Abstract: Considering the process characteristics and control requirements of line cut-off valves in urban natural gas high-pressure pipeline networks, this paper outlines the technical specifications for selecting direct-buried, fully welded ball valves and their electro-hydraulic actuators from the perspective of the end user. To prevent large-scale gas leaks and secondary disasters caused by pipeline accidents, relevant standards require the installation of line cut-off valves along the pipeline. This paper offers selection recommendations designed to improve system safety and enhance emergency response efficiency.
1. Requirements for Line Cut-Off Valves and Their Drive Mechanisms
Line cut-off valves are typically installed in unattended valve chambers along high-pressure pipelines, where they must be capable of rapid and automatic closure. Due to the difficulty of replacement and the need for high sealing performance, high-quality fully welded forged steel direct-buried ball valves should be chosen to ensure long-term sealing reliability and service life. Given the limited power supply conditions along the pipeline and the general unavailability of dual-circuit power sources, the drive system should use an electro-hydraulic actuator to enhance power reliability and ensure rapid valve closure in emergency situations. This configuration allows for automatic valve shutdown under preset fault conditions, effectively isolating the pipeline and preventing large-scale natural gas leakage—without requiring manual intervention.
The supply scope for the direct-buried fully welded electro-hydraulic linkage ball valve includes the ball valve (hereinafter referred to as the "ball valve") and the electro-hydraulic linkage actuator. The ball valve and actuator must be assembled into a complete unit for testing, with both a test report and a certificate of conformity provided.
The scope of supply for the direct-buried fully welded electro-hydraulic linkage ball valve includes the ball valve (hereinafter referred to as "the ball valve") and the electro-hydraulic actuator. The valve and actuator must be assembled into a complete unit and subjected to the relevant tests. A test report and certificate of conformity shall be provided.
The direct-buried fully welded electro-hydraulic linkage ball valve is installed directly in valve chambers along the natural gas high-pressure pipeline network. According to IEC 60079-10 (International Electrotechnical Commission Standard for Electrical Equipment in Explosive Gas Atmospheres, Part 10: Classification of Hazardous Areas), the environment is classified as Zone 1 for explosion hazards.
Design pressure: ANSI Class 300
Operating pressure: ≤ 4.0 MPa
Medium temperature: –10°C to 50°C
Operating modes: Open, Stop, Close
① Design and Manufacturing
a. General Requirements
The design and manufacture of the ball valve shall comply with the relevant technical standards. The valve body and pressure-containing components must conform to ASME Section VIII, Division 1 (Boiler and Pressure Vessel Code).
b. Valve Bodies
The valve body shall feature a fully spherical design with an integral full-stem connection. The internal bore must be full-port, and the ball diameter must be consistent with the internal diameter of both the valve body and the connected pipeline. The face-to-face dimensions between the end faces connected to the sleeves shall comply with ANSI B16.10. The butt welding ends shall conform to ANSI B16.25. Welding processes shall comply with applicable AWS (American Welding Society) standards and ASME Section IX requirements. All welds shall undergo stress-relief treatment. The valve body and ball must be equipped with static discharge devices.
c. Balls
The ball passage shall be circular and coaxial with the valve body bore when fully open. The ball must be fixed, supported by a reliable pivot or an independent bearing. The stem should transmit only torque and must not bear any radial loads, ensuring low operating torque. The ball may use either an integrated fixed shaft or a replaceable pivot design and should incorporate a cavity drainage system. Torque reduction methods must not compromise the integrity of the valve body structure. The ball shall be forged steel and meet the material specifications of ASTM (American Society for Testing and Materials). The outer surface of the ball shall be uniformly electroplated with a nickel layer 0.025–0.030 mm thick to improve hardness, corrosion resistance, and surface smoothness. The Rockwell hardness after plating shall be 60 HRC.
