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 fastened by screwing the pin onto the box,
• the pin comprising, in order from a tubular body having the pin toward a free end thereof:
• a tapered male threaded portion with dovetail threads;
• and a lip portion including a sealing surface,
• the box comprising:
• a tapered female threaded portion with dovetail threads corresponding to the male threaded portion of the pin;
• and a recessed portion corresponding to the lip portion, the recessed portion including a sealing surface,
• wherein,
• the lip portion includes, in order from the male threaded portion toward the free end of the pin:
• a neck portion;
• and a sealing head portion including the sealing surface,
• the sealing surface is disposed on a region in the sealing head portion, the region having a maximum outside diameter that is larger than an outside diameter of the neck portion at a boundary between the neck portion and the male threaded portion,
• the sealing head portion has an inside diameter that is smaller than an inside diameter of the tubular body, and
• the lip portion has an inner peripheral surface, the inner peripheral surface including, in order from the free end of the pin:
• a tapered surface increasing in diameter toward the free end of the pin;
• a cylindrical surface that is continuous with the tapered surface;
• and
• an inside tapered surface decreasing in diameter toward the free end of the pin
• wherein,
• the neck portion has an outer peripheral surface, the outer peripheral surface being a cylindrical surface, and
• the sealing head portion has an outer peripheral surface, the outer peripheral surface including:
• a tapered surface that is continuous with the outer peripheral surface of the neck portion and increases in diameter at an angle in a range of 5° to 20° with respect to the pipe axis;
• a cylindrical surface that is continuous with the tapered surface;
• and the sealing surface, the sealing surface including a curved surface that is continuous with the cylindrical surface and a tapered surface that decreases in diameter toward the free end of the pin.