Mechanical Analysis and Design of Press-Fit Interlocking Joints for Thin-Walled Pipes

Urso A. Campos, Louisiana Tech University


Interlocking pipe joints have been utilized in the Trenchless Technology (TT) industry for over 20 years. This technology allows a pipe segment with a notched male end to be joined to a pipe segment with a notched female end by pressing them together using axial force, eliminating the need for circumferential welding of the segments and consequently decreasing the construction time. Although industry familiarity with these joints is well established, the mechanics of the interlocking process has received little attention in the literature.

This study explores the mechanics of uniform, press-fit joints, discussing general topics such as contact pressures, stresses and strains, engage and disengage forces, and elastic and plastic material behavior. Once a firm mechanical background has been established for uniform press-fit joints, the adaptability of press-fits to join thin-walled steel pipes is explored. The study uncovers the mechanics and the relationships among geometric parameters such as pipe diameter, thickness, interference, and joint length. The aim of this study is to (1) gain an in-depth understanding of the mechanics of the press-fit interlocking system for thin-walled pipes, and (2) offer valuable tools that aid in the design of pipe joints that may lead to the optimization of geometric parameters.

Two simplified equations applicable to thin-walled rings and pipes to calculate contact pressure and hoop stress are presented with the purpose of simplifying the analysis of press-fit joints. In addition, three simplified equations to calculate the force required to assemble press-fit rings and pipes are provided. The equations estimate the assembly force within, resulting from both elastic and elastic/plastic materials’ behavior as well as the insertion force due to initial contact of joint members. Experimental and finite element results for assembly and disassembly of steel press-fit interlocking joint are presented and discussed. Additionally, a set of guidelines and recommendations to design press-fit and interlocking joint is provided based on the findings previously discussed. This work concludes with an interlocking joint prototype based on the insight gained throughout the study.