Carbon steel to Stailess steel

[Dj364]

Hello evey one,
as my best knowledge, using flange CS assembled to SS flange,will create a galvanic corrosion unless the bolts are isolated.
The issue is this, we are using lapjoint flange ( stub end SS, lap joint flange is CS) connected to equipement which have SS flange nozzle.
the material engineer said thats an usual practice and since we have a large anode (CS) compared to the cathode (SS).
I am not a 100% convinced,
In the past I have seen in the chemical plant this glvanic corrsion, I thought that we are not designing this anymore without isolating bolts.
I hope I made it clear.
Your comments will be very welcomed.

 

[metengr]

What is the service environment (fluid type and temperature conditions internally to the pipe systems) for this dissimilar metal connection? The statement regarding the area of the anode to cathode is correct, but there is more to this than just this one statement.

 

[unclesyd]

The CS flange and fastener components of the connection will not enter into the picture unless you have a process leak that would corrode the CS.

We have used this combination for many years on processes that are corrosive to CS. The only time we restrict this combination is hen the process is extremely corrosive and would cause catastrophic destruction of the flange and fasteners. We replace the CS flange with SS and use SS fasteners.

 

[MJCronin]

Bj364..

Carbon steel/stainless steel is not "dissimilar" enough on the galvanic scale to require an electrically isolated joint.

Just because you saw that someone did it once on a plant that you visited, does not make it an "industry practice"

Relative areas of the cathode an annode does have an affect on the rate of corrosion.

Repost this question on the corrosion forum..

-MJC