| 摘要 |
<p>A thread joint capable of economically imparting effective sealability to a metal surface contact seal section and preventing seizure during fastening is composed by fastening a steel pipe (1) having a male thread (1b) at an end and a non-threaded seal surface (1a) to a coupling (2) having a female thread (2b) in the inner peripheral surface and a non-threaded seal surface (2a). In this thread joint, letting Py be the inner surface yield pressure of the pipe, either (1) the mean surface pressure Pm of the annular contact portion satisfies Pm/Py = 3, the axial width of the portion receiving the surface pressure Ps that satisfies Ps/Py >= 1 in the annular contact portion is not less than 1 mm (or not less than 2 mm), and the surface roughness (Ry) of the non-threaded seal surface is not more than 25 mum (or not more than 30 mum) or (2) the relationship between the mean surface pressure Pm of the annular contact portion and the surface roughness (Ry) (mum) of the non-threaded seal surface satisfies Pm/Py >= 0.0032 x Ry2 + 1.0, and in the annular contact portion, the axial width of the portion receiving the surface pressure Ps that satisfies Ps/Py >= 1 is not less than 1 mm.</p> |
