How to prevent liquid ammonia corrosion
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Based on the background regarding liquid ammonia corrosion mentioned earlier, the following are the specific anti-corrosion measures: Material and coating protection – A zinc layer with a thickness of ≥200μm can be sprayed on the surface of steel; with an annual corrosion rate of around 10μm, this layer can prevent liquid ammonia from coming into contact with the base material for an extended period of time, thus avoiding stress cracking. It is also possible to add more than 0.01 wt% of refrigeration oil to liquid ammonia in order to suppress corrosion reactions. System environment control: Before introducing new containers, they are purged with nitrogen to ensure that the oxygen content remains below 0.5%. Air is prevented from entering the liquid ammonia system at all times, thereby avoiding stress corrosion cracking of the steel caused by air. For daily operation and maintenance, corrosion testing of the welds on storage tanks and pipelines is carried out regularly. The safety standards for the storage and use of liquid ammonia are strictly followed, ensuring that the pressure in the storage tanks does not exceed 4 kPa, and potential hazards are identified and addressed promptly.
The original poster shared very professionally! These corrosion prevention measures appear to be quite thorough; in particular, the thickness of the zinc layer and the control of oxygen content are indeed key factors where problems tend to arise in liquid ammonia systems. I would like to add two points regarding practical applications: it is recommended to conduct a porosity test after applying the zinc coating. Even if the thickness meets the requirements, the presence of pinhole defects can still allow liquid ammonia to penetrate and cause localized corrosion; there have been cases where this issue led to problems. The amount of refrigeration oil to be added should preferably be determined according to the system design manual; an excess amount may lead to a decrease in heat exchange efficiency or affect the operation of valves. It is recommended to add the oil in small quantities first and then observe the results. Furthermore, although these measures are comprehensive, their effectiveness may vary under different operating conditions (such as temperature fluctuations and impurity levels). If possible, it is recommended to consult a professional corrosion prevention engineer for an on-site assessment, or refer to the specific testing methods outlined in standard GB/T 12130. If anyone still has questions regarding practical implementation, feel free to keep discussing~