Abstract: During conditions of use of a threaded joint comprising a box portion and a pin portion used to threadingly join oil well pipes, the stress acting on the outer surface of the box portion is prevented from exceeding the yield strength of the base metal of the joint, and the occurrence of stress corrosion in the joint portion is prevented. Specifically, the amount of thread interference T is controlled to be at most a specified value calculated as a function of the inner diameter D1 of the pin portion, the thread effective diameter D2 at the basic diameter position, the outer diameter D3 of the box portion, the internal pressure Pi, and the yield strength &sgr;y and Young's modulus E of the base metal. As a result, a threaded joint which is suitable for joining of oil well pipes can be provided.

Abstract: A tightening method for a special joint having unthreaded metal-to-metal sealing surfaces and unthreaded shoulder portions. By controlling the ratio of the tightening torque at the completion of tightening to the shouldering torque at the time when the unthreaded shoulder portions come into contact to be in the range of 1.25-20 and more preferably 1.4-10, sufficient gastightness can be guaranteed and plastic deformation due to overtightening can be prevented regardless of the type of pipe joint or the conditions of use. As a result, it can be widely utilized in the tightening of special joints used with oil well pipes even under the present state of increasingly severe oil well environments.

Abstract: The joint according to the invention relates to a sealed connection between metal pipes used for producing petroleum tubings or casings. This joint comprises a sleeve fitted with two threaded housings suitable for receiving the male ends of two pipes. The end faces thereof come to bear one against the other inside the sleeve. An annular convex tapering zone near the end face of each pipe bears in a sealing manner against an annular concave tapering zone of the sleeve. Shoulder stops 16 ensure the centering of each male end.