Threaded connection for steel pipe

A threaded connection for steel pipe, comprising:

• a tubular pin;
• and
• a tubular box, the pin being screwed into the box such that the pin and the box are made up,
• the pin including:
• a tapered inner male thread provided on an outer periphery of the pin and located adjacent to a tip of the pin;
• a tapered outer male thread provided on the outer periphery of the pin and located adjacent to an end of the pin opposite to the tip;
• and
• a pin intermediate shoulder surface located between the inner male thread and the outer male thread,
• the box including:
• a tapered inner female thread provided on an inner periphery of the box to correspond to the inner male thread;
• a tapered outer female thread provided on the inner periphery of the box to correspond to the outer male thread;
• and
• 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 are made up,
• wherein each of the inner male thread, the outer male thread, the inner female thread and the outer female thread includes a perfect thread portion, and each of the perfect thread portions includes an inner end located adjacent to the tip of the pin and an outer end located adjacent to the end of the pin opposite to the tip,
• the pin and the box, when made up, have a longitudinal cross section containing an axis of the steel pipe, and an orthogonal coordinate system introduced in the longitudinal cross section has an x-axis represented by the axis of the steel pipe, a y-axis represented by a radius of the steel pipe, and an origin (0,0) represented by an intersection of (a), a plane containing the pin intermediate shoulder surface and the box intermediate shoulder surface and (b) the axis of the steel pipe, and
• the threaded connection satisfies the following expressions, Expressions (1) and (2):
• x1+L1<X2 (1), and
• u1+L2<U2 (2),
• where, in Expressions (1) and (2),
• L
• 1
• =
• (
• β
• pi
• -
• β
• bi
• )
• α
• pi
• ,
• ⁢
• L
• 2
• =
• (
• β
• po
• -
• β
• bo
• )
• α
• po
• ,
• ⁢
• α
• pi
• =
• y
• 2
• -
• y
• 1
• x
• 2
• -
• x
• 1
• ,
• ⁢
• α
• po
• =
• v
• 2
• -
• v
• 1
• u
• 2
• -
• u
• 1
• ,
• ⁢
• β
• pi
• =
• -
• x
• 1
• ⁢
• y
• 2
• +
• x
• 2
• ⁢
• y
• 1
• x
• 2
• -
• x
• 1
• ,
• ⁢
• β
• po
• =
• -
• u
• 1
• ⁢
• v
• 2
• +
• u
• 2
• ⁢
• v
• 1
• u
• 2
• -
• u
• 1
• ,
• ⁢
• β
• bi
• =
• -
• X
• 1
• ⁢
• Y
• 2
• +
• X
• 2
• ⁢
• Y
• 1
• X
• 2
• -
• X
• 1
• ,
• and
• β
• bo
• =
• -
• U
• 1
• ⁢
• V
• 2
• +
• U
• 2
• ⁢
• V
• 1
• U
• 2
• -
• U
• 1
• ,
• (x1,y1) denote the coordinates of the inner end of the perfect thread portion of the inner male thread;
• (x2,y2) denote the coordinates of the outer end of the perfect thread portion of the inner male thread;
• (u1,v1) denote the coordinates of the inner end of the perfect thread portion of the outer male thread;
• (u2,v2) denote the coordinates of the outer end of the perfect thread portion of the outer male thread;
• (X1,Y1) denote the coordinates of the inner end of the perfect thread portion of the inner female thread;
• (X2,Y2) denote the coordinates of the outer end of the perfect thread portion of the inner female thread;
• (U1,V1) denote the coordinates of the inner end of the perfect thread portion of the outer female thread;
• and
• (U2,V2) denote the coordinates of the outer end of the perfect thread portion of the outer female thread.