What Are The Precautions To Be Taken When Selecting A Pump

Oct 09, 2025

The petroleum and chemical industries occupy a very important position in the national economy, and three screw pumps and single screw pumps, as key supporting equipment, are also receiving increasing attention from people. Due to the complex characteristics of chemical media and the increasing demand for environmental protection, how should we select chemical pumps? What aspects should be focused on and so on are particularly important.

Note 1: Corrosion resistance issue

Corrosion has always been one of the most troublesome hazards of chemical equipment. A slight carelessness can cause damage to the equipment, and in severe cases, it can lead to accidents or even disasters. According to relevant statistics, about 60% of the damage to chemical equipment is caused by corrosion, so the scientific selection of materials should be the first thing to pay attention to when selecting chemical pumps. There is usually a misconception that stainless steel is a "universal material" that can be used in any medium or environmental conditions, which is very dangerous.
Below are some key points for selecting materials for 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.
The corrosion of materials varies greatly with different concentrations and temperatures of sulfuric acid. For concentrated sulfuric acid with a concentration above 80% and a temperature below 80 ℃, carbon steel and cast iron have good corrosion resistance, but they are not suitable for high-speed flowing sulfuric acid and are not suitable as materials for pumps and valves; Ordinary stainless steels such as 304 (0Cr18Ni9) and 316 (0Cr18Ni12Mo2Ti) also have limited applications in sulfuric acid media.
Therefore, pumps and valves for transporting sulfuric acid are usually made of high silicon cast iron (difficult to cast and process) and high alloy stainless steel (alloy 20), but their processing difficulty and high price are not favored by people.

 

Fluoroplastic alloy has excellent resistance to sulfuric acid, and there is currently no chemical medium that can react with it. Therefore, using a fluorine lined pump (F46) is a more economical choice.

 

2. Hydrochloric acid

The vast majority of 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 below 50 ℃ and 30%. Unlike metallic materials, the vast majority of non-metallic materials have good corrosion resistance to hydrochloric acid, so lined rubber pumps and plastic pumps (such as engineering plastics, fluoroplastics, etc.) are the best choices for transporting hydrochloric acid.

3. Nitric acid

Most metals are rapidly corroded and destroyed in nitric acid, and stainless steel is the most widely used nitric acid resistant material. It has good corrosion resistance to all concentrations of nitric acid at room temperature. It is worth mentioning that molybdenum containing stainless steel (such as 316, 316L) not only has no better corrosion resistance to nitric acid than ordinary stainless steel (such as 304, 321), but sometimes even inferior. For high-temperature nitric acid, fluoroplastic alloy materials are usually used.

4. Acetic acid

It is one of the most corrosive substances in organic acids. Ordinary steel will corrode severely in 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 for high temperatures and dilute acetic acid vapor.
For high temperature and high concentration acetic acid or other corrosive media with strict requirements, high alloy stainless steel or fluoroplastic pumps can be selected. Such as CQB magnetic pump and CQ stainless steel magnetic pump.

5. Alkali (sodium hydroxide)

Generally, the corrosiveness is not very strong, but generally alkaline solutions will produce crystals. Therefore, FSB type fluorine alloy alkali pumps with mechanical seals made of siliconized graphite 169 material can be selected.

6. Ammonia (ammonia hydroxide)

Most metals and non metals have mild corrosion in liquid ammonia and ammonia water (ammonia hydroxide), only copper and copper alloys are not suitable for use. At this time, it is better to choose CQF engineering plastic magnetic pump and FSB fluorine alloy centrifugal pump.

 

 

7. Saltwater (seawater)

Ordinary steel has a relatively low corrosion rate in sodium chloride solution, seawater, and saltwater, and generally requires coating protection; Various types of stainless steel also have low uniform corrosion rates, but may cause localized corrosion due to chloride ions. 316 stainless steel is usually preferred.

8. Alcohols, ketones, esters, ethers

Common alcohol media include methanol, ethanol, ethylene glycol, propanol, etc. Ketone media include acetone, butanone, etc. Ester media include various methyl esters, ethyl esters, etc. Ether media include methyl ether, ethyl ether, butyl ether, etc. They are generally not corrosive, so ordinary stainless steel can be used. When selecting, a reasonable choice should be made based on the properties and relevant requirements of the medium.
Additionally, it is worth noting that ketones, esters, and ethers have solubility in various types of rubber, so errors should be avoided when selecting sealing materials. Suggest choosing an inorganic sealed fluoroplastic magnetic pump.
There are many other media that cannot be introduced here one by one. In short, when selecting materials, one should not be arbitrary or blind, and should consult relevant materials or draw on mature experience.

 

Note 2: Sealing issue

Leak free is the eternal pursuit of chemical equipment, and it is this requirement that has led to the increasing application of magnetic pumps.
However, there is still a long way to go to truly achieve zero leakage, such as the lifespan of magnetic pump isolation sleeves, material corrosion issues, reliability issues of static seals, and so on.
Here are some basic information about sealing:

1. Sealing form

For static seals, there are usually only two forms: gaskets and seals, with O-rings being the most widely used.
For dynamic seals, chemical pumps rarely use packing seals, mainly mechanical seals. Mechanical seals are divided into single end and double end, balanced and unbalanced types. The balanced type is suitable for sealing high-pressure media (usually referring to pressures greater than 1.0 MPa), while the double end mechanical seal is mainly used for high-temperature, easily crystallized, viscous, particle containing, and toxic volatile media. The double end mechanical seal should inject isolation liquid into the sealing chamber, and its pressure is generally 0.07-0.1 MPa higher than the medium pressure.

 

 

2. Sealing material

The material for the static seal of chemical magnetic pumps is generally fluororubber, and polytetrafluoroethylene material is only used in special cases; The material configuration of the dynamic and static rings of mechanical seals is crucial, and it is not necessarily the best choice for hard alloys. The high price is one aspect, and the lack of hardness difference between the two is not reasonable. Therefore, it is best to treat them differently based on the characteristics of the medium.
(Note: The American Petroleum Institute API 610 Eighth Edition provides detailed specifications for typical configurations of mechanical seals and piping systems in Appendix D.)

Note 3: Viscosity

The viscosity of the medium has a significant impact on the performance of the pump. As the viscosity increases, the pump's head curve decreases, and the optimal operating head and flow rate both decrease, while the power increases, resulting in a decrease in efficiency.
The parameters on general samples are the performance when transporting clean water, and should be converted when transporting viscous media.
For the transportation of high viscosity slurries, pastes, and viscous liquids, it is recommended to use mortar pumps.