Titanium and its alloys provide excellent resistance to general localized attack under most oxidizing, neutral and inhibited reducing conditions. They also remain passive under mildly reducing conditions, although they may be attacked by strongly reducing or complex media. Titanium metal’s corrosion resistance is due to a stable, protective, strongly adherent oxide film. This film forms instantly when a fresh surface is exposed to air or moisture. The oxide film on titanium is very stable and is only attacked by a few substances, most notably, hydrofluoric acid. Titanium is capable of healing this film almost instantly in any environment where a trace of moisture or oxygen is present because of its strong affinity for oxygen. Because of the excellent properties of titanium and titanium alloys, these materials are commonly applied in equipment fabrication.
Industrial Applications of Titanium
Titanium and titanium alloy equipment is commonly applied in industries of the following corrosion resistant services: Alkaline Media Bromine Iodine and Fluorine Chlorine, Chlorine chemicals and chlorides Inorganic Salt Hydrochloric Acid Oxidizing acids Phosphoric Acid Seawater Sulfuric Acid
Titanium is very resistant to alkaline media including solutions of sodium hydroxide, potassium hydroxide, calcium hydroxide and ammonium hydroxide. Regardless of concentration, titanium generally exhibits corrosion rates of less than or equal to 5 mpy (0.127 mm/yr). Near nil corrosion rates are exhibited in boiling calcium hydroxide, magnesium hydroxide, and ammonium hydroxide solutions up to saturation.
Bromine Iodine and Fluorine
The resistance of titanium to bromine and iodines is similar to its resistance to chlorine. It is attacked by the dry gas but is passivated by the presence of moisture. Titanium is reported to be resistant to bromine water. However, titanium is not recommended for use in contact with fluorine gas.
Chlorine, Chlorine chemicals and chlorides
Chlorine and chlorine compounds in aqueous solution are not corrosive toward titanium because of their strongly oxidizing natures. Titanium is unique among metals in handling these environments. The corrosion resistance of titanium to moist chlorine gas and chloride containing solutions is the basis for the largest number of titanium applications. Titanium is widely used in chlor-alkali cells; dimensionally stable anodes; bleaching equipment for pulp and paper; heat exchangers, pumps, piping and vessels used in the production of organic intermediates; pollution control devices; and even for human body prosthetic devices. The equipment manufacturer or user faced with a chlorine or chloride corrosion problem will find titanium’s resistance over a wide range of temperatures and concentrations particularly useful.
Inorganic Salt
Titanium is highly resistant to corrosion by inorganic salt solutions. Corrosion rates are generally very low at all temperatures to the boiling point. The resistance of titanium to chloride solutions is excellent. Other acidic salt solutions, particularly those formed from reducing acids, may also cause crevice corrosion of unalloyed titanium at elevated temperatures.
Hydrochloric Acid
Pure titanium is corrosion resistant to about 7% hydrochloric acid at room temperature.
Oxidizing Acids
Titanium is highly resistant to oxidizing acids over a wide range of concentrations and temperatures. Common acids in this category include nitric, chromic, perchloric, and hypochlorous (wet Cl2) acids.
Titanium resists corrosion by seawater to temperatures as high as 500°F (260°C). Titanium tubing, exposed for 16 years to polluted seawater in a surface condenser, was slightly discolored but showed no evidence of corrosion. Titanium has provided over thirty years of trouble-free seawater service for the chemical, oil refining and desalination industries. Exposure of titanium for many years to depths of over a mile below the ocean surface has not produced any measurable corrosion. Pitting and crevice corrosion are totally absent, even if marine deposits form. The presence of sulfides in seawater does not affect the resistance of titanium to corrosion. Exposure of titanium to marine atmospheres or splash or tide zone does not cause corrosion.
Sulfuric Acid
Titanium is resistant to corrosive attack by dilute solutions of pure sulfuric acid at low temperatures. At 32°F (0°C), unalloyed titanium is resistant to concentrations of about 20 percent sulfuric acid. The presence of certain multi-valent metal ions or oxidizing agents in sulfuric acid inhibit the corrosion of titanium in a manner similar to hydrochloric acid.
Phosphoric Acid
Unalloyed titanium is resistant to naturally aerated pure solutions of phosphoric acid up to 30 percent concentration at room temperature. This resistance extends to about 10 percent pure acid at 140°F (60°C) and 2 percent acid at 212°F (100°C). Boiling solutions significantly accelerate attack.
Titanium Process Equipment Fabrication
Suntech Metal Equipment is capable to design and fabricate the following types of titanium process equipment and parts:
If you need more information for Titanium applications or fabrications of titanium process equipment, please contact us at Technical Solutions, Suntech Metal Equipment will provide satisfactory solutions.
