| 摘要 |
<p>PURPOSE: To improve compressive and bending strengths of a thread by forming the thread, such that flanks of the respective thread members come into contact with the range of at least a part of the thread length, when applying torque larger than the torque that brings a torque shoulder of a box member in a tube fitting into the first contact with a torque shoulder of a pin member. CONSTITUTION: When a casing pipe and a tube pipe in petroleum and gas industries are connected with a screw coupling, a pin thread 4 to be provided on a pin member having a central axis 3 is formed by a top of thread 14, a bottom of thread 10, a loading flank 8, and a sinking flank 6. The respective flanks 8, 6 are formed so as to extend from the top of thread 14 and the bottom of thread 10 making angles A, B with respect to the radial lines perpendicular to the central axis 3. The angle B is chosen, such that an angle C made by both flanks 6, 8 is larger than 0 deg.. In addition, the thread of a box member is formed so as to correspond to the pin thread 4, and a length L2 of the top of the box thread 11 is formed larger than the length L1 of the bottom 10.</p> |
