Threaded connection for steel pipe

A threaded connection for steel pipe, comprising:

• a tubular pin formed by one tip portion of a steel pipe;
• and
• a tubular box adapted to be made up on the pin as the pin is inserted into the box, the pin including:
• a pin shoulder provided on the tip portion of the pin, the pin shoulder having a toroidal surface;
• a male thread provided on an outer peripheral surface of the pin, the male thread being a wedge thread;
• and
• a pin seal provided between the pin shoulder and the male thread, the pin seal being provided on the outer peripheral surface of the pin, the box including:
• a box shoulder corresponding to the pin shoulder and provided on an innermost face of the box, the box shoulder having a toroidal surface;
• a female thread corresponding to the male thread and provided on an inner peripheral surface of the box, the female thread being a wedge thread;
• and
• a box seal corresponding to the pin seal and provided on the inner peripheral surface of the box,
• wherein the pin shoulder is spaced apart from the box shoulder when the pin and the box have been made up, and
• the threaded connection satisfies the following expression, (1):
• 3% (LP−SP)/LP≤7% (1),
• where, in expression (1), LP is the pitch between loading flanks of the male thread, and SP is the pitch between stabbing flanks of the male thread.