| 摘要 |
PURPOSE:To increase the strength of piping effectively, by heating the piping at a uniform temp., then by heating its outer surface at a temp. higher than that at which its inner surface is heated. CONSTITUTION:A piping 2 is heated by a coil 3 connected to an induction current oscillator 1. In the middle of heating step, the heating is once discontinued at a temp. of whole piping of about 200 deg.C so as to keep small the yield stress of the material of the piping 2. Then the piping is heated again by the heating coil 3 and hot water or air, which indicates comparatively small cooling effect, is passed through the piping, hereby temp. difference of about 200-450 deg.C is developed between the outer and inner surfaces of the piping 2. This temp. difference produces tensile yield and compression yield respectively in the inner and outer surfaces of the piping. When the whole piping is returned to the room temp., compressive residual stress is produced on the inner surface of the piping, so that the strength of the piping 2 is increased. |
