Hydrogen embrittlement of titanium vessels

1.Why is it that almost all the bad accidents occurred in titanium equipment used in chemical industry are caused by hydrogen embrittlement rupture? How to prevent hydrogen embrittlement?

Because titanium is very easy to absorb hydrogen, even at low temperatures, due to the hydrogen diffusion rate is large, it is easy to make titanium hydrogen embrittlement and produce intergranular microcracks. The sources of hydrogen are as follows.

a- Hydrogen, an impurity element contained in titanium;

b- Because the hydrogen in the environment reaches a certain concentration, titanium in a high temperature state or the surface passivation film is damaged titanium easy to absorb hydrogen embrittlement;.

c - due to material selection errors(chose Titanium Plate, Titanium Forging), the use of titanium or titanium alloy in the environment should not be used titanium; or due to structural design (such as the existence of gaps or contact with dissimilar metals to produce galvanic coupling corrosion) caused by localized corrosion, resulting in hydrogen embrittlement.

d - processing and manufacturing process is not appropriate (such as the wrong pickling formula or too much pickling time, welding failed to protect the surface of the titanium material in the manufacturing process and iron contamination, etc.) caused by hydrogen embrittlement.

Measures to prevent hydrogen embrittlement of titanium equipment are as follows:

a. Selection of titanium materials containing less hydrogen.

b. Prevent hydrogen absorption in the processing and manufacturing process: to avoid cutting, stamping, rolling, welding and other processing and manufacturing process of titanium surface embedded iron particles, heat processing and heat treatment heating must be carried out in the micro-oxidizing atmosphere of the heating furnace; for some of the complex structure of the titanium equipment, the back of the welded joints is difficult to realize the gas protection to prevent the welding of the pollution absorption of hydrogen.

c- Select the appropriate use of the environment: when the temperature in the 71 ~ 316 ° C of dry hydrogen and wet hydrogen in the environment, such as containing a certain amount of oxygen and moisture can prevent hydrogen absorption. Titanium metal in oxidizing media, neutral media, weakly reducing media or reducing acids containing oxidizing agents, hydrogen absorption usually does not occur or very slowly; but when the surface is contaminated, surface defects, localized corrosion occurs or abnormal working conditions occur, hydrogen absorption embrittlement may occur. Titanium in the occurrence of total corrosion or localized corrosion environment, hydrogen embrittlement is prone to occur.

d. Through the surface treatment (high temperature oxidation, anodizing treatment, etc.) can improve the hydrogen resistance. The use of corrosion-resistant titanium alloy, improve the corrosion resistance of titanium, to prevent hydrogen embrittlement.

2, titanium in which medium is easy to produce stress corrosion rupture? What are the factors that cause stress corrosion rupture?

Practice shows that in the stainless steel stress corrosion damage environment, usually titanium does not produce stress corrosion rupture. However, titanium has been found in fuming nitric acid, methanol, three gas ethylene, high temperature chloride, liquid nitrogen tetroxide, molten metal salts, carbon tetrazolium, uracil, organic solvents, hydrogen and bromine vapors, and other media in the occurrence of stress corrosion rupture.

Factors causing stress corrosion rupture are as follows.

(1) Environment The factors include the type and concentration of ions, the cation H value of the solution, temperature, conductivity, additives and flow rate.

(2) Mechanical factors in the occurrence of stress corrosion rupture system must exist tensile stress. Tensile stress comes from residual stresses and working stresses generated during processing and manufacturing. Stress corrosion rupture usually occurs only when the stress intensity factor of the system is greater than the critical stress intensity factor and the strain rate exceeds a certain range.

(3) Metallurgical Factors Industrial pure titanium increases the susceptibility to stress corrosion rupture as the oxygen content increases.