Selection of high pressure pipeline and accessories materials

　　1. Characteristics of high-pressure pipeline materials

　　For high purity gas pipeline, the main characteristics of pipeline materials affecting gas quality are gas permeability, gas outflow rate, adsorption, surface roughness, wear resistance and corrosion resistance.

　　2. High pressure pipeline permeability

　　The phenomenon that gas flows from the high pressure side to the low pressure side through the material is called gas penetration. Because the partial pressure of oxygen and nitrogen in the air is relatively large and the gas molecules are relatively small, the permeability of pipe to gas mainly reflects the permeability of oxygen and nitrogen. Generally, there are many oxygen permeability tests. Permeability of different materials to oxygen permeability of materials to oxygen in the atmosphere stainless steel pipe o copper pipe o polypropylene pipe 1L Teflon pipe 12 ordinary steel pipe 203 it can be seen from the table that stainless steel pipe or steel pipe must be selected from the perspective of air permeability for transporting gases with ppm grade and higher purity requirements. If we choose improper pipe materials that do not meet the requirements, no matter what purification method is adopted, it will be useless.

　　3. Air release rate of high pressure pipeline

　　There are some impurities in the pipeline materials formed in the material smelting process, such as nitrogen and hydrocarbons, such as nitrogen and hydrocarbons. These impurities will be released slowly during the transportation of high-purity gas and pollute the pipeline. High purity gases, especially impurities, require high purity gases above ppb. The degassing rate of general low-carbon stainless steel pipe is very low.

　　4. High pressure pipeline adsorption

　　Because impurities such as water are polar molecules, they have strong adsorption. Rubber, plastic or some materials with rough surface are easy to absorb moisture and other impurities. Copper material has strong water absorption. Transporting high purity gas with these materials is easy to be polluted. In addition to delivering oxygen below ppm, copper tubes are also used. Copper and plastic pipes are not used for high-purity gas, and rubber or plastic materials (including polytetrafluoroethylene) shall not be used for gaskets and fillers in gas contact.

　　5. Surface roughness and wear resistance of high pressure pipeline

　　In order to ensure the purity of the transmitted gas, the inner surface of the pipe is required to have a very high finish, which can prevent pollutant particles and moisture from staying on the pipe wall, and is easy to blow away in the purification process. The pipe is relatively smooth and wear-resistant, and less metal particles are produced under high-speed air flow. Stainless steel produces less particles than copper pipe, so the wear resistance of stainless steel pipe is better than that of steel pipe.