All high-purity and clean gas in high-purity gas pipeline BA / EP should be transported to the instrument point (POU) through the pipeline. In order to meet the gas quality requirements of the instrument, when the gas outlet index is fixed, more attention should be paid to the material selection and construction quality of the piping system.

For the pipeline conveying high purity gas, the main characteristics of pipeline materials that affect the gas quality are gas permeability, outgassing rate, adsorption and surface roughness.

Gas permeability different materials oxygen permeability materials oxygen permeability in the atmosphere (PPM) stainless steel tube o copper tube o polypropylene tube 1L polytetrafluoroethylene tube 12 ordinary steel tube 203 It can be seen from the table that stainless steel pipe or steel pipe should be selected from the point of view of gas permeation for transporting gases with ppm level and higher purity requirements. If we improperly select pipeline materials that do not meet the requirements, no matter what purification means we take, it will not be helpful. There are some impurities, such as nitrogen, hydrocarbons, etc., in the intergranular or lattice of pipeline materials formed in the smelting process of outgassing rate materials. In the process of high purity gas transportation, these impurities will slowly release and pollute the high purity gas, especially the high purity gas whose impurities are required to be above ppb. Generally, the outlet velocity of low carbon stainless steel pipe is very low.