Note 1: Corrosion resistance

Corrosion has always been one of the hazards of chemical equipment headaches. If you are not careful, 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 material selection for some common chemical media:

1 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. Not suitable for pump valve materials; ordinary stainless steel such as 304 (0Cr18Ni9), 316 (0Cr18Ni12Mo2Ti) also has limited use of 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), but it is difficult to process and expensive, so it is not favored by people.

Fluoroplastic alloy has good sulfuric acid resistance. It is a material of Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences. It has been proved by the Chinese Academy of Sciences that there is no chemical medium that can react with it. Therefore, the fluorine-lined pump (F46) is a A more economical choice.

2 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 engineering plastics, fluoroplastics, etc.) are good choices for transporting hydrochloric acid.

3 nitric acid

Generally, most metals are rapidly corroded and destroyed in nitric acid. Stainless steel is widely used as a nitric acid-resistant material. It has good corrosion resistance to all concentrations of nitric acid at normal temperature. It is worth mentioning that it contains molybdenum-containing stainless steel (such as 316 and 316L). The corrosion resistance to nitric acid is not only not superior to ordinary stainless steel (such as 304, 321), and sometimes even worse. For high temperature nitric acid, a fluoroplastic alloy material is usually used.

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. Such as CQB magnetic pump, CQ stainless steel magnetic pump.

5 alkali (sodium hydroxide)

Generally, the corrosivity is not very strong, but generally the alkali solution will produce crystals. Therefore, an FSB type fluorine alloy alkali pump equipped with a mechanical seal of silicified graphite 169 may 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. At this time, it is better to use CQF engineering plastic magnetic pump and FSB fluorine alloy centrifugal pump.

7 brine (sea water)

Ordinary steel in the sodium chloride solution and seawater, salt water corrosion rate is not too high, generally must be protected by paint; 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.

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 not corrosive, so ordinary stainless steel can be used. When selecting specifically, it should be made 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. It is recommended to choose an inorganic sealed fluoroplastic magnetic pump.

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.

Note 2: Sealing problem

No leakage is the eternal pursuit of chemical equipment, and it is this requirement that has led to the expansion of the application of magnetic 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, 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:

1 sealed form

For static sealing, there are usually only two types of gaskets and seals, and the seals are widely used in O-rings.

For dynamic sealing, chemical pumps rarely use packing seals, mainly mechanical seals, mechanical seals have single-end and double-end, balanced and unbalanced types, and balanced type is suitable for high-pressure medium sealing (usually refers to pressure greater than 1.0MPa), double-face machine seal is mainly used for high temperature, easy to crystallize, have viscosity, contain particles and toxic volatile medium. Double-end machine seal should inject spacer liquid into the sealed cavity, the pressure is generally higher than the medium pressure 0.07~0.1 MPa.

2 sealing material

The material of the chemical magnetic 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 high price is on the one hand, two It is not reasonable to have no hardness difference, so it is better to treat it 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)

Note 3: 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 excellent working conditions decrease, and the power increases, so the efficiency decreases.

The parameters on the general sample are the performance when the water is delivered. When the viscous medium is transported, the conversion should be performed (the correction coefficient for different viscosities can be found in the relevant conversion chart).

For the transport of higher viscosity pulps, pastes and viscous liquids, it is recommended to use a mortar pump.

Pump selection principle

When designing equipment, the design institute should determine the pump's purpose and performance parameters and select the pump type. This choice must first start with the choice of pump type and form, then what principle to choose the pump? What is the basis?

1. Make the type and performance of the selected pump meet the requirements of process parameters such as flow, lift, pressure, temperature, NPSH, and suction.

2, must meet the requirements of the media characteristics

For pumps that transport flammable, explosive, toxic or valuable media, shaft seals are required to be reliable or leak-free pumps, such as magnetically driven pumps (without shaft seals, indirectly driven by isolated magnetic forces);

For pumps that transport corrosive media, corrosive materials such as fluoroplastic corrosion resistant pumps are required for convection components;

For pumps containing solid particulate media, it is required that the convection component be made of wear-resistant material, and if necessary, the shaft seal should be flushed with a cleaning liquid.

3. Mechanical requirements require high reliability, low noise, and low vibration.

4. Calculate the input cost of pump procurement correctly.

5. When conveying highly corrosive media (such as "concentrated sulfuric acid, concentrated nitric acid"), when transporting inflammable and explosive media, and the use environment must not have any pollution: optional magnetic pump, such as "CQB series magnetic pump, IMD series magnetic force Pump, if you need to self-prime, you can use FZB fluoroplastic self-priming pump.

6. IHF centrifugal pump and FSB centrifugal pump have the characteristics of high speed, small volume, light weight, high efficiency, large flow, simple structure, no pulsation of infusion, stable performance, easy operation and convenient maintenance, etc. When using a centrifugal pump, it is better.

7. When pumping a chemical medium containing solid particles, it is required to use wear-resistant materials for convection parts: UHB mortar pump is an excellent choice object, UHB anti-corrosion wear-resistant mortar pump material is high-strength new engineering plastic UHBWPE, it is a modification Ultra-high molecular weight (more than 5 million) polyethylene. In plastics, it has excellent wear resistance. Compared with the test, its wear resistance is much higher than that of stainless steel, and it is resistant to impact, creep resistance and excellent corrosion resistance (comparable to F4). Unique properties such as adhesion.

8. When the medium level is below the pump installation position: FZB fluoroplastic self-priming pump should be used. If the characteristics of the magnetic pump are still needed, ZMD fluoroplastic self-priming magnetic pump can be used.

9. Select the excellent specification model according to the performance curve of the pump: When the usage requirements can not find the suitable model in the performance parameter table, refer to the pump performance curve to select the appropriate pump type.

Shanghai Suochuan Pump & Valve Co., Ltd. specializes in fluorine plastic pump, fluorine plastic centrifugal pump, fluorine plastic magnetic pump, fluorine plastic alloy pump, fluorine-lined magnetic pump, fluorine-lined centrifugal pump, etc. Welcome to call 18821237168