Threaded connection for steel pipes

1. A threaded connection for steel pipes comprising a tubular pin and a tubular box, wherein

the pin includes, in the order from a free end side of the pin toward a tubular body side thereof, an inner sealing surface, an inner male threaded portion, a shoulder portion, an outer male threaded portion, and an outer sealing surface,

the box includes, in the order from a tubular body side of the box to the free end side thereof, an inner sealing surface, an inner female threaded portion, a shoulder portion, an outer female threaded portion, and an outer sealing surface,

the threaded connection includes at least one of the following configurations (1) and (2):

(1) an inner groove along a circumferential direction is provided between the inner sealing surface and the inner female threaded portion of the box, and some threads of the inner male threaded portion of the pin are contained in the inner groove, the inner groove including at least one of a tapered surface that is adjacent to the inner sealing surface and decreases in diameter as the tapered surface extends to the inner sealing surface and a tapered surface that is adjacent to the inner female threaded portion and decreases in diameter as the tapered surface extends to the inner female threaded portion, and

(2) an outer groove along a circumferential direction is provided between the outer sealing surface and the outer male threaded portion of the pin, and some threads of the outer female threaded portion of the box are contained in the outer groove, the outer groove including at least one of a tapered surface that is adjacent to the outer sealing surface and decreases in diameter as the tapered surface extends to the outer sealing surface and a tapered surface that is adjacent to the outer male threaded portion and decreases in diameter as the tapered surface extends to the outer male threaded portion, and

the outer sealing surface of the pin and the outer sealing surface of the box are tapered.

2. The threaded connection for steel pipes according to claim 1 , wherein

when the configuration (1) is provided, a length along a pipe axis of the inner groove of the box is larger than a thread pitch of the inner female threaded portion, and

when the configuration (2) is provided, a length along a pipe axis of the outer groove of the pin is larger than a thread pitch of the outer male threaded portion.

3. The threaded connection for steel pipes according to claim 2 , wherein

when the configuration (1) is provided, the length along a pipe axis of the inner groove of the box is not more than 4 times of the thread pitch of the inner female threaded portion, and

when the configuration (2) is provided, the length along a pipe axis of the outer groove of the pin is not more than 4 times of the thread pitch of the outer male threaded portion.

4. The threaded connection for steel pipes according to claim 1 , wherein

when the configuration (1) is provided, a depth of the inner groove of the box is not less than a thread height of the inner female threaded portion, and not more than twice the thread height, and

when the configuration (2) is provided, a depth of the outer groove of the pin is not less than a thread height of the outer male threaded portion, and not more than twice the thread height.

5. The threaded connection for steel pipes according to claim 1 , wherein

an outer diameter of the box is not more than 110% of an outer diameter of the tubular body of the pin.

6. The threaded connection for steel pipes according to claim 1 , wherein

a threaded portion consisting of the inner male threaded portion and the inner female threaded portion, and a threaded portion consisting of the outer male threaded portion and the outer female threaded portion are each a tapered thread of buttress type.

7. The threaded connection for steel pipes according to claim 6 , wherein

each of the tapered threads includes crests, roots, stabbing flanks, and load flanks,

the crests of the inner male threaded portion and the roots of the inner female threaded portion are in contact with each other, and the load flanks of the inner male threaded portion and the load flanks of the inner female threaded portion are in contact with each other,

the roots of the outer male threaded portion and the crests of the outer female threaded portion are in contact with each other, and the load flanks of the outer male threaded portion and the load flanks of the outer female threaded portion are in contact with each other.

8. The threaded connection for steel pipes according to claim 1 , wherein

regarding the inner groove, the tapered surface that is adjacent to the inner sealing surface has a taper angle not less than 1° , and the tapered surface that is adjacent to the inner female threaded portion has a taper angle not less than 5° .

9. The threaded connection for steel pipes according to claim 1 , wherein

regarding the inner groove, the tapered surface that is adjacent to the inner sealing surface has a taper angle not more than 50° , and the tapered surface that is adjacent to the inner female threaded portion has a taper angle not more than 45° .

10. The threaded connection for steel pipes according to claim 1 , wherein

regarding the outer groove, the tapered surface that is adjacent to the outer sealing surface has a taper angle not less than 1° , and the tapered surface that is adjacent to the outer male threaded portion has a taper angle not less than 5° .

11. The threaded connection for steel pipes according to claim 1 , wherein

regarding the outer groove, the tapered surface that is adjacent to the outer sealing surface has a taper angle not more than 50° , and the tapered surface that is adjacent to the outer male threaded portion has a taper angle not more than 45° .