In the Expansion Joint design project for gas transmission lines, the main focus has been on developing a reliable solution to increase the safety and stability of the transmission network. This equipment has been designed in such a way that it can absorb changes caused by thermal expansion and contraction, vibrations and mechanical displacements of the pipeline without creating destructive stresses. In this project, in addition to the detailed modeling of the assembly in the SolidWorks environment, structural details including metal jumpers, flanges, braces and the movement limiting system have been designed taking into account the functional requirements and manufacturability. The result of this process is an engineered product with high reliability that plays an effective role in increasing the life of the equipment, reducing maintenance costs and maintaining the stability of gas transmission lines.