Titanium and titanium alloy valves

Thread Content

1. Overview of titanium valves Titanium is a metal with high chemical reactivity. However, it exhibits particularly excellent corrosion resistance to many corrosive media. The reason is that titanium has a strong affinity for oxygen; it reacts easily with oxygen to form a strong and dense passive oxide film on its surface. In many media under harsh corrosion conditions, this oxide film is highly stable and difficult to dissolve; even if it is damaged, it can repair itself and regenerate rapidly as long as there is sufficient oxygen available. Titanium valves take advantage of the excellent stability and self-passivation ability of the oxide film formed on titanium metal in highly corrosive environments, to resist severe corrosion under various demanding operating conditions. Whether a titanium valve can resist corrosion by the media in its operating environment depends on the chemical stability of its surface \"passive oxide film\" in the corrosive medium. In neutral, oxidizing, and weakly reducing medium environments, the \"passive oxide film\" possesses excellent stability on its own. For high-temperature or low-PH reducing corrosive media, in order to enhance the stability of their \"passive oxide film,\" it is possible to improve the corrosion resistance and surface hardness of \"titanium\" in such media by adding corrosion inhibitors (such as air, water, heavy metal ions, and anions), as well as through methods like ion modification treatment of the titanium surface and anodization, in order to meet the required performance standards. 2. Corrosion resistance characteristics and applications of titanium and titanium alloy valves. Commonly used titanium and titanium alloy materials include: TA1, TA2, TA9, TA10, TA12, TC4, Gr2, Gr3, Gr5, Gr12, Gr31. ■ Titanium valves show almost no corrosion in atmospheric conditions, fresh water, seawater, and high-temperature steam ； ■ Titanium valves are highly resistant to corrosion in alkaline media ； ■ Titanium valves have a very strong resistance to chloride ions (CI), exhibiting excellent corrosion resistance to chloride ions ； ■ Titanium valves in aqua regia and sodium hypochlorite. It exhibits excellent corrosion resistance in media such as chlorine water and wet chlorine gas ； ■ The corrosion resistance of titanium in organic acids depends on the reducing or oxidizing nature of the acid ； ■ The corrosion resistance of titanium valves in reducing acids depends on whether the medium contains a corrosion inhibitor ； ■ Titanium valves are lightweight and possess high mechanical strength, and are widely used in the aviation and military industries. Due to their excellent cost-performance ratio and ability to resist corrosion from various corrosive agents, titanium valves can address the corrosion issues that arise with valves made of stainless steel, copper, or aluminum in civil corrosion-resistant industrial pipelines. It has advantages such as safety, reliability, and a long service life. It is widely used in the chlor-alkali industry, soda ash industry, pharmaceutical industry, fertilizer industry, fine chemical industry, textile fiber synthesis and dyeing industry, the production of basic organic acids and inorganic salts, the nitric acid industry, and more. 3. Precautions for selecting titanium valves ■ Titanium valves are not suitable for red fuming nitric acid with a concentration greater than 98% or containing more than 6% free NO2 ； ■Titanium valves should not be used in dry chlorine with a moisture content of less than 1.5%; they can experience spontaneous explosion in pure oxygen (PO2 > 35%) ； ■For titanium valves exposed to corrosive media containing hydrogen, in addition to considering corrosion, due attention must be paid to the hazard of hydrogen embrittlement caused by hydrogen to these valves ； ■Titanium valves must take into full account the risk of crevices in corrosive media as well as the tendency to stress corrosion ； ■The operating temperature for titanium valves should not exceed 330°C; if this limit is exceeded, it is recommended to use a heat-resistant titanium alloy material instead. When selecting titanium valve materials, it is necessary to fully consider four aspects: the operating temperature of the corrosive medium in the working environment, the composition of the medium, the concentration of various components, and the water content. Special attention should be paid to the tendency of titanium valves to develop cracks and suffer from stress corrosion in such media, as well as to the risk of spontaneous explosion. Moreover, catastrophic failures caused by titanium absorbing hydrogen due to various factors, such as hydrogen embrittlement, must also be taken into account. Titanium valves must not be used in operating conditions where the above types of damage may occur.