Threaded connection

A threaded connection including a tubular pin and a tubular box, the pin and the box being made up as the pin is screwed into the box,

• the pin including:
• a male thread provided on an outer periphery of the pin and constituted by a tapered thread with a diameter gradually decreasing toward a tip;
• a pin inner sealing surface provided on the outer periphery of the pin and located further toward the tip than the male thread;
• a nose located further toward the tip than the pin inner sealing surface and having an outer peripheral surface smoothly contiguous to the pin inner sealing surface;
• a torque shoulder surface formed by a tip face of the nose;
• and a pin outer sealing surface provided on the outer periphery of the pin and located further toward a basement than the male thread,
• the box including:
• a female thread provided on an inner periphery of the box and adapted to be in engagement with the male thread when the connection is made up;
• a box inner sealing surface provided on the inner periphery of the box and adapted to be in contact with the pin inner sealing surface when the connection is made up;
• a threadless portion having an inner peripheral surface facing the outer peripheral surface of the nose such that these surfaces are arranged in a radial direction and leave a clearance when the connection is made up;
• a torque shoulder surface facing the torque shoulder surface of the pin such that these surfaces are arranged in an axial direction, the torque shoulder surface being in contact with the torque shoulder surface of the pin when the connection is made up;
• and a box outer sealing surface provided on the inner periphery of the box and adapted to be in contact with the pin outer sealing surface when the connection is made up,
• the male thread and the female thread being constructed such that,
• when the connection is made up, a clearance is formed between a stab flank of the male thread and a stab flank of the female thread when no axial compression load is applied and, when a predetermined axial compression load acts on the threaded connection, the pin and the box elastically deform such that the stab flank of the male thread and the stab flank of the female thread come into contact such that some of the axial compression load is transmitted between these stab flanks,
• the pin outer sealing surface and the box outer sealing surface being shaped such that, when the pin as made up on the box is pushed into the box by an axial compression load in a direction of the tip, the box sealing surface increases its diameter, wherein a shoulder angle is not smaller than 0° and smaller than 10°,
• the shoulder angle being defined as the angle formed by a plane perpendicular to the pipe axis and a straight line passing through a radially outer edge and a radially inner edge of the torque shoulder surface of the box as viewed in a longitudinal cross section, where a positive angle means that the radially outer edge is located further toward the tip than the radially inner edge.