- Installation Program
Material entry → cleaning → blowing → sealing → installation → temporary sealing → pressure testing → blowing → cleaning or disinfection → commissioning. The installation and construction of clean pipeline systems should be carefully and meticulously explained to the construction team before the start of the project, so that the operators can master the operating essentials, improve their understanding, and lay a solid ideological foundation for ensuring installation quality. The entire construction process from preparation to completion and operation must be strictly monitored at every step to ensure quality. Construction operators must have a high sense of responsibility and operate strictly according to requirements. At the same time, the quality assurance system should strengthen supervision and inspection to ensure the quality of work at every stage.
2.Inspection and storage of materials
Pipes and valves entering the site must be isolated and stacked from other materials. The storage area should be cleaned and moisture-proof measures should be taken. All materials used should be qualified products. Construction personnel should refuse to use materials and equipment with obvious defects or severe corrosion.
3 Degreasing and cleaning
Before installation, pipelines, valves, and fittings must be strictly degreased and cleaned according to requirements. It is best to choose a pre built factory or a room with a floor that can be enclosed, with good ventilation conditions. The on-site environment should be clean and dry, and the tools used should be clean. Operators must wear clean work clothes and rubber gloves to ensure the quality of cleaning work. Industrial grade carbon tetrachloride or trichloroethylene are generally used as cleaning agents.
3.1 Degreasing and cleaning of pipes
When the pipe diameter is large or the quantity is large, a dedicated cleaning tank should be made to remove the dirt and dust inside and outside the pipe, and then soak it in the cleaning agent in the tank for about 10 minutes; After removal, rinse with filtered oil-free dry compressed air for about 5 minutes or rinse with pure water; After drying, wipe the inner wall of the tube with a white silk cloth, check for cleanliness and dirt, then close the tube mouth and place it in a dry place for future use. It is more convenient to use self-adhesive aluminum foil tape for sealing the pipe mouth.
When the diameter or quantity of small pipes is small, use a conical rubber plug (purchased from the market or customized according to the pipe specifications at the rubber factory) to tightly plug one end of the pipe and place it at an angle; Pour cleaning agent into the tube from the other end using a funnel, plug it with a rubber stopper, roll the tube on a wooden frame for 10-15 minutes, and then discharge the cleaning agent into a plastic bucket. Blow clean, inspect, seal, and place it for loading according to the above method. This method is easy to operate, saves cleaning agents, and does not require the creation of a cleaning tank.
3.2 Cleaning of pipe fittings and valves
Pipe fittings such as tees, elbows, etc., including finished and prefabricated parts, need to be degreased and cleaned; Valves should be disassembled, degreased, and cleaned. Firstly, make a cleaning tank according to the volume size of the valve, inject cleaning agent, put the pipe fittings and valves in it, soak for about 10 minutes, then take them out and clean them with a white silk cloth, place them in a clean place, and let them ventilate naturally for about 30 minutes before installation (the ventilation time in winter is slightly longer). If the valve packing is oily, it should be replaced after cleaning, and polytetrafluoroethylene is generally used as the sealing packing. If pipes, fittings, valves, etc. are corroded and cannot meet the process requirements after degreasing and cleaning, they should be pickled for rust removal, and then passivated, reduced, and cleaned.
- Pipeline connection methods and processing of pipeline accessories
Generally, the working pressure of clean pipelines belongs to the low pressure range, and only high cleanliness is required. Therefore, there are many ways to connect pipelines, such as butt welding, flange blue butt welding, sleeve connection, and loose sleeve blue connection. For pipe fittings such as tees and elbows, in addition to purchasing finished parts, due to the high market price of stainless steel fittings, economic and technical comparisons can be made. On the premise of ensuring installation quality, it is recommended to choose self processing as much as possible when conditions permit, using connection methods that are aesthetically pleasing, easy to construct, and cost-effective. When it is difficult to process tees, elbows, and reducers with larger diameters on site, finished parts can be purchased. However, it is still necessary to prefabricate and extend straight pipe sections at each end of the pipe (the length should be convenient for operation) to facilitate sleeve connection during high-altitude pipeline installation. Specially processed (or purchased) pipeline connectors are used in sleeve connection form to ensure that the inner wall of the pipe is not contaminated after installation, and the inner wall of the pipe interface is smooth and clean, in order to compensate for the limitations of stainless steel pipe processing.
