Threaded connection for steel pipe
View Patent ↗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. α 1 is a taper slope of the inner male thread, and α 2 is a taper slope of the outer male thread. α 1 > α2 , and ( 1 ) 0.5 ≦ L 1 α1 L 2 α2 ≦ 1.2 ( 2 ) In expression (2), L 1 is 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 L 2 is 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.
1. A threaded connection for steel pipe, comprising:
a tubular pin; and
a tubular box adapted to be made up on the pin as the pin is screwed in,
wherein the pin includes:
a nose provided at a tip portion of the pin;
a tapered inner male thread located close to a tip of the pin, the inner male thread provided on an outer periphery of the pin;
a tapered outer male thread located close to a body of the steel pipe, the outer male thread provided on the outer periphery of the pin;
a pin inner sealing surface provided between the nose and the inner male thread;
a pin intermediate shoulder surface provided between the inner male thread and the outer male thread;
a pin intermediate sealing surface provided between the outer male thread and the pin intermediate shoulder surface; and
a pin annular portion provided between the pin intermediate shoulder surface and the pin intermediate sealing surface,
the box includes:
a recess corresponding to the nose;
a tapered inner female thread corresponding to the inner male thread, the inner female thread provided on an inner periphery of the box;
a tapered outer female thread corresponding to the outer male thread, the outer female thread provided on the inner periphery of the box;
a box inner sealing surface facing the pin inner sealing surface, the box inner sealing surface being in contact with the pin inner sealing surface when the pin and the box have been made up;
a box intermediate shoulder surface facing the pin intermediate shoulder surface, the box intermediate shoulder surface being in contact with the pin intermediate shoulder surface when the pin and the box have been made up;
a box intermediate sealing surface facing the pin intermediate sealing surface, the box intermediate sealing surface being in contact with the pin intermediate sealing surface when the pin and the box have been made up; and
a box annular portion facing the pin annular portion, the box annular portion being apart from the pin annular portion when the pin and the box have been made up,
the threaded connection satisfying the following expressions (1) and (2):
α1>α2 (1),
in expression (1), α 1 is a taper slope of the inner male thread, and α 2 is a taper slope of the outer male thread, and
0.5
≦
L
1
α1
L
2
α2
≦
1.2
,
(
2
)
in expression (2), L 1 is 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 the box have not been made up, and L 2 is 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 the box have not been made up.
2. The threaded connection for steel pipe according to claim 1 , wherein the pin further includes: a pin inner shoulder surface provided on the tip of the pin, and
the box further includes: a box inner shoulder surface facing the pin inner shoulder surface.
3. The threaded connection for steel pipe according to claim 2 , wherein the pin inner shoulder surface is in contact with the box inner shoulder surface when the pin and the box have been made up.
4. The threaded connection for steel pipe according to claim 3 , satisfying the following expression (4):
A
2
A
0
≧
0.3
,
(
4
)
in expression (4), A0 is a cross-sectional area of the body of the steel pipe along a plane perpendicular to the pipe axis, and A2 is a total of the projected area of the pin inner shoulder surface and the projected area of the pin intermediate shoulder surface on a plane perpendicular to the pipe axis.
5. The threaded connection for steel pipe according to claim 2 , satisfying the following expression (4):
A
2
A
0
≧
0.3
,
(
4
)
in expression (4), A0 is a cross-sectional area of the body of the steel pipe along a plane perpendicular to the pipe axis, and A2 is a total of the projected area of the pin inner shoulder surface and the projected area of the pin intermediate shoulder surface on a plane perpendicular to the pipe axis.
6. The threaded connection for steel pipe according to claim 1 , satisfying the following expression (3):
A
1
A
0
≧
0.3
,
(
3
)
in expression (3), A0 is a cross-sectional area of the body of the steel pipe along a plane perpendicular to the pipe axis, and A1 is a projected area of the box intermediate shoulder surface on a plane perpendicular to the pipe axis.