Evolution law of dynamic response of buried bolt flange pipeline structure under multiple blasting vibrations

To address the safety operation issues of in-service buried bolted flange pipelines subjected to repeated blasting vibrations, a combined approach of refined model testing and numerical simulation was adopted. A model test system for investigating the blasting dynamic response of bolted flange cast iron pipelines was established, and ten blasting tests were conducted. The axial strain characteristics of the bolts, as well as the strain characteristics of the pipe body and flange, were analyzed. Based on the model tests and their results, a numerical model for the blasting dynamic response of buried bolted flange pipelines was established using the LS-DYNA dynamic finite element software. The wear theory model was employed to simulate bolt loosening, enabling multiple blasting cycle calculations. The response characteristics of vibration velocity, stress, and flange rotation angle of the buried bolted flange pipelines were analyzed. The results indicated that the peak vibration velocity along the pipeline axis gradually increase from the two ends toward the center. The blasting vibrations cause bolt loosening, with the peak resultant velocity of the bolts increasing slightly as the number of blasting cycles increase. Furthermore, increasing the preload is observed to decrease the peak resultant velocity of the bolts. Stress concentration occurs at the connection between the pipe body and the flange, with a maximum effective stress of 157.5 MPa. Stress concentration is also observed at the connection between the nuts, bolts, and flanges, with a maximum effective stress of 151.4 MPa. A marked stress redistribution in the bolts is observed after blasting. The stress on the opposite side of the bolts is significantly lower than that on the blasting side. The axial pressure on the blasting side of the spacer increase, while that on the opposite side decrease. Flange rotation manifests as compression on the blasting side and tension on the opposite side. The flange at Bolt 1# on the blasting side exhibits the largest rotation, with a flange rotation angle of 0.029°.