Influence of Roll Rotational Speed on inside Bore and Lamination Defects in Rotary Piercing Large Diameter Heavy Wall P92 Steel Pipe Process

Abstract

To investigate the influence of different roll rotational speeds on tendency of inside bore and lamination defects of large diameter heavy wall seamless P92 (9Cr-0.5Mo-1.8WVNb) steel pipe pierced by two-high rotary piercing process, with the aid of commercial FE code MSC. SuperForm, 3D thermo-mechanical coupled simulations were presented. The damage field of the rolled piece during rotary piercing process, and the tendency of forming inside bore and lamination defects were analyzed using Oyane ductile fracture criterion. The results show that When roll rotational speed increases from 7rpm to 11rpm, the maximal damage characteristic value decreases from 0.4279 to 0.3340 in center area of rolled piece in front of the plug, but which increases from 0.3780 to 0.4858 in a certain depth zone (15~25mm) adjacent to the internal surface of the rolled piece contacting with the front end of the plug. With the increase of roll rotational speed, the tendency of forming inside bore defects of rolled piece reduces, but the tendency of forming lamination defects increases. Therefore, there exists a critical roll rotational speed to make the tendency of both inside bore and lamination defects reduce. This study provides scientific basis for formulating reasonable rotational speed schedule to prevent or reduce inner overlap and lamination defects.