An exhaust pipe system comprising at least one exhaust pipe coaxially surrounded by least two combustion air pipes (20, 21) disposed edge to edge, their circumferential joint being surrounded by a pipe clamp for engaging around a circumferential joint between two axially adjacent combustion air pipes (20, 21) of an exhaust pipe system of a heating system, the pipe clamp having a contact ring for contacting circumferential surfaces (13, 14) of the two combustion air pipes (20, 21) and being tightened around the combustion air pipes (20, 21) by means of fixation means, the contact ring having a first and a second free end portion (3, 4) for opening the contact ring for installation purposes, and an overlap section at the end of the first end portion overlapping a tongue at the end of the second end portion in the circumferential direction on the radial outside in the installed state, the overlap section covering the tongue in both axial directions (7, 8) in the installed state and having a contact surface (11, 12) on each of the two axial sides of the tongue and being supported on the outer circumferential surfaces of the combustion air pipes (20, 21) on both sides of the joint axially adjacent to the tongue by means of a respective contact surface (11, 12), at least part of an inner surface of the contact ring having a groove in the circumferential direction, the groove serving to engage around pipe end flanges which are formed at least at part of the joint of the combustion air pipes (20, 21) and extend in the circumferential direction, the groove having at least one inlet slope extending from the contact surface (11, 12) to a groove base in the axial direction, the joint having at least two axially contacting pipe end flanges (17, 18) at least partially extending in the circumferential direction, the inlet slope forming a cone seal in cooperation with at least one pipe end flange (17, 18) and the at least one pipe end flange (17, 18) having an at least partially conical tapering on a side facing away from the pipe end. the overlap section covering the tongue in both axial directions (7, 8) in the installed state and having a contact surface (11, 12) on each of the two axial sides of the tongue and being supported on the outer circumferential surfaces of the combustion air pipes (20, 21) on both sides of the joint axially adjacent to the tongue by means of a respective contact surface (11, 12), at least part of an inner surface of the contact ring having a groove in the circumferential direction, the groove serving to engage around pipe end flanges which are formed at least at part of the joint of the combustion air pipes (20, 21) and extend in the circumferential direction, the groove having at least one inlet slope extending from the contact surface (11, 12) to a groove base in the axial direction, the joint having at least two axially contacting pipe end flanges (17, 18) at least partially extending in the circumferential direction, the inlet slope forming a cone seal in cooperation with at least one pipe end flange (17, 18) and the at least one pipe end flange (17, 18) having an at least partially conical tapering on a side facing away from the pipe end.