Inspectioneering Journal

Troubleshooting Vibration of an Overhead Piping System in a Gas Condensate Plant with FEA and CFD - Part 2 of 2

By Aslam Kittur, P.Eng., Operations Engineering Specialist at Saudi Aramco. This article appears in the January/February 2023 issue of Inspectioneering Journal.
This article is part 2 of a 2-part series.
Part 1 | Part 2


Part 1 of this two-part series on troubleshooting vibration of an overhead piping system (published November/December 2022) detailed the overall assessment methodology along with the qualitative, quantitative, and visual assessments which laid the foundation for the specialized predictive techniques presented in this article.

Specialist Measurement Techniques (TM-07 and TM-08)

Vibration measurements were taken in the field during each of the throughputs of 225 MBD, 245 MBD, and 250 MBD, and compared for the three locations shown in Figure 1.

Figure 1. Location of Field Vibration Survey.
Figure 1. Location of Field Vibration Survey.

The velocity readings give a more uniform weighting over the required range and are most directly related to the resulting dynamic stress. They were therefore used as vibration measurements for the analysis, as shown in Tables 12, and 3 [1]. The piping vibration criticality assessment and velocity graph for the above readings were plotted as shown in Figure 2. From this plot, the nature of the vibrations was found to move from the “Acceptable” region during the normal flow rates at 225 MBD to the region of “Concern” at 250 MBD.

Table 1. Point 1 (Velocity and Frequency).
Flow 250 MBD 245 MBD 225 MBD
Spectrum RMS in/sec Hz RMS in/sec Hz RMS in/sec Hz
Horizontal 0.2434  8.7500 0.1852 8.7500  0.1688  19.380
Vertical  0.2506 6.8750 0.1981 6.8750  0.2307 8.750
Axial  0.1314 8.7500 0.0906 19.3800 0.0852 19.380 


Table 2. Point 2 (Velocity – RMS in/sec).
Flow 250 MBD 245 MBD 225 MBD
Spectrum RMS in/sec Hz RMS in/sec Hz RMS in/sec Hz
Horizontal  0.0725 5.0000 0.0639  5.0000  0.0631  5.000
Vertical 0.0918  5.0000  0.0585 5.0000   0.0561 8.750
Axial  0.0750 4.3750  0.0553 3.7500 0.0519 4.3750


Table 3. Point 3 (Velocity – RMS in/sec).
Flow 250 MBD 245 MBD 225 MBD
Spectrum RMS in/sec Hz RMS in/sec Hz RMS in/sec Hz
Horizontal 0.2679  8.7500 0.2008   8.7500 0.1995  8.750 
Vertical  0.2478  5.0000 0.1984    5.0000 0.1789    5.000
Axial 0.0948   6.2500 0.0773  8.7500 0.0793  18.750

The most significant factors were attributed to the increased flow rates due to debottlenecking studies being carried out on gas condensate fractionation plants, resulting in higher flow velocities with a correspondingly greater level of turbulent energy in process systems. The excitation was found to be broadband (i.e., energy is input over a wide frequency range) in our case, as shown in Figure 3.

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