Natural Gas Valves: Guardians of Underground Pipeline Safety

In our daily lives, natural gas, as a clean and efficient energy source, has been widely used in residential, industrial, and commercial sectors. However, the flammable and explosive nature of natural gas, along with its potentially corrosive components during transportation, makes the safety and reliability of natural gas valves a crucial element in ensuring public safety. This article will delve into the importance of natural gas valves in underground pipelines, key considerations in material selection, characteristics of different valve types, and how to reduce costs while ensuring safety.

The Importance of Natural Gas Valves

Natural gas valves play a vital role in the transportation process, whether it is from gas fields to urban pipelines or from urban pipelines to end-users. The primary function of valves is to control the flow of natural gas, ensuring that the gas supply can be quickly cut off when needed to prevent leaks and explosions. Additionally, valves must have excellent sealing properties to prevent gas leakage during transportation, which can lead to resource waste and environmental pollution.

Natural gas contains a significant amount of hydrogen sulfide before desulfurization, a highly toxic and corrosive gas. Even after desulfurization processes, a small amount of hydrogen sulfide may still remain. Hydrogen sulfide reacts with iron to form iron sulfide, which flakes off and can corrode mechanical equipment. Therefore, the material selection for natural gas valves must consider sulfur resistance and corrosion resistance to ensure the stability and reliability of the valves over long-term use.

Key Considerations in Material Selection for Natural Gas Valves

The material selection for natural gas valves is critical to ensuring their safety and durability. Given the flammable, explosive nature of natural gas and its potentially corrosive components, the choice of valve materials must be made with caution.

1. Sulfur-Resistant and Corrosion-Resistant Materials

Since natural gas may contain corrosive components such as hydrogen sulfide, valve materials must be sulfur-resistant and corrosion-resistant. Commonly used materials include stainless steel and special alloys. These materials can maintain stability in environments containing hydrogen sulfide, preventing valve failure due to corrosion.

2. Material Selection Based on Pressure

Low-Pressure Urban Gas Pipelines (P ≤ 0.2 MPa): Gray cast iron valves are recommended. Although gray cast iron has lower strength and ductility, it offers good corrosion resistance and is cost-effective, making it widely used in low-pressure urban gas pipelines.

Medium-Pressure Gas Pipelines (0.2 MPa < P ≤ 0.8 MPa): Ductile iron or cast steel valves are recommended, with a preference for ductile iron valves. Ductile iron has better corrosion resistance and casting properties than cast steel, and it is 30% cheaper than cast steel valves. However, if ductile iron is chosen, strict quality control of the material is necessary.

High-Pressure Gas Pipelines (P > 0.8 MPa): Cast steel valves are recommended. Cast steel valves have high strength and toughness, capable of withstanding high-pressure environments, ensuring safe operation in high-pressure gas pipelines.

3. Application of Special Materials

In recent years, the application of PE ball valves in medium and low-pressure gas pipelines (P ≤ 0.4 MPa) has gradually increased. PE ball valves can be directly buried and have good sealing performance, but their import prices are relatively high, especially for larger diameters (above DN100). Currently, PE ball valves are still in the promotion phase, and their practical application effects need further experience summarization.

Common Valve Types for Natural Gas

In natural gas transportation systems, there are various types of valves, each with unique designs and functions suitable for different application scenarios. Understanding the characteristics of these valves can help us better select the appropriate valves to meet specific process requirements and safety standards. Below are some common types of natural gas valves and their characteristics.

1. Gate Valves

Gate valves are common valves in natural gas pipelines, known for their good sealing performance and low flow resistance, making them suitable for applications requiring frequent opening and closing. Here are several types of gate valves and their characteristics:

Parallel Double Disc Gate Valve

The parallel double disc gate valve is designed for gas pipelines. During the opening and closing process, it can scrape off the “gas tar” on the sealing surface, solving the problem of gas impurities adhering to the sealing surface and affecting valve sealing. The valve is equipped with a valve stem protector to prevent the valve stem from being eroded by “gas tar.” The valve has a blow-off hole side cover at the bottom to clean debris that falls into the valve cavity. Its full-bore design offers low flow resistance and allows the passage of pipeline cleaning pigs. The valve body features a specially designed “cage frame reinforcement,” reducing the overall weight of the valve while enhancing the strength and rigidity of the shell. Additionally, this series of gate valves comes with a fully enclosed opening and closing indicator, enabling operators to clearly understand the valve’s status.

