disk in the embodiment of fig3 a to 3 d the disk is placed in position fig3 a and a first plenum section put into position between two aerofoils 14 fig3 b an adjacent plenum 32 is then placed in position to surround the aerofoil 14 fig3 c once both plenums have been correctly located it is possible to attach the heaters not shown and flow manifolds thereto each plenum section is shaped to lie close to the aerofoil without touching each of the plenums has a plurality of apertures for directing the heated gas to the respective aerofoil preferably each of the plenums is shaped such that it seals against the adjacent plenum so that the heating gas is directed along the blade towards the root or tip once the system has been fully constructed it is possible to turn the gas on and supply the heating fluid to the aerofoil fig3 d for the heat treatment of contaminant sensitive components it is desirable that the structure is constructed in a tightly controlled inert atmosphere environment the manipulation of the components for the construction described can be done using gloves mounted in the side of the unit and which are hermetically sealed on the chamber minimising oxygen ingress to a predetermined part per million ppm level as mentioned above the system can be configured to exhaust the spent gas either towards the root of aerofoils in which case a baffle system may be required to protect the root regions from attaining too high a temperature or it can exhaust down the bottom of the system out of the head unit region in a vertical manner.