater at temperatures above 180 degrees F (82 degrees C). TIMETAL Code-12 and 50A Pd offer resistance to crevice corrosion in seawater at temperatures as high as 500 degrees F (260 degrees C) and are discussed more thoroughly in the section on chlorides.

GALVANIC CORROSION
Titanium is not subject to galvanic corrosion in seawater, however, it may accelerate the corrosion of the other member of the galvanic couple (see Galvanic Corrosion).

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