11933 Titanium and Its Alloys

Titanium and its alloys combine good mechanical properties of strength, toughness, and fatigue with high corrosion resistance, particularly in seawater environments. Titanium is, however, an expensive material. Ti and its alloys are finding increasing applications in deep seas, heat exchangers, drilling risers, pumping, and piping of fresh and seawater. A distinct advantage of Ti and its alloys is its high resistance to microbial-induced corrosion (MIC). Care, however, should be taken in high-carbonate-containing waters where carbonate deposits can build up and accelerated underdeposit corrosion can occur. The Ti/6%Al/4%V grades have good resistance to SCC in brackish or seawaters. Of added value, particularly for thin-wall applications, for example, heat exchangers, is the very high resistance to pitting of Ti and its alloys. Caution should be taken when coupling Ti and its alloys to other materials as in most cases Ti will act as the cathode and can be harmful where conditions can lead to the uptake of hydrogen. In the case of Ti used in conjunction with cathodic protection, potentials less than -0.9V (vs. SCE) should be used. Similarly, the application of Ti and its alloy should be restricted to pH ranges between 3 and 12 to avoid possible hydrogen damage. Crevice corrosion of Ti and Ti alloys will not occur in environments of any pH below 70°C [59].

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