d. Valve Stem, Valve Seat, and Sealing Structure
The valve stem’s cross-section and its connection to the ball must withstand the maximum operating torque. The stem must not bear any radial loads and should incorporate an anti-blowout mechanism. The valve seat shall feature a double-seat design comprising both metal and non-metal components, providing reliable bidirectional sealing on both the upstream and downstream sides. The sealing system shall be of the floating seat type, incorporating a self-relieving pressure mechanism. The seat back ring must contain at least three sealing elements, including a self-energizing seal and a fire-safe sealing ring. The valve seat shall be resistant to erosion and wear, with a service life equivalent to that of the valve body. It must include internal features to prevent localized erosion. The valve stem shall have a clear position indicator to enable accurate limit switch settings for the electro-hydraulic actuator. The valve seat preload spring shall be a disc spring to ensure even load distribution and prevent failure caused by debris accumulation, which is common in spiral springs. The valve stem sealing system shall incorporate at least three sealing rings, including a self-energizing seal and a fire-safe seal. In emergencies, the sealing system must permit injection of emergency sealing grease, which remains chemically and physically stable between –25°C and 100°C. The grease injection extension pipe must be installed above ground and equipped with a check valve rated to ANSI Class 300. The ball valve’s sealing performance shall comply with applicable technical standards. A fire-safe sealing structure is required, and fire resistance certification must be provided in accordance with API 607 or API 6FA.
e. Online Maintenance, Drainage, and Pressure Relief
The ball valve shall be capable of drainage and cavity pressure relief in both the fully open and fully closed positions. It shall also support online maintenance. The valve cavity shall be capable of automatically and safely relieving overpressure, either through an automatic downstream relief mechanism or via a relief piping system. If the relief pipe method is used, a safety relief pipe shall be installed above ground, fitted with a forged steel safety valve rated to ANSI Class 300. In the event of overpressure, the valve cavity shall automatically relieve pressure through this system. A drainage pipe shall also be installed above ground and equipped with a forged steel drain valve rated to ANSI Class 300.
f. Valve Position Indication and Remote Transmission
A contact switch shall be installed on the valve body to provide remote indication of valve position. The switch shall be rated for 24 V DC, 2 A.
g. Connection Type
The ball valve shall be connected to the pipeline by butt welding. The sleeve length on both ends shall be no less than 500 mm to ensure that the sealing materials are not affected during on-site welding. The transition section shall be welded to the valve body prior to all welding inspections. The connection between the ball valve and the pipeline shall ensure compatibility in terms of material strength and weldability. The butt-weld groove shall conform to the requirements of ASME B31.8 (Gas Transmission and Distribution Piping Systems).
h. Materials
All valve components shall be made from materials conforming to applicable ASTM and AISI standards. The valve body shall be constructed of forged steel.
Materials:
The ball shall be made of forged steel (A105). The valve stem for A105 valves shall be made of alloy steel. The valve seat shall be made of forged steel conforming to AISI 4140. The valve seat material AISI 4140 is forged steel. The valve seat is made of forged steel A105 with a lining of reinforced polytetrafluoroethylene (RPTFE). The valve stem and valve seat back ring use a triple sealing ring made of PTFE (polytetrafluoroethylene), PIFE, special graphite, or VITON (fluororubber). The sealing packing is made of PIFE. Materials for other components shall comply with the relevant international technical specifications and standards followed by the ball valve manufacturer. Certificates verifying the chemical composition and mechanical properties of all pressure-bearing parts shall be provided in accordance with applicable standards.
i. Surface Corrosion Protection
The buried sections of the ball valve shall be coated with an epoxy resin anti-corrosion layer at a thickness exceeding 400 μm. Above-ground components shall be coated with anti-rust paint. Products from reputable European and American manufacturers generally meet these requirements, including the T831 series full-bore butt-welded long-stem direct-buried fully welded ball valves and the DBW series fully welded ball valves.
