Necessary condition for hydrogen embrittlement of titanium rods in electrolyte solution

In chemical plants, the environmental conditions for hydrogen embrittlement can be roughly divided into: non-oxidizing acids with pH below 3; Strong alkali solution with pH higher than 12; Organic acids with pH = 3; Salt solution containing F-, I-, neutral solution containing H2S. Under the above conditions, some cases are due to homogeneous corrosion, and some are related to local corrosion, but all are due to the generation of hydrogen by electrochemical reactions. Of course, there's another category where hydrogen is already in the environment.

For titanium condenser or condenser cooled by sea water, when titanium metal and aluminum brass tube are mixed or titanium metal tube and Muntz copper alloy tube plate are used at the same time, cathodic protection is usually used to reduce the corrosion of copper alloy, when the protection potential is too low, it will cause hydrogen absorption of the efficiency tube. From the analysis of these hydrogen kneeling cases, the hydrogenation of titanium rods in the electrolyte solution generally must meet the following three conditions at the same time:

(1) The pH of the solution (which may also be local) must be below 3 or above 12.

(2) There must be some mechanism for producing hydrogen, such as through uniform corrosion, local corrosion, surface mechanical scratches or pollution to reduce the corrosion potential (overall or local) of titanium metal in the electrofresh to below the hydrogen evolution potential, or because the cathodic protection potential is too negative directly on the surface of titanium hydrogen evolution.

(3) The ambient temperature must be higher than 80 ℃, otherwise although there is a mechanism of hydrogen evolution and cause titanium to absorb hydrogen, hydrogen diffusion is slow when it is lower than 80 ° C, and hydrogen kneeling is difficult to occur, unless the serious tensile stress promotes the low temperature diffusion of hydrogen or the hydrogen generated by the electrochemical reaction sometimes causes a high chamber partial pressure.

The electromotive force of hydrogen evolution corrosion is much lower than that of oxygen reduction corrosion, and is oxidized with titanium. The reaction potential of Ti - I ++ne is similar. When the addition of oxygen (including oxidizer) in the solution is slow and difficult to compete with hydrogen evolution, hydrogen evolution corrosion is often dominant. Hydrogen evolution usually occurs under the following conditions.

(1) The standard potential of the metal is very negative, such as titanium metal in the case of continuous removal of the film.

(2) The corrosion potential of the metal is lower than the hydrogen evolution potential in the electrolyte. At high concentrations, as in strongly reducing acids.

(3) Due to the formation of complex ions, the concentration of titanium ions in the solution is always kept very low.