Material selection for sodium hydroxide storage tanks
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This post was last edited by sunjl1981 on 2013-1-6 at 20:07. The following two storage tanks have a capacity of 1,200 cubic meters each; they contain 50% sodium hydroxide, and are at normal temperature and pressure. 2,1000 cubic meters, 30% sodium hydroxide (prepared by diluting 50% sodium hydroxide; the temperature may be slightly higher due to the heat released during dilution). Normal temperature and pressure. Environmental temperature: Temperatures are low in winter, with a minimum of -40 degrees Celsius, while the maximum in summer is 36 degrees Celsius. How should I choose the material? Please help me; I’d appreciate any good suggestions. 30 points as reward -
Since it is at normal temperature and pressure, if the quality requirements are not high, grade 20 steel will suffice; 304 stainless steel or steel lined with rubber can also be used
50% of it needs to be insulated, as it will crystallize when exposed to the outdoors in winter. Q235 material is sufficient; if higher quality is required, use 304. Diluting 50% to 30% results in little heat being released, so this can be ignored
Choosing 304 might be a bit expensive; are there any cost-effective alternatives with a lining?
A carbon steel tank will suffice. Given the low temperatures in winter, which can cause the alkaline solution to crystallize, you can install coiling heating elements inside the tank.
50% of the materials are 304; heating for insulation is required in winter； 30% of the materials can be Q235. To facilitate production and management, it is recommended to use 304 material along with heat tracing for insulation, which makes it easier to use storage tanks in situations where operating conditions change. I think you only have 2 slots, so it’s entirely possible for the usage conditions to change. The material prices are low now, making it cost-effective.
Carbon steel material will suffice. Because our factory has the 30% alkali and 50% alkali mentioned by the poster, but it’s ion-exchange membrane alkali; carbon steel has been used for over 2 years without any problems. The key is to maintain normal temperature conditions, as high-temperature alkali causes quite severe corrosion. If it is diaphragm alkali, salt may precipitate in winter, so heating and insulation are required. Generally, there is no condensation or precipitation of alkali in winter; this can be determined by checking the freezing point temperature of the alkali. The occurrence of alkali precipitation can be assessed by looking at its solubility at winter temperatures.
Carbon steel lined with 304 can also be used, but heat tracing is required in winter; otherwise, low temperatures will cause crystallization and blockage of the tank and outlets.
Our company has also been using carbon steel tanks; they have been in use for 3 or 4 years now and are working well without any problems. This post was last edited by limingshuguang on 2008-11-4 20:50]
1. If the temperature is relatively low, it is not recommended to use carbon steel, as insulation can cause changes in the properties of the alkali； 2. Using a carbon steel lining with stainless steel is more practical ； 3. Of course, if the quality requirements are not high, using carbon steel directly will not pose too many problems ； 4. The storage tanks for the ion-exchange membrane caustic we use currently are made of carbon steel with a resin coating on their interior; the result has been good, and they’ve been in use for five years now, hehe.
As tanks for storing alkaline solutions, generally, as the concentration and temperature of the alkaline solution increase, its corrosivity also increases. One of these two tanks operates at room temperature with a high concentration； One with a slightly higher temperature, but lower concentration. Therefore, it is recommended to use SS304 alone, which is quite common in evaporation production. If 50% of the alkaline solution is at a very high temperature, approaching 100 degrees, then 316L steel is required; at even higher temperatures, only ferritic stainless steel can be used