A recuperator to be located in the exhaust duct of a gas turbine engine having a compressor section, a combustor section and a turbine section with a gas exhaust duct downstream of the turbine section, the recuperator comprising: a casing containing at least a core made up of spiral cross channels for the passage of hot gases from the turbine section in heat exchange relationship with pre-combustion stage air, the casing having a circular configuration relative to the axis of the spiral core; inlet and outlet openings defined in the casing for the passage of hot exhaust gases through the exhaust gas channels in the core, wherein the casing is defined by a thin wall interrupted by an expansion portion of the thin wall, allowing the thin wall to expand or contract in response to at least one of thermal stresses and vibrations; feeder members extending radially across the outlet opening for passing the air through the air channels of the core and radially from an axial center of the core to the periphery of the casing; header members extending radially across the inlet opening of the casing and radially from an axial center of the core to the periphery of the casing for receiving and redirecting air from the air channels in the core towards the combustor section, the feeder and header members each having an inverse tapered configuration relative to the axial center of the casing so as to maintain a relatively constant pressure over the radial extent of the respective feeders and headers; and an outer casing surrounding and being spaced apart from the casing surrounding the core, to form air passage ducts leading to the core, wherein the outer casing is defined by a thin wall interrupted by an expansion portion of the thin wall, allowing the thin wall to expand and contract in response to at least one of thermal stresses and vibrations. a casing containing at least a core made up of spiral cross channels for the passage of hot gases from the turbine section in heat exchange relationship with pre-combustion stage air, the casing having a circular configuration relative to the axis of the spiral core; inlet and outlet openings defined in the casing for the passage of hot exhaust gases through the exhaust gas channels in the core, wherein the casing is defined by a thin wall interrupted by an expansion portion of the thin wall, allowing the thin wall to expand or contract in response to at least one of thermal stresses and vibrations; feeder members extending radially across the outlet opening for passing the air through the air channels of the core and radially from an axial center of the core to the periphery of the casing; header members extending radially across the inlet opening of the casing and radially from an axial center of the core to the periphery of the casing for receiving and redirecting air from the air channels in the core towards the combustor section, the feeder and header members each having an inverse tapered configuration relative to the axial center of the casing so as to maintain a relatively constant pressure over the radial extent of the respective feeders and headers; and an outer casing surrounding and being spaced apart from the casing surrounding the core, to form air passage ducts leading to the core, wherein the outer casing is defined by a thin wall interrupted by an expansion portion of the thin wall, allowing the thin wall to expand and contract in response to at least one of thermal stresses and vibrations.