How to prevent corrosion when the circulating water in the heat exchanger of an open-loop circulating water system is stopped?
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Hello, experts. To save costs, the circulating water for the heat exchangers in some of the open-loop cooling water systems at my company has been stopped. However, there is no standard procedure to guide operations and prevent corrosion. Does your company have heat exchangers whose circulating water supply has been shut off? How do you handle such situations to prevent corrosion? Could you please give some advice? Thank you!
Seeing your post, it’s indeed a pretty practical question. If no protection is provided after shutting down the circulating water, the risk of corrosion on the inner walls of the heat exchanger is very high; especially in open systems, where an increase in dissolved oxygen due to exposure to air makes problems more likely to occur. My company has encountered similar situations before; we took the following steps, which may be useful for your reference: Thorough emptying and drying: After shutting down the system, drain all the water from the heat exchanger, then use compressed air to remove any remaining moisture inside, ensuring that it remains dry. If conditions permit, nitrogen can be introduced to seal it and isolate oxygen. Addition of corrosion inhibitors (wet protection): If it is not possible to empty the system for operational reasons, a certain amount of water can be retained; however, special corrosion inhibitors designed for this purpose (such as those based on nitrites or molybdates) must be added, and the pH level as well as the concentration of these inhibitors should be monitored regularly. However, it is necessary to pay attention to whether the corrosion inhibitor imposes any restrictions on subsequent wastewater discharge. Ensure proper sealing and labeling of the inlet and outlet: Close the valves at the inlet and outlet of the heat exchanger tightly, and attach a warning sign stating “Out of service – under protection” to prevent accidental activation of the circulation system. Of course, the specific plan also depends on the material of the heat exchanger and the duration of its shutdown. It is recommended that you consult industry standards (such as HG/T 20660 or relevant petrochemical specifications), or seek advice from equipment manufacturers and professional wastewater treatment companies, as they can provide more suitable chemical formulations and operating procedures. I hope this is helpful to you; I also welcome other experienced friends to share their insights.