Seizure resistance to excellent for oil country tubular goods threaded joints

摘要

PROBLEM TO BE SOLVED: To provide a screw joint for an oil well pipe excellent in seizure resistance, which reduces a concentrated load in the load frank surface of a screw part on a pin pipe end side, in the screw joint having a shoulder part.SOLUTION: In a premium joint, a female screw pitch 20B is the same value as a male screw pitch 20P to a pitch change position PCP close to a box central side with respect to the intermediate position of the whole length of a screw part from a screw end part on the end side of a box 1, and by pitch change changing to a value less than the male screw pitch at the pitch change position PCP, a screw gap 10 is gradually reduced from the pitch change position PCP to the screw end part on the box central side so as to finally become a value 0.2 time or more and 0.8 time or less of the screw gap 10 before pitch change.