The tube has a rigid shaft (1) which is attached with an end-fitting (15) and cooled so as to shield it from corrosion and melt. The end-fitting houses a thermocouple (9) on an end of the tube and is constructed from a noble metal which is resistant to corrosion and high melting point. Alumina coatings separate the shaft and the end-fitting which are concentric, where the shaft and end-fitting are pressed one on the other and on both sides of the coatings by soldering points.
