To provide a threaded joint having excellent tensile performance and airtightness after compression load and further with high resistance to loosening torque by specifying the load face flank angle and insert face flank angle of a thread, and setting the positive thread inteference quantity between an external thread and an internal thread.
A threaded joint for an oil well pipe is formed of a taper thread and provided with a pin part 11 with an external thread and a box part 21 with an internal thread, and these parts 1, 21 are provided with seal forming unthreaded parts to constitute a seal part. Torque shoulder forming unthreaded parts provided at the tip of the pin part 11 and the box part 21 are made butt each other to form a torque shoulder part. In this case, the load face flank angle α of the thread is set to be not less than -20° and less than 0°, and an insert face flank angle θ is to be more than 30° and not more than 60°. Positive thread interference quantity is provided between the external thread and internal thread so that the load face and insert face of the external and internal thread come in mutual contact during and after fastening so as to form a clearance between the top face and the bottom face.
NARITA AKIRA
MAEDA ATSUSHI
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