Although titanium flanges have good corrosion resistance, they may suffer from corrosion and stress corrosion in some environmental media.The test shows that, except pure titanium, almost all titanium flanges have the same degree of thermal salt stress corrosion tendency under high temperature, stress and working environment with halides (such as NaF, NaCl, NaBr and NaI).For most alloys, thermal-salt stress corrosion sensitive temperature range must be 288-427℃.The corrosion tendency is related to the composition of the alloy, the processing history and other metallurgical factors.
The reason for metal embrittlement caused by heat-salt stress corrosion is believed to be related to hydrogen embrittlement. Under the action of high temperature and stress, the halide hydrolyzes to form HCl gas. HCl further interacts with titanium to form hydrogen, that is
NaCl 10 H20 -- HCl 10 NaOH
2HCl 10 Ti -- TiCl2 for 12 hours
In addition to hot-salt stress corrosion, titanium flange has a tendency of stress corrosion in the solution of red fuming nitric acid, N204, methanol containing hydrochloric acid and sulfuric acid to a certain extent. When stress corrosion and turbidity tests are conducted with sharp notch specimens, the 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.On the contrary, the addition of b stabilizing elements in the alloy, such as aluminum, vanadium, group, silver, etc. can alleviate the stress corrosion effect.
Some titanium flanges have a tendency to embrittlement of liquid metals such as molten cadmium in contact with titanium causing cadmium embrittlement, and mercury has a similar effect.Above 340℃, silver can induce corrosion and cracking of alloys such as TA7.