② Test
Pressure and air tightness tests shall be carried out in accordance with the requirements of the relevant document and API Spec 598 (American Petroleum Institute Standard: Inspection and Testing of Valves), and a test report shall be issued. Each ball valve must undergo performance testing, with the test content, procedures, requirements, and equipment complying with the applicable standards. The test equipment must simulate the load on the ball valve and perform two operational cycles at the specified test pressure. Each cycle consists of operating the valve from fully closed to fully open, then returning it from fully open to fully closed. A test certificate shall be included in the final technical documentation accompanying the equipment shipment. Inspection and testing shall be conducted in accordance with the requirements of the relevant document, API Spec 598, and ASME B16.34 (American Society of Mechanical Engineers Standard: Valves—Flanged, Threaded, and Welding End). All testing shall be completed prior to surface treatment and painting. All assembled ball valves shall be inspected prior to leaving the factory. The valve testing shall include the following:
Hydrostatic pressure test of the valve body
Operation test of the valve under full pressure differential, recording the torque required to open the valve
Hydrostatic sealing test of the valve seat
Hydrostatic test of the double block and bleed (DBB) valve seat
Low-pressure air sealing test of the valve seat
Before performing valve seat pressure tests, the ball valve should be cycled open and closed two to three times. Test pressures and durations shall comply with the requirements specified in Chapter 5 of the referenced document. Upon completion of testing, the test medium inside the valve body must be completely drained.
③ Storage and Transportation
The welded ends of the ball valve must be protected to prevent mechanical damage during transportation. The ball valve and the electro-hydraulic linkage actuator should be assembled by the valve supplier before delivery. The supplier must ensure that the assembled valve and actuator remain clean, dry, and intact during packaging, transportation, and storage until installation. Additionally, the supplier shall ensure that the ball valve is transported in the open position.
④ Data Requirements
When supplying ball valves, at minimum, the following data must be provided:
Ball valve structural drawings
Rated torque of the ball valve under full pressure differential conditions
Procedures and methods for chemical nickel plating inspection
Material chemical composition and mechanical property test reports
Water and air pressure test reports, including time and pressure change records
Non-destructive testing (NDT) inspection reports
Ball valve operation test reports
Any other test reports and certificates required by applicable standards or specifications
⑤ Other Requirements
The valve body shall be equipped with lifting lugs for safe handling. To mitigate potential damage from earthquakes and ground movements, the valve must feature a ball-type body structure capable of withstanding pipeline stresses. This capability must be verified through compression and bending tests to ensure no failure occurs. Furthermore, the ball valve should be designed without brackets or foundations to guarantee that seismic activity does not compromise its safety or integrity.
① Composition
The electro-hydraulic actuator is a drive system that uses a self-contained hydraulic power unit to operate the ball valve via a hydraulic actuator. It primarily consists of four components: the hydraulic actuator, control system, hydraulic power unit, and control operation cabinet. The hydraulic actuator must be capable of continuous operation under the specified conditions. Failure of the hydraulic actuator or control system associated with the ball valve shall not affect the normal operation of other valve components. Maintenance and replacement of these parts shall be possible without interrupting normal valve operation.
a. Hydraulic Actuator
A double-acting hydraulic actuator shall be employed. The actuator design shall be either rotary vane or fork type to ensure high starting torque. To prevent jamming, all moving parts shall incorporate bearings and bushings. Sealing materials shall be resistant to deterioration and aging caused by variations in ambient temperature.
b. Control Systems
A switch-type control system shall be employed. To facilitate on-site testing, the system must provide both local and remote valve position indication and control functions. The system shall enable rapid valve closure within 10 seconds and also support valve opening operations. The control system comprises a switch-type controller, power supply, electronic pipeline break detection system, and necessary pressure transmitters. All components, including control buttons, shall be housed within a locked protective cabinet to prevent external damage or accidental operation. The electronic pipeline break detection system shall continuously monitor the natural gas pipeline pressure, pressure drop, and rate of pressure drop within a specified time interval. It shall trigger an alarm and send a valve-closing control signal—with a configurable delay—if the pressure parameters exceed preset limits. The control unit must have one RS-232 interface and one RS-485 interface, both supporting the MODBUS standard protocol and featuring hot-plug capability. The RS-232 interface connects to on-site laptops, while the RS-485 interface is used for remote control and signal transmission. Pressure drop rate thresholds shall be adjustable, and the detection system shall be equipped with a maintenance-free battery backup.
