How to choose natural gas valve

The valve is an important equipment necessary for the safe operation, maintenance, transformation and development of gas transmission and distribution and storage system. If the gas valve selection is improper or the quality is poor, it may cause leakage, production and other accidents. Once the accident occurs, the light will affect the normal life and production of the society, and the heavy will bring great losses to the country and people's lives and property. Therefore, the selection of gas valves must be careful.

1, gas valve application status

With the development of the gas industry, the demand for special gas valves is increasing, and Shanghai valve valve manufacturers continue to introduce new products to meet the needs of market competition. At present, China's buried gas valves are mainly divided into gate valves, ball valves and butterfly valves. The main transmission modes are manual, worm gear drive, electric, pneumatic, gas-liquid linkage and so on. There are two installation methods: need to build sluice shaft and directly buried. According to relevant data, the manual gate valve is the most widely used in the urban coal-to-gas transmission and distribution system. Taking Tianjin as an example, Hebei, Hongqiao, Beichen three districts in the city have a total of more than 120 kilometers of medium pressure pipelines, more than 300 valves, of which more than 80% are gate valves, followed by butterfly valves and ball valves. Before the implementation of the gas source conversion project, artificial gas was running in the gas pipelines in the above three areas. Artificial gas contains more impurities, especially the "gas glue" formed by the mixture of tar, aromatic hydrocarbons and dust often affects the valve seal and even "bites" the valve stem. Therefore, in the selection of valves, we mainly choose those valves that can solve this problem from the structural characteristics, so as to ensure that the valve is flexible and has no leakage. After years of practice and data analysis, we found that gate valves (including parallel double gate valves and elastic seal single gate valves) are suitable. However, with the end of the Tiandai coal project, the nature of gas has changed. Natural gas is cleaner and drier than coal gas, but it contains sand dust, and the pressure is higher than coal gas. Under high pressure, sand dust will form a strong scouring effect on the valve cavity and natural gas contains highly corrosive hydrogen sulfide. Therefore, how to choose natural gas valves on urban underground pipelines is a new topic in front of us.

2, natural gas valve selection analysis

2.1 Buried natural gas valves should meet the requirements

Natural gas has the characteristics of inflammable, explosive and corrosive, so the natural gas valve installed on the underground pipe network should meet the following requirements:

2.1.1 Material corrosion resistance

The natural gas transported by the pipeline contains large amounts of hydrogen sulfide (a toxic and highly corrosive gas that reacts with iron to form iron sulfide, which flakes off and corrodes machinery) before it is desulfurized. Even after desulfurization and other processes of natural gas, there are still residual hydrogen sulfide. Therefore, the selection of pipeline valves should be sulfur resistant corrosion resistant materials.

2.1.2 Reasonable structure

The buried gas valve should be fully diameter designed to reduce flow resistance, facilitate the passage of pipeline cleaners or pipeline detectors, and save operating costs; Reduce the height of the structure as much as possible to save installation costs; The top of the valve should be equipped with a fully closed opening and closing indicator, so that the operator can see the state of the valve at any time to avoid misoperation.

2.1.3 Good sealing

The leakage requirements of natural gas valves are very strict, and the CJ3055-95 "Experiment and Inspection of urban gas valves" standard stipulates that the soft-sealed valve does not allow any perceived internal leakage under 1.1 times the nominal rated use pressure, and the hard-sealed valve is less than 0.3DNmm3/s under 1.1 times the nominal rated use pressure. As for outside leakage is absolutely not allowed. Usually buried and more important valves are all welded body structure. In order to ensure the sealing performance of the pipeline valve, the sealing pair is required to have excellent corrosion resistance, wear resistance, self-wetting and elasticity.

2.1.4 Easy operation

The vast majority of underground pipeline valves are manually opened and closed, so it is required that the opening and closing torque of the valve is small, and the number of turns in the whole process can not be too much, so that the air source can be cut off as soon as possible after the accident.

2.1.5 Simple Maintenance

The design of valve parts should consider the use of less maintenance, maintenance-free structure, as far as possible to reduce the workload of maintenance and maintenance, reduce the closure of roads due to valve maintenance and affect traffic