×
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

Galvanic corrosion bewteen 316L st st and 6Mo st st subsea

Galvanic corrosion bewteen 316L st st and 6Mo st st subsea

Galvanic corrosion bewteen 316L st st and 6Mo st st subsea

(OP)
Hello all,
I have an application where I need to connect a 316L st steel component to a 6Mo st steel component.
I have been prompted to assess the potential (no pun intended) for galvanic corrosion between these two components.

I would appreciate your thoughts and advice.
Here are my thoughts:
1. They are both austenitic st steels, so should be close on the galvanic series? (need to be <-0.15V potential difference).
2. Would adding sacrificial anodes (zinc) immediately adjacent to the joint prevent the galvanic corrosion?
3. Separate the compnents with an intermadiate material that would be compatible with the other two, e.g. Inconel625 / Titanium?  All materials must be non-magnetic due to high electrical current passing within the items.
4. Components cannot be (electrically) isolated from each other as a metal-metal seal ring must fit between the two items.

Many thanks in anticipation of your advice,
Rob

RE: Galvanic corrosion bewteen 316L st st and 6Mo st st subsea

If the assembly is hooked into a cathodically protected structure, the risk of galvanic interaction is minimised.  Coating with thermal spray aluminium could be an option to achieve the same result.  Examine the area ratios - if they are favourable to the 316 (i.e. the 6Mo has significantly less area)  no other measures may be needed but 316L is not ideal as a subsea material without CP.

Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdoweb/

RE: Galvanic corrosion bewteen 316L st st and 6Mo st st subsea

I would suggest some galvanic protection.  You will probably get some crevice corrosion of the 316 at the connection.

There should be "dissimilar metal crevice corrosion" data in the AL-6XN source book at the Allegheny Ludlum web site that shows 6XN-316-6XN tested in seawater for one year.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

RE: Galvanic corrosion bewteen 316L st st and 6Mo st st subsea

it seems that there could be a galvanic corrosion and some caution in design should be used.. the final decision also depends on the type of component we are talking, if it's accessible for inspection/maintenance, criticality of the service...

this doc can give you some advice, but not much..

http://www.csidesigns.com/PDFs/AL-6XNCatalog.pdf


this doc can also help you, look at page 67-69.
http://www.corrdefense.org/Key%20Documents/Corrosion%20Prevention%20and%20Control--A%20Program%20Management%20Guide%20for%20Selecting%20Materials.pdf

hope this help

S.

Corrosion Protection & Corrosion Control
 

RE: Galvanic corrosion bewteen 316L st st and 6Mo st st subsea

Robwyatt
 If  two dissimilar metals are immersed in seawater and a potential exist between them, then ,  even if the assembly is subject to a cp system, that same potential will still exist, and , presumeably there will be massively increased corrosion on the least noble of the immersed metals.
You can minimise corrosion by coating both of the immersed metals.  you can eliminate it by electrically insulating all metals from each other (but you say this is not possible ).  Best of luck.
CM

RE: Galvanic corrosion bewteen 316L st st and 6Mo st st subsea

Corrosionman,

That 'same potential' may not exist if an external anode is added.  The resultant potential difference between the two alloys will be dependent upon their polarisation behaviour in seawater and not their individual rest potentials in seawater.   

Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdoweb/

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