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Example: A chemical plant is considering using aluminum heat exchanger tubes for ammonia recovery heat exchangers. As a precaution, a field testing experiment was conducted by fixing aluminum test pieces to the housing of the original equipment for 6 months, and no corrosion was observed. However, the aluminum alloy condenser tube bundle had to be replaced after just one week due to corrosion damage. It was checked that the housing had not corroded, while the pipe had corroded and perforated. Comment: Condenser tubes not only come into contact with corrosive media but also serve the function of transferring heat. In the hanging plate test, the test piece is fixed to the housing, which makes it impossible to reflect the effect of heat transfer on material corrosion. When a heating medium (such as steam) flows through the heat exchange tube, the surface temperature of the tube is higher than the temperature of the solution in the shell side. Not only that, but there is also a temperature gradient in the solution, which creates density differences and facilitates the diffusion of oxygen to the surface of the heat exchange tubes. Bubbles can also form on the metal surface, causing localized damage to the passivation film and leading to pitting. Recommendation: When selecting materials for heat transfer equipment (heat exchangers, heating coils, etc.), it is not sufficient to rely solely on test data obtained under conditions without heat transfer; corrosion tests on the heat transfer surfaces should also be conducted. In this case, if a tube made of the test material could be installed on the original condenser to conduct corrosion resistance tests under production conditions, more reliable data could be obtained.