What are the common pump body materials for centrifugal pumps? What are the characteristics of different materials?

Common materials for centrifugal pump bodies include cast iron, stainless steel, cast steel, bronze, composite materials, carbon structural steel, alloy steel, and non-metallic materials. Factors to consider when selecting materials include: a. strength; b. corrosion resistance; c. abrasive wear resistance; d. casting and machining performance; e. welding repair performance; and f. cost. Let's take a closer look.

1. Cast Iron

For most liquid conveying applications, gray cast iron is a better material for the pump casing. For single-stage pumps, gray cast iron is usually strong enough to withstand the pressure generated. Ductile iron is widely used in medium-pressure and temperature ranges. In applications where gray cast iron and ductile iron cannot achieve sufficient corrosion resistance, corrosion-resistant high-nickel cast iron is usually used as the pump body material. In recent years, a new type of corrosion-resistant nickel cast iron material (named D2W) with good welding properties has been developed, which contains a small amount of niobium to improve its welding properties. Typical austenitic cast iron contains 15920% nickel and is widely used in salt water.

Gray cast iron is the most commonly used cast iron, and the national standard code is HT. The pump body, impeller pump cover, suspension, etc. of general clean water centrifugal pumps are made of this material, and three grades are usually used: HT150, HT200, and HT250. HT150 is mostly used for non-main parts such as base and back plate, HT200 is mostly used for pump body, pump cover, suspension, etc., while HT250 is mostly used for impeller, stopper, sleeve, etc. The representation method of gray cast iron varies in different countries, such as FC in Japan, GG in Germany, and Cass4 in the United States.

Ductile iron is a kind of cast iron with good comprehensive performance, and its national standard code is QT. Because its mechanical properties are close to steel and its casting processing performance is better than steel, it is usually used as a substitute for cast steel. The most commonly used grades are: QT450-10, QT500-7, QT600-3. Due to the limitations of casting process and other reasons, the impeller of water pumps is mostly made of this material, especially the cut-open impeller. The DN standard represents ductile iron as GGG, and the American standard represents it as Ductile iron

2. Stainless steel

The most widely used stainless steel is austenitic stainless steel. Except for a few media, such as hydrochloric acid and dilute sulfuric acid, austenitic stainless steel is an excellent corrosion-resistant material and the most commonly used corrosion-resistant material for chemical pumps. In addition, high-alloy stainless steel (alloy 20) and duplex stainless steel are also ideal corrosion-resistant materials.

3. Cast steel

For corrosive and harmful petroleum products, or when the outlet pressure of a multistage pump reaches 13.8MPa, specified cast steel or cast stainless steel must be used. In boiler feed pumps and many hydrocarbon applications, martensitic stainless steel is often used. Martensitic stainless steel has good mechanical properties and is suitable for high-pressure conditions, but its corrosion resistance is not as good as other types of stainless steel in chemical applications and other corrosive application environments. Austenitic stainless steel (CF-8M, CF-3M, etc.) is often used as a pump casing material. In addition, austenitic stainless steel is corrosion-resistant due to its high speed and can be welded and repaired on-site relatively easily. High-pressure shallow seawater injection pumps have higher requirements for corrosion resistance and mechanical properties. The pump casing is made of duplex stainless steel (50% ferrite + 50% austenite).

As the strength of cast steel becomes higher and higher, usually when the pressure is greater than 16Mpa, pressure-bearing parts are mostly made of cast steel. The national standard code is ZG, and the most commonly used grade is ZG230-450. Japan and the United States usually use CS to represent cast steel.

4. Carbon structural steel

Usually divided into common carbon structural steel and high-quality carbon structural steel. The most representative common carbon structural steel is Q235, which is mostly used for various steel plates and steel sections; the most representative high-quality carbon structural steel is No. 45 steel, which is widely used as a pump shaft material when corrosion is not required.

5. Alloy steel

The most representative alloy steel is 40Cr, which is usually used as a material for high-strength pump shafts.

6. Non-metallic materials

Non-metallic materials for pumps are mainly used for sealing, such as polytetrafluoroethylene, fluororubber, nitrile rubber, etc. Among them, polytetrafluoroethylene has excellent corrosion resistance and high temperature resistance, and is used for static sealing of chemical pump gaskets and mechanical seals, and is suitable for almost all chemical media within 250°C. Its disadvantages are high hardness and difficult assembly.
Fluororubber is also a material with good heat and corrosion resistance, with an upper temperature resistance of 160°C. When the user has no special requirements, our chemical pumps all use seals made of this material, while nitrile rubber is mainly used for static sealing of oil-resistant or clean water media.

7. Bronze

Bronze materials are also used as pump bodies in many water pump applications. Lead bronze is often used in small, low-pressure pumps, and the lead helps seal the pump body. Tin bronze is used as the pump body material for large centrifugal pumps. Although nickel-aluminum bronze has the best mechanical properties and corrosion resistance, it is expensive and lacks competitiveness.

8. Composite materials

In order to improve the chemical corrosion resistance of the pump, a lining can be installed in the volute. Lining materials include polytetrafluoroethylene, rubber, etc. Integral ceramic pumps and graphite pumps are used to transport highly corrosive liquids, such as hydrofluoric acid in the paper and pulp industry and metal finishing industry, while composite materials (such as epoxy resin) are used to manufacture pump bodies.