Condensers are important auxiliary equipment for thermal power units. Condenser Pipe At present in the thermal power plant, the condenser commonly used pipe mainly copper alloy tube (including brass alloy tube, white copper alloy tube), titanium tube, stainless steel tube three categories. Condenser Pipe The corrosion problem of the condenser has always been an important issue in the power plant boiler accident.
At present, the main pipe of the condenser is copper alloy, Condenser Pipe and corrosion is affected by many factors, corrosion type is also varied, mainly in the following several.
1. Selective corrosion. Mainly copper-based selective corrosion of zinc. Because the copper tube of the condenser is composed of copper and zinc alloy, because the potential of zinc is lower than copper, Condenser Pipe zinc is easy to become the anode of the corrosion battery and the zinc is selectively dissolved and the copper pipe is corroded. The theory and practice have proved that the corrosion process of brass pipe is related to the performance of copper foil surface protective film. If the maintenance work of brass tube is not good before and after operation, it is more prone to dezincification corrosion. If the coating device is not installed over the same period, Condenser Pipe the condenser copper tube is not the initial coating of FeSO4 and daily film, but also lead to local dezincification corrosion of the important reasons.
2. Brass pitting This corrosion is easy to occur at the rupture of the protective film on the surface of the copper tube. As the cooling water containing C1 - and copper oxidation of Cu + generated unstable Cucl, Condenser Pipe can be hydrolyzed into a stable Cu2O, and the solution of local acidification of thermal equipment corrosion. In addition, if the water quality is unstable, and no comprehensive treatment, Condenser Pipe will inevitably lead to condenser copper pipe scaling, if not on schedule cleaning, uneven surface corrosion to promote corrosion, Condenser Pipe and corrosion and further lead to increased sediment, and ultimately lead to point corrosion perforation.
3. Brush erosion of brass. This type of corrosion can occur in the water side, can also occur in the steam side, but the former mainly. Circulating cooling water suspended solids, Condenser Pipe sediment and other solid granular hard objects on the condenser inlet copper tube impact, friction, after a long run, Condenser Pipe the inlet side of the copper tube before the tube wall rough, although no significant corrosion pits, but the surface rough, Brass matrix exposed, brass thinning. The erosion process of the anode is copper dissolution, Condenser Pipe the cathode process is O2 reduction. Corrosion pit no corrosion products, the surface was copper alloy qualities. Flow rate is too high, will hinder the formation of a stable protective film, but also the cause of erosion erosion, the general flow rate of not more than 2m / s.
4. NH3 corrosion. The excess NH3 in the feed water enters the condenser with steam and is locally enriched in the condenser. If both O2 are present, Condenser Pipe the NH3 corrosion is generated in the copper side of the copper tube in this area, Thin, when the water content of 300mg / L ammonia prone to NH3 corrosion. The condensate is too cold and the dissolved ammonia concentration increases, causing the copper tube to produce annular band erosion.
5. Galvanic corrosion. When two different metal materials in the corrosive medium in direct contact, there may be galvanic corrosion. In the condenser, Condenser Pipe the condenser tube material is different from the tube sheet material, with fresh water as the condenser of the cooling water, the pipe is usually brass or copper. As the pipe and tube sheet material in the cooling water in the potential difference between the two there is the possibility of galvanic corrosion occurred. The potential of the copper tube of the condenser is higher than that of the tube plate, Condenser Pipe so that the corrosion of the tube plate is accelerated. If the use of fresh water for cooling water, Condenser Pipe condenser with brass tube and carbon steel pipe plate with the carbon steel tube corrosion increased, but because of the larger thickness of carbon steel tube plate, usually 25 ~ 40mm, Condenser Pipe so in clean fresh water, galvanic corrosion There is little impact on the use of safety, but in the high concentration of salt water in the water is more prone to galvanic corrosion.
6. Stress corrosion cracking. Condenser Pipe When the condenser copper pipe installation is not properly, the operation will produce vibration and alternating stress on the surface of the copper tube protective film damage and corrosion, resulting in transverse cracks to break the copper tube. Condenser Pipe This is mainly in the alternating stress under the copper tube within the relative displacement of the grain, in the corrosive medium produced by the formation of anodic dissolution, mostly in the middle of the copper tube occurred.