Slab Gate Valve

The slab gate valve is a general-purpose valve that has been used in gas pipelines in recent years. Its full-bore design offers low flow resistance, with sealing on both sides achieved by pressing polytetrafluoroethylene or rubber O-rings against the gate. However, this valve cannot achieve a gas-free cavity when fully closed or open, making it inconvenient for users to quickly determine whether the valve is tightly closed during emergency repairs. To achieve a gas-free cavity, the opening and closing torque will increase rapidly. Therefore, slab gate valves are suitable for applications with lower pressure levels and smaller nominal diameters.

Elastomer-Seated Gas Gate Valve

The elastomer-seated gas gate valve is a gas-specific valve that differs from the slab gate valve. Its gate features an elastomer floating structure on both sides of the sealing seat, ensuring that the sealing surfaces remain tightly together during the opening and closing process, compensating for wear of the sealing pair. This valve is suitable for high-pressure applications. When fully open or closed, the valve cavity can be gas-free, and even after venting the remaining gas in the cavity, there will still be no pressure inside.

2. Butterfly Valves

Butterfly valves are lighter, have larger diameters, and are less expensive compared to other valves, but their sealing performance is relatively poor. The narrow isolation width of the sealing pair can easily cause the valve disc to close too far or not far enough during the closing process, affecting sealing. The valve disc is located in the middle of the valve cavity, resulting in high flow resistance and the inability to pass cleaning pigs. Since part of the sealing pair is made of rubber or polytetrafluoroethylene, it is prone to damage or detachment during gas flushing, leading to a shorter service life. Therefore, except in special locations, butterfly valves are not recommended for gas pipelines.

3. Trunnion Mounted Ball Valves

Trunnion mounted ball valves are specifically designed and manufactured for the gas industry, suitable for gas transmission lines and urban gas facilities. They have excellent fire resistance. In the event of a fire, even if the polytetrafluoroethylene material on the sealing seat is burned off at high temperatures, the metal sealing seat and other sealing parts can form a metal-to-metal sealing structure, preventing the spread of gas and further escalation of the disaster. These ball valves also have anti-static functions, which can direct static electricity into the ground, ensuring the safety of the equipment. Additionally, the ball valve design includes a limit and locking feature to prevent accidents caused by misoperation by operators or unauthorized personnel. The valve stem sealing of the ball valve is designed with an anti-valve stem impact device and uses special O-rings for sealing, resulting in low torque, easy operation, and rapid opening and closing.

Key Characteristics of Natural Gas Valves

Natural gas valves possess several important characteristics that are crucial for ensuring their safety and reliability in practical applications. These characteristics include sealing performance, reliability and durability, rapid response capability, and adaptability.

1. Sealing Performance

The sealing performance of natural gas valves is of utmost importance. High sealing performance can reduce safety risks and ensure the effective operation of the system. Natural gas valves must be able to withstand high-pressure environments to prevent valve failure or leakage. Additionally, valve designs typically incorporate explosion-proof functions to minimize damage and injury caused by explosions. For electric valves or solenoid valves used with natural gas, explosion-proof designs are generally required.

2. Reliability and Durability

Natural gas valves need to have high reliability and durability, capable of operating stably over long periods without frequent maintenance or replacement. The design of valve components should consider low-maintenance or maintenance-free structures to minimize the workload of inspections and maintenance, reducing the occurrence of road closures due to valve maintenance that can affect traffic.

3. Rapid Response

Natural gas valves must be able to quickly respond to control signals to open or close rapidly when needed, ensuring the safety and controllability of the system. This is crucial for preventing accidents and minimizing their impact.

4. Adaptability

Natural gas valves must be able to adapt to different process conditions and environmental requirements, including changes in temperature, pressure, and flow rate. This requires valves to be designed and manufactured with consideration for a wide range of possible operating conditions to ensure stable operation under various circumstances.

Conclusion

The safe operation of natural gas valves in underground pipelines is essential for ensuring public safety and the efficient transportation of natural gas. Selecting appropriate valve materials, optimizing valve design, choosing the right valve types, and considering cost factors are all key to ensuring the long-term stable operation of natural gas valves. By gaining a deep understanding of the characteristics and material selection considerations of natural gas valves, we can optimize costs while ensuring safety, providing a solid guarantee for the efficient and safe transportation of natural gas.

In practical applications, we need to take into account various factors, including the specific pressure of the gas pipeline, environmental conditions, and budget requirements, to select the most suitable natural gas valves. Only in this way can we ensure that natural gas valves play their intended role in underground pipelines, safeguarding our safety and environment.