Design Considerations for Long-Distance Pipeline Ball Valves

 
In long-distance pipeline applications, industrial ball valves must operate efficiently and reliably under extremely harsh conditions. Despite initial processing, crude oil and natural gas still contain sulfur compounds, impurities, and foreign matter, necessitating zero-leakage sealing, which places stringent technical demands on ball valves. This article will explore the critical aspects that must be addressed in the design and application of ball valves for long-distance pipelines to ensure their reliable operation in complex environments.

Environmental Adaptability

 
Ball valves used in long-distance pipelines must possess strong environmental adaptability to handle harsh operational conditions. These valves must not only withstand internal media pressure but also resist temperature fluctuations, external loads, and extreme climate challenges.
 
Internal Media Pressure: The valve must be able to handle the internal pressure from the media. This requires that the valve materials and design have sufficient strength and durability.
 
Axial Force and Pressure: Variations in ambient temperature can lead to changes in axial force and pressure, so valve design must account for these factors to avoid stress concentration caused by thermal expansion and contraction.
 
External Loads: Long-distance pipelines may be affected by external loads such as landslides, ground subsidence, and floods. Valve designs should consider these factors to ensure continued operation under external impacts.
 
Low-Temperature Impact Toughness: In cold and freezing regions, valve materials need to have excellent low-temperature impact toughness to prevent brittle fracture in low temperatures. This requires materials to maintain sufficient toughness under cold conditions.
 
Welds and Heat-Affected Zones: For fully welded valve body ball valves, the design of welds and heat-affected zones should be assessed according to fracture mechanics principles to ensure that their fracture toughness meets the required standards.

Sealing Performance

 
Sealing performance is a key requirement for ball valves in long-distance pipelines, encompassing the following aspects:
 
Zero-Leakage Sealing: The valve must have zero-leakage sealing capability to ensure effective isolation of downstream pipelines. Zero-leakage sealing prevents media leakage, maintaining the integrity of the pipeline system.
 
Sealing Materials: To address the impact of metal particles in the media on sealing, valves typically use metal-to-metal seals as primary seals and PTFE/rubber-to-metal seals as secondary seals. Additionally, emergency sealing measures should be in place to prevent accidents if the primary seal fails.

Safety and Anti-Static Measures

 
For the safe operation of ball valves in long-distance pipelines, designs must consider fire safety and anti-static measures.
 
Fire Safety: Valve designs must meet fire safety requirements, ensuring that in the event of a fire, external and internal leakage does not exceed the leakage standards specified by API 607. This helps prevent further fire spread and ensures safety for personnel and equipment.
 
Anti-Static Design: Since static electricity may be generated by non-metallic materials clamping the ball, the valve must be grounded to the valve body to prevent static accumulation. Under 24VDC, the resistance should be less than 10Ω to prevent static-related safety hazards.

DBB Function (Double Block & Bleed)

 
The DBB (Double Block & Bleed) function is an important design requirement for ensuring safe emissions.
 
Double Block: During valve cavity venting, both the upstream and downstream valve seats should automatically block simultaneously to ensure safety during the venting process.
 
Venting System: The valve cavity venting system should effectively discharge media and allow online sealing testing through venting ports to ensure no leakage during operation.

Cavity Pressure Protection

 
Cavity pressure protection is crucial for the safety of ball valves in long-distance pipelines. The design must prevent media from being trapped within the valve cavity and ensure that gas or liquid media can automatically vent.
 
Prevent Pressure Trapping: Whether the valve is open or closed, media should not be trapped in the valve cavity. For gas or liquid media, the cavity pressure must automatically vent, with the maximum venting value not exceeding the valve's rated pressure limit. External pressure relief valves should have a diameter of DN15 or larger.
 
Online Testing: The media in the valve cavity should be able to vent, with online sealing testing through venting ports to ensure the valve’s sealing performance.

Drive and Indication

 
The drive and indication systems of ball valves in long-distance pipelines must ensure reliable operation and visibility.
 
Valve Position Indication: Whether manually or power-driven, valves must be equipped with clear valve position indicators to show the open or closed status of the valve.
 
Transmission Chain Design: The design torque of the transmission chain should be at least twice the maximum torque of the ball valve to ensure reliability and stability during actual operation.

Material Requirements

 
Material selection for ball valves in long-distance pipelines must meet stringent standards.
 
Pressure-Containing Components and Bolt Materials: Pressure-containing components and bolt materials must possess stress corrosion cracking resistance and meet NACE MR0175 standards to ensure long-term performance in harsh environments.
 
Corrosion Protection Design: Long-distance pipeline ball valves should feature a fully welded valve body structure, with pipeline cathodic protection and external corrosion treatment to prevent galvanic corrosion and stress corrosion from underground water.
 
Ball valves for long-distance pipelines face numerous challenges, from environmental adaptability and sealing performance to safety, anti-static measures, and material selection. Each aspect requires careful consideration to ensure reliable operation under extreme conditions. By thoroughly analyzing and optimizing these key factors, the performance and safety of ball valves can be significantly improved, ensuring the stability and long-term efficiency of pipeline systems. Future applications will benefit from continuous attention to these technical requirements and design principles, laying a solid foundation for safe and efficient pipeline operation.