PURPOSE: To secure sealing ability in hot working, by shrinkage fitting together outer and inner pipe stocks, having different linear thermal coefficients of expansion respectively, to seal their top parts by welding, and projecting the pipe stock, having the smaller coefficient of expansion, at their bottom parts to bulge it in the edge direction of the other pipe end.
CONSTITUTION: A cylindrical inner pipe stock 2 having a large linear thermal coefficient of expansion is inserted into the inside space of a cylindrical outer pipe stock 1, having a small linear thermal coefficient of expansion, by shrinkage fitting. The T side, the top of this billet at the time of hot working, is sealed 4 by welding. On the other hand, at the B side, the bottom of this billet, the end of outer pipe 1 is projected from the end of inner piper 2, and the inner peripheral surface 3 of its projected part (e) is bulged from the end-edge contact position P of pipe 2 to the direction of inner pipe stock 2. In this way, the invasion of air into between the outer and inner pipe stocks is properly prevented at the time of hot working, and moreover its manufacturing process is simplified.
FURUKAWA HIDETOSHI
ARAI SEIICHI
TERAOKA KOZO
