Corrosion resistance
Corrosion has always been one of the most headaches of chemical equipment. If it is slightly careless, it will damage the equipment and cause accidents and even disasters. According to relevant statistics, about 60% of the destruction of chemical equipment is caused by corrosion. Therefore, in the selection of chemical pumps, we must first pay attention to the scientific nature of material selection. There is usually a misunderstanding that stainless steel is a “universal material†and it is dangerous to hold stainless steel regardless of the medium and environmental conditions. Here are some key points for selecting materials for some common chemical media:
Sulfuric acid
As one of the strong corrosive media, sulfuric acid is an important industrial raw material with a wide range of uses. Different concentrations and temperatures of sulfuric acid have a great difference in corrosion of materials. For concentrated sulfuric acid with a concentration above 80% and temperature less than 80 °C, carbon steel and cast iron have good corrosion resistance, but it is not suitable for high-speed flowing sulfuric acid. It is not suitable as a material for pump valves; ordinary stainless steels such as 304 (0Cr18Ni9) and 316 (0Cr18Ni12Mo2Ti) are also limited in their use for sulfuric acid media. Therefore, the pump valve for conveying sulfuric acid is usually made of high-silicon cast iron (difficult to cast and process) and high-alloy stainless steel (20 alloy). Fluoroplastics have better sulfuric acid resistance, and a fluorine-lined pump (F46) is a more economical option. The company's applicable products are: IHF lining fluorine pump, PF (FS) strong corrosion resistant centrifugal pump, CQB-F fluoroplastic magnetic pump.
Hydrochloric acid
Most metal materials are not resistant to hydrochloric acid corrosion (including various stainless steel materials), and molybdenum-containing high-silicon iron can only be used for hydrochloric acid at 50 ° C and 30%. Contrary to metal materials, most non-metallic materials have good corrosion resistance to hydrochloric acid, so rubber pumps and plastic pumps (such as polypropylene, fluoroplastics, etc.) are the best choice for transporting hydrochloric acid. The company's applicable products are: IHF lining fluorine pump, PF (FS) strong corrosion resistant centrifugal pump, CQ polypropylene magnetic pump (or fluoroplastic magnetic pump).
3.
Generally, most metals are rapidly corroded and destroyed. Stainless steel is the most widely used material. It has good corrosion resistance to all concentrations at room temperature. It is worth mentioning that the stainless steel containing molybdenum (such as 316, 316L) is correct. Corrosion resistance is not only not superior to ordinary stainless steel (such as 304, 321), and sometimes even worse. For high temperatures, titanium and titanium alloy materials are usually used. The company's applicable products are: DFL (W) H chemical pump, DFL (W) PH shielding chemical pump, DFCZ process pump, DFLZP self-priming chemical pump, IH chemical pump, CQB magnetic pump, etc., the material is 304.
4. Acetic acid
It is one of the most corrosive substances in organic acids. Ordinary steel is severely corroded in acetic acid of all concentrations and temperatures. Stainless steel is an excellent acetic acid resistant material. Molybdenum-containing 316 stainless steel can also be used for high temperature and dilute acetic acid vapor. . High-alloy stainless steel or fluoroplastic pumps are available for demanding requirements such as high temperature, high concentration acetic acid or other corrosive media.
5. Alkali (sodium hydroxide)
Steel is widely used in sodium hydroxide solutions below 80 ° C and 30% concentration. Many factories still use ordinary steel at 100 ° C and below 75%. Although the corrosion is increased, the economy is good. The corrosion resistance of ordinary stainless steel to lye has no obvious advantages compared with cast iron. Stainless steel is not recommended as long as a small amount of iron is allowed in the medium. For high-temperature alkaline liquids, titanium and titanium alloys or high-alloy stainless steels are often used. The company's general cast iron pumps can be used for low-concentration lye at room temperature. For special requirements, all kinds of stainless steel pumps or fluoroplastic pumps can be used.
6. Ammonia (ammonium hydroxide)
Most metals and non-metals are slightly corrosive in liquid ammonia and ammonia (ammonium hydroxide), and only copper and copper alloys are not suitable. Most of the company's products are suitable for the transport of ammonia and ammonia.
7. Salt water (sea water)
Ordinary steel in the sodium chloride solution and seawater, salt water corrosion rate is not too high, generally must use paint protection; all kinds of stainless steel also has a very low uniform corrosion rate, but may cause local corrosion due to chloride ions, usually 316 stainless steel better. The company's various chemical pumps have 316 material configurations.
