| 摘要 |
PROBLEM TO BE SOLVED: To impart an economically effective pressure resistance to a metal surface contact seat part and prevent seizure at the time of tightening. SOLUTION: An external screw 1b and a seal surface 1a without screws which forms a seal part by abutting to an opponent tightened are mounted on the outer periphery at the end part of a pipe material 1. An internal screw 2b tightened to the pipe material 1 by engaging with the external screw 1b and a seal surface 2a without screws which forms a seal part by abutting to the seal surface 1a and mounted on the inner periphery at the end part of a coupling 2. This screw joint for pipe has the seal surface whose the width in the axial direction along the seal surface is not less than 1 mm so that the relation between a mean surface pressure Pm in a ring-shaped contact part forming a seal part and a surface roughness Ry satisfies 0.0032×Ry<2> +1.0<=Pm/ Py when the inside yield pressure of the pipe material 1 is Py, and the surface pressure Ps of the ring-shaped contact part satisfies Ps/Py>=1. The more economically effective screw joint having the seal of the metal surface contact can be obtained.
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