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Advantages and major problems of titanium tubes for power stations

Through a large number of experiments and application examples, it is proved that the application of titanium tube in power plant condenser has great technical and economic advantages. From the economic point of view, taking the condenser tube price of 1000MW nuclear power unit (about 50,000 pieces) as an example, the average annual leakage of aluminum copper tube is lO, while the titanium tube has no leakage for 40 years, according to the calculation of the condenser's service time. The problems existing in the application of titanium tubes in power stations are summarized as follows:

1. Corrosion problem
Coastal power station condensers use seawater as cooling water. Because sea water contains a large amount of sediment, suspended matter, Marine life and various corrosive substances, the situation is more serious in the salt water alternating with the river water. The traditional corrosion methods of copper platform metal tubes include integral corrosion (uniform corrosion), corrosion, stress corrosion, etc. Because titanium has excellent corrosion resistance, it eliminates the seawater leakage accident caused by corrosion of titanium tube condenser. But because titanium tubes are not as resistant to corrosion as copper alloy tubes, they can produce toxic substances on their surfaces. Therefore, Marine organisms are easy to attach to the inner wall of the titanium tube, affecting the heat transfer effect. Therefore, it is necessary to have the corresponding cleaning device.

2. Hydrogen absorption
Titanium and hydrogen affinity is very high, the surface has a dense passivation film, in many strong corrosive media has a strong corrosion resistance. It absorbs hydrogen very easily. It occurs at room temperature and rapidly absorbs hydrogen at high temperatures (such as 100 ° c), the solution limit of hydrogen in titanium is very small (about 20ppm), if the limit is exceeded, hydride (TtH2) will precipitate on the titanium surface. With the increase of titanium content on the surface, the impact value and elongation of titanium decreased rapidly. In addition, when the old unit is reformed, because the tube plate is made of copper alloy material and the condensing tube is made of titanium material, cathodic protection devices need to be installed to prevent electrochemical corrosion. For example, the condenser at the Hitachi power plant, which is cooled with seawater, has titanium tubes and copper alloy plates. When the protective potential is lower than 0.75V (ScE), the outlet of the titanium tube absorbs hydrogen, and the hydrogen content reaches 650ppm after one year of use. At a potential of 0.5 to 0.75 V (SCE), titanium does not absorb hydrogen at room temperature.

3. Vibration problem
Titanium tube has good corrosion resistance. The titanium condenser will not be damaged by corrosion leakage, but the titanium tube may be damaged by vibration. In order to avoid the vibration problem of titanium tubes, it is necessary to determine the appropriate partition spacing when making titanium capacitors. When the old unit is reformed, it is necessary to investigate whether the original partition spacing is suitable for the titanium tube.