Cooling method of a steel pipe

Abstract

A method of cooling a steel pipe which can effectively suppress quenching-induced bending which occurs when quenching a thin-walled steel pipe with a wall thickness/outer diameter ratio of at most 0.07 without decreasing the manufacturing efficiency of the steel pipe comprises cooling the inner surface of the steel pipe by spraying cooling water into the interior of a horizontally-disposed steel pipe 2 while rotating the pipe in its circumferential direction, and the outer surface is cooled by producing a downward flow of cooling water streams 5 a and 5 b in a planar shape from above onto the outer surface along the axial direction of the steel pipe 2 . Cooling of the inner surface is started at least 7 seconds before cooling of the outer surface. Cooling of the outer surface is carried out by producing downward flow in a planar shape of cooling water 5 a and 5 b at two locations 4 a and 4 b at approximately equal distances from the uppermost portion of the steel pipe 2 , and the flow rate of cooling water 5 a which flows down at a location on the upstream side in the rotational direction of the steel pipe 2 is made larger than the flow rate of cooling water 5 b which flows down at a location on the downstream side in the rotational direction.

1 . A method of cooling a steel pipe in which the inner surface and the outer surface of a horizontally-disposed steel pipe are cooled while the steel pipe is rotated in its circumferential direction, characterized in that
 cooling of the inner surface of the steel pipe is carried out by spraying cooling water inside the steel pipe,   cooling of the outer surface of the steel pipe is carried out by producing downwards flow of cooling water in a planar shape along the axial direction onto the outer surface of the steel pipe from above at two locations approximately equal distances from the uppermost portion of the steel pipe on both sides of the uppermost portion, wherein the flow rate of cooling water which flows downwards at a location on the upstream side in the rotational direction of the steel pipe is equal to or greater than the flow rate of cooling water which flows downwards at a location on the downstream side in the rotational direction, and   cooling of the inner surface of the steel pipe is started at least 7 seconds before cooling of the outer surface of the steel pipe.   
   
   
       2 . A method of cooling a steel pipe as set forth in  claim 1  wherein the ratio of the wall thickness to the outer diameter of the steel pipe is at most 0.07.