Pipeline Valves for Pig Launching and Receiving: Full Bore Requirements and Design

Pipeline pigging is an essential maintenance and inspection practice in the oil and gas industry, used to clean internal pipe walls, perform inline inspection of pipe condition, and separate product batches during product change operations. Pigs (Pipeline Inspection Gauges) are cylindrical or spherical devices that travel through the pipeline propelled by the flowing process fluid. For pigs to pass through valves without becoming stuck, the valves must meet specific bore and clearance requirements. Understanding these requirements is critical for specifying pipeline valves in piggable systems.

Full Bore Valve Requirements

A full bore (or full port) valve has an internal bore diameter equal to or greater than the internal diameter of the connected pipe. This is a fundamental requirement for all valves in piggable pipeline sections, as a reduced bore valve would obstruct or trap the pig. For gate valves, the port must be round and equal to the nominal pipe bore. For ball valves, the ball port diameter must match the pipe internal diameter throughout the full valve length. API 6D, the pipeline valve standard, defines bore dimension requirements for pipeline valves intended for piggable service, and these requirements must be specified in the valve datasheet.

• Full bore internal diameter equal to or greater than the pipe inside diameter per the wall thickness schedule

• Smooth transition from valve bore to pipe bore with no steps or sharp edges that could catch a pig

• No internal protrusions from stem, seat inserts, or body features extending into the bore clearance zone

• Trunnion-mounted ball valves preferred for pipeline service due to consistent bore geometry

• Cavity-fill plugs or floating seat designs prevent pig fingers from entering the cavity behind the ball

Gate Valve Design for Pigging

Gate valves used in piggable pipelines require special consideration. The gate recess (the cavity in the body that receives the gate in the open position) must not trap or damage the pig as it passes. Through-conduit gate valves use a solid slab gate with a full bore opening that completely aligns with the pipe bore in the open position and provides a clean, uninterrupted flow path. The gate cavity is sealed when the valve is open, preventing the pig from entering the cavity and becoming jammed. This design is specifically required for regular pigging operations and is standard in natural gas transmission and crude oil trunk line applications.

Ball Valve Selection for Pigging

Trunnion-mounted ball valves are the preferred choice for most modern pipeline pigging applications. The trunnion design holds the ball securely in position, ensuring the bore remains perfectly concentric with the pipe axis. Floating ball designs are generally not recommended for large-diameter pigging service because the ball position can shift slightly under line pressure, potentially creating a misalignment that could snag the pig. For sphere pigging operations using foam or wire brush spheres, the ball valve cavity must be designed to prevent sphere fragments from becoming lodged. Cavity-fill or cavity-relief designs address this concern by either filling the cavity to the bore level or providing controlled drainage of the cavity.