Effect of Peak Excitation Frequency on Seismic Fatigue Damage of Plant Pipelines

In a previous report, a new method of calculating the approximate seismic cumulative fatigue damage of plant pipelines was developed, in which the sum of the cumulative absolute velocities (CAV) of the pipeline response per cycle was calculated, and the result was applied to the allowable vibration velocity described in the ASME Operation and Maintenance (O/M) code 2012. The new method provided a conservative value of cumulative fatigue damage. In this present study, a parameter showing the effect of a concentrated mass attached to the tip of a cantilever pipe was obtained as a function of the ratio of the concentrated mass to the mass of the cantilever pipe by eigenmode calculation using ABAQUS. In the previous report, the new method was based on the relative response of the pipeline, whereas in this present study, the application of the method was expanded to evaluations using the CAV of the excitation input for each cycle. We conducted the fast forward simulation of a real earthquake to determine the effect of the peak frequency change on cumulative fatigue damage, and we found that the response of cumulative fatigue damage at the peak frequency tends to decrease with increasing peak excitation frequency, which was consistent with the results obtained using the previously reported new method. Both the new method and the newly expended method are based on the ASME O/M code, and the results obtained by these methods suggest that the peak frequency tends to affect general pipelines. In the calculations, when the configuration of the pipeline is fixed and the mode shape does not change, the cumulative fatigue damage was found to decrease with increasing peak frequency of input acceleration. If the mode shape changes with the peak input acceleration frequency, then cumulative fatigue damage is affected. Moreover, if the participation factor has a larger value in a higher mode, the cumulative fatigue damage also has a larger value.