Because titanium (refers to titanium and titanium alloy) has good mechanical and physical properties, its density is small and high strength, tensile strength σb and density ρ ratio σ B/P equal to 200, is almost the highest in all metal materials.

At the same time, it has very excellent corrosion resistance, titanium in the strong corrosive environment shows excellent chemical stability and in the electrolyte (water) has a strong self-passivation ability, so that the application and promotion of titanium materials faster than many other metals.

Selection principle

1) Deformed titanium materials shall be supplied in the annealed state (M) and titanium castings shall be supplied in the cast state.

2) TA3 of pure titanium TAO, TA1, TA2, TA3, due to its poor cold deformation ability, is generally not suitable for cylinder, head and bubble cover and can only be used for parts without cold deformation or with small amount of cold deformation.

3) TA9 Ti/Pd alloy (Ti-0.2Pa) and TA10 Ti/Ni-Mo alloy (Ti-0.8Ni-0.3Mo) are mainly used in high temperature medium containing wet chlorine and where crevice corrosion may exist (especially TA9 is more resistant to crevice corrosion). They are especially suitable for tube plate, flange and other parts.

4) If there is a galvanic couple, usually the following measures can be taken:

①A metal (usually a galvanic corrosion metal), with insulation materials;

②A completely isolated insulating material is added between the two metals to avoid the formation of corrosion batteries;

③Open the distance between different metals, or change the position between them, to avoid cathode pollution;

④ Avoid the formation of a large cathode, small anode corrosion battery between the two metals;

⑤ Use cathodic protection.

5) If there is crevice corrosion, the following measures can usually be taken:

① Adopt reasonable structural design, try to avoid or eliminate the gap retention area and scale phenomenon, improve the flow state of fluid in the equipment, avoid the formation of dead zone, internal bolt connection, try to use welding connection, spot welding lap welding or butt welding as far as possible.

②On the surface where crevice corrosion may occur, surface palladium coating, oxidation or anodization are used.

③Filling the gap with putty mixed with NiO or nickel powder or MoO3 powder can sometimes avoid crevice corrosion.

④ Choose more crevice corrosion resistant titanium materials, such as titanium palladium alloy (TA9) or titanium nickel-molybdenum alloy (TA10), these titanium materials are especially suitable for flange sealing surface has crevice corrosion flange.

6) In case of hydrogen embrittlement rupture, the following measures can usually be taken:

①  Select titanium with less hydrogen.

② Prevent hydrogen absorption in the process of processing and manufacturing, that is, to avoid the titanium surface embedded in iron particles in the process of cutting, stamping, rolling, welding and other manufacturing; Thermal processing and heat treatment heating must be carried out in a heating furnace with a slightly oxidizing atmosphere; For some titanium equipment with complex structure, it is difficult to realize the inert gas protection welding joint on the back, so as to prevent the pollution of hydrogen absorption during welding.

③Choose the appropriate use environment: in the temperature of 71~316℃ dry hydrogen and wet hydrogen environment, such as containing a certain amount of oxygen and moisture, can prevent hydrogen absorption. Titanium in oxidizing medium, neutral medium, weak reducing medium or reducing acid containing oxidant, usually does not occur titanium hydrogen absorption, or very slow hydrogen absorption; However, when the titanium surface is contaminated by iron, the surface has defects, local corrosion or abnormal conditions occur, hydrogen absorption embrittlement of titanium may occur. Titanium is prone to hydrogen absorption embrittlement in the environment of overall or local corrosion.

④Through surface treatment, such as high temperature oxidation, anodizing treatment, can improve the hydrogen absorption resistance.

⑤The corrosion resistant alloy is adopted to improve the corrosion resistance of titanium and prevent hydrogen absorption embrittlement of titanium.

7) Titanium is strictly prohibited to be used in liquid chlorine and dry chlorine.

8) Titanium material is strictly prohibited to be used in the water content of less than 2% or free nitrogen dioxide is greater than 6% fuming nitric acid.

9)Titanium materials should be avoided in the stress corrosion environment. Any media with a tendency to stress corrosion, even if the corrosion of titanium is slight, there is still a risk of stress corrosion rupture, is not to be used.of stress corrosion rupture, is not to be used.