Corrosion issues in frozen saline pipelines
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This post was last edited by yuchenchf on 2011-9-22 at 13:03. Due to the high concentration of chloride ions in frozen brine, corrosion of the pipelines used for its transport has always been a problem that plagues chemical manufacturing processes. In our factory, we usually replace the salt water pipes at regular intervals; I think this approach is not reasonable. I’m wondering if there are any better methods that could be adopted.
There are many methods; if the pressure is not high, thermoplastic pipes, glass fiber reinforced plastic pipes, or FRP/PVC composite pipes can be used； Use rubber-lined or plastic-lined pipes when the pressure is high.
You can consider plastic-lined steel pipes; the downside of these pipes is that they are difficult to maintain, but otherwise they are fine. I’ve seen some old factories use ordinary thermoplastic pipes for frozen brine; haha! Using carbon steel is definitely not a good idea; if it’s a coil, the problem becomes even worse, as leaks can result in a large amount of chloride ions appearing in the product.
It’s calcium chloride saline, right? Generally, carbon steel is used. The corrosion of carbon steel by chloride ions is uniform corrosion; therefore, it is sufficient to thicken the material during design, that is, to increase the design margin for corrosion resistance. Replacing the component every few years is a relatively more economical approach. If a lining is used, it is best to avoid non-metallic linings, as they tend to peel off or crack under alternating hot and cold conditions.
Saltwater corrosion inhibitors can be used to slow down corrosion, or alternative corrosion-resistant pipes can be chosen.
Controlling the pH of the saline solution and maintaining the integrity of the system as much as possible (to prevent dissolved oxygen) can effectively prevent pipe corrosion.
A large amount of chloride ions can easily combine with hydrogen ions to form hydrochloric acid, which is highly corrosive. The best solution is to replace the pipes with plastic or corrosion-resistant ones
Our factory is in the same situation too! Currently, considering the addition of a corrosion inhibitor, and corrosion resistance tests have been conducted on it; the results do not seem very satisfactory. It might be because there are too many impurities in the frozen saline.
Fiberglass reinforced plastic pipes can be used as an alternative; they have excellent resistance to saltwater corrosion and low-temperature conditions.
Titanium tubes are the best choice, as they do not corrode in saltwater for a hundred years. Titanium pipes are used for the chilled brine in the Jiangsu Yangnong Caustic Soda Plant.
CS material can be used, by adopting the following approach: 1. Prepare a saline solution using high-purity salt； 2. Reduce the chances of the solution coming into contact with air by using a closed-loop system or by covering the salt water tank ； 3. Add an appropriate amount of corrosion inhibitor to make the solution slightly alkaline, with a pH value maintained between 7.5 and 8.5. Commonly used ones are sodium hydroxide (NaOH) and sodium dichromate (Na2Cr2O7), with a mass ratio of NaOH:Na2Cr2O7 = 27:100.