Titanium tubes are light in weight, high in strength and have superior mechanical properties. It is widely used in heat exchange equipment, such as tube heat exchangers, coil heat exchangers, serpentine tube heat exchangers, condensers, evaporators and delivery pipes. Many nuclear power industries use titanium tubes as standard tubes for their units
Titanium alloy is an alloy based on titanium and added with other elements. There are two types of isomorphic crystals of titanium: below 882°C, it is α-titanium with a close-packed hexagonal structure, and above 882°C, it is β-titanium with a body-centered cubic structure.
Alloying elements can be divided into three categories according to their influence on phase transformation temperature:
① Elements that stabilize the α phase and increase the phase transition temperature are α-stabilizing elements, including aluminum, carbon, oxygen, and nitrogen. Among them, aluminum is the main alloying element of titanium alloy. It has obvious effects on improving the normal and high temperature strength of the alloy, reducing the specific gravity and increasing the elastic modulus.
② Elements that stabilize the β phase and lower the phase transition temperature are β-stabilizing elements, which can be divided into two types: isomorphous and eutectoid. Products using titanium alloy. The former includes molybdenum, niobium, vanadium, etc.; the latter includes chromium, manganese, copper, iron, silicon, etc.
③ Elements that have little effect on the phase transition temperature are neutral elements, including zirconium, tin, etc.
Oxygen, nitrogen, carbon and hydrogen are the main impurities in titanium alloys. Oxygen and nitrogen have a large solubility in the α phase and have a significant strengthening effect on titanium alloys, but they reduce the plasticity. It is usually stipulated that the oxygen and nitrogen contents in titanium are below 0.15~0.2% and 0.04~0.05% respectively. The solubility of hydrogen in the α phase is very small. Excessive hydrogen dissolved in titanium alloys will produce hydrides, making the alloy brittle. Usually the hydrogen content in titanium alloys is controlled below 0.015%. The dissolution of hydrogen in titanium is reversible and can be removed by vacuum annealing.
