With the development of the natural gas pipeline industry, the amount of natural gas pipeline valves is increasing, and the natural gas pipeline industrial valves are different from ordinary valves. Specifically, there are the following points.
Because the management and control personnel are generally in the station or the central control room, it is required that the pipeline valve can be automatically cut off in the event of a major accident such as pipeline rupture. The pipeline valve requires a small operating force, and can achieve accurate operation when the temperature and external force changes have an impact. In particular, the emergency shut-off valve must be able to be fully open for a long time, and the pipeline must be quickly blocked if necessary. At the same time, the opening and closing position and opening indicator of the valve are required to be accurate and easy to understand, and to meet the appropriate switching speed.
Most natural gas pipeline networks are built on the fringes of cities, and their operation and management are not like ordinary factories, where workers are often operated, maintained and inspected. Generally, urban natural gas pipelines are more than 100 kilometers long, and can only be patrolled and inspected regularly. Sometimes pipelines need to pass through areas with complicated conditions, and the leakage of medium may cause serious fire accidents. Especially for pipelines close to the city, it is particularly important to prevent the leakage of the valve.
The leakage requirements of natural gas industry valves are very strict, and usually buried and more important valves adopt fully welded valve body structures. In order to ensure the sealing performance of pipeline valves, the sealing pair is required to have excellent corrosion resistance, wear resistance, moisture and elasticity. In recent years, the development of polymer materials has provided a broad selection of materials for pipeline valve sealing materials, such as polytetrafluoroethylene, nylon, nitrile rubber, special synthetic rubber, etc.
Because the natural gas transported by the pipeline contains a large amount of hydrogen sulfide before desulfurization (this is a toxic and highly corrosive gas, it reacts with iron to form iron sulfide, which can peel off in flakes and penetrate mechanical equipment). Even the natural gas that has undergone desulfurization and other processes still has residual hydrogen sulfide. Therefore, the selection of pipeline valve products should be made of corrosion-resistant and sulfur-resistant materials.
Once the pipeline is put into operation, it is not allowed to stop running within a few years. The longer the running time, the better. Unlike general chemical plants or oil refineries, there is an overhaul period. The natural gas transported by pipeline faces a large number of users in the whole city, including residents, enterprises, factories, etc., especially the enterprise users who use natural gas as a raw material, and no interruption is allowed for a moment. Once the pipeline valve products connected in series on the pipeline fail, the consequences will be disastrous. Therefore, the main sealing wearing parts of pipeline valves, such as valve seats, require long life. Generally, the service life of main line pipeline valves is required to be more than 30 years.