High speed heating of multilayer tubes - using both hot combustion gases and electric resistance heating

摘要

The tubes possess several layers, and/or consist of several rings butt-welded together; they are heated in a furnace using both the circulation of hot combustion gases and also electric resistance heating. At the start of resistance heating, the gas is pref. at the temp. of the tube, but is gradually heated to the desired final temp. of the tube. The gas pref. travels in a closed circuit at a speed which increases during the resistance heating of the tube. Rapid and accurate heating, e.g. of tubes with a wall thickness above 15 mm. and several metres in length.