Optimized design of large-diameter directly buried heating pipe

Abstract The elbow of a large-diameter directly buried hot water heating pipeline is the weak part of the whole pipe system. The foam cushion is often used to reduce the stress on the elbow. However, the foam cushion raises the temperature on the outer protective pipe’s surface, which may trigger thermal stress damage to the pipes. In this paper, the insulating pipe at the elbow section is designed with a variable diameter. The numerical simulation of the thermal stress for the outer protective pipe and the working pipe was conducted. The maximum stress for the outer protective pipe is about 3 MPa, and the average stress for the working pipe is 83 MPa, much smaller than the yield stress. Combined with the simulation results, the design ensures the reliability of the elbow and provides a reference for the design of large-diameter and high-temperature heat transfer pipelines.