Common Pigging Failures in Gas Transmission Systems

Gas transmission pigging programs fail more often than operators admit. The failures are rarely due to a single technical oversight — they typically result from a combination of inadequate feasibility assessment, poor communication between operations and integrity teams, and assumptions that don't hold under actual operating conditions.

Stuck or Lost Pigs

The most serious pigging failure is a pig that cannot be recovered. Common causes include:

• Underestimated debris volumes — particularly in older systems where deposition history is incomplete
• Incorrect pig body / cup selection for the actual bore condition (dents, ovality, internal coatings)
• Insufficient driving pressure or flow rate to maintain pig velocity through low-point accumulations
• Launcher/receiver valve sequencing errors during run execution

Prevention starts with a proper feasibility study that includes bore condition data, historical debris records and a realistic assessment of minimum driving conditions.

Receiver Flooding and Liquid Handling

Gas transmission systems often carry entrained liquids that accumulate at low points. When a pig pushes this liquid ahead of it, receiver capacity can be overwhelmed — leading to flooding, pressure spikes and emergency shutdowns.

Mitigation options include:

• Pre-run liquid draining at known accumulation points
• Reduced pig speed through critical sections
• Adequate receiver slug catcher capacity and drain procedures
• Batch pigging with intermediate trap operations on long lines

Program Degradation Over Time

Many operators launch an effective pigging program after a commissioning or integrity campaign, then allow it to degrade. Run frequency slips, pig selection reverts to "whatever is in stock," and lessons learned from failed runs are not captured in updated procedures.

Sustainable pigging programs require:

• Documented run procedures with clear acceptance criteria
• Post-run reporting that feeds back into program optimization
• Periodic program reviews tied to integrity management cycles
• Training for operations staff on pig handling and emergency response

When to Seek External Support

If your team is facing repeated pigging failures, stuck pig incidents or declining program effectiveness, an independent review can identify systemic issues before they escalate into integrity or safety events. Nonlinear Engineering provides pigging feasibility studies, failure investigations and program optimization support for gas transmission operators worldwide.