Method of producing a seamless metallic tube by the cold rolling

In cold rolling of a seamless metallic tube by a cold pilger mill, the circumferential direction strain in the flange side the outer diameter reduction rate is excessively large as compared to the thickness reduction ratio becomes excessively large, resulting in circumferential compression stress wrinkles flaw occurs in the tube surface becomes excessive, it becomes Orekomi flaws convolved with the groove bottom side, which develops the internal surface flaws are repeated. Apart If mother tube is manufactured by extrusion process, there is an inner surface wrinkle flaws in mother pipe stage by the constant-radius rolling (stretch reducer or sizer) when produced by Mannesmann mandrel process, further cold rolled because it is conducive it requires attention. Considering these circumstances, the ratio of the outer diameter reduction rate / thickness reduction ratio in the cold pilger mill is 1/2 or less. Thus, it is possible to obtain a high-quality seamless metal pipe inner surface defects due to cold rolling is suppressed.