When conducting corrosion resistance tests on heat exchange tube materials, it is essential to take into account all factors related to the corrosive environment

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This post was last edited by Wang Wei2 on 2023-12-27 at 09:48. When conducting corrosion resistance tests on heat exchange tube materials, it is essential to take into account all factors related to the corrosive environment. Issue: A soda ash plant is considering using aluminum heat exchangers for its ammonia recovery condensers. To this end, an on-site testing period of 6 months was conducted with the aluminum test pieces fixed to the cast-iron housing of the original equipment, and no noticeable corrosion was observed. However, the aluminum alloy condenser had to be replaced after just one week due to corrosion damage. The wall of the inspector was not corroded, while the tube was corroded through. Analysis: 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 impact of heat transfer on material corrosion. When a heating medium (such as steam) flows through the heat exchange tubes, the surface temperature of the tubes is higher than the temperature of the solution in the shell side (as described in the previous example). Not only that, but there is also a temperature gradient in the solution, which creates density differences and allows oxygen to diffuse more easily 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.