Leakage problems in the water coolers of petrochemical plants
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The last edit to this post was made by Wang Wei2 on 2023-7-24 at 15:12. Regarding the leakage problems in the water coolers of petrochemical plants, let’s first understand what the main mechanisms of corrosion of circulating water are Is it corrosion caused by chloride ions? Is it the low flow rate causing under-scale corrosion due to scaling, or are there other factors? Circulating water corrosion is primarily electrochemical corrosion of water; chloride ions have an influence here, but they are not the main factor. The impact is small in slightly alkaline conditions and greater in slightly acidic conditions. Low flow rates can lead to accelerated scaling; do not use valves to adjust the cooling effect. Corrosion mechanisms on the circulating water side: Scaling: Since cooling water contains bicarbonates, carbonates, chlorides, phosphates, etc., it is the dissolved bicarbonates such as Ca(HCO3)2 and Mg(HCO3)2 that are the most unstable. When the cooling water flows over the metal surfaces involved in heat transfer, the following reactions occur: Ca(HCO3)2 → CaCO3 ↓ + H2O + CO2↑; Mg(HCO3)2 → MgCO3 ↓ + H2O + CO2↑. Corrosion: The corrosion of metal surfaces by water is primarily electrochemical corrosion. In the corrosion cell, the cathodic reaction is mainly the reduction of oxygen, while the anodic reaction is the dissolution of iron. The corrosion reaction of carbon steel in water is as follows: Anodic reaction: 2Fe → 2Fe2+ + 4e-; Cathodic reaction: O2 + 2H2O + 4e- → 4OH-; Overall reaction: 2Fe + 2H2O + O2 → 2Fe(OH)2↓. During corrosion, iron is converted into iron hydroxide, which precipitates out of the solution. Since this ferrous compound is unstable in oxygenated water, it will further react with oxygen to form iron hydroxide. Recommendation: Apply coating for corrosion protection to the tubes
The problem of leaks in water coolers in petrochemical plants is mainly caused by the corrosion and scaling of the circulating water. The corrosion of circulating water is mainly electrochemical corrosion of water, rather than corrosion caused by chloride ions. In circulating water, alkalinity has a minor impact on corrosion, whereas acidity increases the corrosion rate. Furthermore, low flow rates can lead to accelerated scaling; therefore, it is best not to use valves to control the flow rate when adjusting the cooling effect. The corrosion mechanisms on the circulating water side mainly include scaling and corrosion. Scaling occurs due to the presence in cooling water of substances such as bicarbonates, carbonates, chlorides, and phosphates; among these, the dissolved bicarbonates like Ca(HCO3)2 and Mg(HCO3)2 are the most unstable. When cooling water flows over the metal surface, the following reactions occur: Ca(HCO3)2 → CaCO3 ↓ + H2O + CO2↑ Mg(HCO3)2 → MgCO3 ↓ + H2O + CO2↑ Corrosion is primarily an electrochemical process that affects the metal surface. In a corrosion cell, the cathodic reaction is primarily the reduction of oxygen, while the anodic reaction is the dissolution of iron. The corrosion reaction of carbon steel in water is as follows: Anodic reaction: 2Fe → 2Fe2+ + 4e-; Cathodic reaction: O2 + 2H2O + 4e- → 4OH-; Overall reaction: 2Fe + 2H2O + O2 → 2Fe(OH)2↓. During corrosion, iron is converted into iron hydroxide, which precipitates out of the solution. Since ferrous compounds are unstable in oxygenated water, they further oxidize to form iron hydroxide. To address the issue of frequent leaks in water coolers, it is recommended to apply anti-corrosion coatings to the tube bundles. This can help mitigate the effects of corrosion and scaling, thereby prolonging the service life of the water coolers. .