Patent ID: 7900975

Claim:
A threaded joint for steel pipes comprising a pin having male threads and a box having female threads, wherein the male threads and the female threads are tapered threads having at least a complete thread portion, the threads in the complete thread portion having a roughly trapezoidal thread shape having a crest, a loading flank, and a stabbing flank with threads being separated from each other by thread roots, characterized in that at least part of the threads in the complete thread portion of either the box or the pin as a first tubular member has a two-step stabbing shape having a stabbing flank with a chamfer, said two-step stabbing shape having a stabbing flank angle α of 5-45° and a chamfer angle β of 20-60° and meeting either the following condition (1) or (2): (1) the ratio h/H of the height h of the chamfer of the two-step stabbing shape to the thread height H of the pin is 0.25-0.50; or (2) the following inequality (3) is satisfied, h ′ h ′ + H ′ ⁢ ( h / H = 0.25 ) ≤ h ′ h ′ + H ′ ≤ h ′ h ′ + H ′ ⁢ ( h / H = 0.50 ) , wherein ⁢ ⁢ h ′ = h - z · ( 1 - sin ⁢ ⁢ β ) cos ⁢ ⁢ β - y · sin ⁡ ( β / 2 - α / 2 ) , ⁢ H ′ = H - h - x cos ⁢ ⁢ α + x · sin ⁢ ⁢ α - y · sin ⁡ ( β / 2 - α / 2 ) , and ( 3 ) wherein α is the stabbing flank angle (degrees) of the two-step stabbing shape, β is the chamfer angle (degrees) of the two-step stabbing shape, H is the thread height (mm) of the pin thread, h is the chamfer height (mm) of the two-step stabbing shape, x is the radius of curvature (mm) of the stabbing flanks at the thread crests of the pin, y is the radius of curvature (mm) at the starting point of the chamfer of the two-step stabbing shape, and z is the radius of curvature (mm) of the two-step stabbing shape at its thread crest.