Introduction
This case involved fulfilling a client’s request to perform a surge analysis and static and dynamic stress analysis about the cooling water lines and associated supporting steel on a dredger.
Analysis
The objective of the surge analysis was to define the cooling water flow rates during a steady state and the unbalanced loads during several upset scenarios. The upset scenarios considered were a pump trip scenario and a valve closure scenario.
Results from the pump trip scenario demonstrated that pressure levels remained within acceptable thresholds for the relevant piping specifications. Similarly, the pressure results from the valve closure scenario adhered to allowable limits, with the scenario based on a valve closure rate of 1 second per inch. The time histories of unbalanced loads derived from these scenarios were integrated into the dynamic stress analysis.
The stress analysis focused primarily on fiberglass sections within the cooling water system. It encompassed assessing thrust loads at stops, pipe stress along sections between stops and bulkhead penetrations, lateral pipe stability, and the design of supporting steel. Unbalanced forces derived from the surge analysis were utilized in the dynamic stress analysis.
A static analysis was conducted to validate the adequacy of the initial supporting arrangement, followed by a dynamic analysis to evaluate the impact of the surge scenarios on the system.
“Pressure results for a pump trip.”
Results
Pressure results from the pump trip scenario remained within allowable limits for the applicable piping. The valve closure scenario, based on a specified closure rate, also yielded pressure results within acceptable parameters.
The dynamic analysis results showed that the following adjustments to the standard arrangement were required:
- Removal of three axial stops due to excessive axial loads.
- Elimination of the axial stop in the offset near the ID450 branch to alleviate loads and stresses.
Overall, deflections and dynamic responses aligned with the introduced recommendations, ensuring acceptable system performance.
