From an economic point of view, the price of titanium tubes for a 1000Mw condenser nuclear power unit (about 50,000 condenser tubes are needed) is taken as an example. Assuming the service life of the condenser is 40 years, the average annual leakage of aluminum brass tubes is 10, while the titanium tube has no leakage in 40 years. A large number of tests and application examples have proved that the use of titanium tubes in power station condensers has great advantages both technically and economically. The following are three problems to be solved by the application of titanium tubes in power stations:
1. Corrosion problem
The condenser of the power station uses seawater as cooling water. Since seawater contains a large amount of sediment, suspended matter, marine organisms and various corrosive substances, the situation is more serious in the alternating fresh and salty water of seawater and river water. The traditional copper titanium tubes are corroded in the following ways: Corrosion (uniform corrosion), erosion, erosion and stress corrosion, etc. Because titanium has excellent corrosion resistance, seawater leakage accidents caused by corrosion of titanium tube condensers have been eliminated. However, due to the good corrosion resistance of titanium tubes, unlike copper alloy tubes, a toxic substance is not produced on the surface. Therefore, marine organisms are easily attached to the inner wall of the titanium tube, thus affecting the heat transfer effect, so a corresponding cleaning device must be provided.
2. Hydrogen absorption problem
Although the surface of titanium has a dense passivation film and is very corrosion-resistant in many highly corrosive media, it is very easy to absorb hydrogen due to the great affinity between titanium and hydrogen. It occurs at room temperature and absorbs hydrogen rapidly at high temperatures (such as 100°C). The solid solution limit of hydrogen in titanium is very small (about 20ppm). If the limit is exceeded, hydride (TtH2) will be precipitated on the titanium surface. As the surface TiH2 increases, the impact value and elongation of titanium decrease rapidly. In addition, when renovating old units, since the tube sheet is made of copper alloy and the condenser tube is made of titanium, it is necessary to use a cathodic protection device to prevent electrochemical corrosion. For example, the condenser of Hitachi's power plant uses seawater cooling, and titanium tubes and copper alloy plates form a couple. When the protection potential is lower than -0.75 v (ScE), the outlet titanium tube end absorbs hydrogen, and the hydrogen content reaches 650 ppm after one year of use; if the potential is selected to be -0.5~0.75 v (scE), titanium will not absorb hydrogen at room temperature."
3. Vibration problem
Due to the good corrosion resistance of titanium tubes, titanium condensers will not leak and be damaged due to corrosion, but titanium tubes may be damaged due to vibration. To avoid the vibration problem of titanium tubes, when manufacturing titanium condensers, it is necessary to determine the appropriate partition spacing; when renovating old units, it is necessary to examine whether the original partition spacing is suitable for titanium tubes.
