Patent ID: 11905765
Assignee: JFE STEEL CORPORATION
Field: Mechanical elements (Mechanical engineering)
Classification: CPC E  F | IPC E  F

Claim 0:
1. A threaded joint for pipes, comprising
a pin provided with a male thread portion, which is a male tapered thread, at one end of a first pipe, and
a box provided with a female thread portion, which is a female tapered thread to be screwed with the male thread portion, at one end of a second pipe, wherein
the female thread portion has a plurality of thread grooves,
each of the plurality of thread grooves has a corner portion on a load flank side and a corner portion on a stabbing flank side on a thread bottom side,
a flank angle of the plurality of thread grooves, which is defined as positive when a flank surface is inclined toward the thread and negative when it is inclined towards the opposite side of the thread, with respect to a straight line perpendicular to a pipe axis, satisfy the following conditions (a) and (b):
(a) an angle of the stabbing flank is +5 to +40 degrees with respect to a straight line perpendicular to the pipe axis; and
(b) an angle of the load flank is −10 to 0 degrees with respect to a straight line perpendicular to the pipe axis,
the corner portion on a load flank side of a first thread groove, which is the thread groove farthest from an end of the box among the plurality of thread grooves, comprises a first arc portion that is directly connected to a load flank and has a first curvature radius, and a second arc portion that is directly or indirectly connected to the first arc portion and has a second curvature radius, and
a ratio of curvature radius, which is a ratio of the second curvature radius to the first curvature radius, is 3 or more.