What to do if the circulating water system is severely corroded
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What to do about severe corrosion in the circulating water system? Guys, in the closed-loop water system of a steel plant I work for, the circulating water was turned on during the day and off at night during the system commissioning phase; as a result, there was a lot of rust in the system. After it operated for some time, the water became clearer, but there was still a considerable amount of rust sediment, along with a low pH level. Whoever has experience dealing with such situations, please share your insights~~~~ Thank you!
The pipes are corroded; let’s analyze the water quality. If the water quality is poor, it needs to be improved!
Yes, I agree with the above statement; I have been working in circulating water treatment before
Perform cleaning and pre-coating, and add chemicals regularly!
Thank you all. Rust appearing in water is usually due to corrosion, but I don’t understand why the pH level also decreased Could it be that the hydrolysis of iron salts by someone has produced strong acids? I would like experts to analyze the reasons
Reply to 1# aqiao1011: An increase in iron ion concentration, if accompanied by a decrease in pH. It is quite obvious that this corrosion is caused by acidity. Points to note: 1. Whether sulfuric acid is added to the circulating water; if so, consider whether the amount of sulfuric acid added is excessive ； 2. To check whether there is a leak in the heat exchangers of the steel plant that could allow acidic substances to enter, it is possible to determine this by testing for the presence of specific components in the medium being heated and comparing them with those present in the circulating water.
In addition to treating water quality, it is also necessary to consider using corrosion-resistant pipe materials, such as non-metallic pipes. After all, the corrosiveness of circulating water cannot be ignored.
Is it due to a low pH value control, or is the low pH value of the circulating water caused by a leak in the heat exchanger? It happened once in my company. There are two reasons: first, excessive addition of acid resulted in a low pH value ； Secondly, a leak in the unit’s heat exchanger allowed acidic gases to enter the cooling water system, resulting in a low pH value.
In a closed-loop system, the water used for replenishment is deionized water, which has a low pH value. Such corrosion is primarily caused by microorganisms or sulfate-reducing bacteria, which is why the pH remains low. Solution: First, cleaning and pre-coating must be carried out; during operation, sterilization is required, as well as the addition of a small amount of corrosion inhibitor. When the system is shut down, the entire pipeline should be filled with water. If the water cannot be kept in place, the valves need to be checked, otherwise corrosion will continue to occur.
First, it is necessary to determine what is causing the low pH level. Then, you need to know what the control parameters for the circulating water are, and whether any chemicals have been added. Pre-coating should be carried out before operation, and it is best not to operate the system intermittently. It is recommended that you have follow-up visits at each stage, as this will be of great help in analyzing the reasons. At the start of the debugging phase, it is necessary to first perform a water wash, followed by an alkali wash, then an acid wash, and finally a pre-coating step; high levels of iron ions can occur during all these stages.
A comprehensive analysis of the water quality should be conducted; it’s possible that the pH of the incoming water is low, or that too much acid has been added. I recommend having a manufacturer clean and coat the system, and after analyzing the water quality, add corrosion and scale inhibitors as well as biocides and algaecides as appropriate. I still need to remind you to keep a close eye on your operators; human error is what causes the greatest damage to the system in such situations.