5 Welding
The welding wire should be placed on a wooden board or box, in a dry place, and wiped clean with acetone before use. The welding machine can use a simple argon arc (argon itu welding). Its welding process is the same as that of an argon arc welding machine (with no attenuation during arc starting and ending), making it easy to use and operate. It has a large working surface and can adapt to the installation needs of construction sites like ordinary welding machines. Even when welded on high-pressure pipelines, the quality meets the requirements (working pressure of 15MPa, pressure test of 22.5MPa, and conveying medium of compressed air or nitrogen).
5.1 All prefabricated machining joints are welded using argon arc protection with argon filling inside the pipe. The welding quality requires full penetration and good inner wall formation, without defects such as weld bead, incomplete penetration, and burn through. When the pipe diameter is large, in order to save argon gas, protective argon gas is introduced into the weld joint.
5.2 Sleeve connection is used for welding joints that are inconvenient to protect inside argon gas. By using sleeve welding, there is no need for argon gas protection inside the tube, and there is no problem with the formation of welding joints on the inner wall of the tube. The connection has the same function as flange blue welding connection.
- Pipeline installation
The spacing between supports and the setting of sleeves for pipeline installation shall comply with the design and specification requirements. However, a thin rubber gasket shall be used at the contact between the support and the pipeline to prevent carbonization at the direct contact between the carbon steel support and the stainless steel pipe. Alternatively, a plastic hose set free of chloride ions can be used for isolation. The pipeline is placed on a wooden board and first straightened with a wooden hammer. During installation, remove the end cap of the pipe and check for secondary contamination. If it has been contaminated, it needs to be cleaned before installation. The method is as before.
Before installing the alignment, the outer end of the pipe should be cleaned of dust with a white silk cloth within 10cm, and then cleaned with acetone before connection. When cleaning, the pipe should be wiped backwards from the depth of the pipe end. During intermittent pipeline installation work (such as after work or suspension of construction), the pipe end should be temporarily closed according to the previous method to prevent pollution. Prefabrication should be used for pipeline installation as much as possible to reduce high-altitude operations. Prefabrication on the ground is convenient for operation, which is conducive to ensuring welding quality and safe production.
7 pressure test
The pressure testing of the pipeline system should be carried out in isolation from the process equipment, and the instruments installed in the pipeline should be removed and replaced with temporary short pipes. The test pressure shall be carried out in accordance with the relevant provisions of the design and specifications.
(1) Strength test: Pure water and distilled water can be used as pressure testing media. When it is difficult to solve the problem of pure water on site in low-pressure systems, oil-free dry compressed air, nitrogen and other purified gases can be considered for pressure testing. The test pressure should be carried out according to the specifications. When the pipeline system is small or the pipe diameter is small, the gas consumption is low, and the on-site gas source is difficult to solve, bottled nitrogen can be considered to be directly filled into the pipeline through a pressure reducer for pressure testing.
(2) Tightness test and leakage test: Purified compressed air or nitrogen is used as the pressure testing medium for gas pipeline systems; The pipeline system for conveying process media uses pure water or purified gas as the pressure testing medium; The pure water pipeline uses pure water as the pressure testing medium. The selection of pressure testing medium should be based on the on-site conditions, taking into account the safety of the work and the principle of not causing pollution to the pipeline.
8 Cleaning
After the cleaning and pressure test of the pure water pipeline system is qualified, connect the pure water source and send in pure water. Starting from the farthest water point, open each water point one by one and discharge pure water for flushing until the water quality of the water point is inspected and qualified. The general flushing time is about 32 minutes, then connect the process equipment and instruments, close the inlet and outlet valves, seal the system, and wait for it to be put into operation.
After the cleaning and pressure test of the clean gas and process medium transportation pipeline system is qualified, nitrogen is filled into the system, and the gas points are opened one by one for blowing. White silk cloth is used as a target plate to inspect the discharge points one by one, and cleanliness without pollution is considered qualified. After all are qualified, connect the process equipment and instruments, close the inlet and outlet valves, seal the system (fill the purified gas to maintain positive pressure inside the pipe), and the blowing pressure should not exceed 80% of the working pressure. For the blowing and cleaning of gas pipeline systems, it is best to connect the gas source or turn on the gas source equipment if conditions permit (except for flammable and explosive gases), which is convenient and easy to ensure quality.
9 Disinfection
Ultra pure water and high-purity gas piping systems should be cleaned and sterilized by injecting hydrogen peroxide into the pipes before being put into use.