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Overview: Due to its excellent mechanical and physical properties, titanium (and titanium alloys) has a low density combined with high strength. The ratio of its tensile strength σb to its density ρ, namely σb/p, is 200, which is almost the highest among all metal materials. At the same time, it possesses excellent corrosion resistance; titanium’s outstanding chemical stability in highly corrosive environments, along with its strong self-passivation ability in electrolytes (aqueous solutions), have led to its faster adoption and spread compared to many other metals. Generally speaking, industrial pure titanium is the most commonly used material in titanium containers due to its better corrosion resistance compared to α-phase titanium alloys and β-phase or α+β-phase titanium alloys, which allows for a wider range of applications. Although its strength is not as high as that of β-phase or α+β-phase titanium alloys, it has good plasticity and is easy to shape. Selection principles: 1) Deformed titanium materials should be supplied in the annealed state (M), while titanium castings should be supplied in their cast state. 2) Among the wrought industrial pure titanium grades TAO, TA1, TA2, and TA3, TA3 is not suitable for use in components such as cylinders, heads, and bellows due to its poor cold formability; it can only be used in components that are not subjected to cold deformation or in which the degree of cold deformation is minimal. 3) The TA9 titanium-palladium alloy (Ti-0.2Pa) and the TA10 titanium-nickel-molybdenum alloy (Ti-0.8Ni-0.3Mo) are mainly used in high-temperature, humid chlorine-containing environments as well as in situations where crevice corrosion may occur (with TA9 being particularly resistant to crevice corrosion); they are especially suitable for use in components such as tube sheets and flanges. 4) When a galvanic couple is present, the following measures can usually be taken: ① Coat one of the metals (usually the metal that is corroded by the galvanic couple) with an insulating material ； ②A completely insulated insulating material is added between the two metals to prevent the formation of a corrosion cell ； ③Increase the distance between different metals, or change their positions, to avoid cathode contamination ； ④Avoid the formation of a corrosion cell with a large cathode and a small anode between the two metals ； ⑤Cathodic protection is used. 5) In the event of crevice corrosion, the following measures can generally be taken: ① Adopt a reasonable structural design to minimize or eliminate areas where fluid can get trapped and the formation of deposits, thereby improving the flow of fluid within the equipment and preventing the creation of dead zones. When using bolt connections internally, welding should be preferred; for spot welds, continuous lap welding or butt welding should be used. ②Palladium plating, oxidation, or anodization is applied to the surfaces where crevice corrosion may occur. ③Filling the gaps with putty mixed with NiO or nickel powder or MoO3 powder can sometimes also prevent gap corrosion. ④Titanium materials that are more resistant to crevice corrosion, such as titanium-palladium alloys (TA9) or titanium-nickel-molybdenum alloys (TA10), should be used; these materials are particularly suitable for flanges where there is crevice corrosion on the sealing surfaces. 6) In the event of hydrogen embrittlement cracking, the following measures can generally be taken: ① Use titanium materials with a low hydrogen content. ②To prevent hydrogen absorption during the manufacturing process, it is necessary to avoid the incorporation of iron particles into the titanium surface during operations such as cutting, stamping, rolling, and welding ； Heat processing and heat treatment heating must be carried out in a heating furnace with a slightly oxidizing atmosphere ； For some titanium devices with complex structures, it is difficult to create weld joints that are protected by an inert gas on the back side; therefore, it is necessary to prevent hydrogen absorption during welding. ③Select an appropriate operating environment: When used in dry or wet hydrogen environments at temperatures ranging from 71 to 316°C, the presence of a certain amount of oxygen and moisture can prevent hydrogen absorption. In oxidative media, neutral media, weakly reducing media, or reducing acids containing oxidants, titanium generally does not absorb hydrogen, or it absorbs hydrogen very slowly ； However, titanium hydrogen embrittlement may occur when the titanium surface is contaminated with iron, has defects, suffers local corrosion, or is under abnormal operating conditions. Titanium is prone to hydrogen embrittlement in environments where it suffers from general corrosion or localized corrosion. ④The hydrogen absorption resistance can be improved through surface treatments such as high-temperature oxidation and anodization. ⑤Corrosion-resistant alloys are used to improve titanium’s corrosion resistance and prevent hydrogen-induced embrittlement. 7) Titanium materials must not be used in environments with liquid chlorine or dry chlorine gas. 8) Titanium materials must not be used in fuming nitric acid with a water content of less than 2% or a free nitrogen dioxide content of more than 6%. 9) Titanium materials should be avoided in stress-corrosion environments. Any medium with a tendency to stress corrosion cannot be used, even if its corrosive effect on titanium is mild and there is still a risk of stress corrosion cracking.