On Galvanic corrosion between stainless steel and aluminium
On Galvanic corrosion between stainless steel and aluminium
(OP)
I have a question regarding corrosion because of galvanic coupling.
I am designing a plant where there is a water tank in Stainless steel 316 with a 6" flanged opening on the top. I am planning to mount an aluminium element on that flange. Thus there will be two flanges put together, one in SS, and the other one in aluminium. Bolts, washers and nuts will be in SS also.
My question is: Is there a risk of galvanic corrosion? I suppose stainless steel would "promote" the corrosion of aluminium, but since this metal is by nature passivated I think there should not be any problem. Anyway, the bolts will not suffer.
Is it right?
I am designing a plant where there is a water tank in Stainless steel 316 with a 6" flanged opening on the top. I am planning to mount an aluminium element on that flange. Thus there will be two flanges put together, one in SS, and the other one in aluminium. Bolts, washers and nuts will be in SS also.
My question is: Is there a risk of galvanic corrosion? I suppose stainless steel would "promote" the corrosion of aluminium, but since this metal is by nature passivated I think there should not be any problem. Anyway, the bolts will not suffer.
Is it right?





RE: On Galvanic corrosion between stainless steel and aluminium
Regards,
Cory
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: On Galvanic corrosion between stainless steel and aluminium
If you want to avoid galvanic corrosion the main possibilities are:
- install dielectric insulation between the flanges and on the bolts
- install a dielectric spool of pipe (it could be an internally lined pipe)
- paint the cathode of the galvanic couple (in this case the SS)
S
http://www.corrosionist.com
RE: On Galvanic corrosion between stainless steel and aluminium
There will be no water flowing through those elements, only rain at the outside.
One solution may be to put ceramic washers to avoid direct contact between the two metals. But maybe it is unnecessary, since aluminium is already covered by a aluminium oxide layer in natural state. This is what I wanted to confirm.
Regards
RE: On Galvanic corrosion between stainless steel and aluminium
RE: On Galvanic corrosion between stainless steel and aluminium
There are several type of Aluminum Alloys for different application, "in general" the Aluminum is protected by an oxide layer but this is a general rule. The behaviour of your aluminum alloy depends on its composition, there are some series like 5000 if a remember well, which are used in marine atmosphere for example.
In your case i don't know if it's a marine exposure but as you said it's expodes to the atmosphere so you will have an electrolyte and two dissimilar material, and your Al will act as an anode and corrode.
Look at this example from NASA:
"For example, when aluminum alloys or magnesium alloys are in contact with steel (carbon steel or stainless steel), galvanic corrosion can occur and accelerate the corrosion of the aluminum or magnesium. This can be seen on the photo above where the aluminum helicopter blade has corroded near where it was in contact with a steel counterbalance."
http://corrosion.ksc.nasa.gov/galcorr.htm
S.
http://www.corrosionist.com
RE: On Galvanic corrosion between stainless steel and aluminium