×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

316, Electropolish or hand polish for corrosion in Sea

316, Electropolish or hand polish for corrosion in Sea

316, Electropolish or hand polish for corrosion in Sea

(OP)
I recently purchased some items used on my boat. They are welded 316 SS tubing that has been polished with some kind of rubbing compound.  I was told that this is better than Electropolishing.  I think this salesman is mis-informed.  I was educated that Electropolishing is the best way to finish 316 SS for corrosion protection because it dissolves the free iron on the surface leaving chrome to form chromium oxide and prevent corrosion.  This is especially true when welding has been performed.  Can anybody confirm???

RE: 316, Electropolish or hand polish for corrosion in Sea

The nitric acid passivation that is supposed to precede mechanical polishing selectively removes iron so that the polished finish will not turn red.

Electropolishing uses an electroplating bath, with the current reversed.  I'm getting the impression that it removes iron, or something, far beyond the surface.  I'm not real impressed with its corrosion performance, especially near welds, especially on parts that don't drain or rinse well.


Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

RE: 316, Electropolish or hand polish for corrosion in Sea

EP is much better than mech pol in terms of corrosion resistance.  Mech pol results in smearing of the surface and the formation of lots of laps and crevices.
The big deal with EP isn't the iron removal, that is a side benifit.  The real issue is the cleaning and building of a very stable passive film.
EP on a mill finished part will perform better than a mech pol even when it is very rough.
The other issue that you have though is the use of 316 in seawater.  This may be common pratice, but there is no reason to expect 316 to stand up to any seawater exposure.  It doesn't have enough pitting resistance.
Make sure that water cannot be trapped anywhere and keep everything clean.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.
http://www.trenttube.com/Trent/tech_form.htm

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources