Pump Material Selection

Factors to consider when selecting pump materials: 1 strength; 2 corrosion resistance; 3 wear resistance; 4 casting and machinability; 5 weld repair performance; 6 Cost

1, Cast iron

For most liquid delivering applications, grey cast iron is a good material for making pump casing. For single stage pumps, usually grey cast iron has sufficient strength to withstand the pressure generated. Ductile iron is widely used for medium pressure and temperature.When the corrosion resistance of gray cast iron and ductile cast iron is insufficient, corrosion resistant high nickel cast iron is often used as the pump casing material.In recent years, a new type of corrosion resistant high nickel cast iron material (named D2W) with good weldability has been developed.It contains a small amount of niobium which improves its weldability. Typical austenitic cast irons contain 15% to 20% nickel and are widely used in salt water.

Gray cast iron is the most commonly used type of cast iron, and its national code is HT.This material is used in the following parts of general clean water pumps: pump casing, impeller, pump cover, suspension, etc. Three grades are usually used: HT150, HT200, HT250.For non-main parts such as base and pad, HT150 is commonly used; for pump casing, pump cover, suspension, etc., HT200 is commonly used; for impeller, ring, bushing, etc.; HT250 is commonly used.Different countries have different codes for gray iron, such as Japan's code name FC, Germany code GG, and the US class 4.

Ductile iron is a kind of cast iron with better comprehensive performance. The national code is QT.Because its mechanical properties are close to steel, and its casting performance and processing performance are 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 limitation of casting and so on, the impeller of the water pump is currently used with the material, and the cutting type open impeller is superior in cost performance.The DIN standard call ductile iron is GGG, and the US call it ductile iron.

2, Cast steel

For corrosive and hazardous petroleum products, or multi-stage pump outlet pressures up to 13.8 MPa, cast steel or cast stainless steel is required.Martensitic stainless steels are often used in boiler feed pumps and many hydrocarbon applications.Martensitic stainless steel has good mechanical properties and is suitable for high pressure applications, but its corrosion resistance is not as good as other stainless steels. Austenitic stainless steels (CF-8M, CF-3M, etc.) are commonly used as pump casing materials in chemical applications and other corrosive environments.In addition, Austenitic stainless steel is resistant to corrosion due to high speed and can be easier to be repaired in the site.High-pressure water injection pumps have higher requirements for corrosion resistance and mechanical properties. Duplex stainless steel (50% ferrite + 50% austenite) is used as the material of the pump casing.Due to the high strength of cast steel, it is usually used for pressure-bearing parts when the pressure is >1.6Mpa.Its national code is ZG, and the most commonly used grade is ZG23 0-450. Japan and the United States usually use CS to call cast steel.

3, Bronze

In many pump applications, bronze materials are also used as the pump body. Lead bronze is commonly used in small low pressure pumps. Lead helps the seal of the pump body. Tin bronze is used as the pump material for larger centrifugal pumps. Nickel-aluminum bronze has the best mechanical properties and corrosion resistance, but it is expensive.

4, Composite materials

In order to improve the chemical resistance of the pump, a lining can be added to the volute. Material used as a lining : Teflon, rubber, etc .Monolithic ceramic and graphite pumps are used in strong corrosive liquids such as hydrofluoric acid.In the paper and pulp industry, the metal finishing industry, composite materials such as epoxy resins are used to make pump casings.

5, Stainless steel

The most widely used stainless steel is austenitic stainless steel, such as 0Cr18Ni9, 1Cr18Ni9Ti, 0Cr18Ni12Mo2Ti, etc . Austenitic stainless steel is an excellent corrosion-resistant material, except for hydrochloric acid and dilute sulfuric acid, etc .It is the most commonly used corrosion-resistant material for chemical pumps.Japan and the United States usually use SS304, SS316, SS316L to represent austenitic stainless steel.Martensitic stainless steels such as 2Cr13 and 3Cr13 have better mechanical properties than austenitic stainless steels and are commonly used as materials for pump shafts and shaft sleeve.The corresponding code name in Japan and the United States is SS420.In addition, high alloy stainless steel (20# alloy) and duplex stainless steel are also ideal corrosion resistant materials.

6, Carbon structural steel

Usually divided into ordinary carbon structural steel and high quality carbon structural steel. The most representative ordinary carbon structural steel is Q235, which is widely used in various steel plates and profile steel.The most representative high-quality carbon steel is 45# steel, which is widely used in pump shaft materials without corrosion resistance requirement.

7, Alloy steel

The most representative alloy steel is 40Cr, which is commonly used for high strength pump shaft materials.

8, Non-metallic materials

Non-metallic materials for pumps are mainly used for sealing, such as PTFE, fluororubber, nitrile rubber, etc.Due to its excellent corrosion resistance and high temperature resistance, PTFE is used for chemical pump seals and mechanical seals. It is suitable for nearly all chemical media within 250 °C. Its disadvantages are high hardness and difficult assembly.Fluororubber is also a good temperature and corrosion resistant material with an upper temperature limit of 160 °C.When the user has no special requirements, it is recommended to use this material as the sealing ring of the chemical pump;Nitrile rubber is mainly used for static sealing when it is resistant to oil or water.

Table 1 Common materials for domestic pumps