In chemical plants, the environmental conditions where hydrogen embrittlement occurs can be roughly divided into: non-oxidizing acids with a pH value below 3; strong alkaline solutions with a pH value above 12; organic acids with a pH value of 3; containing F- and I- Salt solution, a neutral solution containing H2S. Under the above conditions, some cases are due to homogenous corrosion, and some are related to localized corrosion, but all produce hydrogen due to electrochemical reactions. Of course, there are other types of environments that already contain hydrogen.
For titanium condensers or condensers that use sea water cooling, when titanium and aluminum brass tubes are used together or when titanium tubes and Montz copper alloy tube sheets are used at the same time, cathodic protection is usually used to reduce the corrosion of the copper alloy. When the protection potential is too low Will cause the effect tube to absorb hydrogen.
Analysis of these hydrogen knee cases shows that the hydrogenation of titanium rods in the electrolyte solution must generally meet the following three conditions:
(1) The pH of the solution (it may also be local) must be below 3 or above 12.
(2) There must be some mechanism for generating hydrogen, such as uniform corrosion, local corrosion, surface mechanical scratches or pollution to reduce the corrosion potential (whole or partial) of titanium in the fresh food to below the hydrogen evolution potential, or due to the cathode If the protection potential is too negative, hydrogen is directly deposited on the titanium surface.
(3) The ambient temperature must be higher than 80 ℃, otherwise there is a mechanism of hydrogen evolution and titanium absorption of hydrogen, but hydrogen diffusion is slow when it is lower than 80 ℃, and hydrogen kneeling is difficult to occur, unless severe tensile stress promotes the low temperature diffusion of hydrogen or electricity The hydrogen produced by the chemical reaction sometimes causes a high chamber partial pressure.
The electromotive force of the hydrogen evolution type corrosion is much lower than that of the oxygen reduction type corrosion, and it is oxidized with titanium; the reaction potential of Ti-Ti ++ ne is close. When the supplement of oxygen (including oxidant) in the solution is difficult to compete with hydrogen evolution, hydrogen evolution corrosion is often dominant. Hydrogen evolution usually occurs in the following cases. Titanium plate
(1) The standard potential of the metal is very negative, such as the case where titanium is continuously removed.
(2) The corrosion potential of the metal is lower than the hydrogen evolution potential in the electrolyte. When the concentration is very high, such as strong reducing acid.
(3) Due to the formation of complex ions, the concentration of titanium ions in the solution is always kept very low.