When selecting a pump, you must pay attention to these issues!

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The petroleum and chemical industries play a very important role in the national economy, and chemical process pumps, as key supporting equipment, are attracting increasing attention. Given the complex nature of chemical media, along with the increasing demands for environmental protection, how should we select chemical pumps? It is particularly important to pay close attention to certain aspects and so on. Today, let’s talk about the things to keep in mind when selecting chemical pumps! I hope fellow sea lovers can fill in the gaps. Note 1: Corrosion resistance. Throughout the years, corrosion has been one of the most troublesome problems affecting chemical processing equipment. Even a slight carelessness can lead to equipment damage; in severe cases, it can result in accidents or even disasters. According to relevant statistics, about 60% of the damage to chemical processing equipment is caused by corrosion; therefore, when selecting chemical pumps, it is essential to pay attention to the scientific choice of materials. There is a common misconception that stainless steel is a \"universal material\" that can be used in any medium or under any environmental conditions; this is very dangerous. Below are the key points for material selection regarding some commonly used chemical media: 1. Sulfuric acid – As one of the highly corrosive media, sulfuric acid is an important industrial raw material with a wide range of applications. Sulfuric acid at different concentrations and temperatures causes varying degrees of corrosion to materials. For concentrated sulfuric acid with a concentration of over 80% and a temperature below 80°C, carbon steel and cast iron exhibit good corrosion resistance; however, it is not suitable for sulfuric acid that flows at high speeds, and it cannot be used as material for pumps and valves ； Common stainless steels such as 304 (0Cr18Ni9) and 316 (0Cr18Ni12Mo2Ti) also have limited utility in sulfuric acid media. Therefore, pump valves for transporting sulfuric acid are usually made of high-silicon cast iron (which is difficult to cast and process) or highly alloyed stainless steel (grade 20 alloy), but their difficulty in processing and high cost render them less attractive. Fluoroplastic alloys exhibit excellent resistance to sulfuric acid. They are patented materials developed by the Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences. Experiments conducted by the Academy have shown that no chemical medium is currently capable of reacting with them; therefore, using fluorine-lined pumps (F46) represents a more economical choice. Salts and acids: The vast majority of metal materials are not resistant to corrosion by salts and acids (including various stainless steel materials); high-molybdenum, high-silicon iron can only be used in salts and acids at temperatures below 50°C and with a concentration of less than 30%. Unlike metal materials, the vast majority of non-metallic materials exhibit good corrosion resistance to acids, so rubber-lined pumps and plastic pumps (such as engineering plastics and fluoroplastics) are the best choices for transporting acids. 3*ao acid: Most metals are rapidly corroded and damaged by *ao acid. Stainless steel is the most widely used material resistant to *ao acid, exhibiting good corrosion resistance against *ao acid at all concentrations at room temperature. It is worth noting that stainless steels containing molybdenum (such as 316 and 316L) do not have better corrosion resistance to *ao acid than ordinary stainless steels (such as 304 and 321); in some cases, their resistance is even lower. For high-temperature *ao acids, fluoroplastic alloy materials are typically used. 4. Acetic acid: It is one of the most corrosive organic acids; ordinary steel is severely corroded by acetic acid at all concentrations and temperatures. Stainless steel is an excellent material resistant to acetic acid, and 316 stainless steel containing molybdenum can also be used in high-temperature environments as well as with dilute acetic acid vapor. For demanding applications such as high-temperature, high-concentration acetic acid or environments containing other corrosive substances, high-alloy stainless steel or fluoroplastic pumps can be used. Such as CQB magnetic pump, CQ stainless steel magnetic pump. Alkalis 5 (hydrogen, oxygen, sodium hydroxide) generally do not have strong corrosive properties, but crystallization occurs in most alkaline solutions; therefore, an FSB-type fluoropolymer alkali pump equipped with a mechanical seal made of siliconized graphite material 169 can be used. 6 Ammonia (ammonium hydroxide): Most metals and non-metals suffer only mild corrosion in liquid ammonia and ammonia water (ammonium hydroxide); only copper and its alloys are not suitable for use. In this case, it is better to use a CQF engineering plastic magnetic pump or an FSB fluoropolymer centrifugal pump. 7 Saltwater (seawater): Ordinary steel exhibits a low rate of corrosion in sodium chloride solutions as well as in seawater and brackish water; coating protection is generally required ； Various types of stainless steel also have very low uniform corrosion rates, but local corrosion may occur due to chloride ions; therefore, 316 stainless steel is generally the better choice. Alcohols, similar compounds, esters, and ethers: Common alcohol-based media include methanol, ethanol, ethylene glycol, propanol, etc.; similar compounds include propyl alcohol, butyl alcohol, etc.; ester-based media include various methyl esters, ethyl esters, etc.; ether-based media include dimethyl ether, diethyl ether, butyl ether, etc. These substances generally have low corrosivity, so ordinary stainless steel can be used for them. However, a proper choice should still be made based on the properties of the medium and relevant requirements. It is also worth noting that alcohols, esters, and ethers are soluble in various rubbers, which helps to avoid mistakes when selecting sealing materials. It is recommended to choose a fluoroplastic magnetic pump with an inorganic seal. There are many other media that cannot be listed here one by