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topic 1672

Electro polishing defects


what are the principal reasons for the following two types of defects encountered when electropolishing T316?

- orange peel

- rippling (streaking)

Richard C Dibling
- Melbourn, Royston, Herts, UK



Orange peel is most often caused by stretching of the metal in drawing, stamping, and similar operations. The surface requires mechanical finishing prior to electropolishing. Some references also attribute orange peel to low current density, probably a result of etching at the grain boundaries.

Rippling or streaking may be caused by the stream of oxygen gas bubbles formed at the surface of the part during electropolishing. Agitation of the parts with respect to the solution, or of the solution with respect to the parts, is normally used to overcome gas streaks.

Ed Bayha
Metal Coating Process Corporation - Charlotte, North Carolina


Subject Matter is EP of a large (in excess of 12K liters)Vessel that is SS316L material. When a surface finish of 10 ra or less is achieved is there a limit of how many times the material can withstand an EP? If during the mechanical polish of the vessel, vertical ribbon marks became evident could the EP process result in an unidirectional pattern that is stress-free, microscopically smooth and highly reflective? Sincerely, Frank Ventre

Francesco Ventre
genetics - Andover, Massachusetts



During my recent employment I have been introduced to electropolishing. First I would like to say that I have witnessed "orange peel" even after the surface has been finished by mechanical polishing to a .8 r.a value. Other thing I have experienced are a glassing effect where the surface in the centre of the defect is really shiny and is surrounded by bubbles. Also a dulling effect usually internal. I like the comment on agitating the surface, although I don't know of a cost effective way of doing this in an Automated E.P tank if it was not already bought with this facility, maybe manually would be a different proposition. Lastly a question, Is there a way to get a consistent finish on a vessel be it 2" or 30" without jig marks or any of the above details?.

David Lang
vessel manufacture - Southampton, United Kingdom

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