The selection of pipeline materials for reverse osmosis equipment should consider both internal and external factors. The internal factors are the corrosion caused by water quality on the pipeline, while the external factors are the operating environment. The operating environment of reverse osmosis equipment determines the external corrosion of pipelines. If the operating environment is good, surface coatings (such as paint or galvanizing) are generally used. The corrosion of pipelines by water quality should consider residual chlorine, chemicals, pH value, temperature, etc.
Stainless steel pipeline
The basic advantage of stainless steel is its good resistance to general corrosion. Stainless steel rarely undergoes current corrosion and stress corrosion damage, but it is prone to pitting and crevice corrosion. Pitting represents local corrosion of the metal, causing concave holes on its surface. If the chromium oxide passivation layer is damaged, chloride ions will attack the exposed metal to form pitting. Gap corrosion is related to pitting corrosion caused by a small amount of static water around small holes, gasket surfaces, sediments, and cracks under screws. To avoid pitting and crevice corrosion of high-pressure pipelines in membrane systems, the following suggestions are suggested:
For general water sources, 304 stainless steel can be used;
1. When the salt content of the raw water is between 2-5000PPM, it is recommended to use 316 stainless steel with a carbon content of less than 0.08%;
2. When the salt content of the raw water is between 5-7000PPM, it is recommended to use 316L stainless steel with a carbon content of less than 0.03%;
3. When the salt content of raw water is between 7-30000PPM, it is recommended to use 904L stainless steel with a molybdenum content of 4% -5%.
316 stainless steel is the second widely used steel type after 304, mainly used in the food industry and surgical equipment. Adding molybdenum element gives it a special corrosion-resistant structure. Due to its better resistance to chloride corrosion compared to 304, it is also used as "ship steel". SS316 is commonly used in nuclear fuel recovery devices.
UPVC pipeline
The characteristics of UPVC pipes are as follows:
1. Strong corrosion resistance: Compared with general cast iron pipes and galvanized pipes, PVC pipes have extremely strong corrosion resistance, can withstand strong acids and alkalis, and will not rust or scale. Don't worry about the phenomenon of "red water" when using.
2. Low fluid resistance: The inner wall of the PVC pipe is very smooth. Its surface roughness coefficient is only 0.009, and the fluid resistance is very small, so it will not excessively reduce water pressure.
3. High mechanical strength: UPVC pipes for water supply have good water pressure resistance, impact resistance, and tensile strength. They can withstand 110 atmospheres of pressure for 1 hour at room temperature without breaking.
4. Sanitary and non-toxic: UPVC pipes for water supply use adopt a unique green and environmentally friendly lead-free formula system instead of the traditional composite lead salt formula system, which will not damage water quality or affect human health.
5. Lightweight texture and easy installation and construction: The density of PVC pipes is one-fifth of that of general cast iron, making transportation, loading, and unloading convenient. And special adhesive or elastic sealing components are used for bonding, making installation and construction simple and fast.
6. Temperature adaptability of water supply pipes: UPVC pipes for water supply should be used within the temperature range of room temperature. Low temperature, increased brittleness, unfavorable for installation and construction; The temperature is too high, the tensile strength decreases, and the water pressure resistance decreases.
7. Good water tightness: After 15 minutes of adhesive bonding, the bonding strength can reach 12.5/C or above, and there will be no significant decrease after many years of use. The sealing ring at the joint of the elastic sealing element also has a considerable service life compared to PVC pipes, and there is no concern of aging and water leakage.
