Technical Capabilities of Titanium
Titanium has excellent resistance to the following types of corrosion:
Uniti Titanium supplies and markets commercially pure titanium products that have excellent resistance to corrosion in a wide variety of environments including seawater, salt brines, inorganic salts, bleaches, wet chlorine, alkaline solutions, oxidizing acids, and organic acids. Titanium is incompatible with fluorides, strong reducing acids, very strong caustic solutions, and anhydrous chlorine. Due to its combustibility, titanium is not suitable for pure oxygen service. Titanium does not release any toxic ions into aqueous solutions, which would contribute to pollution.
Crevice Corrosion Cracking
Uniti Titanium products have excellent resistance to crevice corrosion cracking in salt solutions and generally outperform stainless steels. Unalloyed titanium products (grades 1, 2, 3 and 4) typically do not suffer crevice corrosion at temperatures below 80°C (175°F) at any pH. Palladium alloyed CP titanium products (grades 7, 11, 16 and 17) are more resistant and typically do not suffer crevice corrosion at temperatures below 250°C (480°F) at pH greater than 1.
Microbiologically Influenced Corrosion (MIC)
Titanium alloys appear to be immune to MIC. They do suffer bio-fouling, but this can be controlled by chlorination (which does not impair titanium).
Although it is a reactive metal, due to the extreme stability of the passive film which forms on its surface, titanium typically exhibits noble behavior. Thus it functions as the cathode when coupled with other metals. Titanium is not affected by galvanic corrosion, but can accelerate corrosion of other metals.
Stress Corrosion Cracking
Uniti Titanium products have excellent resistance to stress corrosion cracking in hot chloride salt solutions.
Titanium alloys exhibit excellent resistance to flow induced and erosion corrosion at velocities to above 40 m/sec.
Titanium alloys are susceptible to hydrogen embrittlement under some circumstances. This is generally less of a problem for the low-strength grade 1 and grade 2 titanium alloys than for higher strength titanium alloys. Absorption of hydrogen by titanium normally occurs when the temperature is above 80°C (175°F), and the titanium is galvanically coupled to an active metal or an impressed current or the pH is less than 3 or greater than 12.
Uniti Titanium CP products are readily weldable using GTAW (gas tungsten arc welding) or TIG (tungsten inert gas) processes if adequate shielding is provided using pure inert gas (argon or helium). Use of a trailing shield is recommended. Titanium must be free of oil, grease or other contamination before welding. Pre-heat or post-heat are not required. Friction welding, laser welding, resistance welding, plasma arc welding, electron beam welding, and diffusion bonding can also be used.
Uniti Titanium is readily formed at room temperature, using techniques and equipment suitable for steel. When correct parameters have been established, tolerances similar to those attainable with stainless steel are possible with titanium and its alloys.
Three factors make forming of titanium somewhat different from forming of other metals.
- The room temperature ductility of titanium, as measured by uniform elongation, may be less than that of other common structural metals. This means that titanium may require more generous bend radii and has lower stretch formability.
- The modulus of elasticity of titanium is about half that of steel. This causes significant spring back after forming titanium for which compensation must be made.
- The galling tendency of titanium is greater than that of stainless steel. This necessitates close attention to lubrication in any forming operation in which titanium is in contact (particularly moving contact) with metal dies or other forming equipment. The various grades of titanium exhibit differences in formability. Grades 1, 11 and 17 titanium, which are the softest and most ductile grades, exhibit the greatest formability. The slightly greater strengths of Grades 2, 7 and 16 titanium are still quite formable, but less so than Grades 1, 11 or 17. The higher strength of Grade 4 titanium makes it the least formable of the CP titanium alloys. Normally, titanium surfaces are acceptable for forming operations as received from the mill. Gouges and other surface marks introduced during handling should be removed by sanding. To prevent edge cracking, burred and sharp edges should be filed smooth before forming.