How to select materials for chemical pumps?

The key points and principles of material selection for chemical pumps.

 

Corrosion has always been one of the most headache inducing hazards in chemical equipment. Slight carelessness can cause equipment damage, accidents, and even disasters. According to relevant statistics, about 60% of the damage to chemical equipment is caused by corrosion. Therefore, when selecting chemical pumps, the first thing to pay attention to is the scientific selection of materials.

 

There is usually a misconception that stainless steel is a "universal material", and it is dangerous to hold stainless steel out regardless of the medium and environmental conditions.

 

Below are some key points for selecting materials for 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. The corrosion of materials varies greatly with different concentrations and temperatures of sulfuric acid. For concentrated sulfuric acid with concentrations above 80% and temperatures below 80 ℃, carbon steel and cast iron have good corrosion resistance, but they are not suitable for high-speed flowing sulfuric acid and are not suitable as materials for pumps and valves; Ordinary stainless steels such as 304 (0Cr18Ni9) and 316 (0Cr18Ni12Mo2Ti) also have limited applications in sulfuric acid media. Therefore, pumps and valves for transporting sulfuric acid are usually made of high silicon cast iron (difficult to cast and process) and high alloy stainless steel (No. 20 alloy), but their processing difficulty and price are high, so they are not favored by people. Fluoroplastic alloys have excellent sulfuric acid resistance, and using a fluorine lined pump (F46) is a more economical choice. Applicable products include: IHF fluorine lined pump, FSB strong corrosion resistant centrifugal pump, IMD fluoroplastic magnetic pump, etc.

 

2. Most metal materials, including various stainless steel materials, are not resistant to hydrochloric acid corrosion. Molybdenum containing high silicon iron can only be used for hydrochloric acid below 50 ℃ and 30%. Contrary to metal materials, the vast majority of non-metallic materials have good corrosion resistance to hydrochloric acid, so lined rubber pumps and plastic pumps (such as engineering plastics, fluoroplastics, etc.) are the best choices for transporting hydrochloric acid. Applicable products include: CQB fluoroplastic leak free acid resistant pump, CQF engineering plastic magnetic pump (or fluoroplastic magnetic pump), etc.

 

3. Most metals in nitric acid are rapidly corroded and destroyed in nitric acid. Stainless steel is the most widely used nitric acid resistant material and has good corrosion resistance to all concentrations of nitric acid at room temperature. It is worth mentioning that stainless steel containing molybdenum (such as 316, 316L) not only has inferior corrosion resistance to nitric acid compared to ordinary stainless steel (such as 304, 321), but sometimes even worse. For high-temperature nitric acid, fluoroplastic alloy materials are usually used. Applicable products include: CQB fluoroplastic alloy magnetic pump, FSB fluoroplastic alloy centrifugal pump, etc.

 

4. Acetic acid is one of the most corrosive substances among organic acids. Ordinary steel will suffer severe corrosion in all concentrations and temperatures of acetic acid. Stainless steel is an excellent acetic acid resistant material, and 316 stainless steel containing molybdenum can also be suitable for high temperatures and dilute acetic acid vapors. For high temperature and high concentration acetic acid or other corrosive media with strict requirements, high alloy stainless steel or fluoroplastic pumps can be selected. Applicable products include: CQB magnetic pump and CQ stainless steel magnetic pump.

 

5. Alkali (sodium hydroxide) is generally not very corrosive, but alkali solutions usually produce crystals. Therefore, FSB fluorine alloy alkali pumps equipped with silicified graphite 169 material mechanical seals can be selected

 

6. Ammonia (hydroxide ammonia) Most metals and non-metals have slight corrosion in liquid ammonia and ammonia water (hydroxide ammonia), and only copper and copper alloys are not suitable for use. Our products are mostly suitable for the transportation of ammonia and ammonia water. CQF engineering plastic magnetic pump and FSB fluorine alloy centrifugal pump are better

 

7. Salt water (seawater): Ordinary steel has a low corrosion rate in sodium chloride solution, seawater, and saline water, and generally requires coating protection; Various types of stainless steel also have a very low uniform corrosion rate, but may cause localized corrosion due to chloride ions. Generally, 316 stainless steel is preferred. Our various chemical pumps are equipped with 316 materials, such as IH chemical centrifugal pumps.

 

8. Alcohols, ketones, esters, and ethers. Common alcohol media include methanol, ethanol, ethylene glycol, propanol, etc. Ketone media include * *, butanone, etc. Ester media include various methyl esters, ethyl esters, etc. Ether media include methyl ether, ether, butyl ether, etc., which have relatively low corrosiveness. Therefore, ordinary stainless steel can be used. When selecting, reasonable choices should also be made based on the properties and relevant requirements of the media. Additionally, it is worth noting that ketones, esters, and ethers have solubility in various types of rubber, so errors should be avoided when selecting sealing materials. Suggest choosing an inorganic sealed fluoroplastic magnetic pump.

 

 

Principles of pump material selection:

 

Correctly determining the material of a centrifugal pump is an important factor in ensuring its safe operation and prolonging its service life when selecting the model of the centrifugal pump. The selection of materials should comprehensively consider the influence of various factors from multiple aspects, in order to select the most suitable material.

 

(1) The properties of the medium transported by the pump and the operating conditions of the pump, such as temperature, pressure, corrosiveness, viscosity, and the presence of solid particles. In addition, it is necessary to consider whether there are other special circumstances, such as the pharmaceutical and food industries requiring the medium to be transported to be particularly clean to prevent metal ion pollution, and pumps transporting media containing solid particles requiring good material wear resistance.

 

(2) The mechanical properties of the material should be suitable for the requirements of the pump. There are many indicators that reflect the mechanical properties of materials. For the materials used in pumps, the main considerations are the strength, steel degree, hardness, plasticity, impact toughness, and fatigue resistance of the materials.

 

(3) The processing performance of materials is directly related to the manufacturing, installation, and maintenance of pumps. Most parts of a centrifugal pump, such as the impeller, housing, and balance plate, are cast from metal materials and then machined, with some parts requiring heat treatment. The performance of material processing technology directly affects the use of materials and the cost of pumps.

(4) The quality of corrosion resistance is an important issue that cannot be ignored in the selection of pump materials. For the petrochemical production industry, the corrosion resistance of pumps is particularly important.