The selection of pump body materials takes into account factors such as strength, corrosion resistance, abrasion resistance, casting and mechanical processing performance, welding repair performance, and cost.
1. Cast iron
For most liquid conveying applications, gray cast iron is a better material for manufacturing pump casings. For single-stage pumps, gray cast iron usually has sufficient strength to resist the pressure generated. Ductile iron is widely used in the medium pressure and temperature range. In applications where gray cast iron and ductile iron cannot achieve sufficient corrosion resistance, corrosion-resistant high nickel cast iron is often used as a pump body material. In recent years, a new type of corrosion-resistant high nickel cast iron material (named D2W) with good welding performance has been developed, which contains a small amount of niobium element to improve its welding performance. Typical austenitic cast iron contains 15% to 20% nickel and is widely used in saltwater.
Gray cast iron is the most commonly used type of cast iron. Generally, the pump body, impeller, pump cover, suspension, etc. of clean water pumps are made of this material, and three grades are commonly used: HT150, HT200, and HT250. For non essential parts such as the base and gasket, HT150 is often used, while HT200 is commonly used for the pump body, pump cover, suspension, etc., and HT250 is commonly used for impellers, mouth rings, shaft sleeves, etc. The representation of gray iron varies among countries, such as FC in Japan, GG in Germany, and Class4 in the United States.
Ductile iron is a type of cast iron with good comprehensive performance. Due to its mechanical properties being close to steel, and its casting and processing properties being superior to steel, it is usually used as a substitute for cast steel. Due to limitations such as casting, the impeller of water pumps currently uses this material, especially the cutting type open impeller, which has superior cost-effectiveness. The representation method for ductile iron in the IN standard is GGG, and the representation method in the United States is Ductileiron.
2. Cast steel
For corrosive and harmful petroleum products, or when the outlet pressure of multi-stage pumps reaches 13.8 MPa, it is necessary to use specified cast steel or cast stainless steel. Martensitic stainless steel is commonly used in boiler feed pumps and many hydrocarbon applications. 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. Austenitic stainless steel (CF-8M, CF-3M, etc.) is commonly used as pump casing material in chemical applications and other corrosive environments. In addition, austenitic stainless steel can resist erosion caused by high speed and can be relatively easily welded and repaired on site. The high-pressure shallow water injection pump has higher requirements for corrosion resistance and mechanical performance, and its pump casing is made of duplex stainless steel material (50% ferrite+50% austenite).
