This case study examines the cooling water and foam systems located in two jetties (Jetty A and Jetty B) of a major industrial facility. These systems, critical for fire protection, have experienced significant issues related to water hammer effects and structural integrity. The primary objectives of this study are to identify the root causes of the system failures, assess their compliance with industry standards, and propose effective solutions to ensure safe operation.
The fire protection systems at Jetty A and Jetty B remain dry until an emergency triggers flooding, leading to rapid flood and drain cycles. These cycles have resulted in severe water hammer conditions, compromising the structural integrity of the pipe systems and creating unsafe operating conditions. This case study aims to provide a comprehensive analysis of the problem and propose effective solutions to mitigate these issues and ensure compliance with EN 13480 standards.
Key Challenges in Fire Protection Systems
The technical issues identified in the Jetty A and Jetty B fire protection systems include:
- Bending deformations and significant displacements in pipelines, leading to support slide-off in certain areas.
- Water hammer conditions caused by fast flood and drain cycles during emergency operations.
- Surge pressures exceeding the allowable pressure limit (as per EN 13480), making the system unsafe to operate.
- Insufficient support in the pipeline systems, resulting in unacceptable pipe displacements and stresses.
The primary aim is to comply with EN 13480 standards, which specify a maximum allowable surge pressure of 1.2 times the design pressure. The systems must be modified to operate safely within these limits while maintaining their emergency response capabilities.
System Modeling and Dynamic Analysis
To analyze the problem and develop effective solutions, the following steps were followed:
Model Review
Pressure and Force Analysis
- The existing model developed using BOSfluids was reviewed and enhanced to provide more realistic results.
- Dynamic analysis was conducted to calculate pipeline displacements and assess surge forces.
- Surge pressures were analyzed against the EN 13480 standard.
- Structural displacements were calculated using unbalanced forces from the dynamic analysis.
Scenario-Based Analysis
Mitigation Measures
- Various scenarios were analyzed, including foam rings, cooling water towers, and individual jetty lines, to identify critical areas of overpressure and structural displacement.
- Multiple mitigation solutions were modeled and compared, including layout modifications, venting valves, addition of dead volumes and anti-surge valves.
Optimizing Piping Configurations to Mitigate Water Hammer Effects
Based on the analysis, the following modifications are recommended to address the overpressure and structural issues:
- Modify piping configuration in critical areas to prevent water front collisions and reduce surge pressures.
- Install remote-controlled venting valves in cooling water towers and specific cooling water lines to manage flow and reduce pressure surges.
- Add dead volume above monitors combined with partial valve closure to reduce pressures and forces in certain areas.
- Implement anti-surge valves with specific closing times as an alternative to venting valves in some locations.
- Conduct a stress analysis and redesign the support configuration to address structural displacements and ensure proper restraint.
Key Design Modifications to Improve Fire System Reliability
The effectiveness of the proposed solutions was evaluated using the improved hydraulic model. The results indicate:
- Minor modifications of the piping configurations significantly reduced surge pressures, bringing them within acceptable limits.
- Installation of remote-controlled venting valves effectively managed flow and reduced pressure surges to compliant levels.
- The addition of dead volume and partial valve closure provided effective pressure reduction in specific areas.
- Anti-surge valves offered an alternative solution with comparable effectiveness to venting valves.
- Redesigning the support configuration is expected to address structural displacement issues, though further stress analysis is needed for validation.
While some areas may still require fine-tuning, the proposed modifications significantly improved system performance and brought the fire protection systems closer to full compliance with industry standards.
Lastly, by addressing these water hammer effects and improving compliance with industry standards, the fire protection systems achieved enhanced reliability, reduced risk of failure, and improved overall performance.
