In natural gas transmission and distribution systems, valves are the core components of fluid control, and their selection, installation, and maintenance directly affect the safety, continuity, and regulatory compliance of the system. Natural gas itself has characteristics such as flammability, explosiveness, and easy leakage, so it is necessary to strictly follow engineering specifications and safety standards during the use of valves, especially in long-distance pipelines, high-pressure conditions, and complex environments. This article systematically analyzes the selection principles, installation requirements, material adaptation, operation and maintenance, and safety control of valves in natural gas pipelines.
1、 Valve selection and structural design
In natural gas transmission systems, valve selection should fully consider the characteristics of the medium (whether it contains sulfur, dry/wet gas), pressure rating, temperature range, and operating conditions.
Valve type selection: Common valve types include full bore ball valves (suitable for gas transmission pipelines, with good sealing and quick opening and closing), gate valves (suitable for long-term constant opening or full closing), butterfly valves (used for medium and low pressure regulation occasions), and emergency shut-off valves (used for accident response).
Sealing structure: Natural gas medium has extremely high sealing requirements, and metal to metal sealing or wear-resistant soft sealing materials should be used to ensure zero leakage (API 6D or ANSI VI level sealing).
Anti static design: To prevent natural gas from generating static electricity and causing fires at high flow rates, valves must be equipped with anti-static devices to ensure that the valve stem and body are connected to the ground.
Explosion proof certification for actuators: Electric or pneumatic actuators installed in explosion-proof areas such as Zone 1 and Zone 2 must pass ATEX, IECEx and other explosion-proof certifications to prevent ignition hazards.
2、 Installation and layout specifications
Reasonable valve layout: Natural gas pipelines should be equipped with valves at key locations such as the starting and ending ends, branch lines, densely populated areas, and river crossing points to facilitate accident isolation and maintenance. The mainline pipeline needs to be equipped with segmented valves (block valves) every 20-50 kilometers.
Installation requirements: Valves must be installed in the direction recommended by the manufacturer (such as the installation direction and sealing end of ball valves), and brackets should be set up to prevent pipeline stress from being transmitted to the valve body, causing distortion or leakage.
Airtightness test: After installation, leakage detection and strength testing (such as API 598 standard) must be carried out, and commonly soap water method or electronic leak detector is used for sealing confirmation.
3、 Material and corrosion resistance adaptability
Valve body material: To adapt to environments containing hydrogen sulfide (H2S), it is recommended to use stainless steel 316L, Inconel alloy, or carbon steel coated with epoxy or PTFE to enhance corrosion resistance.
Low temperature toughness: In high latitude regions with low temperatures, low-temperature carbon steel (such as A350 LF2) or austenitic stainless steel should be selected to prevent material failure due to cold brittleness.
Sealing material selection: The sealing element should be made of PTFE, PCTFE, graphite or metal spring loaded structure, taking into account both air tightness and aging resistance.
4、 Operation and maintenance management
Reliability of actuators: Pneumatic or pneumatic hydraulic actuators are commonly used in natural gas systems. The emergency shut-off valve is required to quickly shut off within 1 second, and the control system should regularly test the response and effectiveness of the backup power supply.
Maintenance system: Develop a periodic maintenance plan, including valve chamber cleaning, seal replacement, valve stem lubrication, etc. Valves that are not opened for a long time should be opened and closed regularly to prevent rusting or jamming.
Information management: Manage valve positioning, status, maintenance records, and other information through GIS or SCADA systems, and set clear signage on site.
5、 Safety control and emergency measures
Leakage detection: Install natural gas detectors in critical valves or central control areas, which will automatically trigger sound and light alarms and emergency shutdown when the concentration exceeds the set level.
Cathodic protection system: Underground steel valves and pipelines require cathodic protection to effectively suppress electrochemical corrosion in the soil.
Accident response mechanism: In emergency situations (such as pipeline rupture, earthquakes, etc.), the valve system should be able to achieve remote or automatic interlocking closure, cutting off the gas source.
Valves in natural gas pipelines are not only the basic units for controlling and regulating fluids, but also the key nodes for accident prevention and system safety operation. Its selection, installation, and maintenance need to comprehensively consider the characteristics of the medium, environmental conditions, and industry standards. Through scientific layout, explosion-proof design, corrosion-resistant material selection, and intelligent management, the reliability and safety level of natural gas transmission and distribution systems can be significantly improved.
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