Abstract: The duct slide bearing plates are used to reduce the friction force as the duct expands and contracts under temperature variations, but can not be used for seismic isolation without the re-centering capability. In this paper, a double concave friction pendulum system (DCFP) with tri-linear hysteretic behavior is adopted for the gas duct both for thermal displacement and seismic isolation. The seismically isolated duct is modeled as a three-degree-of-freedom system in the transverse direction. The first order state space formulation of the equations of motion is derived, and the theoretical analysis is verified by the finite element analysis. Then the effects of the DCFP on a gas duct and its hysteretic behavior are investigated under various earthquake excitations. Comparing with a duct without the seismic isolation, the reaction force on the DCFP and the shear force on the pier are both greatly reduced.