A gas metering skid is being designed for use in a flow station. DRG was commissioned by a client to conduct a comprehensive noise and vibration study of the metering skid to assess its vulnerability to fatigue failure. The potential for fatigue failure arises if the mechanical resonance modes of the metering skid are excited. Possible excitation mechanisms include upstream sources such as compressors, acoustic resonance within the metering skid, or vortex shedding from tees.
Analysis
To determine the mechanical resonance frequencies of the metering skid, a piping model was developed using CAESAR II, a widely used software for piping analysis. The dynamic module of CAESAR II was employed to identify the dynamic resonance frequencies. While CAESAR II is effective at identifying beam-type resonance modes, it is limited in its ability to detect higher-order resonance modes associated with the shell of the piping, known as breathing modes. To address this, theoretical predictions were utilized.
Acoustic and Mechanical Resonance Assessment
The study demonstrated that vibrations of the metering skid induced by potential upstream vibration sources conformed to the fatigue limits specified in the ASME B&PV code. It was found that while acoustic resonance modes within the piping of the metering skid could potentially excite mechanical resonance modes, the amplitude of pressure oscillations did not result in stresses exceeding the fatigue limits set by the ASME B&PV code.
DRG utilized the vibration limits proposed in the VDI 3842 to conduct a vibration analysis in accordance with the ASME B&PV code. The analysis revealed that pressure oscillations in the fluid, caused by vortex shedding from the tees, had the potential to induce fatigue failure in the piping. To mitigate the risk of fatigue problems, a recommendation was made regarding the layout of the downstream piping.
Conclusion
The noise and vibration analysis of the metering skid revealed that while certain conditions could lead to potential fatigue issues, the design parameters and recommendations provided ensure compliance with industry standards. The assessment effectively addressed potential sources of excitation and provided actionable insights to enhance the durability and reliability of the metering skid.