8. Alcohols, ketones, esters, ethers
Common alcohol media are methanol, ethanol, ethylene glycol, propanol, etc., ketone media are acetone, methyl ethyl ketone, etc., ester media have various methyl esters, ethyl esters, etc., ether media are methyl ether, ether, Butyl ether, etc., they are basically non-corrosive, and commonly used materials can be applied. When selecting specifically, they should also make reasonable choices according to the properties of the medium and related requirements. It is also worth noting that ketones, esters, and ethers are soluble in a variety of rubbers and avoid errors when selecting sealing materials.
There are many other media that can't be introduced here. In short, you should not be random and blind when selecting materials. You should consult relevant materials or learn from mature experience.
Cooling problem
The transportation of high-temperature medium puts higher requirements on the structure, materials and auxiliary system of the pump. Let's talk about the cooling requirements of different temperature changes and the company's applicable pump type:
1. For media with a temperature below 120 °C, there is usually no special cooling system, and the medium itself is used for lubrication and cooling. Such as DFL (W) H chemical pump, DFL (W) PH shielding chemical pump (protection level of shielded motor should exceed H grade when over 90 °C); and DFCZ common type and IH chemical pump can use temperature to adopt suspension structure The upper limit is 140 ° C ~ 160 ° C; IHF lining fluorine pump can be used up to 200 ° C; only CQB ordinary magnetic pump use temperature does not exceed 100 ° C. It is worth mentioning that the medium that is easy to crystallize or contains particles should be equipped with a sealing surface flushing line (designed with an interface).
2. For mediums above 120 °C and below 300 °C, a cooling chamber shall be provided on the pump cover. The sealing chamber shall also be connected to the coolant (with double mechanical seal), when the coolant is not allowed to penetrate into the medium. It should be taken after cooling its own medium (can be realized by simple heat exchanger). At present, the company has DFCZ type chemical process pump, GRG high temperature pipeline pump and HPK hot water circulation pump (under development), and CQB-G high temperature type magnetic pump can be used for high temperature medium within 280 °C.
3. For high temperature medium above 300 °C, not only the pump head part needs to be cooled, but also the suspension bearing chamber should be equipped with a cooling system. The pump structure is generally in the form of a central support. The mechanical seal is preferably a metal bellows type, but the price is high ( The price is more than 10 times that of a normal machine seal). At present, only the DFAY centrifugal oil pump can reach a temperature of 420 °C (under development).
Sealing problem
No leakage is the eternal pursuit of chemical equipment. It is this requirement that has led to the expansion of the application of magnetic pumps and shielded pumps. However, there is still a long way to go before there is no leakage, such as the life of the magnetic pump isolation sleeve and the shielded pump shield, the pitting problem of the material, the reliability of the static seal, and so on. Some basic information on sealing is briefly introduced as follows:
Sealed form
For static sealing, there are usually only two types of gaskets and sealing rings, and the sealing ring is the most widely used O-ring; for dynamic sealing, the chemical pump rarely uses packing sealing, mainly mechanical sealing, mechanical sealing There are single-end and double-end, balanced and unbalanced types, balanced type is suitable for high-pressure medium sealing (usually refers to pressure greater than 1.0MPa), double-faced machine seal is mainly used for high temperature, easy to crystallize, have viscosity, contain particles As well as the toxic and volatile medium, the double-end machine seal should inject the isolation liquid into the sealed chamber, and the pressure is generally higher than the medium pressure of 0.07~0.1MPa.
2. Sealing material
The material of the chemical pump static sealing is generally made of fluororubber. In special cases, the PTFE material is used. The material arrangement of the mechanical seal static and dynamic ring is more critical. It is not the hard alloy to the hard alloy, the price is high, on the one hand, two It is not reasonable to have no hardness difference, so it is best to treat them differently according to the characteristics of the medium.
(Note: The typical configuration of the American Petroleum Institute API 610 eighth edition for mechanical seals and piping systems is detailed in Appendix D)
Viscosity problem
The viscosity of the medium has a great influence on the performance of the pump. When the viscosity increases, the lift curve of the pump decreases, and the head and flow rate of the optimal working condition decrease, and the power increases, so the efficiency decreases. The parameters on the general sample are the performance when conveying clean water, and should be converted when conveying the viscous medium (the correction coefficient for different viscosities can be found in the relevant conversion chart). For the transportation of higher viscosity pulp, paste and viscous liquid, it is recommended to use screw pump. The company DFGG single screw pump is suitable for medium viscosity up to 1000000cst.
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Tag: Chemical pump Corrosive medium Dynamic seal Pump type Best working condition
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