Galvanic Action Piping Systems

[FIF99]

Hi,

Within our company it's always a discussion to specify flange insulation sets (gaskets, bushing and washers) for flange connections of dissimilar materials (CS to SS) or not.
We don't have a corrosion engineer within our company.

Could anybody give me some reference to available publications and/or experiences?
Criteria would be nice, such as applicability of electrolyte, mass diferences of the materials, etc.

Some companies don't want these sets since they do not work anyhow.

Thanks in advance.
Regards,
fke

 

[macmet]

http://www.corrosion-doctors.org/

has some info.

You could buy a text that may be used at a university. I have

Principles & Prevention of Corrosion by Jones.

It's alright, but there may be better ones.

Cheers

 

[mshimko]

Not sure what you mean by "Some companies don't want these sets since they do not work anyhow".

They work great, IF installed properly AND every electrical path is isolated. The problem is, if you don't provide 100% isolation, you fail. This means brackets, foundations, gage lines, electrical connections, EVERYTHING!

Personally, though, I prefer connecting dissimilar metals, but adjusting the design or configuration to account for/allow for the expected galvanic corrosion. Others will disagree, of course.

 

[SJones]

http://www.npl.co.uk/ncs/docs/bimetallic.pdf

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[FIF99]

Hi,

Thank you all for your help!

Regards,
FKE

 

[drozic]

Greetings:

Sorry for the late post. I just recently found this website.

I agree with mshimko. Dissimilar metals form a galvanic cell. The less noble metal sacrificially oxidizes (corrodes) to protect the other. See the Galvanic Series to determine whether the metals are anodic or cathodic when joined.

This is the principle for electroplating steel, galvanizing steel, passivating stainless steel, and attaching zinc anodes to ship hulls and buried iron piping.

In some cases the sacrificial metal does not need to completely cover the other metal. There are methods of accelerating corrosion to determine if enough coverage exists: neutral salt fog, copper accelerated salt fog, high humidity & temperature, and outdoor exposure.

National Association of Corrosion Engineers:

http://www.nace.org

American Electroplaters and Surface Finishers Society:

http://www.aesf.org