Because the titanium material is very easy to absorb hydrogen, even in the temperature is not high in the environment, due to the hydrogen diffusion rate is large, but also easy to make the titanium hydrogen embrittlement and produce intergranular microcracks.

1、Why is hydrogen embrittlement the cause of almost all the accidents that occur in titanium equipment used in the chemical industry? How to prevent hydrogen embrittlement rupture?
Because titanium is very easy to absorb hydrogen, even in the temperature is not high environment, due to the hydrogen diffusion rate is large, but also easy to make titanium hydrogen embrittlement and intergranular microcracks. The sources of hydrogen are as follows.

a. Hydrogen, an impurity element contained in titanium;

b - Due to the hydrogen in the environment to a certain concentration, in the high temperature state of titanium or surface passivation film is destroyed titanium easy to absorb hydrogen embrittlement;
c - Due to the selection of the wrong material, the use of titanium should not be used in the environment of titanium; or due to the structure of the design of the irrational (such as the existence of crevices or with the contact of dissimilar metals produced by galvanic coupling erosion) caused by local corrosion, resulting in the absorption of hydrogen embrittlement; d - Processing and manufacturing processes, which can also lead to hydrogen embrittlement and intergranular microcracks.

d - Processing manufacturing process (such as the wrong acid washing formula or excessive ⻓ acid washing time, welding failed to protect the surface of titanium material and manufacturing process of iron contamination, etc.) caused by hydrogen absorption
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 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-oxidising atmosphere of the heating furnace; for some of the complex structure of the titanium equipment, the back of the welded joints is difficult to achieve the gas protection to prevent the welding of hydrogen absorption pollution.

c- Select the appropriate use of the environment: when the temperature of 71 ~ 316 ° C in the dry hydrogen and wet hydrogen environment, such as containing a certain amount of oxygen and moisture can prevent hydrogen absorption. Titanium in oxidising media, neutral media, weakly reducing media or reducing acids containing oxidising agents usually does not absorb hydrogen or absorbs hydrogen very slowly; however, hydrogen embrittlement may occur when the surface is contaminated, when surface defects, localised corrosion occurs, or when abnormal working conditions occur. Titanium is susceptible to hydrogen embrittlement in environments where general or localised corrosion occurs.

d. Hydrogen resistance can be improved by surface treatment (high temperature oxidation, anodisation, etc.). 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, it has been found that titanium stress corrosion rupture occurs in fuming nitric acid, methanol, tri-gas ethylene, high temperature chlorides, molten metal salts, carbon tetrazolium, uracil, organic solvents, hydrogen and bromine vapour and other media.

Factors causing stress corrosion cracking are as follows.
(1) Environment The factors include the type and concentration of ions, the cationic H value of the solution, temperature, conductivity, additives and flow rate.
(2) Mechanical factors Tensile stress must be present in the system where stress corrosion rupture occurs. Tensile stresses arise 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 The sensitivity of industrial pure titanium to stress corrosion cracking increases as the oxygen content increases.