Cooling Water Piping on a Dredger

Introduction

In this case, the client requested a surge analysis, and static and dynamic stress analysis for the cooling water lines including 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.

The pressure results for the pump trip scenario stayed within the allowable figures for the applicable piping. The pressure results for the valve closure scenario stayed within the allowable figures for the applicable piping. The valve closure scenario is based on a valve closure rate of 1 second per inch. The unbalanced load time histories will be implemented in the dynamic stress analysis.

The scope of stress analysis was limited to the fiberglass sections in the cooling water system. The stress analysis focused on the determination of the thrust loads at the stops, the pipe stress in the sections between stops and bulk-head penetrations, the lateral pipe stability, and, the supporting steel design. The unbalanced forces used in the dynamic analysis were obtained from the surge analysis results.

A static analysis has been performed to check if the initial supporting arrangement is correct. Further, a dynamic analysis has been performed to analyze the effects of the two surge scenarios on the system.

“Pressure results for a pump trip.”

Results

The pressure results for the pump trip scenario stayed within the allowable figures for the applicable piping. The valve closure scenario was based on a valve closure rate of 1 second per inch.
The dynamic analysis results showed that the following adjustments to the standard arrangement were required:

  • Three axial stops were removed due to the high axial loads resulting from these supports.
  • The axial stop in the offset near the ID450 branch was removed to decrease loads and stresses.

Deflections and the dynamic response were acceptable to the introduced recommendations.

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