1. Overview of Titanium Valves
Although titanium is a highly chemically active metal, it has excellent corrosion resistance to many corrosive media. Because titanium has a low affinity for oxygen, it is very easy to combine with oxygen to form a strong and dense passive oxide film on its surface. This oxide film is very stable and difficult to dissolve. Even if it is damaged in many harsh corrosive working conditions, it can repair and regenerate itself as long as there is sufficient oxygen. Titanium valves mainly use the good stability and self-passivation ability of the oxide film of titanium metal materials in a strong corrosive environment to resist strong corrosion in a variety of harsh working conditions.
The key to whether titanium valves can resist the corrosion of working environment media lies in the chemical stability of the "passive oxide film" on its surface in the corrosive medium. For neutral, oxidizing, and weakly reducing media environments, the "passive oxide film" itself has good stability. For high temperature or low pH reducing corrosive media, in order to improve the stability of its "passive oxide film", corrosion inhibitors (such as air, water, heavy metal ions and anions, etc.) can be added, such as titanium surface ion modification treatment, anodizing treatment and other methods to improve the corrosion resistance and surface hardness of "titanium" in reducing media to meet the use requirements. For various treatment methods of titanium valves, our company has mastered a complete set of treatment processes through cooperation with metal research institutes, major universities, etc., after years of research.
2. Corrosion resistance characteristics and applications of titanium and titanium alloy valves
Common titanium and titanium alloy materials are: TA1, TA2, TA9, TA10, TA12, TC4, Gr2, Gr3, Gr5, Gr7, Gr12.
(1) Titanium valves are almost not corroded in the atmosphere, fresh water, sea water, and high-temperature water vapor;
(2) Titanium valves are very resistant to corrosion in alkaline media; Titanium valves have strong resistance to chloride ions (CI-) and have excellent resistance to chloride ion corrosion;
(3) Titanium valves have good corrosion resistance in media such as aqua regia, sodium hypochlorite, chlorine water, and wet chlorine gas; The corrosion resistance of titanium in organic acids depends on the reducing or oxidizing properties of the acid;
(4) The corrosion resistance of titanium valves in reducing acids depends on whether the medium has a corrosion inhibitor;
(5) Titanium valves are light in weight and have high mechanical strength, and are widely used in aviation and military fields.
Titanium valves have high cost-effectiveness and can resist the erosion of various corrosive media. In civil corrosion-resistant industrial pipelines, they can solve corrosion problems that are difficult to solve with stainless steel, copper or aluminum valves. They have the advantages of safety, reliability, and long service life. Widely used in chlor-alkali industry, soda ash industry, papermaking industry, smelting industry, pharmaceutical industry, fertilizer industry, fine chemical industry, textile fiber synthesis and bleaching and dyeing industry, basic organic acid and inorganic salt production, nitric acid industry, etc.
3. Precautions for the selection of titanium valves
(1) Titanium valves should not be used for red smoke nitric acid with a concentration of ≥98% or containing >6% free NO;
(2) Titanium valves should not be used in dry chlorine gas with a water content of less than 1.5%. Natural explosions will occur in pure oxygen (PO>35%);
(3) Titanium valves should not only consider corrosion in corrosive media containing hydrogen, but also pay full attention to the harm of hydrogen embrittlement to titanium valves;
(4) Titanium valves should fully consider the point gap and stress corrosion tendency in corrosive media;
(5) The operating temperature of titanium valves should not exceed 330℃. If it exceeds, it is recommended to use heat-resistant titanium alloy materials.
When selecting titanium valve materials, the working temperature of the corrosive medium, the composition of the medium, the concentration of each component, and the water content should be fully considered. Special consideration should be given to the tendency of titanium valves to have cracks and stress corrosion in the working medium, spontaneous combustion and explosion, and attention should be paid to catastrophic damage factors such as hydrogen embrittlement caused by titanium absorbing hydrogen due to various reasons. It is strictly forbidden to use titanium valves in working conditions where the above damage may occur.
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