Moisture-proof layer and protective layer of insulated valves

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Moisture-proof layer and protective layer of insulated valves (1) Technical requirements for the moisture-proof layer: To prevent the outer surface of the insulation layer from becoming damp, thereby reducing its insulating efficiency, a moisture-proof layer must be installed for insulated valve pipelines that are buried, located in trenches, or installed outdoors. Its technical requirements are as follows: ① It must have good bonding and sealing properties, with a bonding strength of not less than 0.15 MPa at 20°C. ② It has strong moisture and water resistance, with a water absorption rate of no more than 1%. ③ It has a wide safe operating temperature range and certain heat resistance ； The softening temperature is not lower than 65°C; it does not soften, bubble, or flow in summer, and has a certain degree of frost resistance – it does not become brittle, crack, or fall off in winter. ④ It should have flame retardancy and self-extinguishing properties. ⑤ It has good chemical stability and low volatility. ⑥ It has a short drying time, can be used at room temperature, and is easy to apply. Common materials used for moisture barriers include the following: ① Petroleum asphalt or modified asphalt glass cloth. ② Petroleum asphalt mat glass cloth ③ Asphalting glass cloth. ④ Polyethylene film. ⑤ Flame-retardant, waterproof cold adhesive rubber fabric. ⑥ A new type of waterproof and anti-corrosion CPU coating material; CPU is a polyurethane rubber substance that can be used as a moisture-proof layer or protective layer for pipes, as well as an anti-corrosion layer for buried pipes. (2) Technical requirements for the protective layer: To prevent the insulation layer from being damaged by external factors, all insulated valves and pipes should be equipped with a protective layer, and the technical requirements are as follows: ① Light weight and high pressure resistance. ② It has good chemical stability and is not flammable. ③ Easy to construct and aesthetically pleasing in appearance. Commonly used protective layers are generally made from the following materials: ① For soft and semi-soft insulation materials, a galvanized thin steel sheet is suitable as the protective layer; for pipes with a diameter of DN≤200 mm, a 0.3 mm thick sheet is used, while for pipes with a diameter greater than 200 mm, a 0.5 mm thick sheet is employed. For hard insulation materials, an aluminum or aluminum alloy sheet with a thickness of 0.5–0.8 mm is appropriate, or a 0.5 mm thick galvanized steel sheet can also be used. ② For pipe insulation materials used in production units or equipment whose fire hazard does not fall under categories A, B, or C, as well as in pipelines that are not classified as explosive hazard areas, materials such as flame-retardant aluminum foil glass steel plates with a thickness of 0.5–0.8 mm can be used. ③ The wrapped composite protective layer is a lightweight structure, suitable for protecting insulated pipes indoors, outdoors, and in trenches. Commonly used are glass cloth, fiberglass reinforced with polyurethane coating applied on a glass cloth substrate, as well as glass cloth CPU coatings and CPU sheets. ④ A coating-type protective layer, suitable for protecting insulation pipes indoors and in trenches. Common materials include asphalt, mortar, and asbestos cement. When the outer diameter of the insulation layer is ≤200 mm, the coating thickness is 15 mm; when the outer diameter is >200 mm, the coating thickness is 25 mm. The formula for the asphalt mortar is shown in Table 2-. Table 2 – Formulation of self-extinguishing asphalt mortar Material Name Mass Percentage (%) Maoming No. 5 Asphalt Rubber powder (particle size 0.56 mm) Medium-density asbestos putty Tetrafluoroethylene Chlorinated paraffin 1.5 0.2 2 1.5 0.52 6.3 3.5 31.5 26.3 8.8