Nippon Steel Corporation

Kyohei Murata

Kazushi Maruyama

Haruyuki Nagayoshi

Fujio Ohkubo

Etuji Kajiki

Junichi Hayashi

Heiji Morise

Hiroshi Tamaki

Yoichi Yazaki

Nobuyuki Mizushima

A method and apparatus for cooling at least the inside of steel pipes. Cooling is effected while restraining the radial displacement of a pipe at a point not more than 500 mm, or preferably not more than 250 mm, away from each end of the pipe and at intermediate points spaced at intervals of 1.0 m to 2.5 m. Elliptical deformation in the cross section of larger-diameter pipes also is prevented by adding to the aforementioned cooling method and apparatus a device and step to rotate the pipe being cooled at a rate of 30 to 150 times per minute. The restraining device at one end of the pipe is designed to move in the direction of the pipe axis so that the restraint of the radial displacement at a point not more than 500 mm away from that end is at all times ensured even when the pipe length varies.

Apparatus for cooling steel pipe

Quenched steel pipe is first held at a tempering temperature for a given period of time, then cooled relatively rapidly. While carrying the pipe in the direction of its length, cooling water is sprayed from outside onto its external surface at an average water flux of not lower than 0.05 m.sup.3 /min.m.sup.2 and not higher than 2 m.sup.3 /min.m.sup.2. This cooling is started when the pipe temperature is between 400.degree. C. and 700.degree. C. and ended between room temperature and 350.degree. C. Also, the cooling is effected at a mean cooling rate of not lower than 5.degree. C./sec. and not higher than 40.degree. C./sec. This cooling method improves the collapse strength of a pipe by providing an appropriate tensile residual stress to the internal surface of the pipe and reduces the cooling floor area without sacrificing the collapse strength of the pipe.

Method of cooling steel pipes

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Kitakyushu, Japan

Kyohei Murata