Several Local Corrosion Characteristics Of Titanium Tube Materials

Crevice corrosion
The resistance of titanium pipes to crevice corrosion is particularly strong, and crevice corrosion only occurs in a few chemical media. The crevice corrosion of titanium is closely related to temperature, chloride concentration, pH value, and crevice size. It is reported that crevice corrosion is prone to occur when the temperature of wet chlorine gas is above 85 ℃. Practice has proven that reducing temperature is one of the effective methods to prevent crevice corrosion, and titanium crevice corrosion has also occurred in high-temperature sodium chloride solutions. In summary, titanium alloys such as Ti-0.2Pd should be used for parts and components that are prone to crevice corrosion, such as sealing surfaces, expansion joints between tube plates and tubes, plate heat exchangers, contact areas between tray and tower body, and fasteners inside the tower. Gaps and stagnant flow areas should be avoided during design. The fasteners inside the tower should not be connected with bolts as much as possible. The expansion joint with dense sealing welding structure is better for the tube plate and tube than simple expansion joint. For flange sealing surfaces, asbestos pads should not be used, and polytetrafluoroethylene film wrapped asbestos pads should be used.
High temperature corrosion
The high-temperature corrosion resistance of titanium pipes depends on the characteristics of the medium in which they are located and the performance of their own surface oxide film. Titanium can be used as a structural material up to 426 ℃ in air or oxidizing atmospheres, but at around 250 ℃, titanium begins to significantly absorb hydrogen. In a complete hydrogen atmosphere, when the temperature rises above 316 ℃, titanium becomes brittle in hydrogen absorption. Therefore, without extensive testing, titanium is not suitable for use in chemical equipment with temperatures above 330 ℃. Considering hydrogen absorption and mechanical properties, the operating temperature of all titanium pressure vessels should not exceed 250 ℃, and the upper limit of the operating temperature for titanium tubes used in heat exchangers is about 316 ℃.
Stress corrosion
Except for a few media, industrial pure titanium has good resistance to stress corrosion, and the phenomenon of titanium equipment damage caused by stress corrosion is still rare. Industrial dull titanium only produces stress corrosion in media such as fuming nitric acid, certain methanol or hydrochloric acid solutions, high-temperature hypochlorite, molten salt with a temperature of 300-450 ℃, or NaCl containing atmosphere, carbon disulfide, n-hexane, and dry chlorine gas. The tendency of stress corrosion cracking of titanium in nitric acid gradually increases with the increase of NO2 content and the decrease of water content. The stress corrosion tendency of titanium reaches a high level in anhydrous nitric acid containing 20% free NO2. When concentrated nitric acid contains more than 6.0% NO2 and less than 0.7% H2O, even at room temperature, industrial pure titanium will undergo stress corrosion cracking. China has experienced severe stress corrosion and explosion when using titanium equipment in 98% concentrated nitric acid. Industrial pure titanium exhibits sensitivity to stress corrosion cracking in a 10% hydrochloric acid solution, while titanium undergoes stress corrosion in a solution containing 0.4% hydrochloric acid and methanol.
In summary, titanium has strong corrosion resistance in acidic and alkaline environments. It can form an oxide film in acidic and alkaline environments, but there are also conditions. We hope this can be helpful for you when using our materials.