JPS566729A - Production of steel pipe having high collapse strength for oil well - Google Patents

Abstract

PURPOSE: To improve the roundness of a steel pipe, decrease its residual stress and obtain its high collapse strength by warm straightening the steel pipe then evenly cooling it in a state of not allowing the steel pipe to bend.

CONSTITUTION: The temperature of a steel pipe is raised to the specified tempering temperature conforming to the material of the steel pipe, after which it is warm- straightened while being held at the tempering temperature of ≥150°C. The steel pipe having undergone the warm straightening is sent to an even cooling device, where it is so placed as to ride on the skew rolls 25, 26 on both sides across these. Both skew rolls 25, 26 revolve at an equal speed in the same direction and while the steel pipe P is also revolved in the same direction, it is transferred in the arrow direction, during which time it receives the jet fluid from a nozzle 27 evenly over its entire outside circumferential surface and is cooled over its entire part at an even temperature at the specified rate of cooling, thus it is cooled down to an ordinary temperature without causing bending. These improve the roundness of the steel pipe while maintaining its straightness, prevent the decrease in yield ratio due to a Bauschinger effect and enhances its collapse strength considerably.

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