How to select the impeller material for a multistage pump?

Many people wonder why multistage pump impellers are prone to damage-usually, this isn't a problem with the equipment itself. The root cause is usually the improper selection of impeller materials. Choosing the wrong material can lead to rapid impeller wear and a sharp drop in efficiency, or even impeller breakage and complete pump failure.

 

 

• Common materials for multistage pump impellers:

 

1. Cast Iron

Cast iron is the most common material for water pump impellers. It's used for conveying non-corrosive media. Common grades include HT150, HT200, and HT250. HT150 is used for non-critical parts like the base and pad, HT200 for the pump body, pump cover, and suspension, and HT250 for the impeller, wear ring, and shaft sleeve.

Different countries use different designations for gray iron. For example, Japan uses FC, Germany uses GG, and the United States uses Class.

 

2. Ductile Iron

Ductile iron has good overall performance. Its national standard designation is QT. Because its mechanical properties are close to steel, and its forging and machining properties are superior, it's generally used as a replacement for cast steel. Common grades include QT450-10, QT500-7, and QT600-3.

DIN standards denote ductile iron as GGG, while the American standard uses "Ductile iron."

Other types include corrosion-resistant cast iron (high-silicon cast iron), wear-resistant cast iron (white cast iron), and high-toughness cast iron (malleable cast iron).

 

3. Cast Steel

Cast steel has high strength. When the pressure is >1.6 MPa, pressure-bearing parts are mostly made of cast steel. The national standard designation is ZG, and commonly used grades are ZG230-450. Japan and the United States usually use CS to denote cast steel.

 

4. Stainless Steel

The most commonly used stainless steel is austenitic stainless steel, such as 0Cr18Ni9, 1Cr18Ni9Ti, and 0Cr18Ni12Mo2Ti. Except for a few media such as hydrochloric acid and dilute sulfuric acid, austenitic stainless steel is an excellent corrosion-resistant material and is the most commonly used corrosion-resistant material for chemical pumps. Japan and the United States usually use SS304, SS316, and SS316L to denote austenitic stainless steel.

Martensitic stainless steels such as 2Cr13 and 3Cr13 have superior mechanical properties compared to austenitic stainless steels and are commonly used as materials for pump shafts and bushings. The corresponding designation in Japan and the United States is SS420.

In addition, high-alloy stainless steel (Alloy 20) and duplex stainless steel are also ideal corrosion-resistant materials.

 

5. Alloy Steel

The most representative alloy steel is 40Cr, commonly used for high-strength pump shafts.

 

6. Carbon Structural Steel

Generally divided into ordinary carbon structural steel and high-quality carbon structural steel.

The most representative ordinary carbon structural steel is Q235, widely used in various steel plates and sections; the most representative high-quality carbon steel is 45 steel, widely used for pump shafts where corrosion resistance is not a requirement.

 

7. Non-metallic Materials

Non-metallic materials for pumps are mainly used for sealing, such as polytetrafluoroethylene (PTFE), fluororubber, and nitrile rubber. Polytetrafluoroethylene (PTFE) is used for gaskets in chemical pumps and static seals in mechanical seals due to its excellent corrosion resistance and high temperature resistance. It is suitable for almost all chemical media within 250℃. Its disadvantages are high hardness and difficult assembly.

 

• Select impeller material according to the conveying medium.

 

Clean Water Media

For conveying pure water free of impurities or solid particles, gray cast iron is sufficient. It is inexpensive, rigid, and has excellent casting and machining properties, making it the most cost-effective choice for standard water purification applications.

 

Water containing silt or small amounts of particulate matter (e.g., wastewater)

Ordinary gray cast iron has extremely poor wear resistance and is easily worn down when pumping sandy water for extended periods. In such cases, high-chromium wear-resistant cast iron must be used. High-chromium wear-resistant cast iron has significantly improved wear resistance and a service life 3-5 times longer than ordinary cast iron. It is particularly suitable for river water containing particulate matter, construction site wastewater, and mine water.

 

Corrosive liquids (acids, alkalis, salts)

Cast iron should never be used in corrosive environments-it is extremely prone to rusting and perforation! For mildly corrosive media, choose 304 stainless steel. For moderate to strong acid and alkali corrosion, 316L stainless steel is recommended. For seawater or high-chloride salt environments, upgrade to 2205 duplex stainless steel, which has excellent resistance to chloride corrosion.

 

High-temperature and high-pressure conditions

In applications such as boiler feedwater, high-temperature circulating water, and high-pressure piping systems, cast iron and ordinary stainless steel should be avoided. Carbon cast steel or alloy cast steel should be selected instead. These materials possess high mechanical strength, high temperature resistance, and high pressure impact resistance, ensuring stable and safe operation under high temperature and high pressure without deformation or cracking.

 

In conclusion, when selecting impeller materials for multistage pumps, it is necessary to comprehensively consider the characteristics of the medium, the working environment, the cost budget, and the long-term reliability. Correct material matching not only improves pump efficiency but also effectively avoids equipment failures caused by inappropriate materials, thereby ensuring the stability and safety of the production process.