Aluminum column bearing on HSS 1

[JoeBaseplate]

Obvious concern is the connection of dissimilar metals. I was thinking the steel tube can have a plate welded to it, and the aluminum post can have a plate welded to it. And the two would be bolted together with stainless steel bolts and there would be a bituminous coating between the aluminum and steel plates to prevent contact. Does this sound reasonable?

The connection is for vertical (including uplift) and some shear loads.

 

[JAE]

You could also use a thin neoprene pad/gasket.

 

[MiketheEngineer]

Pad/gasket used all the time

 

[paddingtongreen]

You still have to insulate the nut and bolt from one or both of the metals!!

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[JoeBaseplate]

Paddington, I am using SS bolts.

 

[paddingtongreen]

That still makes an electrical connection that localizes the corrosion.

http://www.farwestcorrosion.com/ccp/flange/pikotek04-insulating.htm

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[JoeBaseplate]

Wow, so how do I get around that, do I use neoprene washers @ ea end.

 

[Ron]

You don't have to isolate the stainless steel from either. Just isolate the aluminum from the steel. Many ways to do, but I would stay with the pad as suggested or felt.

 

[paddingtongreen]

@Ron, tell me why you would bother with the pad if you are going to make an electrical connection between the two metals with the stainless steel bolt.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[JAE]

We've used SS bolts with aluminum-steel connections - no problems - even outdoors with -10 deg F to 100 deg F range.

 

[Ron]

Michael,
It has more to do with the relative size of the members in contact than the electrical connection. Yes, the electrical connection plays a part, but if the area of aluminum is much greater than the area of the stainless steel, then preferential and localized corrosion won't likely occur.

That's why you wouldn't use an aluminum fastener in stainless steel...the corrosion due to the area difference would concentrate in the aluminum fastener.

The most common occurrence in that case is that the aluminum is attacked over its larger surface, resulting in a light passivation layer forming from the oxides. When this occurs, it then protects the aluminum from further corrosion. It can, in fact, reverse the corrosion potential.