1. VCR connection
The connection between high-purity gas pipelines and accessories such as valves should be made using specialized joints that are sealed and not prone to leakage. There are two commonly used joint methods: VCR (Vacuum Coupling Retainer) and SWG (Swaglok). VCR uses excellent metal pads and is compressed by longitudinal pressure, resulting in an extremely low leakage rate of about 10-9A cc/s and high pressure resistance. It is commonly used in high-purity gas transmission systems with gas impurity content of 1.0 × 10-9 levels, while SWG is not as safe as VCR and has lower pressure resistance. Basically, these two joint methods are sufficient to replace welding in terms of safety.
2. Flange connection
The connection between pipelines and equipment, pipelines and valves, in some gas pipelines with low requirements, flange connections can be used, and soft metal gaskets or polytetrafluoroethylene gaskets can be used as gaskets. Due to the dust generated by asbestos and the high permeability and water absorption of rubber, as well as its susceptibility to aging, asbestos gaskets or rubber sheets are not used.
Surface sealed connector connection
When flange connection is used, the contact surface between gas and sealing material is large, and the surface wear is also significant, so flange connection is not used for high-purity gas pipelines. Most of them use surface sealed connectors, and the vast majority use V-CR seals. The V C R connection method ensures that the gas does not come into contact with the sealing material, and there is almost no wear on the flow surface. It is compressed by longitudinal pressure and uses high-quality metal pads to achieve good sealing without leakage and minimal pollution. Therefore, it is widely used. When selecting, ensure that the material of the connecting piece is consistent with the material of the main pipe, and the inner surface smoothness level is consistent.
3. Threaded connection
When using galvanized steel pipes, threaded connections are used for gas pipelines with low purity requirements for bulk gases. The sealing material for threaded connections shall be polytetrafluoroethylene sealing tape, and traditional oil hemp shall not be used. The sealing tape should be wrapped properly. It is not allowed to wrap too thick or too long. If the wrapping is too thick or too much beyond the end groove of the pipe thread, the sealing tape will be bitten and cut off by the thread during tightening, and will fall into the pipeline, forming a large amount of pollutants. Therefore, it is necessary to leave 2-3 protruding teeth from the groove of the port thread without wrapping the sealing tape.
4. Welding
Welding connection of pipelines can be achieved through butt welding, socket welding, or sleeve welding.
Docking welding
For pipelines that require high purity, butt welding with scar free inner walls is used. High purity argon gas shielded welding.
Socket welding
For pipelines with relatively low purity requirements, socket welding or sleeve welding can be used. Socket welding has a relatively large residual gas space.
Sleeve welding
Blowing it clean is quite difficult, and now more commonly, sleeve welding is used. The welding of casing should ensure that the casing and the main pipe have the same material and inner surface grade. The gap between the joint should not be too large, and the overlapping part should not be too long. The more suitable overlapping length is within 5mm. When processing the inner pipe of the casing, the main pipe should be interference fit, so that the main pipe is tightly wrapped by the casing before welding, and welding slag will not fall into the pipe. And the dead space of the gas is also small, making it easy to blow clean.
