The installation of industrial oxygen piping is very important, and improper construction can easily lead to safety accidents. In this paper, the characteristics of industrial oxygen pipeline installation and construction, the installation and construction process should pay attention to the relevant procedures.
With the development of national economy and the progress of science and technology. Oxygen has been widely used in metallurgy, chemical industry, machinery, electronics and other industries. It has played a very important role in the development of these industries. However, the high purity and strong oxidation of oxygen, from time to time, there will be combustion, explosion and other accidents, resulting in huge economic losses and casualties. Therefore, the installation and construction of oxygen piping must be carried out in strict accordance with the relevant national specifications.
1. Construction process
1.1 Inspection of materials
Oxygen pipeline construction should be carried out in strict accordance with the design drawings. To modify the design or material substitution, the consent of the design department should be obtained, and tampering with the material type is strictly prohibited.
Inspection of piping materials: pipe, pipe accessories and valves for appearance inspection, the surface should be free of cracks, shrinkage, central slag, folding, heavy skin and other defects. Alloy steel pipe should be material mark. Non-ferrous metal pipe internal and external surfaces should be smooth and clean, there should be no pinholes, cracks, delamination and other defects, brass pipe can not have green rust and serious dezincification phenomenon.
Valve incoming inspection: valve requirements for strength and tightness test one by one. The test medium is clean, oil-free water. Strength test pressure is 1.5 times the nominal pressure, the test time is 5 minutes, no leakage of shell packing for qualified. Tightness test for the nominal pressure, the valve seal does not leak for qualified.
1.2 Pipeline rust removal
When the pipe and pipe fittings are made of carbon steel, the inner wall of the pipe should be thoroughly descaled, and the descaling methods are spray noisy descaling and pickling descaling.
The rust removal by sandblasting should be in accordance with the process requirements of sandblasting. The metal surface shall not be damp when sandblasting, and the sandblasting operation shall be stopped when the metal surface is below the dew point temperature of 3°C. The compressed air pressure used in sandblasting operation shall not be less than 0.4 MPa, and the grade of sandblasting and rust removal shall reach Sa3.
Pickling and rust removal
Pickling is carried out by tank immersion method, dipping method and electrolysis method. The general process of pickling and rust removal: pickling → clear water rinsing → neutralization treatment → clear water rinsing again → drying (blowing dry) → passivation treatment (painting).
Make a suitable pickling tank according to the pipeline specifications, inject water into the tank first, then inject the prepared pickling solution into the tank slowly along the stirring bar, do not add the pickling solution first and then add water, otherwise it will cause acid splashing and injury. The amount of acid cleaning solution should be 2/3 of the circumference of the pipe to be submerged. Operators should wear protective clothing, gloves, protective glasses, etc.
Soak the pipe in the acid bath for 5-50min depending on the degree of corrosion. Rinse off the residual acid on the inner and outer surface of the pipe with clean water. Soak the pipe in a special neutralization and passivation tank for 10-15 min. Rinse off the residual liquid on the inner and outer surface of the pipe with clean water again (if not cleaned, the pipe will be painted on the surface with lower adhesion and uneven color). Blow dry the pipe with bottled nitrogen, and then close the pipe mouth with sealing plastic film.
Pickling quality inspection: no adhesion on the inner wall of the pipe after pickling with sulfuric acid solution. The pipe wall should be grayish white.
Operation safety precautions.
- a. The pickling place should be well ventilated.
- b. Acid pickling solution, passivation solution and rinsing water are prohibited to be placed indiscriminately and handled reasonably to protect the environment.
- c. Operators should wear protective gear when working.
- d. The water used for pickling, rinsing and passivation must be clean.
- e. When pickling, master the time. Do not cause excessive pickling.
Pipes, accessories, valves and instruments should be degreased. If the valves and instruments have been degreased at the factory. There is a reliable sealing package and proof, no more degreasing. Degreasing agent should have product certificate, and its appearance and grease content should be checked before use. Degreasing agent is a chemical corrosive drug, when degreasing should wear a good gas mask, rubber gloves and good work clothes. Work clothes, shoes, gloves and other labor protection products should be clean and oiled. The degreasing place should be outdoors or in a well ventilated room, free from rain, dust, etc. Degreasing agent should not be exposed to direct sunlight.
