Hot salt stress corrosion of titanium flange and titanium alloy flange

Although titanium flanges have good corrosion resistance, they may still suffer from corrosion and stress corrosion in some environmental media, among which the hot salt stress corrosion is the first to be noticed. The results show that, except pure titanium, almost all titanium flanges have the same degree of thermosalt stress corrosion tendency under high temperature, stress and the presence of halides (such as NaF, NaCl, NaBr, NaI). For most alloys, the thermosalt stress corrosion temperature range is 288 - 427℃. The corrosion tendency is related to the metallurgical factors such as alloy composition and processing history. The high-alumina and high-oxygen alloys and the coarser weidler microstructure processed by B or B are more sensitive to stress corrosion.

The cause of metal embrittlement caused by salt stress corrosion is believed to be related to hydrogen embrittlement. Under the action of high temperature and stress, the halide hydrolyzes and generates HCl gas. HCl further interacts with titanium to generate hydrogen, i.e

NaCl+H20—HCl+NaOH

2HCl+Ti—TiCl2+2H

In addition to hot salt stress corrosion, titanium flanges have a certain degree of stress corrosion tendency in red smoky nitric acid, N2O4, methanol solution containing hydrochloric acid and sulfuric acid. When using specimens with sharp notch for stress corrosion and turbidity test, aqueous solution containing 3.5%NaCl may reduce the corrosion fracture life.

The stress corrosion tendency of titanium flange is related to the alloy composition and heat treatment. Increasing the content of aluminum, tin and oxygen can accelerate the stress corrosion. On the contrary, the addition of B stabilizing elements, such as aluminum, vanadium, group, silver, etc. in the alloy can alleviate the effect of stress corrosion. Titanium flange has a tendency to liquid metal embrittlement such as molten cadmium and titanium contact will cause cadmium brittle, mercury has a similar effect. Above 340℃, silver can promote corrosion cracking of TA7 alloys.