How to prevent ice and salt water pipes from rusting?
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During production, it is often found that ice and salt water pipelines are severely corroded. How to prevent ice and salt water pipelines from rusting? Or how to remove rust?
Mainly caused by electrochemical corrosion caused by chloride ions, it belongs to oxygen depolarization corrosion, and its manifestations are pitting corrosion and crevice corrosion. It is best to use titanium pipes, but the cost is too high. Carbon steel pipes are better than stainless steel pipes. Generally, corrosion inhibitors can be added, such as sulfate, nitrate, and hydroxide. The pH value is generally greater than 8 and less than 9. 5. The pipeline should reduce the retention area, increase the flow rate as much as possible, and avoid using different materials in the pipeline.
The anti-corrosion of brine ice and salt water pipelines is a very mature technology. 1. Use ABS thermoplastic pressure plastic pipes, which must comply with AS3518-1 specifications. Minimum working temperature -40℃. 2. When using metal pipes, the piping system needs to be equipped with negative electron anti-corrosion devices.
The problem of salt water pipeline is more complicated. Both carbon steel and stainless steel can be used, but they will cause corrosion. It is better to use carbon steel. The best choice is carbon steel lined rubber pipe, which is the most economical, but requires flange connections every 6 meters, which increases leakage points.
Regarding the issue in this post, the detailed explanation is as follows:； The definition of ice water or low-temperature cold water generally refers to operating temperatures below 4°C. To avoid freezing caused by water temperature, affecting flow or damaging pipe fittings, an appropriate percentage of salts will be added to the water as antifreeze. Salts that can be used include NaCl, CaCO3, NaOH, EG, ˙˙˙. Because the corrosion of NaCl is serious and CaCO3 is easy to scale, the current brine additives are mainly EG (ethylene glycol). EG will corrode steel pipes and stainless steel pipes, causing the white mixture of EG and water to quickly turn into a brown color. This is rust water. For stainless steel pipes, it is called peroxidation (rouging or rouge). Therefore, this problem is a very simple rust oxidation phenomenon. When the concentration of reddish-brown rust water deepens, the corrosion rate on the surface of the copper pipe of the chiller gradually increases, the corrosion area increases or thickens, the heat exchange capacity of the chiller declines, and the temperature of low-temperature ice salt water or brine becomes difficult to drop. The freezing capacity of the chiller appears to be insufficient, resulting in a waste of energy. The pipe material of this system is changed to ABS pressure thermoplastic pipe, which can completely solve the phenomenon of rust water and pipeline corrosion. Materials engineering knowledge 20 years ago used stainless steel and metal pipes lined with plastic or rubber to solve this problem. Since 1990, thermoplastic pipes have been widely used in industrial piping systems in factories and utilities. Taking the brine chilled water system discussed in this post, thermoplastic pipes are used in industrial systems, food pipelines, etc. in Europe, Australia, Asia, etc. to solve problems such as corrosion, insulation, and construction.
Generally, carbon steel pipes are used for ice and salt water pipelines, and corrosion inhibitors are added to the salt water. Sodium dichromate (Na2Cr2O3) containing NaOH is generally used as a preservative. 1.6kg of sodium dichromate should be added to 1m3 of calcium chloride brine. 2.7kg of NaOH must be added to every 10kg of sodium dichromate. When adding preservatives, the brine must be slightly alkaline (pH=8.5). This can be determined using phenolphthalein reagent. Phenolphthalein reagent must turn pale rose when mixed with saline. It should also be noted that sodium dichromate can rupture human skin, so be careful when preparing the solution. for your information.