Commonly used degreasing methods are wiping method and soaking method, degreasing agent using carbon tetrachloride. Soaking method: Turn over the degreasing tank and pour the degreasing agent into the tank. The amount of degreasing agent should be sufficient to submerge 2/3 of the circumference of the pipe being treated. There should be no moisture on the surface of pipes, accessories and valves before degreasing, otherwise the degreasing agent and water decomposition will corrode the metal. Put the fittings, pipes and valves into the degreasing tank and soak them for 1-1.5 hours, then pour out the degreasing agent inside them, wipe the walls of the pipes with filter paper, and irradiate the filter paper with ultraviolet light, and no purple orchid fluorine is qualified. Need to degrease the valve before degreasing should be disassembled into parts to remove rust and other debris. Bolts and metal gaskets are degreased by the same method. For inconvenient dipping such as valve shell, then manually dipped in degreasing agent rubbing test. After degreasing, the pipes, valves and accessories should be closed with clean plastic cloth in time to prevent re-pollution. At the same time, strictly isolate the degreased qualified pipes from the pipes that have not reached the qualified standard or have not been degreased to avoid confusion.
After degreasing is finished, degreasing waste liquid is strictly prohibited to be dumped indiscriminately and should be packed in a packaging barrel and handled according to the requirements of environmental protection department.
The pipes, accessories and valves should be checked again before installation to see if there is still oil, rust, sand and other dirt inside them and treated, and only after they are qualified can they be installed. Oxygen piping, if found to have rust and oil, must be re-rusted and degreased.
The minimum spacing between oxygen piping and other overhead piping is as follows.
Pipeline counterpart should be straight, and should not be strongly counterpart with equipment and valve. The allowed deviation of the counterpart is 1mm/m, and the full length is not more than 10mm. flange connection should be kept parallel, and the deviation is not more than 1.5/1000 of the outer diameter of the flange, and not more than 2mm tee and size head should be pressed fittings as far as possible, and should not be made on site and open hole welding. The pipeline with threaded connection, the filling material at the threaded connection should use PTFE raw material tape, and the use of oil linen or cotton yarn head is strictly prohibited.
Pipeline welding is carried out according to the requirements of the "Welding Work Instruction". Pipeline weld inspection and non-destructive testing shall be carried out in accordance with the requirements of the design and construction drawings.
The pipeline should have lightning protection and anti-static grounding device. Grounding devices shall be set at the bifurcation of pipeline and at the building in and out of the workshop.
3. Pressure test and blowing of pipeline
Before the test pressure of the pipeline, check the pipeline to confirm that the pipeline has been installed and qualified, and the bracket is fixed firmly. The compensator must take temporary reinforcement measures. Test media: strength test can be used oil-free water compressed air, nitrogen or clean oil-free water for the medium; tightness test can be used oil-free water compressed air or chlorine; stainless steel pipeline test pressure water chloride ion content shall not exceed 25PPM.
Strength test: water for the medium, should be carried out at an ambient temperature of 5 ℃ or more. The pressure should be raised slowly and maintained at the test pressure for 10min, with no visible change, no pressure drop, no leakage as qualified. Use gas as medium: safety measures should be formulated, and the consent of the construction party should be reported. The pressure should be raised slowly, first to 50% of the test pressure for inspection, and then in accordance with 10% of the test pressure step by step to the test pressure. Each level of steady pressure not less than 3min, steady pressure at the test pressure, no leakage, invisible into qualified.
After passing the strength test of tightness test, lower the pressure to the working pressure and stabilize for 24 hours. Average hourly leakage rate: indoor and trench pipes not more than 0.25%; outdoor pipes not more than 0.5%.
Blowing: After the pipeline test is passed, blowing with nitrogen, blowing speed is not less than 20m/s. Repeatedly blow the pipeline, set rigid target plate at the mouth of the pipeline blowing, and paint white paint on the target plate, so that there is no rust, dust, water, welding slag and other debris on the target plate is qualified.
4. Pipeline painting
Remove rust, welding slag, burr, oil, water and other dirt from the pipeline surface before painting, and paint according to the design requirements.
5. Gas replacement and delivery
Before the pipeline is put into operation, the piping system is filled with nitrogen, and then oxygen is gradually added until finally replaced with full oxygen, and the oxygen replaced is not less than three times the total volume of the replacement pipeline until it is qualified. The oxygen discharged from the replacement is discharged to an open, non-flame (smoking) place more than 4m above the nearby operating surface.
Source: China Piping Solutions Provider - Yaang Pipe Industry Co., Limited (www.yaang.com)