A typical dew point corrosion process
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The feed to a distillation column in a factory consists of fluorinated hydrocarbons, hydrogen chloride gas, trace amounts of hydrogen fluoride, and chlorine gas. The chlorine and hydrogen chloride emerging from the top of the tower are cooled by a brine condenser. After just a few weeks of use, the cold end of the condenser tubes (saline inlet) suffered corrosion damage on the process side. It turns out that the inlet gas to the distillation tower contained trace amounts of water (a few ppm), which were not detected by the factory’s analysis instruments. The coexistence of chlorine gas, hydrogen chloride gas, and water vapor raises the dew point; water condenses at the lowest temperature points in the pipes, forming a highly corrosive substance that causes corrosion and perforation of the condenser tubes.
During this process, the presence of trace amounts of moisture in the feed to the distillation tower, along with chlorine and hydrogen chloride gases, led to an increase in the dew point. When these gases are cooled in the brine condenser, water condenses into droplets at the parts with the lowest temperature (i.e., the condenser tubes at the brine inlet), resulting in a highly corrosive medium. This environment accelerates the corrosion of the condenser tubes, ultimately leading to tube perforation and equipment damage. .
Corrosion that occurs on heated surfaces at lower temperatures is therefore known as low-temperature corrosion； This type of corrosion occurs only after dew forms on the heated surface, which is why it is called dew point corrosion.
Individuals tend more toward low-temperature corrosion, but dew point corrosion also plays a role. This is because low-temperature environments create conditions conducive to corrosion; acidic gases (hydrogen chloride and chlorine) can produce acidic solutions that cause corrosion due to the condensation of water vapor at low temperatures. Coupled with the high corrosiveness of trace amounts of hydrogen fluoride at low temperatures, all these factors contribute to the corrosion and damage of the cold ends of the condenser tubes.