Finite-Element Modeling of the Dynamic Behavior of a Crack-like Defect in an Internally Pressurized Thin-Walled Steel Cylinder

Abstract

This article presents one part of a study on the dynamic deformation and fracture of sections of steel gas pipelines with an external crack-like defect under the action of internal pressure. This work was performed on the basis of finite-element simulations using a cylindrical shell model executed by ANSYS-19.2 on the example of the section of the steel gas pipeline “Beineu–Bozoy–Shymkent” in the Republic of Kazakhstan. The propagation of the incipient crack-like defect along the pipeline and the resulting dynamic fracture in its tip area were investigated. The options of pipeline loading by working and critical internal pressure were both considered. It was found that, within the time of 1.0 ms, the formed crack expanded in the circumferential direction up to the maximum value, which depended on the value of the internal pressure. A further growth of cracks occurred along the longitudinal direction. At the operating pressure, the initial length of the crack increased by a factor of 5.6, while the equivalent stresses increased by a factor of 1.53 within 3.5 ms. Within the time of 3.75 ms, the equivalent stresses stopped growing due to the gas decompression. Specifically, there was a stop to the crack growth along the longitudinal direction. Vice versa, at the maximum pressure, the pipeline fracture did not change qualitatively, while at the time of the process, it decreased up to 3.5 ms. The finite-element results of the stress–strain state and pipeline fracture in the crack tip area at the working pressure showed that, within the time of 1.0 ms, the distance between the crack walls reached 23 mm at the free edge. Conversely, within the time periods of 2.25 and 3.5 ms, it increased two and three times, respectively. The crack elongation in the longitudinal direction occurred 5.8 times with time. Together, within the time of 3.5 ms, the equivalent stresses increased twice, after which the growth of the crack stopped due to the gas decompression. Moreover, studies on the growth of the crack-like defect in its tip area at the maximum pressure showed that additional considerations on the pressure on the crack edges led to an increment of 3.6% of the crack length. The results of this work can be used for the development of measurements for operating gas pipelines in the field of structural reinforcement.

Keywords

• crack-like defect
• damaged area
• fracture
• finite-element
• shell model
• steel gas pipeline