Threaded joint for steel pipes

A threaded joint for steel pipes, comprising:

• a tubular pin and a tubular box, the pin and the box being made up by screwing the pin onto the box,
• the pin comprising:
• in order from an end of the pin, a shoulder surface;
• a seal surface;
• and a male threaded portion, the male threaded portion being a tapered threaded portion with trapezoidal threads,
• the box comprising:
• a shoulder surface corresponding to the shoulder surface of the pin;
• a seal surface corresponding to the seal surface of the pin;
• and a female threaded portion corresponding to the male threaded portion of the pin, the female threaded portion being a tapered threaded portion with trapezoidal threads,
• the male threaded portion including:
• crests;
• roots;
• stabbing flanks;
• and load flanks, the stabbing flanks being in a leading position in the screwing of the male threaded portion into the female threaded portion, the load flanks being located opposite from the stabbing flanks,
• the female threaded portion including:
• roots facing the crests of the male threaded portion;
• crests facing the roots of the male threaded portion;
• stabbing flanks facing the stabbing flanks of the male threaded portion;
• and load flanks facing the load flanks of the male threaded portion,
• the load flanks of the male threaded portion and the load flanks of the female threaded portion having a flank angle that is less than 0 degrees,
• the female threaded portion being composed of:
• in order from near the seal surface of the box, an incomplete thread section;
• and a complete thread section,
• wherein:
• in the female threaded portion, over an entire area thereof including the incomplete thread section and the complete thread section, the roots collectively define a single tapered periphery having a single taper angle over the entire area including the incomplete thread section and the complete thread section,
• the incomplete thread section has a length along the pipe axis, the length being at least three times a thread pitch of the female threaded portion, and the incomplete thread section has a thread height lower than a thread height of the complete thread section, and
• in a made-up state:
• the shoulder surfaces are in contact with each other, and the seal surfaces are in contact with each other;
• in the complete thread section, the roots of the male threaded portion are in contact with the crests of the female threaded portion, and the load flanks of the male threaded portion are in contact with the load flanks of the female threaded portion;
• and in the incomplete thread section, clearances are provided between the roots of the male threaded portion and the crests of the female threaded portion, and the load flanks of the male threaded portion are in contact with the load flanks of the female threaded portion.