c. Hydraulic Station
The hydraulic station shall provide energy storage and voltage stabilization functions. The hydraulic pump shall operate intermittently in single-mode. The control system shall maintain hydraulic pressure within preset limits. In the event of a power failure, the hydraulic station must supply sufficient energy to operate the ball valve through one full switching cycle and maintain pressure for at least 120 hours.
d. Control Operation Cabinet
The control operation cabinet collects all signals in the valve room—including those from the ball valve, pipeline break detection system, pipeline pressure sensors, UPS status, video monitoring, and access control systems—and transmits them to the adjacent RTU (Remote Terminal Unit) room. The RTU then uploads these signals to the dispatch center, enabling remote monitoring and control of the ball valve.
② Basic Functional Requirements
As the driving device for the ball valve, the electro-hydraulic linkage actuator must be capable of automatically, quickly, and reliably driving the valve to the closed position under any accident or failure conditions. The associated monitoring and control equipment shall be capable of protecting pipeline and equipment safety without reliance on external power. The electro-hydraulic linkage actuator must include a mechanical limit device and support local control, remote control, and emergency shutdown functions during accident conditions. The actuator’s output torque must reliably operate the ball valve under actual working conditions, particularly ensuring valve opening and closing under the maximum design pressure differential. The torque required for emergency shutdown after the valve has been fully open for an extended period must be considered during the design and selection process. The selected torque output shall incorporate a safety factor of no less than [value]. The power supply for the electro-hydraulic actuator shall be three-phase AC, 220 V ± 33 V, 50 Hz ± 0.5 Hz. The system design must ensure that the actuator can close the valve during short-term power outages (up to 120 hours) under unreliable power conditions. The actuator must be capable of long-term, maintenance-free operation in harsh field environments. It shall be fully sealed, waterproof, and dustproof, conforming to all-weather operating conditions with a protection rating of IP65 or higher. The electrical components of the electro-hydraulic actuator shall have an explosion-proof rating of at least Exd IIB T[temperature class]. Leading actuator manufacturers such as BIFFI, ROTORK, and SHAFER typically provide suitable process flows and equip systems to meet these requirements.
③ Inspection and Testing
a. Inspection and Testing of Electro-Hydraulic Actuators
This includes electrical and mechanical operation tests, hydraulic circuit sealing tests, operation time control tests, and functional tests of limit devices.
b. Inspection and Testing After Assembly
After individual testing of the electro-hydraulic actuator, it shall be assembled with the ball valve for comprehensive testing. This comprehensive test covers maximum load valve opening performance and timing, no-load switching performance and timing of the ball valve, operation of the mechanical limit device, electronic limit signal feedback, and sealing tests for the oil and gas pipeline.
c. On-Site Testing
On-site testing involves verifying the operation of the ball valve and actuator prior to installation and ensuring their normal function under operating conditions after installation.
④ External Coating and Packaging
All component surfaces must be thoroughly cleaned, free of rust and lubricants, and coated with an anti-corrosion layer suitable for full outdoor exposure. Packaging shall be secure, moisture-proof, and impact-resistant, and must include assembly instructions and labeling.
⑤ Data Requirements
The provided data shall include overall dimensions and equipment weight; circuit diagrams and electro-hydraulic linkage function diagrams; specifications for the electrical junction box; hydraulic oil brand and grade; and installation and connection outlines for the actuator and ball valve.
Since manufacturing quality, on-site installation, and commissioning critically affect the sealing reliability of direct-buried fully welded electro-hydraulic linkage ball valves, the control stability of the actuator, and the service life of the equipment, purchasing decisions must comprehensively consider both the manufacturer’s strength and the capabilities of their installation service agents. Prudent supplier selection is critical to ensuring long-term system reliability and optimal performance.
