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Clean room gas pipeline installation requirements

(Summary description)

Clean room gas pipeline installation requirements

(Summary description)

Information

The construction of high-purity and high-clean gas pipelines is different from general industrial pipelines, and slight negligence may destroy the quality of the gas. Therefore, it is necessary to understand the significance of the installation gas quality, to strictly comply with the design and construction requirements, to work seriously and meticulously, to attach great importance to all small links, and to build a piping system that meets the requirements.

 

Clean room gas pipeline installation requirements

 

1. Appearance inspection

(1) The pipe materials, valves and all accessories of the piping system shall be selected according to strict design requirements and shall not be changed or replaced at will.

(2) All pipes should be carefully kept indoors, and should not be stacked in the open, exposed to sunlight or rain.

(3) The end of the pipe section shall be sealed with a plastic or rubber sealing cover, and shall not fall off or break.

(4) Before using pipes, fittings, valves, etc., perform the following visual inspections in detail:

1) No cracks, shrinkage holes, folding, heavy leather and other defects.

2) No rust, pitting, etc.

3) The tube is straight and smooth, without partial depression, scratches, extrusions and other defects.

4) Whether the "roughness" of the inner surface of the pipe meets the design requirements, and whether the screw thread is well sealed and protected.

5) The outsourcing finished product "super smooth inner surface clean pipe" must have a factory certificate, relevant grade certificate and qualification certificate. Random samples should be sampled for inspection under the microscope, which must meet the design requirements.

6) Check whether the outer packaging of the finished product "super-smooth clean pipe with inner surface" and the sealing measures such as caps and plugs at the corresponding end of the pipe meet the requirements.

7) The sealing surface of the flange should be flat and smooth, free of burrs and radial grooves, the concave-convex flange should be able to fit naturally, and the height of the convex surface should not be lower than the depth of the groove.

8) Non-metallic gaskets such as rubber and plastic should be soft in texture, free from aging and delamination, and the surface should not be damaged or wrinkled. The processing size, accuracy, thickness, surface roughness, hardness, thickness, etc. of the metal gasket must meet the requirements, and the surface must not have defects such as cracks, burrs, grooves, radial scratches, and rust spots. 

 

2. Preparation of piping

(1) Regardless of the pressure, medium and purpose of the piping, no oxygen or acetylene flame can be used for cutting. Regardless of whether it is mechanically or manually unloaded, no grease or lubricant shall be applied to the sections.

(2) The cut of the pipe should be strictly perpendicular to the axis of the pipe, and the surface of the cut should be flat and free of cracks and burrs.

(3) Various valves should be cleaned before installation. Before cleaning, they should be ground and pressure tested, then disassembled into parts and immersed in trichloroethylene or carbon tetrachloride solvent for 1~1.5h. After the safety valve is cleaned, the pressure should be retested.

(4) Valves that cannot be disassembled into parts, such as bellows, should be cleaned when assembled. The cleaning effect can be checked by the following method: inject the cleaning solvent from the inlet of the valve and let the solvent flow through the valve. After the solvent flowed out of the valve is filtered, use a microscope to check whether the surface of the filter meets the design requirements.

(5) When using ordinary stainless steel pipes, if oil stains adhere to the surface, it is very difficult to clean after installation. The original pipes should be placed in the cleaning tank for cleaning. The pickling of the inner wall of the pipeline must ensure that the rusted part is removed without damaging the uncorroded surface.

(6) The valves and accessories of the oxygen pipeline should be strictly banned from oil, and should be strictly degreased according to relevant requirements before installation.

 

3. Connection of metal pipes

(1) Pipe material. The metal pipe materials used to transport high-purity gas mainly include:

1) Low-carbon stainless steel. In principle, low-carbon stainless steel pipes are used for large-flow, high-purity and high-clean gas.

2) Copper pipe. In semiconductor companies, individual production processes such as gallium arsenide operations, in order to prevent device resistance, are not allowed to use copper pipes and accessories, and can only use stainless steel materials.

(2) Connection method:

1) Welding. High-purity and high-clean gas pipelines should be welded in principle, but not directly butt welded. Casing joints should be used.

a. Welding of stainless steel pipe: Argon arc welding is used, and argon gas of the same purity is passed into the pipe to prevent oxidation of the welding part.

b. Welding of steel pipes: 40% silver electrode and nitrogen shielded welding are used, and nitrogen with the same purity of process gas is passed into the pipe. However, it should be noted that once the nitrogen is interrupted or the purity of the nitrogen drops, copper oxides will be formed near the weld, resulting in the possibility of wetting the surface. Therefore, after the copper pipe is welded, wipe the inside of the pipe with acetone-impregnated gauze to eliminate the oxides that may be generated at the weld.

2) Threaded connection. The air tightness of threaded connection is not as good as that of welding, and it is not suitable for high-purity and high-clean gas pipeline connection. The seal packing residue used in the threaded connection may bring in gas, and when the internal and external threads are tightened, the friction between the metals will generate metal dust particles and pollute the gas. If necessary, a certain amount of welding rod should be evenly hung on the external thread when the copper-to-copper or copper-to-copper alloy accessories are threaded to improve the sealing effect and reduce metal dust as much as possible.

3) Flange connection. The sealing material of the thread or flange connection should be polytetrachloroethylene. To ensure the sealing effect, a small amount of fluorine rubber (white, curing at room temperature) should be coated on the gasket.

(3) Use of pipeline accessories:

1) The selection principle of the material of the piping accessories should be consistent with the selection principle of the pipe material.

2) In piping systems using copper materials, stainless steel piping accessories can be used; but in stainless steel piping systems, copper piping accessories cannot be used.