A threaded connection for pipes includes a pin, a box, a shoulder part plating layer, and a non-shoulder part plating layer. The shoulder part plating layer has an outermost layer formed of a high friction coefficient plating layer, and is arranged on a pin side shoulder part and/or a box side shoulder part. The non-shoulder part plating layer has an outermost layer formed of a low friction coefficient plating layer having a coefficient of friction lower than a coefficient of friction of the high friction coefficient plating layer, and the non-shoulder part plating layer is arranged on at least one of a pin side thread part, a pin side metal seal part, a box side thread part, and a box side metal seal part.

A threaded connection for pipes includes a pin, a box, a shoulder part plating layer, and a non-shoulder part plating layer. The shoulder part plating layer has an outermost layer formed of a high friction coefficient plating layer, and is arranged on a pin side shoulder part and/or a box side shoulder part. The non-shoulder part plating layer has an outermost layer formed of a low friction coefficient plating layer having a coefficient of friction lower than a coefficient of friction of the high friction coefficient plating layer, and the non-shoulder part plating layer is arranged on at least one of a pin side thread part, a pin side metal seal part, a box side thread part, and a box side metal seal part.

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.

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.

A connector assembly includes a first connector, a compression member, a retainer, and a second connector. The first connector includes a first coupling portion, a proximal opening, and an annular inner surface extending from the proximal opening. The compression member includes an inner surface and an outer surface. The outer surface is configured to sealingly engage the annular inner surface of the first connector. The retainer includes a ring portion and a plurality of teeth. The ring portion includes a proximal end and a distal end. Each of the plurality of teeth extends from the distal end and is configured to engage the compression member. The second connector includes a second coupling portion and an engagement surface. The second coupling portion is configured to engage the first coupling portion. The engagement surface is configured to engage the proximal end of the retainer.

A connector assembly includes a first connector, a compression member, a retainer, and a second connector. The first connector includes a first coupling portion, a proximal opening, and an annular inner surface extending from the proximal opening. The compression member includes an inner surface and an outer surface. The outer surface is configured to sealingly engage the annular inner surface of the first connector. The retainer includes a ring portion and a plurality of teeth. The ring portion includes a proximal end and a distal end. Each of the plurality of teeth extends from the distal end and is configured to engage the compression member. The second connector includes a second coupling portion and an engagement surface. The second coupling portion is configured to engage the first coupling portion. The engagement surface is configured to engage the proximal end of the retainer.

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 pipe 1 includes a pin 10 and a box 20. The pin 10 includes: a nose 12; a tapered inner male thread 14; a tapered outer male thread 17; a pin inner sealing surface 13; a pin intermediate shoulder surface 18; and a pin intermediate sealing surface 16. The box 20 includes: a tapered inner female thread 24; a tapered outer female thread 27; a box inner sealing surface 23; a box intermediate shoulder surface 28; and a box intermediate sealing surface 26. Each of the inner male thread 14, outer male thread 17, inner female thread 24 and outer female thread 27 includes a perfect thread portion 141, 171, 241, 271. Each perfect thread portion includes an inner end located relatively close to the tip of the pin 10 and an outer end located relatively close to the end of the pin 10 opposite to its tip. The threaded connection for steel pipe 1 satisfies the following Expressions (1) and (2):

x.sub.1+L.sub.1<X.sub.2  (1), and

u.sub.1+L.sub.2<U.sub.2  (2).

A sealing device is provided for use with a fitting. The fitting has circular port and a flow path with a longitudinal axis. A circular port encircles a portion of the flow path opposite the port with the sealing device inserted into the port. The sealing device has a circular top with two opposing surfaces depending therefrom but inclined so the surfaces are closer at the top. A continuous sidewall joins the periphery of the two surfaces. The opposing surfaces are inclined and spaced apart further at the top than at an end opposite the top. A cylindrical hole through the opposing surfaces encircles the flow path during use.

A sealing device is provided for use with a fitting. The fitting has circular port and a flow path with a longitudinal axis. A circular port encircles a portion of the flow path opposite the port with the sealing device inserted into the port. The sealing device has a circular top with two opposing surfaces depending therefrom but inclined so the surfaces are closer at the top. A continuous sidewall joins the periphery of the two surfaces. The opposing surfaces are inclined and spaced apart further at the top than at an end opposite the top. A cylindrical hole through the opposing surfaces encircles the flow path during use.

A threaded connection for steel pipe that provides high torque performance, high tension performance and high sealability is provided. A threaded connection 1 includes: a tubular pin 10 including a pin shoulder 12, a male thread 11 and a pin seal 13; and a tubular box 20 including a box shoulder 22, a female thread 21 and a box seal 23. The male and female threads 11 and 21 are constituted by wedge threads. The pin seal 13 is provided between the pin shoulder 12 and the male thread 11. The box seal 23 corresponds to the pin seal 13 and is located on the inner peripheral surface of the box 20. When the connection is made up, the pin shoulder 12 is spaced apart from the box shoulder 22. The threaded connection 1 satisfies the following expression, (1):

3%≤(LP−SP)/LP≤7%   (1).

In expression (1), LP is the pitch between loading flanks 111 of the male thread 11, and SP is the pitch between stabbing flanks 112 of the male thread 11.