Threaded connection for steel pipe

Abstract

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. αis a taper slope of the inner male thread, and αis 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.