The above-ground seawater supply header is designed to transport seawater from two tie-ins in a discharge manifold of the seawater pumps to AGA. A comprehensive static stress analysis was necessary to determine the stress levels within the Glass Reinforced Epoxy (GRE) line. Additionally, it was crucial to define a support arrangement that would effectively stabilize the line and keep the stress within allowable limits.
Analysis
The static stress analysis of the line was conducted using the CAESAR II pipe stress analysis software, adhering to ISO 14692 standards. The flange assessment was performed based on the equivalent pressure method. Unbalanced loads due to pressure surges, calculated by a third party, were integrated into the analysis. Multiple combinations of these surge loads were examined to ensure the most critical scenarios were considered.
Given that the surge analysis was conducted by another group, several iterations were necessary. DRG collaborated closely with the client to ensure the analysis was completed efficiently.
Results
The analysis revealed that the length of the DN700 pipe, along with the fixed points on one side and the guide on the other, resulted in relatively high stresses at the bends on the ends. By repositioning the guide slightly further from the bend, these stresses were reduced to within allowable limits.
Additionally, the GRE piping could not accommodate the pressure thrust of the expansion bellow in the system. To prevent damage to the pipe from pressure thrust, a bellow with tie-rods was selected. While straightening the pipe near the bellow was an alternative solution, it was not feasible due to an underlying pipe.
To minimize the stresses in the pipe, the support arrangement was modified to accommodate the surge loads. By implementing these modifications and updating the supports, the system conformed to stress and load requirements.
The static stress analysis of the seawater supply header, utilizing CAESAR II and adhering to ISO 14692 standards, successfully identified and mitigated high-stress points. The strategic repositioning of the guide and the selection of a bellow with tie-rods ensured the integrity of the GRE piping. The updated support arrangement effectively minimized stress and accommodated surge loads, ensuring the system met all necessary requirements.
