PSI - Issue 45

Aditya Khanna et al. / Procedia Structural Integrity 45 (2023) 12–19 Khanna and Young / Structural Integrity Procedia 00 (2019) 000 – 000

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Table 3. Range of parameters simulated in FE study.

Nozzle bore (ID)

Vessel wall thickness

RFLWN flange class

Fixed Dimensions Vessel OD: 700 mm Vessel height: 2800 mm Dependant Dimensions

1” (25 mm) 2” (51 mm) 3” (76 mm) 4” (102 mm)

0.5” (12.8 mm) 0.75” (19 mm)

150 300 600 900

1” (25 mm)

Nozzle length = 1.5x Nozzle OD (dependant on nozzle bore size and flange class)

1.25” (32 mm)

1500

Fig. 6. (a) FE model geometry showing the position of the nozzle on the pressure vessel, (b-c) mode shape for the vertical and lateral vibration modes, respectively, and (d-e) maximum principal stress contours due to harmonic force input at resonant frequencies. 3. Results and Discussion An inverse power law relationship was assumed between the allowable displacement amplitude and the natural frequency of the nozzle, resulting in a best fit exponent of -0.62 in Fig. 7. The obtained exponent is close to the exponent of -0.50 used in the empirical SWRI guidelines and the exponent of -0.52 when the EI guidelines are expressed in the units of peak-peak displacement. Hence, the results of the parametric FE study suggest that Energy Institute (EI) guidelines, are more suitable for assessing vibration severity on pressure vessel nozzles than constant vibration velocity criteria, such as the ISO 20816-8. This outcome is also in agreement with the recommendations of another recent study (Bifano et al., 2018), which suggest the use of EI guidelines for assessing vibration severity on cantilevered small-bore fittings. In fact, the FE results presented herein demonstrate that the lower bound of the stress-based allowable vibration calculations assuming a BS7608 Class D weld detail (design stress of 53 MPa) is roughly equivalent to the EI Problem curve.