Nippon Steel Corporation

Nippon Steel Sumitomo Metal Corporation

Masahide Takagi

Yuki Motegi

Takashi Oosawa

Tetsu Satoh

Shinji Taenaka

This depression-provided steel pipe has plural depressions on an outer peripheral surface, the depressions being formed so as to form a line along an axial direction of the steel pipe, in which each of the depressed portions has, inside thereof, a columnar groove portion extending along the axial direction of the steel pipe and depressed deeper than a bottom surface of these depressed portions; 0.95&#x2266;H/H&#x2266;1.05 is satisfied, where His an average Vickers hardness in each of the depressed portions, and His a Vickers hardness at a portion between the depressed portions adjacent to each other in the axial direction of the steel pipe; and the outer peripheral surface is covered with a mill scale.

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Tokyo, Japan

Masahide Takagi