Analysis of circulating water corrosion required!
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Dear experts in corrosion control: I have a heat exchanger made of grade 20 steel, with circulating water flowing through one side and the fluid to be processed flowing through the tubes. Leaks were detected during operation, and samples from the heat exchanger’s tubes were taken for inspection; the corrosion found was as shown in the image. The corrosion mainly occurred on the side where the circulating water flowed. I would appreciate it if you could help analyze the causes of this corrosion. This is the first time I’ve encountered such a situation – some suggest it might be potential corrosion, while others think it could be caused by organic substances. Please share your opinions!
Water quality analysis of the circulating water should be conducted, along with electron microscopy examination of the corroded areas, in order to determine the cause of the corrosion. Additionally, heat exchangers made of carbon steel actually have very high requirements regarding water quality.
Could you please provide a unit that can be used for monitoring and the approximate cost? You can contact us via text message... We need technical support!
It’s not yet possible to determine what exactly is causing the corrosion!
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It seems to be electrochemical corrosion caused by water; your water is somewhat soft, and water in a gaseous state causes corrosion. The tube bundles require coating for corrosion protection
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. As a result of this reaction, rust gradually forms on the heat transfer surface; when the cooler is in operation, the corrosion of the metal surface is accelerated due to the effect of this scale. Furthermore, the temperature and flow rate of water, as well as the action of microorganisms, all affect the electrochemical corrosion on the metal surface. The presence of soluble solids, particularly oxides and sulfates, exacerbates corrosion. The presence of suspended particles and contaminants in water can lead to localized contamination, making it difficult for a protective metal film to form or causing pitting corrosion due to oxygen concentration gradients. Therefore, corrosion of metals beneath scale is accelerated due to the autocatalytic effect of their inherent electrochemical corrosion. The solution is to move the circulating water to the tube side, thereby causing corrosion inside the tubes. Transfer the non-corrosive medium inside the tube to the shell layer. That solves the problem.
We also have circulating water in the tube side, but during inspections it was found that the weld metal between the tube sheet and the tubes had been corroded... So it’s probably still a problem with the circulating water
Such monitoring is carried out online, and the cost cannot be estimated as it requires on-site inspections and consideration of environmental conditions, etc. If you need technical support, you can send an email to my address: Guodong.qu@hach.com
Firstly, from the perspective of the appearance of corrosion, it is electrochemical corrosion, and protecting against this type of corrosion can be achieved by using magnesium anodes. At the same time, pay attention to the concentration of chloride ions in the water to prevent intergranular corrosion.