METHOD FOR COOLING STEEL TUBE

PROBLEM TO BE SOLVED: To provide a method for cooling a steel tube in which glow deflection generated when quenching a thin steel tube having e.g. ≤0.07 (t/D) ratio of thickness to outer diameter, can effectively be restrained without lowering the producing efficiency. SOLUTION: The inner surface of the steel tube 2 is cooled by spraying cooling water into the inner part while rotating the steel tube 2 set horizontally in the circumferential direction and also, the outer surface thereof is cooled by flowing down the plane-like cooling waters 5a,5b from the upper part onto the outer surface along the axial direction of the steel tube 2. At this time, the cooling of the outer surface is performed by flowing down the plane-like cooling waters 5a,5b to almost symmetrical two positions 4a,4b centering the most upper part of the steel tube 2, respectively. Then, the flow of the cooling water 5a which flows down to the position at the upstream side in the rotating direction of the steel tube 2, is more than that of the cooling water 5b which flows down to the position at the downstream side in the rotating direction, and the ratio of the thickness to the outer diameter of the steel tube to be cooled, is ≤0.07 and also, the cooling of the inner surface is started by preceding ≥7 sec before the cooling of the outer surface. COPYRIGHT: (C)2008,JPO&INPIT