Let’s discuss the measures to prevent corrosion in heat exchangers
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Recently, I’ve encountered small nickel-plated heat exchangers (with a water-side volume of around 4–5 m³ and a nickel plating thickness of 20–30 μm) that suffer from pitting corrosion quite frequently! The water quality is fine, with a pH of 6.8. The conductivity is just 1500 higher, and I suspect it’s due to the porosity issue! So now I have a few ideas regarding nickel plating – what do you all think? Or do you have any suggestions of your own! 1. Due to issues with the nickel plating quality, it is not possible to ensure a consistent porosity level; therefore, a combination of nickel plating and sealing (using an oil-based sealant or a water-based anti-corrosion coating) is planned. This is because the tubes are very small, with a diameter of 19 mm only, and using epoxy resin or paint-based anti-corrosion coatings would involve too many complicated steps.2. Cathodic protection can be employed by adding zinc blocks to the surface.
3. A triple-plating method can be used to enhance the anti-corrosion properties of the coating itself! Now I have some questions: 1. Do you have any good recommendations for anti-corrosion coatings? The application process should be simple, and the coating layer shouldn’t be too thick, as this is a small heat exchanger! 2. The cathodic protection method involves adding zinc blocks, but the problem is that it’s not clear how to add them properly. Do any of you have any suggestions on this? 3. Do you have any recommended manufacturers for triple-coating solutions? It would be ideal if they are located in the Jiangsu, Zhejiang, and Shanghai regions! In addition, if anyone has any good anti-corrosion methods (preferably with specific examples), or any issues related to corrosion, please feel free to share them so we can discuss them together. PS: As far as I know, there are the following anti-corrosion methods: 1. Choosing the right material itself, such as 316L, Hastelloy, or using graphite heat exchangers; 2. Using coatings like nickel or chromium for anti-corrosion; 3. Cathodic and anodic protection methods; 4. Adding anti-corrosion layers such as epoxy resin or PTFE linings, as well as other polymer-based anti-corrosion solutions; 5. Using penetration techniques to introduce elements like Ti or Ni into the material
When considering the corrosion issue on the cooling water side of heat exchangers from economic, practical, and operational perspectives, the first step is to adjust the quality of the cooling water to meet industrial cooling water standards. Corrosion problems caused by cooling water that does not meet industrial cooling water standards often affect not just this heat exchanger, but also most steel equipment that uses cooling water. The second approach is to upgrade the materials used, but this must be done on a basis where the costs remain acceptable. There’s no need to constantly talk about materials such as niobium, tantalum, and zirconium; it’s not that these materials are bad, but their prices are extremely high. If the process conditions permit, graphite heat exchangers represent an excellent choice due to their excellent corrosion resistance. Graphite heat exchangers are more expensive than carbon steel heat exchangers but less expensive than titanium heat exchangers, making them a cost-effective choice. Third is corrosion protection through coating; since corrosion caused by cooling water usually occurs in the shell side of heat exchangers, it is very difficult to provide thorough and effective corrosion protection coating on the shell side during equipment manufacturing or at the user’s site. This is mainly due to the structure of the heat exchanger and the materials used for the coatings, so using coatings for corrosion protection is not the best solution.
I agree with the corrosion resistance of graphite heat exchangers, but I’ve heard that their heat exchange efficiency isn’t very high; they tend to become brittle after operating at high temperatures for extended periods. In my opinion, the cost-performance ratio isn’t great!
Graphite heat exchangers are widely used in basic and fine chemical industries such as chlor-alkali, pesticides, fertilizers, pharmaceuticals, polysilicon, and silicone, as well as in industries such as metallurgy, the nuclear industry, and aerospace. Impermeable graphite materials can be used to manufacture graphite heat exchangers, graphite falling film absorbers, graphite towers, graphite synthesis furnaces, graphite reactors, graphite pressure vessels, as well as various custom-made graphite devices, and graphite bearings, graphite seals, graphite nozzles, and so on. Graphite possesses excellent chemical stability as well as good thermal conductivity; its thermal conductivity is second only to that of pure copper and high-purity aluminum, being twice that of carbon steel and three times that of stainless steel.
Piping side or shell side? If it’s on the shell side, then don’t “plate” it or “coat” it – it won’t yield good results! Why? Due to structural limitations. If it is a pipe lining, it can be \"plated\" or \"coated\"; the key is to ensure good quality control of the coating layer. ““Coatings” are also divided into cold plating and hot plating; of course, hot plating is better.
Neither coating nor plating is a good solution; graphite heat exchangers are the better choice.
Currently, the main methods used for corrosion protection of heat exchangers, in addition to upgrading the material, are corrosion-resistant coatings and plating. Based on the conditions you provided, it is likely that there is a problem with gaps, as a coating thickness of 20-30 micrometers is a bit too thin; generally, for large components, the recommended thickness should be no less than 40-45 micrometers ； Furthermore, the use of anti-corrosion coatings in this environment is likely to be effective, such as TH847 or SHY99 ； The current industrial application of ternary composite plating, especially in heat exchangers for large components, is still subject to many limitations ； Cathodic protection is generally used in combination with coating protection; its effectiveness when used alone is limited. I hope this helps with your question.