To prevent thickness deviation in the peripheral direction after stretch reduction by making temp. deviation in the peripheral direction at the time of starting stretch reduction fall into a proper range.
In this method, a pressure-welded steel tube 10 is heated by adjusting feeding quantity of heat in each part in the peripheral direction corresponding to the temp. distribution in the peripheral direction of the pressure- welded steel tube 10. To decrease the feeding quantity of heat to a high-temp. region 11 including the joined part of the pressure-welded steel tube 10, the distance between the heat source 13 of the heating device 12 which is opposite to the high-temp. region 11 and the high-temp. region 11 is made larger than the distance in each different part in the peripheral direction of the tube. Or, the output of the heat source 13 of the heating device 12 which is opposite to the high-temp. region 11 may be reduced that in each different part in the peripheral direction of the tube. The feeding quantity of heat may be reduced by inserting a radiation preventing plate between the heat source 13 of the heating device 12 and the high-temp. region 11.
KAGAWA MASAHIRO
SAWADA KINGO
SUGANO KOJI
SUGIE YOSHINORI
ONISHI TOSHIO
