If you are a valve dealer, this article can help you understand how to select valves for customers in the natural gas industry.
If you are a customer from the natural gas industry, this article can help you choose a valve.
Because natural gas is flammable, explosive and corrosive, the natural gas valves installed in the underground pipeline network must meet the following requirements in order to ensure long-term safe operation:
1.1 Corrosion Resistance Of Materials
Natural gas delivered in pipelines contains large amounts of hydrogen sulfide (a toxic and highly corrosive gas that reacts with iron to form iron sulfide, which exfoliates and corrodes machinery) before being desulfurized. Even after desulfurization and other processes of natural gas, there are still residual hydrogen sulfide. Therefore the pipeline valve material selection to choose anti-sulfur corrosion-resistant materials.
1.2 Reasonable Structure
Buried gas valves shall be of full-bore design to reduce flow resistance, facilitate passage through the line sweeper or line detector, and save operating costs. The top of the valve should be equipped with a fully closed open-close indicator, easy for the operator to see the valve at any time in order to avoid misoperation.
1.3 Good Sealing
The leakage of natural gas valves is very strict, cJ3055-95″town gas valve test and inspection” Standard: Soft Seal Valve at 1.1 times nominal nominal service pressure shall not allow any detection of internal leakage, hard seal valve at 1.1 times nominal service pressure allowed less than 0.3 DNmm3/S. As far as external leakage is concerned, it is absolutely impermissible. Usually buried and more important valves are used body fully welded structure. In order to ensure the sealing performance of pipeline valves, the sealing pair is required to have excellent corrosion resistance, wear resistance, self-lubrication and flexibility.
1.4 Easy To Use
The majority of underground pipeline valves are opened and closed by manpower, so it is required that the opening and closing torque of the valves is small, and the total number of turns can not be too much, so that the gas source can be cut off as soon as possible after the accident.
1.5 Easy Maintenance
The design of valve parts should consider the use of less maintenance, maintenance-free structure, as far as possible to reduce maintenance workload, to reduce valve maintenance and closed roads, affecting traffic.
2.1 Comparison And Analysis Of Several Commonly Used Valves
At present, there are three main types of gas valves used in natural gas industry in China, they are gate valve, ball valve, butterfly valve, etc. The following three aspects of these valves are analyzed and compared:
2.11 Comparison Of Working Principles And Structural Features
The Gate Valve opens and closes the valve by the up and down movement of the gate plate, in order to realize a certain part of the pipeline system needs “full open, full close” control, and meets the medium through only produces the tiny pressure drop request. Gate Valves are usually used where there is no need to open or close frequently and where the gate is kept fully open or closed. Not Suitable for use as regulation or throttling. Gate Valves are generally of full bore design with low flow resistance and are available through cleaning balls and pipe detectors. The Gate Valve has a High Structure Height (generally 3-5 times of pipe diameter) , which is suitable for the case of deep buried pipeline.
Ball Valve is by rotating the ball to make the valve open and closed (open, closed only to rotate 90 degrees) . Ball valve switch light, small size, can be made of a large diameter, reliable sealing, sealing surface and the ball often in the closed state, not easily eroded by the media, in various industries have been widely used. The utility model has the advantages of simple structure, convenient maintenance, full-path design, small flow resistance, and can be passed through a cleaning ball and a pipeline detector.
Butterfly Valve is designed according to the principle of pipe wrench, its flow control element is an inclined disk, disk fixed on the spindle, and to rotate the spindle to control the opening and closing, valve seat fixed on the valve body wall. The valve body is pancake type, suitable for regulating medium flow. The Butterfly Valve is small in size, light in weight and easy to operate, but has high flow resistance and can not pass through the cleaning ball and pipe detector.
From the above structure characteristics and working principle, gate valve and ball valve are more suitable for natural gas pipeline.
2.12 Economic Comparison
The cost of installing a valve with a nominal pressure of 4 kg and a nominal diameter of DN200 is compared economically. Ball valves are the most expensive, about three times the cost of gate and butterfly valves. Gate valves are much more expensive than Butterfly Valves (about 4 times that of butterfly valves) , but because they can be buried directly, they can save a lot of installation costs, making gate valves comparable to butterfly valves overall. The results show that the performance and service life of the gate valve is much better than that of the Butterfly Valve. So from this point of view, gate valve should be the preferred valve.
2.13 Security Comparison
With the development of technology, the safety of all kinds of gate valves has been improved. the double parallel gate gate valve is equipped with the stem protecting sleeve to protect the stem from the erosion of medium, and the shell adopts the specially designed “Squirrel cage frame stiffener” , which reduces the total weight of the valve and enhances the strength and rigidity of the Shell The elastic seal gate valve uses the elastic hard seal, when the valve is fully open or fully closed, the sealing pair completely separates the medium from the valve inner cavity to make the gate valve have the characteristics of fire resistance, high temperature resistance and corrosion resistance. Gate valves are equipped with fully enclosed opening and closing indicators to enable the operator to clearly understand the valve status.
Ball valve also has fire resistance, high temperature characteristics. After burning the polytetrafluoroethylene materials on the sealing seat, the metal sealing seat and all sealing parts can form a metal-to-metal sealing structure to prevent the diffusion of the gas medium and prevent the disaster from continuing to expand; In addition, it also has anti-static structure, so that the ball valve in the opening and closing process of the formation of static into the ground, to avoid the accumulation of static ignition medium, to ensure the safety of equipment, the ball valve limited position locking mechanism, to prevent operator misoperation or illegal operation.
Butterfly valve sealing pair isolation width is too narrow, easy to cause the disc closed process overshoot or not in place, affect the seal; in addition, because the seal pair-part of rubber or polytetrafluoroethylene, in the gas erosion is easy to damage or fall off, and in case of fire high temperature easy to damage, short service life.
From the above analysis results we can see, no matter from which point of view, Butterfly Valve is not suitable for buried gas pipeline. However, due to space conditions, can only choose butterfly valve. Select Butterfly Valve should be multi-eccentric high-quality Butterfly Valve, sealing material selection or hard seal, debugging must be accurately adjusted to the closed position. polytetrafluoroethylene.
The gate valve and the ball valve are suitable for the buried natural gas pipeline from the structure characteristic and the security. But they all have their flaws. Ball Valves require a high level of technology from design to manufacture, so their cost is high. Gate Valve needs to rotate a lot of turns when opening and closing, opening and closing time is longer. Therefore, when we choose valves, we should synthesize all factors and try our best to save costs while ensuring safety and reliability. From this point of view, we should choose valves rationally according to the characteristics of gas and the operating pressure of pipelines, the utility model can not only satisfy the safe operation of the pipeline, but also reduce the cost and make the best use of the material.
Post time: Jul-28-2021