THREADED CONNECTION FOR PIPES

FIELD: screw-threaded joints. ^ SUBSTANCE: threaded connection comprises steel pipe, whose end is provided with male thread and sealing surface without thread, and coupling, whose inner side is provided with female thread and sealing surface without thread. When the inner surface of the pipe is pressed by the pressure Py, the mean pressure Pm on the ring section of the contact is Pm/Py >=3, and the width of the section in axial direction that undergoes the pressure Ps (Ps/Py >=1) in the ring contact section is no less than 1 mm. The roughness of the surface Ry of both of the sealing surfaces without the thread is no more than 25 mum. The relationship between the mean pressure Pm of the ring section of the contact and roughness of the sealing surface Ry (mum) without the thread is Pm/Py >= 0.0324(Ry)2 + 1.0. The width of the section in axial direction that undergoes pressure Ps that fits a formula Ps/Py >= 1 in the ring contact section is no less than 1 mm. ^ EFFECT: enhanced reliability. ^ 6 cl, 7 dwg