Application of the finite element method for evaluating the stress distribution in buried damaged polyethylene gas pipes

Abstract

During the loading process, buried gas pipes can experience severe stresses due to soil- structure interaction, the presence of traffic load, the soil’s column weight, daily and/or seasonal temperature changes and uniform internal pressure. In this research, the finite element method is employed to evaluate the behavior of buried Medium Density Polyethylene (MDPE) pipes which have been subjected to damage at the pipe crown. The modeled pipe damage ranges from a very small circular hole to a large circular hole and elliptic holes with various minor to major diameter ratios, a/b, to simulate circular to crack-shaped defects. The computer simulation and stress analyses were performed using the ANSYS software finite element package. The stress distribution around the defect was determined under the aforementioned mechanical and thermal loading conditions. Then, the maximum values of Von Mises stresses in the damaged buried PE pipes, which were evaluated by finite element solution, were compared with their corresponding reduced strength for safe operation with a life expectancy of fifty years. Based on the results, the maximum Von Mises stress values in the defective buried polyethylene gas pipeline are significantly above the pipe strength limit at 35 °C. The previously mentioned stress values increase with the following factors: temperature increase, increase in circular hole diameter and decrease in elliptic hole diameter ratio (a/b). The maximum stress in the damaged PE pipe is due to the simultaneous loading effects of soil column weight, internal pressure, vehicle wheel load and pipe temperature increase. Additionally, the novel finite element models and stress plots for the buried damaged pipe and the pipe material allowable strength will be used to investigate the correct repair method for the damaged gas pipeline and to choose the best patch arrangement which will assure a safe repair.