Galvanic Corrosion Between Stainless Steel and Aluminium
Galvanic Corrosion Between Stainless Steel and Aluminium
(OP)
Hi All,
I've run into a bit of an odd issue (for me anyways) on site the other day and was hoping to get some helpful input. For info, this site is in London, UK.
There is a 10mm THK stainless steel bracket (shown in green in the sketch, grade unknown) which is fixed to an aluminium profile that sits inside a brise-soleil panel. The fixing is not protected by the panel as is shown in the drawing, the connection is open to the elements.
As you can see in the photographs I have provided (one of the bracket, one of the aluminium profile), when the brise-soleil panels were removed, a later of aluminium oxide (I am assuming) has formed on the stainless steel, in the area where the two metals were in contact. What I think has happened based on the information I have gathered over the last few days is that the two dissimilar metals in contact and exposed to rainwater has created a galvanic reaction, causing the aluminium to corrode. The galvanic series chart which I am referencing shows stainless steel twice...once in the passive state and once in the active state. Again, what I am assumign has happened is that the stainless and aluminium oxide layers were damged during installation, and since no oxygen can get to the surfaces of these materials, corrosion began to occur. This coul dbe completely wrong...its just my thinking at the moment.
Can anyone provide me with any input on why this is occuring, when a stainless steel is passive or active, and what sort of long term effects can be expected?
Thanks in advance.


I've run into a bit of an odd issue (for me anyways) on site the other day and was hoping to get some helpful input. For info, this site is in London, UK.
There is a 10mm THK stainless steel bracket (shown in green in the sketch, grade unknown) which is fixed to an aluminium profile that sits inside a brise-soleil panel. The fixing is not protected by the panel as is shown in the drawing, the connection is open to the elements.
As you can see in the photographs I have provided (one of the bracket, one of the aluminium profile), when the brise-soleil panels were removed, a later of aluminium oxide (I am assuming) has formed on the stainless steel, in the area where the two metals were in contact. What I think has happened based on the information I have gathered over the last few days is that the two dissimilar metals in contact and exposed to rainwater has created a galvanic reaction, causing the aluminium to corrode. The galvanic series chart which I am referencing shows stainless steel twice...once in the passive state and once in the active state. Again, what I am assumign has happened is that the stainless and aluminium oxide layers were damged during installation, and since no oxygen can get to the surfaces of these materials, corrosion began to occur. This coul dbe completely wrong...its just my thinking at the moment.
Can anyone provide me with any input on why this is occuring, when a stainless steel is passive or active, and what sort of long term effects can be expected?
Thanks in advance.



RE: Galvanic Corrosion Between Stainless Steel and Aluminium
1) someone installs this hardware with a better detail that isolates the two metal parts from each other
2) someone installs this hardware with a better detail that prevents all moisture exposure at the joint
3) the components corrode to the point where they fail
RE: Galvanic Corrosion Between Stainless Steel and Aluminium
RE: Galvanic Corrosion Between Stainless Steel and Aluminium
The remedial strategy at the moment is to remove the panel, install some sort of material seperator (rubber pad or tape likely), then reinstall the panel. It would be nice to have replaced the stainless bracket with an aluminium replacement.......unfortunately they embedded the bracket in silicone when they installed it! So thats not coming out haha.
Can either of you clarify/explain the active vs passive stainless steel? I cant quite wrap my head around it....
RE: Galvanic Corrosion Between Stainless Steel and Aluminium
RE: Galvanic Corrosion Between Stainless Steel and Aluminium
You know to isolate them the bolts have to be fully isolated. There can be no continuity between the Al and SS. This involves and insulating sleeve in the hole and insulating washers.
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P.E. Metallurgy, consulting work welcomed
RE: Galvanic Corrosion Between Stainless Steel and Aluminium
Thanks all for the help. The issue makes a lot more sense to me now.