Corrosion performance analysis of various materials of high pressure anticorrosive sea water pump:
cast iron
For anti-corrosion sea water pumps, the anti-corrosion performance of ordinary cast iron can no longer meet the operation requirements of sea water pumps, and will gradually be eliminated. We can add copper, chromium, nickel, molybdenum and other elements to ordinary cast iron to change its metallographic structure, such as turning it into austenitic structure, to increase the corrosion resistance of cast iron materials. For example, adding 12% to 36% of nickel to cast iron forms austenitic high-nickel cast iron, in which the graphite is spherical or flake. Its anti-corrosion performance, plasticity and strength have been significantly improved. In seawater, the corrosion rate of gray cast iron is as high as 0.070.5 mm per year, and the corrosion rate of high-nickel cast iron is only 0.02-0.06 mm per year. It is suitable for the production of pump bodies, impellers and other parts of seawater pumps.
stainless steel
There are five main types of stainless steel materials currently used in sea water pumps: Nitronic502205 duplex steel, 2507 duplex steel, 316, and 316L. The carbonization corrosion resistance of these stainless steel materials is directly related to the C element content. The lower the C element content, the stronger the carbonization corrosion resistance. Chromium is a key element that affects the ability of stainless steel to prevent rust: Nickel is a key element for the formation of austenite in stainless steel materials. By adjusting the content of nickel in stainless steel materials, the material can show the dual phase characteristics of austenite and ferrite; Adding Fe, M, Si, Mo and other trace elements to the material can enhance the performance of the material, refine the grain, make the material easier to weld and cut, and enhance its resistance to intergranular corrosion.
Figure 2 List of yield strength and tensile strength of several materials. From Figure 2, we can find that Nitronic50 material has the best yield strength and tensile strength, followed by 2507 duplex steel, 2205 duplex steel, and finally 316 and 316L; and 316 stainless steel has the best elongation, followed by 316L stainless steel, 2205 duplex steel, 2507 duplex steel and Nitronic50.
Copper Alloy
Four types of copper alloy materials are often used in the casing and impeller of current seawater pumps:
Aluminum bronze, tin bronze, copper alloy C63000 and C95800. Copper alloy materials mainly contain copper, manganese, iron, nickel, silicon and other elements. In order to make copper alloys perform better and richer, we can adjust the composition of various elements in copper alloys. proportion. The main chemical composition of my country's national standard aluminum bronze is similar to the copper alloy materials C63000 and C95800 standard of the American Society for Testing and Materials. As shown in Figure 3, C63000 has the best yield strength and tensile strength, followed by aluminum bronze, C95800, tin bronze, and the elongation of these copper alloy materials is basically the same
Monel
At present, the bolts and filters of some sea water pumps are made of Monel
material. It mainly includes Monel K500 and Monel400. Monel K500 contains more aluminum and titanium elements than Monel 400, which improves Monel K500's corrosion resistance, non-magnetic properties and strength.
When choosing the material of the sea water pump, in addition to considering the durability of the material, a reasonable choice must also be made in combination with the service life of the sea water pump and the financial situation. For example, among the stainless steel materials, the price of austenitic stainless steel is relatively cheaper, while the price of duplex stainless steel is relatively high. Therefore, we should give priority to lower-priced sea water pump materials when it can meet the needs of use. Among copper alloy materials, the price difference between international and domestic copper alloy materials is not large. Therefore, there is no need to consider too many price factors when choosing copper alloy materials: for Monel materials, Monel400 has a higher price. Unless special circumstances require, we should try to choose other similar performance as a substitute
