What's stainless steel electropolishing?

Stainless steel electropolishing is used to polish, passivate stainless steel part. Stainless steel workpiece is connected to the positive terminal of a DC power. Both the workpiece and the negative terminal are immersed into the temperature-controlled electrolyte together. A current passes from the anode then the surface of workpiece is dissolved, that could improve the the surface, make workpiece shiny and smooth.

Comparison between passivation and electropolishing

a, Electropolishing can remove all surface contaminants but passivation can't

b, Passivation can't be performed on all grades of stainless steel neither

c, Electropolishing is preferred to passivation

d, Someone suggest it's necessary to passivate after electropolishing, because it could improve corrosion resistance.

Note on stainless steel electropolishing:

a, The space between electrolyte level and the top of tank can't be≤ 15cm, because there will be foam in initial use of electrolyte.

b, The moisture must be removed as much as possible before being immersed into electrolyte. Because too much moisture could cause serious pitting even lead to workpiece scrapped

c, During the process of stainless steel electropolishing, the iron and chromium contained in the workpiece continuously transform into metal ions dissolved into electrolyte without being deposited on the cathode surface. As the polish process, the concentration of metal irons increase gradually and when it reaches a certain value, the metal ions precipitated out of the electrolyte in the form of phosphates and sulfates, settling down at the bottom of the tank. So the electrolyte must be filtered regularly to remove the sludge.