An ammonia plant in Australia has experienced recurring failures in its cooling water systems since its commissioning in the mid-2000s. The plant utilizes two primary cooling systems: a Sea Cooling Water (SCW) system and a Fresh Cooling Water (FCW) system. The SCW system, with a high capacity, consists of multiple pumps and primarily underground composite piping. The FCW system, a secondary closed-loop system, also employs underground composite piping. This project aimed to review the design of these systems, identify weaknesses in materials and design, and propose potential improvements to enhance system reliability and performance.
Technical Challenges in SCW and FCW System Design
The technical challenges faced by the cooling water systems at the ammonia plant were multifaceted:
- The SCW system has experienced significant failures, particularly in above-ground sections, due to overstressed piping and material deficiencies.
- The FCW system has also encountered failures, though to a lesser extent.
- Specific issues include:
- Certain pipes failing to meet design pressure levels.
- Stress and surge conditions exceeding allowable limits in both systems.
- Structural weaknesses in piping supports, thrust blocks, and branch connections.
The redesign must align with ISO14692 guidelines and maintain consistency between basic and detailed engineering stages. Material selection for the redesign depends on the supplier, which will influence detailed engineering.
Step-by-Step Review of Design and Performance Issues
The design review study employed a comprehensive approach to analyze the existing systems and identify potential solutions:
- Review of existing design documents, hydraulic studies, and structural design studies.Â
- Analysis of material properties, load conditions, and boundary conditions.Â
- Stress and surge analyses to evaluate the performance of the SCW and FCW systems under various operating conditions.Â
- Iterative modeling and reanalysis of the systems to identify weaknesses and propose solutions.
- Consideration of alternative routing, material reinforcements, and prefabrication options for faster installation.Â
Analysis of SCW and FCW System Failures
The analysis revealed several critical issues within both the SCW and FCW systems:
- Sea Cooling Water System
- Certain pipes were overstressed and failed to meet the required design pressure levels.
- High stresses were found at heat exchanger connections due to the absence of tie rods in expansion joints.
- Wind loads and thermal expansion contributed to overstress in specific sections, particularly in above-ground atmospheric pipes.
- Fresh Cooling Water System
- Surge pressures occasionally exceeded the design pressure for certain pipe types.
- Stress issues were concentrated at small-diameter branch connections due to limited flexibility.
Engineering Solutions for SCW and FCW System Reliability
Based on the analysis, the following solutions were proposed to address the identified issues:
- Replace underperforming pipes with materials capable of withstanding design pressures.
- Reinforce existing materials where possible to reduce costs.
- Introduce tie rods in expansion joints to mitigate pressure thrust.
- Improve support arrangements for above-ground sections and thrust blocks for underground sections.
- Use flexible polystyrene wrapping around branch connections to reduce bending stress in the FCW system.
- Consider alternative routing and prefabrication options for faster installation.
Improving Reliability in Industrial Cooling Systems
The design review study of the cooling water systems at the ammonia plant has revealed significant material and design deficiencies that have led to multiple system failures since commissioning. The SCW system, in particular, has been severely affected by overstressed piping and inadequate pressure ratings, while the FCW system has shown vulnerabilities in surge pressure handling and stress distribution at branch connectionsÂ
The proposed solutions offered a comprehensive approach to rectifying these issues, with a focus on improving system reliability, ensuring compliance with industry standards, and enhancing overall performance.
By implementing the recommended changes and maintaining a proactive approach to system monitoring and maintenance, the ammonia plant can expect to see significant improvements in the reliability and efficiency of its cooling water systems, ultimately leading to enhanced plant performance and reduced operational disruptions.
