Nippon Steel Corporation

Vallourec Oil and Gas France

Hikari Nakano

Masaaki Sugino

Keita Inose

Shin Ugai

A threaded connection for steel pipe is provided in which galling does not easily occur on any of the inner and outer threads. A threaded connection for steel pipeincludes a pinand a box. The pinincludes: a nose; a tapered inner male thread; a tapered outer male thread; a pin inner sealing surface; a pin intermediate shoulder surface; and a pin intermediate sealing surface. The boxincludes: a tapered inner female thread; a tapered outer female thread; a box inner sealing surface; a box intermediate shoulder surface; and a box intermediate sealing surface. Each of the inner male thread, outer male thread, inner female threadand outer female threadincludes a perfect thread portion. Each perfect thread portion includes an inner end located relatively close to the tip of the pinand an outer end located relatively close to the end of the pinopposite to its tip. The threaded connection for steel pipesatisfies the following Expressions (1) and (2):  (1), and  (2).

Threaded connection for steel pipe

A disclosed threaded connection for steel pipes includes a pin and a box. The pin includes, in order from a front end of the pin toward a pipe body of the pin, an annular shoulder surface, an annular sealing surface located adjacent to the shoulder surface, and a male thread part. The box includes, in order from a pipe body of the box toward a front end of the box, an annular shoulder surface, an annular sealing surface located adjacent to the shoulder surface, and a female thread part. The pin shoulder surface and the box shoulder surface incline from a plane perpendicular to a pipe axis in a direction of screwing the pin. A diameter of an inner circumferential edge of the pin shoulder surface is smaller than a diameter of an inner circumferential edge of the box shoulder surface.

Threaded connection for steel pipes

A two-step threaded connection for steel pipe includes an intermediate seal and intermediate shoulders. A pinhas an inner male-threaded sectionand an outer male-threaded sectionA boxhas an inner female-threaded sectionand an outer female-threaded sectionThe pinhas a pin intermediate critical cross section PICCS located near an end of the first male-threaded sectionThe boxhas a box critical cross section BCCS located near an end of the inner female-threaded sectionand a box intermediate critical cross section BICCS located near an end of the outer female-threaded section The pinand the boxsatisfy the following relationships:PICCSA+BICCSA&#x3e;BCCSA, and0.70&#x2264;PICCSA/BICCSA&#x2264;0.95.

A threaded connection for steel pipes is provided that exhibits improved sealability against the external pressure while maintaining the sealability against the internal pressure. A threaded connection for steel pipes includes a pin and a box. The pin includes a nose, a tapered inner male thread, a tapered outer male thread, a pin inner sealing surface, a pin intermediate shoulder surface, a pin intermediate sealing surface, and a pin annular portion. The box includes a recess corresponding to the nose, a tapered inner female thread, a tapered outer female thread, a box inner sealing surface, a box intermediate shoulder surface, a box intermediate sealing surface, and a box annular portion. The threaded connection satisfies expressions (1) and (2), provided below. &#x3b1;is a taper slope of the inner male thread, and &#x3b1;is a taper slope of the outer male thread.  In expression (2), Lis a distance between the tip of the pin and the pin intermediate shoulder surface as measured along the pipe-axis direction when the pin and box have not been made up, and Lis a distance between the box intermediate shoulder surface and the tip of the box as measured along the pipe-axis direction when the pin and box have not been made up.

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Tokyo, Japan

Hikari Nakano