one. In short, when selecting materials, one should not act casually or blindly; it is necessary to consult relevant information and draw on proven experience. ◆ ◆ ◆ Note 2: Sealing issues. Zero leakage is an eternal goal for chemical processing equipment, and it is precisely this requirement that has led to the increasing use of magnetic pumps. However, there is still a long way to go before true leaklessness can be achieved, such as the lifespan issue of magnetic pump isolation sleeves, the pitting problem of materials, and the reliability issues of static seals, among others. Here is a brief introduction to some basic aspects of sealing: 1. Sealing types: For static sealing, there are generally only two types – gaskets and seals; among these, O-rings are the most widely used. For dynamic seals, chemical pumps rarely use packing seals; mechanical seals are preferred instead. Mechanical seals come in single-face and double-face types, as well as balanced and unbalanced versions. Balanced mechanical seals are suitable for sealing high-pressure media (typically those with pressures greater than 1.0 MPa). Double-face mechanical seals are used mainly for media that are high-temperature, prone to crystallization, viscous, contain particles, or are toxic and volatile. An isolation fluid must be injected into the sealing chamber using double-face mechanical seals, and its pressure is generally 0.07–0.1 MPa higher than the pressure of the medium. 2 Sealing materials: The static sealing material for chemical magnetic pumps is generally fluororubber; polytetrafluoroethylene is used only in special cases ； The material selection for the stationary and rotating rings of mechanical seals is quite important. It’s not true that one combination of cemented carbide materials is always the best; high costs are one issue, but it’s also unreasonable if there is no difference in hardness between the two materials. Therefore, it’s best to choose materials based on the characteristics of the medium being handled. (Note: Appendix D of API 610, 8th edition, provides detailed specifications for the typical configurations of mechanical seals and piping systems.) ◆ ◆ ◆ Note 3: Viscosity issue The viscosity of the fluid has a significant impact on the performance of the pump. As viscosity increases, the pump’s head curve declines; both the head and flow rate at optimal operating conditions decrease, while power consumption increases, resulting in reduced efficiency. The parameters for standard samples represent the performance when transporting clean water; adjustments are necessary when transporting viscous media (the correction factors for different viscosities can be found in the relevant conversion tables). For transporting slurries, pastes, and viscous liquids with high viscosity, it is recommended to use a mortar pump. ◆ ◆ ◆ Pump selection principles: When designing equipment and systems, the design institute must determine the purpose and performance parameters of the pump and select the appropriate type of pump. This choice begins with selecting the type and design of the pump. So, what principles should be used to choose a pump? What is the basis then? 1. Ensure that the type and performance of the selected pump meet the requirements of the process parameters such as flow rate, head, pressure, temperature, net positive suction head, and suction lift of the installation. 2. The requirements regarding the properties of the medium must be met. For pumps used to transport flammable, explosive, toxic, or valuable media, it is necessary to have a reliable shaft seal or to use leak-free pumps, such as magnetically driven pumps (which have no shaft seal and rely on indirect magnetic drive) ； For pumps used to transport corrosive media, it is required that the moving parts be made of corrosion-resistant materials, such as fluoroplastic corrosion-resistant pumps ； For pumps that transport media containing solid particles, it is required that the convective components be made of wear-resistant materials, and where necessary, the shaft seals should be flushed with a clean liquid. 3. Mechanically, high reliability, low noise, and minimal vibration are required. 4. Correctly calculate the investment cost for purchasing pumps. 5. When transporting highly corrosive media (such as concentrated sulfuric acid and concentrated nitric acid), flammable and explosive media, or in environments where there must be no contamination at all, magnetic pumps can be used, such as the CQB series of magnetic pumps and the IMD series of magnetic pumps. If self-priming is required, the FZB fluoroplastic self-priming pump can be chosen. 6. IHF centrifugal pumps and FSB centrifugal pumps feature high rotational speed, small size, light weight, high efficiency, large flow rate, simple structure, pulse-free fluid delivery, stable performance, ease of operation, and convenient maintenance. When there are no special requirements regarding the operating conditions, it is advisable to choose a centrifugal pump. 7. For pumps used to transport chemical media containing solid particles, where wear-resistant materials are required for the convective components, UHB mortar pumps are the best choice. The material used in UHB corrosion- and wear-resistant mortar pumps is UHBWPE, a high-strength advanced engineering plastic that is a modified form of polyethylene with an ultra-high molecular weight of over 5 million. In plastics, it exhibits excellent wear resistance; experimental comparisons show that its wear resistance is far higher than that of stainless steel. It also boasts impact resistance, creep resistance, and outstanding corrosion resistance (comparable to F4), as well as unique properties such as non-adhesion. 8. When the liquid level of the medium is below the pump’s installation location, an FZB fluoroplastic self-priming pump should be used. If the properties of a magnetic pump are also required, then a ZMD fluoroplastic self-priming magnetic pump can be chosen. 9. The most suitable model should be selected based on the pump’s performance curve: when no appropriate model is available in the performance parameters table, the performance curve of the pump can be used to determine the most suitable type of pump.