Note one: The problem of corrosion resistance

For a long time, corrosion is one of the most headaches of chemical equipment. If it is a little careless, the device is damaged lightly, and the accident causes the accident and even causes disasters.

According to relevant statistics, about 60%of the destruction of chemical equipment is caused by corrosion. Therefore, when the chemical pump selection is selected, the scientificity of the selection of materials should be paid first.

There is usually a misunderstanding that stainless steel is a "universal material". It is very dangerous regardless of the medium and environmental conditions. This is very dangerous. Let's talk about the main points of selection of materials for some commonly used chemical media:

1

As one of the strong corrosive media, sulfuric acid is an important industrial raw material with a wide range of uses.

Sulfuric acid with different concentrations and temperatures has a large difference in corrosion of materials. For concentrations with concentrations of more than 80%or more than 80 ° C, carbon steel and cast iron have good corrosion resistance, but it is not suitable for high -speed flowing sulfuric acid. It is not applicable to the material of the pump valve; ordinary stainless steel such as 304 (0CR18NI9) and 316 (0CR18NI12MO2TI) are also limited to sulfuric acid medium.

Therefore, the pump valve that transports sulfuric acid is usually manufactured with high silicon cast iron (casting and processing difficulty), high alloy stainless steel (alloy 20), but its processing difficulty is expensive and expensive, so it is not optimistic.

Fluor plastic alloy has a good sulfuric acid resistance. It is a patented material of the Shanghai Institute of Organic Chemical in the Shanghai Academy of Sciences. It has been proven by the Chinese Academy of Sciences that no chemical medium can react with it. Therefore A more economical choice.

2

Most metal materials are not resistant to corrosion of hydrochloride (including various stainless steel materials), and molybdenum high -silicon iron can also be used only for 50 ° C and 30%of hydrochloric acid.

Contrary to metal materials, most non -metallic materials have good corrosion resistance to hydrochloric acid, so the inner lining pump (such as engineering plastics, fluoroplastics, etc.) is the best choice for transporting hydrochloric acid.

3 nitrate

Generally, most metals are quickly corroded and destroyed in nitric acid. Stainless steel is the most widely used nitrogen -resistant material. It has good corrosion resistance to all concentrations of all concentrations at room temperature. It is worth mentioning that molybdenum stainless steel (such as 316, 316L ) The corrosion resistance to nitric acid is not only better than ordinary stainless steel (such as 304, 321), and sometimes even worse. For high temperature nitric acid, fluoroplastic alloy materials are usually used.