Introduction
In this case study, we encountered undesirable vibrations in the downstream line of an angle control valve within a wash oil line. Initially, the upstream wash oil boasted a pressure of 150 bar and a temperature of 400°C. However, downstream of the valve, there was a significant pressure drop to 9 bar, while the temperature remained constant at 400°C. Additionally, the vapor/gas content accounted for 2% of the total mass flow under these conditions. Given these observations, DRG was engaged to investigate and mitigate the vibrations within the system.
Analysis
Upon analysis, it became evident that the vibration amplitude escalated alongside an increase in flow rate. To dive deeper into the potential causes of these vibrations and to devise appropriate remedial measures, a computer model of the system was developed. This model aimed to identify the most probable excitation mechanism and evaluate the dynamic loads expected within the existing situation.
The initial model’s predictions regarding vibration levels and the probable excitation mechanism closely aligned with the observed vibrations. However, for enhanced accuracy, the model required fine-tuning using data obtained from vibration measurements conducted on-site.
Results
- Subsequent examination revealed that the tee within the system bore the highest stress.
- It was determined that an increase in the desired mass flow rate to 5700 tonnes per day could yield an expected fatigue life of 6 years.
- However, it was recommended that future increases in mass flow rate, particularly to 4900 tonnes per day, necessitate modifications to the pipe support arrangement.
“The supporting in the model was modified to improve the dynamic piping response.”
To address these recommendations, modifications were made to the support arrangement in the model, aimed at enhancing the dynamic response of the piping. Following the implementation of these modified support arrangements, a notable improvement in vibration levels was observed for the same excitation mechanism.
