Grinding and machining will cause the surface roughness, are provided with grooves, overlapping and burr. Each defect may also make metal surface damage to a certain depth, so that the metal surface damage cannot be cleared by pickling, electric polishing or shot peening method. The rough surface can become corroded and sedimentary formations birthplace, heavy cleaning before welding weld defects, remove excess weld, are coarse grinding grinding can not be used. In the latter case, with fine abrasive grinding.