A threaded connection for steel pipe is provided that improves its internal-pressure sealability while maintaining the high external-pressure sealability of a threaded connection having a nose used in a steel pipe with large diameter and large wall thickness. In a threaded connection for connecting steel pipe bodies each having an outer diameter equal to or larger than 7 inches and a wall thickness equal to or larger than 0.7 inches, Expression (1) in the description is satisfied and t.sub.B/t.sub.L>1.4, where δ [mm] is the clearance between the outer surface of the pin and the inner surface of the box upon make-up as measured at the borderline between the pin taper surface and the pin round surface, D [inch] is the outer diameter of the steel pipe body, t [inch] is the wall thickness of the steel pipe body, L [mm] is the distance between a pivot point, which is a position, in the region of contact between the pin sealing surface and the box sealing surface, which is closest to the tip of the pin, and the tip of the pin upon make-up as measured along the pipe-axis direction, t.sub.L [mm] is the wall thickness of the pin as measured at the pivot point, and t.sub.B [mm] is the wall thickness of the box as measured at the pivot point.

This invention provides a threaded connection for pipes or tubes having excellent misalignment resistance and high torque on shoulder resistance, and also having excellent corrosion resistance properties, as well as a method for producing the threaded connection for pipes or tubes. The threaded connection for pipes or tubes includes a pin and a box. The pin and the box include contact surfaces having threaded portions and unthreaded metal contact portions. The threaded connection for pipes or tubes includes, on at least one of the contact surfaces of the pin and the box, surface roughness, a Zn—Ni alloy plating layer, a Cu—Sn—Zn alloy plating layer and a solid lubricant coating layer. These are deposited from the contact surface side in the order of: surface roughness, the Zn—Ni alloy plating layer, the Cu—Sn—Zn alloy plating layer and the solid lubricant coating layer.

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.

A two-step threaded connection for steel pipe includes an intermediate seal and intermediate shoulders. A pin 2 has an inner male-threaded section 23 and an outer male-threaded section 26. A box 3 has an inner female-threaded section 33 and an outer female-threaded section 36. The pin 2 has a pin intermediate critical cross section PICCS located near an end of the first male-threaded section 23. The box 3 has a box critical cross section BCCS located near an end of the inner female-threaded section 33 and a box intermediate critical cross section BICCS located near an end of the outer female-threaded section 36. The pin 2 and the box 3 satisfy the following relationships:
PICCSA+BICCSA>BCCSA, and
0.70≤PICCSA/BICCSA≤0.95.

A tubular threaded joint for the drilling, the exploitation of hydrocarbon wells or the transport of oil and gas includes a male tubular element and a female tubular element. The female tubular element includes a female inner threaded portion and a female non-threaded portion. The male tubular element includes a male outer threaded portion and a male non-threaded portion. The male or female tubular element includes a body and an added portion by additive manufacturing that includes at least one first abutment surface.

This invention provides a threaded connection for pipes or tubes having excellent misalignment resistance and high torque on shoulder resistance, and also having excellent corrosion resistance properties, as well as a method for producing the threaded connection for pipes or tubes. The threaded connection for pipes or tubes includes a pin and a box. The pin and the box include contact surfaces having threaded portions and unthreaded metal contact portions. The threaded connection for pipes or tubes includes, on at least one of the contact surfaces of the pin and the box, surface roughness, a Zn—Ni alloy plating layer, a Cu—Sn—Zn alloy plating layer and a solid lubricant coating layer. These are deposited from the contact surface side in the order of: surface roughness, the Zn—Ni alloy plating layer, the Cu—Sn—Zn alloy plating layer and the solid lubricant coating layer.

The threaded joint includes a pin and a box. The pin includes a taper male thread part, and the box includes a taper female thread part to be engaged with the taper male thread part. The male thread part is divided into a first region on the free end side of the pin, and a second region on the tubular side of the pin along a tube axis direction. The taper ratio of the first region is greater than the taper ratio of the second region. The taper ratio of the first region is greater than the taper ratio of the female thread part. The taper ratio of the second region is equal to or greater than the taper ratio of the female thread part.

The disclosed threaded connection for steel pipes includes a pin including a tapered male thread part and a shoulder part, and a box including a tapered female thread part and a shoulder part. In a made up state in which the shoulder parts are in contact with each other, clearances are provided between crests of the male thread part and roots of the female thread part. At a longitudinal section that includes a pipe axis of the threaded connection, the crests of the male thread part are formed in a convex curve that is tangent to both first corner portions which are formed in an arc that connect the crests and load flanks, and second corner portions which are formed in an arc that connect the crests and stabbing flanks. A solid lubricant coating is provided on the surface of the male thread part.

An object of the present disclosure is to ensure good sealability in a threaded connection for steel pipe of a two-step thread construction including an intermediate seal and intermediate shoulders.

The pin 2 includes an intermediate seal section 22, an inner male-threaded section 23, an intermediate shoulder 24, an intermediate seal section 25 and an outer male-threaded section 26. The box 3 includes an intermediate seal section 32, an inner female-threaded section 33, an intermediate shoulder 34, an intermediate seal section 35 and an outer female-threaded section 36. The pin 2 has a pin intermediate critical cross section PICCS located near an end of the first male-threaded section 23. The box 3 has a box critical cross section BCCS located near an end of the first female-threaded section 33 and a box intermediate critical cross section BICCS located near an end of the second female-threaded section 36.

The pin 2 and the box 3 satisfy the following relationships:

PICCSA+BICCSA>BCCSA, and

0.70≤PICCSA/BICCSA≤0.95.

A threaded connection for large diameter steel pipe exhibits high torque resistance and high sealability and, at the same time, provides a shear resistance that suits the size of the steel pipe to be connected. The threaded connection includes a tubular pin provided on a tip of a steel pipe with large diameter, and a tubular box 20 adapted to be drawn up on the pin as the pin is screwed in. The pin includes a male threadform made with a taper thread. The box includes a female threadform made with a taper thread. Each of the threadforms are wedge threads and have a dovetail-shaped cross section. The male threadform is designed such that the width of the thread in an end region of the male threadform closer to the tip is set to a size corresponding to the size of the pipe body of the steel pipe.