Seal welding of titanium tubes to titanium tube sheets

In thermal and nuclear power plants, no-leakage condensers are attempted by means of all titanium structure. As for the problems of jointing the Ti tubes to the Ti tube sheets in this case, seal welding, especially the welded joint characteristics influenced by working conditions, have been investigated. (1) The best welded joint is obtained by first expanding the tube, then making seal welding. Tube expansion also acts as tacking, and prevents the gas absorption through gaps between the sheet and tubes. (2) By the use of double shield, the oxidation discoloring and gas absorption of the weldment can be prevented. However, torch shield alone provides with sufficient strength despite the discoloring. (3) In the case of thin-walled Ti tubes, in order to obtain good welding, it is necessary not to retract the tubes from the tube sheet in tube expansion, with proper tube protrusion. (J.P.N.)