A fiberglass gas pipeline is being implemented to supply gas from a compressor station to a delivery point. As the pipeline approaches completion, ensuring its operational safety and integrity is paramount. This case study examines the surge analysis conducted on the buried portion of the pipeline to identify potential vulnerabilities and provide mitigation strategies for surge events. The objectives of this project are to assess the pipeline’s resilience to pressure fluctuations, evaluate the impact of rapid flow changes, and determine the overall system integrity under various operational scenarios.
Surge Risks in Long-Distance Gas Pipelines
The primary technical challenge is to ensure the safe and efficient operation of the fiberglass gas pipeline under both steady-state and transient conditions. Specific issues include:
- Determining the required pressure at the pipeline start to achieve the intended gas flow rate to the delivery point.
- Assessing the pipeline’s response to rapid compressor run-down during a power cut.
- Evaluating the impact of sudden flow halting at the delivery point, such as during valve closure.
- Identifying potential risks of transient overpressure or underpressure conditions that could damage piping components.
- Analyzing the imbalance of longitudinal forces in the pipeline during surge events.
The analysis must consider these factors while ensuring the pipeline’s integrity and operational safety within the constraints of the fiberglass material specifications.
Hydraulic Simulations for Pipeline Surge Analysis
The surge analysis employed a comprehensive approach using BOSfluids, a specialized surge and water hammer analysis software. The methodology included:
- Steady-State Analysis: Calculation of pressure distribution along the pipeline to determine the required starting pressure for the desired flow rate.
- Transient Analysis: Simulation of various upset scenarios, including:
- Rapid compressor run-down during a power cut
- Sudden flow halting at the delivery point
- Force Analysis: Evaluation of unbalanced forces during transient events and comparison with soil reaction forces on the buried pipeline.
- Data Interpretation: Analysis of simulation results to assess pressure levels, force imbalances, and overall system resilience.
- Assumption Verification: Identification and documentation of assumptions made due to missing input data, with recommendations for verification.
Key Findings from Surge Assessment of Fiberglass Pipelines
The analysis revealed several key findings:
- Steady-State Pressure: The required pressure at the start of the pipeline to achieve 9 MMSCFD flow to the delivery point was calculated as 38.6 barg . This value is crucial for determining the appropriate compressor size and operational parameters.
- Pressure Levels: During all transient scenarios, pressure levels in the pipeline remained well below the material allowables. The maximum discharge pressure of the compressors (700 psig or 48.2 barg) is within the pipeline’s tolerance.
- Unbalanced Forces: Peak unbalanced forces during upset scenarios were calculated at 1.4 kN, which is negligible compared to the opposing maximum soil reaction force on the buried pipeline.
- Compressor Trip: A sudden compressor trip results in a slow pressure drop, preventing significant pressure surges. The pipeline demonstrates resilience to transient conditions during such events.
- Valve Closure: Rapid valve closure at the delivery point does not lead to significant peak pressures due to the gas’s compressibility and limited inertia.
The analysis indicates that the fiberglass pipeline is well-suited for the intended application and demonstrates robust performance under the considered transient conditions.
Measures for Ensuring Pipeline Integrity
Based on the analysis, the following recommendations were proposed:
- Maintain Current Design: The existing pipeline design using fiberglass material is suitable for the intended application and does not require modifications to withstand the analyzed surge conditions.
- Compressor Anti-Surge Study: Conduct an anti-surge study for the compressor system to ensure no reversal of flow occurs during low-flow conditions, which could potentially damage the compressor.
- Operational Guidelines: Develop and implement operational guidelines that account for the maximum allowable pressure and flow rates identified in the analysis.
- Monitoring System: Install a real-time monitoring system to track pressure fluctuations and flow rates, enabling early detection of potential issues.
- Regular Inspections: Implement a schedule for regular pipeline inspections, focusing on areas identified as potentially vulnerable to stress or wear.
The proposed solutions offer a comprehensive approach to ensuring the long-term safety and efficiency of the pipeline. Â By implementing these recommendations, the pipeline operators can confidently operate the gas pipeline while minimizing the risk of failures due to pressure surges or other transient events.
