Keep the fluid flow rate within an \"appropriate\" range to prevent corrosion of the condenser
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This post was last edited by Wang Wei2 on 2024-1-23 at 10:32. It is necessary to keep the fluid flow rate within an \"appropriate\" range in order to prevent corrosion of the condenser. Example: In a certain power plant, condensers made of naval brass suffered from wear and corrosion damage quite quickly because the flow rate at the inlet side exceeded 1.52 meters per second (the critical flow rate). Later, condensers were made from Monel alloy. The critical flow velocity for Monel alloy is 2.1–2.4 meters per second; unfortunately, operators still control it based on the critical flow velocity of naval brass, resulting in pitting corrosion of the Monel alloy pipes. Analysis: This corrosion case shows that a lower flow rate is not necessarily better. For passive metal materials with a protective film formed on their surface, too low a flow rate can lead to liquid stagnation and deposition of solid substances, thereby causing pitting and crevice corrosion. For example, 304 stainless steel pumps are used for transporting seawater, and they are less prone to corrosion during operation. However, if the seawater-related equipment is not cleaned properly when the pump is not in use, pitting corrosion can occur quite quickly. Similarly, carbon steel equipment used for transporting 98% concentrated sulfuric acid also has this problem. The previous example showed that too high a flow rate causes corrosion damage, while too low a flow rate can lead to so-called \"gouge corrosion,\" which results from the breakdown of the surface film on ferrous sulfate due to hydrogen evolution. An appropriate flow rate prevents hydrogen bubbles from accumulating on the metal surface, thus avoiding this type of corrosion. Therefore, a flow rate of no less than 0.3 meters per second is recommended. In summary, for equipment used to handle liquids, maintaining the flow rate within an appropriate range is a fundamental requirement for corrosion control. As for what the range of \"suitability\" is, different materials have different requirements.
This example shows that flow rate is important for preventing corrosion. For metals that can form a protective film, such as stainless steel and Monel alloy, too low a flow rate can cause material deposition and pitting. Too high a flow rate can also lead to physical wear and corrosion. Therefore, the flow rate must be maintained within an appropriate range that prevents material deposition without causing excessive wear. This range varies depending on the materials and conditions; generally, the flow rate should not be less than 0.3 meters per second. .