Stress Analysis of Pressure Equalizing Piping in Reactor Systems

This case study discusses the results of a stress analysis conducted on the external section of the pressure equalizing piping at a reactor. The analysis aimed to ensure the integrity and safety of the system under various operational conditions.


In the external part of the existing pressure equalizing piping, a stainless steel bellow had been incorporated to enhance flexibility. However, bellows can present potential issues. Therefore, a decision was made to explore replacing the bellow with a rigid pipe that would still offer sufficient flexibility through its layout design. To achieve this, several optional layout configurations and two different materials—aluminum and stainless steel—were evaluated.

The external pipe content was safeguarded by a “lead-castle” structure surrounding the pipe. The size of this lead castle limited the possible geometrical configurations. To ensure sufficient flexibility and allow for the application of welding neck flanges, the existing layout was modified while remaining within the constraints of the lead castle. The revised configuration was modeled using the CAESAR II software and verified according to paragraph NC-3650 of Section III of the ASME Boiler and Pressure Vessel Code.


The analysis showed that for both aluminum and stainless steel, the stress on the pipe and the loads on the flanges remained within allowable limits for all applicable load cases, including those involving earthquakes. This confirmed that the selected geometry would perform adequately under the expected conditions.

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