SS/GI connection 1

[afa13]

Hello everyone,
Is there a risk from connecting a Stainless Steel 316L duct to a galvanized steel duct directly together (only thing seperating them is the gasket in between the flanges)?
If so what would be the recommendation to avoid galvanic corrosion?

On a similar note, let us say there are motorized dampers with stainless steel (316L) frames that are to be connected to a GI duct, should there also be a protection if the above holds?

Thanks.

 

[afa13]

Anyone???

 

[EmmanuelTop]

"Galvanised steel in contact with stainless steels is not normally considered to be a serious corrosion risk, except possibly in severe (marine type) environments." (source: British Stainless Steel Association), see

http://www.bssa.org.uk/topics.php?article=89

For galvanic corrosion to occur, the two dissimilar metals must be in electrical contact and "bridged" by an electrically conductive liquid. Your application may not even qualify for galvanic corrosion.

See also

http://www.galvanizeit.org/images/u...ss_Steel_in_Contact_with_Galvanized_Steel.pdf

Dejan IVANOVIC
Process Engineer, MSChE

 

[dbill74]

There may not be much risk between the two metal ducts themselves, but I wonder why would you be changing from stainless to galvanized steel mid system. Understandably the stainless is more expensive, but it provides corrosion resistance against corrosive gases that galvanized does not.

 

[RandomUserName]

dbill74,

Tough I cannot answer for afa13's reasoning for switching materials, I have seen many exhaust duct work systems that use aluminum or stainless steel duct work for the showers, then switch galvanized steel once they are comfortable the combined mixed air streams (usually air from a locker room) will not condense out.

 

[dbill74]

Good point Random. I was thinking more along the lines of lab exhaust.

 

[berkshire]

If this is an exhaust duct, and you need stainless at the hood end , if there is any moisture present in the airstream, galvanic action will occur , and the stainless will strip the galvanizing off.
B.E.

You are judged not by what you know, but by what you can do.

 

[afa13]

Hey Guys,
The switch from GI to SS is for protection purposes. The room the SS duct is serving has batteries in it and due to chemicals GI might corrode thus the change in materials. The SS is used in the supply as well as the exhaust.

 

[Drazen]

in such situation, you should avoid galvanized steel by all means as some corrosive agents will be transmitted along ducting.

this will be trouble in practice.

however, there is even more trouble if you plan to connect this to some centralized system.

 

[dbill74]

Agree with Drazen, the SS is there for protection against chemicals. You would be better off the entire exhaust system that is pulling from battery storage being all SS.

 

[afa13]

guys,
the issue is not thge material of the duct for this has already been agreed upon. Ducting serving hazardous areas will be SS (fully welded).
The issue is the connection between the two materials which will be done in an adjacent room. The ss branch will connect to the GI duct in an adjacent room and then serve the hazardous area. The concer was the connection of the SS to GI.
However, i managed to solve it.
I appreaciate it guys.