As semiconductor and microelectronic technologies develop towards higher performance and higher integration, higher requirements are placed on the purity of electronic special gases. High-purity gas piping technology is an important part of the high-purity gas supply system. It is the key technology for delivering high-purity gases that meet the requirements to the gas use points while still maintaining qualified quality.
High-purity piping technology includes the correct design of the system, the selection of pipe fittings and auxiliary materials, construction and installation and testing.
01General concept of gas transmission piping
All high-purity and high-cleanliness gases need to be transported to the terminal gas point through pipelines. In order to meet the process quality requirements for gas, when the gas export index is certain, it is more necessary to pay attention to the material selection and construction quality of the piping system. In addition to the accuracy of the gas production or purification equipment, it is largely affected by many factors of the pipeline system. Therefore, the selection of pipes needs to abide by the relevant purification industry principles and mark the material of the pipes in the drawings.
02The significance of high-purity pipelines in gas transportation
The significance of high-purity pipelines in high-purity gas transportation During the stainless steel smelting process, each ton can absorb about 200g of gas. After the stainless steel is processed, not only are various pollutants stuck on its surface, but also a certain amount of gas is absorbed in its metal lattice. When there is airflow passing through the pipeline, the part of the gas absorbed by the metal will re-enter the airflow and pollute the pure gas.
When the airflow in the pipe is discontinuous, the pipe forms pressure adsorption on the gas passing through. When the airflow stops passing, the gas adsorbed by the pipe forms pressure reduction analysis, and the analyzed gas also enters the pure gas in the pipe as an impurity.
At the same time, the adsorption and analysis cycle will cause the metal on the inner surface of the pipe to produce a certain amount of powder. This metal dust particle also pollutes the pure gas in the pipe. This characteristic of the pipe is very important. In order to ensure the purity of the transported gas, not only is it required that the inner surface of the pipe has an extremely high smoothness, but also that it should have high wear resistance.
When the gas has strong corrosive properties, corrosion-resistant stainless steel pipes must be used for piping. Otherwise, corrosion spots will appear on the inner surface of the pipe due to corrosion. In severe cases, large pieces of metal will peel off or even perforate, thereby contaminating the pure gas being transported.
03Pipe material
The material selection of the pipe needs to be selected according to the needs of use. The quality of the pipe is generally measured according to the roughness of the inner surface of the pipe. The lower the roughness, the less likely it is to carry particles. Generally divided into three types:
One is EP grade 316L pipe, which has been electrolytically polished (Electro-Polish). It is corrosion-resistant and has low surface roughness. Rmax (maximum peak to valley height) is about 0.3μm or less. It has the highest flatness and is not easy to form micro-eddy currents. Remove contaminated particles. The reaction gas used in the process should be piped at this level.
One is a BA grade 316L pipe, which has been treated by Bright Anneal and is often used for gases that are in contact with the chip but do not participate in the process reaction, such as GN2 and CDA. One is AP pipe (Annealing & Picking), which is not specially treated and is generally used for double sets of outer pipes that are not used as gas supply lines.
04 Pipeline construction
The processing of the pipe mouth is one of the key points of this construction technology. The pipeline cutting and prefabrication are carried out in a clean environment, and at the same time, it is ensured that there are no harmful marks or damage on the surface of the pipeline before cutting. Preparations for nitrogen flushing in the pipeline should be made before opening the pipeline. In principle, welding is used to connect the high-purity and high-cleanliness gas transmission and distribution pipelines with large flow, but direct welding is not allowed. Casing joints should be used, and the pipe material used is required to have no change in structure during welding. If the material with too high carbon content is welded, the air permeability of the welding part will cause the gas inside and outside the pipe to penetrate each other, destroying the purity, dryness and cleanliness of the conveying gas, which will lead to serious consequences and affect the production quality.
In summary, for high-purity gas and special gas transmission pipelines, a specially treated high-purity stainless steel pipe must be used, which makes the high-purity pipeline system (including pipelines, pipe fittings, valves, VMB, VMP) occupy a vital mission in high-purity gas distribution.
Post time: Nov-26-2024