Internal Polishing of Stainless Pipes by Electrochemical Mechanical Polishing

Abstract

This study proposes an electrochemical mechanical polishing process to polish the internal surface of stainless steel SS304 pipes with a centreless rotating system. This process combines electrochemical and mechanical methods to achieve a remarkable surface finish. The SS304 pipe serves as a workpiece (anode), while a copper electrode acts as the cathode material. When the workpiece rotates on the centerless rotation setup, a copper electrode and electrolyte are pumped inside the pipe. To perform this polishing process, sodium nitrate was used as the electrolyte at a concentration of 10% wt. Solution. Eight experiments were designed using the Taguchi method, with current, voltage, feed and speed as input parameters. After the polishing operation, based on the percentage improvement in surface finish, it was found that the best parameter settings were a longitudinal feed of 26.2 mm/min, a rotational Speed of 100 rpm, a voltage of 10 V, and a current of 2 A. The roughness value decreased by 29.56% compared to the as-received material. It was clearly observed that voltage and current play a significant role during the ECMP process. The internal surface of the polished sample is visible under the optical microscope at a magnification of 100x, and it appears to have fewer scratches and pits, which have been largely eliminated, resulting in a smoother and finer surface. Finally, due to chemical action, different phases, including Cr-Ni, Ni-Fe & FeO, are found on the sample with respect to planes (111), (200) & (220) and analysed using XRD data.