Large amplitude vibrations in a process line have resulted in damage to several pipe supports. DRG was engaged to identify the root cause of these vibrations, assess potential fatigue issues, and recommend remedial actions for the client.
Analysis
DRG performed a comprehensive visual inspection to determine the resonance modes being excited by the vibrations. The client provided vibration measurements, which allowed DRG to analyze the amplitude and frequency of these vibrations. Using CAESAR II software, DRG constructed a detailed model of the piping system. By utilizing the dynamic solver features in CAESAR II, the team was able to replicate the observed vibrations’ frequency and amplitude within the model.
To identify the likely cause of the vibrations, DRG calculated the unbalanced force amplitude required to produce the observed vibration levels. This analysis enabled the team to evaluate the likelihood of various mechanisms contributing to the issue.
Results
The analysis indicated that the vibrations were primarily caused by density fluctuations in the fluid. These variations led to inconsistent forces acting on the bends in the piping system, creating a net force on the pipe supports. The damage to the supports resulted in a loss of proper support, which, in turn, increased the primary loads on the piping system significantly. DRG recommended repairing the pipe supports to restore their original design and functionality.
A fatigue assessment was performed in accordance with the ASME B&PV code’s fatigue limits. This assessment revealed that several tees in the system were at risk of fatigue failure. To mitigate the vibrations and prevent further issues, DRG advised the installation of additional axial stops within the system.
Conclusions
Through visual inspections, vibration measurements, and detailed modeling, DRG successfully identified the cause of the vibrations and their impact on the piping system. The recommendations for support repairs and axial stop installations aim to address both the immediate vibration issues and potential long-term fatigue concerns, ensuring the stability and reliability of the process line.
