About corrosion and scaling
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The circulating water used by our company is treated river water. Water is constantly adding medicine to it during the circulation process. However, due to conditional restrictions, the steam condensation water used in our distillation tower now directly returns to the circulating water. The issue I want to discuss is this: Due to the replacement of steam condensate water, the system circulating water is now basically ion-free desalted water. Because the steam condensation water is desalted water. Now there is no need to add scale and corrosion inhibitors, oxidizing bactericides, and non-oxidizing bactericides to the circulating water. However, I consulted the manufacturer that adds chemicals to our circulating water on this issue, and their technicians said: “Due to your current replacement of circulating water, the hardness of the calcium...etc. in the water has decreased, which will lead to increased corrosion of coolers, etc., and it is said that adding preservatives should be considered." I figured why the water hardness decreased and the corrosion on my equipment increased. Please tell me, is there any saying that the hardness of water decreases and the corrosion of equipment increases?
That's it. Water corrosiveness and scaling are generally behavioral manifestations of water-carbonate systems. If the calcium carbonate content exceeds the saturation value, calcium carbonate will precipitate, which is called scaling water. If the calcium carbonate content is lower than the saturation value, calcium carbonate will dissolve, and it will become corrosive water. The semi-empirical index Ryznar Stability Index (RSI) is proposed based on a large amount of production data. The relationship between scaling and corrosion can be seen through the RSI index chart.
I think it will aggravate oxygen corrosion and carbon dioxide corrosion!
As far as scaling is concerned, please consider the growth of microorganisms in the water. If you don’t add enough bleach and the terminal flow rate is slow, problems will arise.
According to this theory, wouldn't it mean that well water is more resistant to corrosion? Then why should scale and corrosion inhibitors be added in the first place? Is it because the technical staff of the manufacturer were fooling people? Ask them in detail, get to the bottom of it, and ask them if the original agent cannot prevent the precipitation of calcium (dereliction of duty). There is a possibility that there is scale in the pipeline and calcium carbonate is deposited. Now that the calcium is gone, some calcium carbonate will be dissolved. In addition, the system will be somewhat acidic due to the presence of carbon dioxide, which will corrode the pipeline? Wouldn't it be enough to test the pH? But I think it's too far-fetched.
Corrosion and scaling need to be controlled at the same time. In fact, early prevention of corrosion and scaling is achieved by controlling the pH value, that is, controlling the pH to make CaCO3 reach the required balance state - CaCO3 can be attached to the metal surface to prevent corrosion without scaling. Circulating water without calcium ions is corrosive! The chemicals added in modern circulating water treatment are called corrosion and scale inhibitors, which are generally compound formulas. Antiscalants generally control scaling (CaCO3 and CaSO4) and dirt (some microorganisms, etc.). The main mechanisms are to remove the components that cause scaling, keep the components that cause scaling in a dissolved or dispersed state, and convert the scaling components into sludge that is easy to drain. The latter two mechanisms are commonly used. Corrosion inhibitors generally form a protective film on metal surfaces.
The pH value should be controlled to prevent carbon dioxide corrosion.
Agreeing with this statement, we must first understand how circulating water can prevent corrosion and scaling by adding chemicals, forming a protective film on the surface of the pipeline through system pre-filming, and then continuously replenishing the film by maintaining the concentration of chemicals. This protective film is a protective film formed by the added chemicals complexing cations such as calcium ions in the water. The calcium ion concentration in the circulating water is now very low, which will definitely not cause scaling, but the film repair effect will be very poor, so anti-corrosion is the key. You should contact the pharmaceutical manufacturer to adjust the pharmaceutical formula, and use corrosion inhibitors containing zinc salts under low calcium conditions to increase the cations in the circulating water, enhance the film repair effect, and achieve the purpose of controlling corrosion.
Scaling and anti-corrosion go hand in hand. Calcium ions are removed, which does cause the possibility of scaling * * Reduced, but the probability of system corrosion increased again, for many reasons: The causes of corrosion include potential corrosion, ion pitting corrosion, polarization corrosion, microbial corrosion, etc. These are closely related to water quality indicators. They are judged based on the water quality indicators and the saturation index LSI. The trend of scaling or corrosion can be determined through LSI calculations, instead of knowing corrosion or scaling based on unknown water quality indicators.
It should be because the hardness has decreased, and calcium carbonate scale is very dense and has a protective effect on the corrosion of steel. As the concentration decreases, it is not easy to form a protective layer of hard scale on the surface of steel, so corrosion will be more severe.
The corrosion and scaling tendency of water quality can be mainly judged by the following indices: Langelier Saturation Index (LSI), Reizner Stability Index (RSI), etc., among which: • LSI < 0, corrosion tendency • LSI = 0, neither corrosion nor scaling will occur • LSI > 0, scaling tendency • RSI > 6, corrosion tendency • RSI = 6, neither corrosion nor scaling • RSI
Corrosion and scaling in water treatment are in a contradictory relationship. A well-treated system has less scaling and a low corrosion rate.； If it is not handled well, there must be a problem in some aspect, either severe corrosion or scaling. Your supplier is right, the lower the hardness of the water, the weaker your shield will be and the corrosion will become more prominent. ； This requires adding more shield elements, which are corrosion inhibitors.
You can use scale-absorbing and rust-removing equipment, which can also sterilize and inhibit algae, save energy and reduce emissions. If you need more information, you can learn more.
This problem is becoming more and more common. Desalted and demineralized water is highly corrosive. In addition to the decreasing tendency of scaling and the increasing tendency of corrosion, the reduction of scaling ions will cause hydrogen evolution corrosion. According to Le Chatelier's principle, the balance of hydrolysis and ionization is broken and needs to be rebalanced. At present, there are two treatment methods for this kind of water. One is to supplement calcium and alkali, and then follow the conventional treatment methods. The other is to add special corrosion inhibitors to control corrosion. Fungicide must be added.
Nowadays, non-chemical treatment of circulating cooling water is at the forefront. We use intelligent infrared audio waves that are very good at inhibiting scale and corrosion, sterilizing and inhibiting algae. No need to add a single drop of medicine, the effect is very good.
The corrosiveness of deionized water is much greater than that of treated river water. The main reason is that oxygen is dissolved in deionized water, and carbon steel causes corrosion due to the formation of micro-batteries in the water. The process of corrosion reaction can be expressed as: Anodic reaction Fe - 2e——Fe2+ Cathodic reaction: 1/2O2＋H2O＋2e——20H- in water: Fe2+ +20H-——Fe (OH)2 Along with the corrosion mechanism of iron oxide, another corrosion cycle reaction also occurs at the same time. 1/2 Fe3+ + Fe2——3 Fe2+ Fe2+ +1/2O2——Fe3+ This is the main cause of deionized water corrosion. Once the corrosion reaction is formed, there is an accelerated process. This corrosion is a reciprocating chain reaction in the presence of oxygen. This is because calcium, magnesium, and alkalinity are protective ions against corrosion, and deionized water removes these ions.