Stress Analysis Review of Critical Fire Water System Sections

In this case study, a number of critical sections in an already installed fire water system were selected for review. At the time of the analysis, earlier on-site interventions had already been made, motivated by pipe failures. The analysis aimed to determine if additional interventions were necessary.


Based on the isometric drawings, a number of critical sections were identified and analyzed using the piping analysis software CAESAR II. A selection process revealed typical layouts and designs for these critical sections. An important aspect of the analysis was the sensitivity of the piping to settlements, especially of thrust blocks.

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The analysis results showed that thrust blocks had been adequately sized concerning pressure thrust. Furthermore, it was observed that stress problems did not occur in piping that had been joined using coupling joints. For one critical section where coupling joints were used, the effect of settlement of thrust blocks was examined. It was concluded that piping with coupling joints is not sensitive to this problem due to the additional flexibility provided by the joints.The most critical observations from the analysis were:

  • The occurrence of high stresses at the elbows directly below the hydrants.
  • The occurrence of high stresses in the case of settlements of thrust blocks.
  • The occurrence of high stresses in the case of settlements of the concrete slabs supporting the hydrants.

It was shown in this assessment that the settlement of thrust blocks may be the main reason for high-stressed regions to occur. However, based on the knowledge that most settlement of thrust blocks would occur in the period immediately following installation, and the fact that no such failure had occurred after the last on-site intervention, a large-scale preventative intervention was not deemed necessary.

Key Takeaways

  • Periodic stress analysis reviews are essential for identifying critical sections in existing piping systems.
  • Piping analysis software like CAESAR II can evaluate stresses in complex piping configurations.
  • Thrust block settlements and support settlements can significantly impact piping stresses.
  • Coupling joints can provide additional flexibility and reduce stress concentrations.
  • On-site interventions may be necessary to address high-stressed regions, depending on the severity and risk.
  • Combining analysis results with operational data and failure history is crucial for informed decision-making.

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