[RE-wrenches] mixing aluminum and galvanized steel

[R Ray Walters]

I haven't seen a reaction between Stainless and Aluminum, if its a high grade Stainless. Lower grade stainless still has magnetic properties, and will corrode.
I think the freezing of fasteners you are referring to is actually the galling of the threads of the stainless. This isn't due to corrosion, but the deformation of the bolt threads from even slight over tightening.
Anti-seize or other lubricant helps this problem.
We also found SS hardware needs to be torqued at much lower torques than a zinc plated bolt.
I agree Zinc plated bolts aren't a good idea near the ocean, but in dryer places, it is a stronger, more trouble free (no jamming) bolt.

R. Walters
ray at solarray.com
Solar Engineer




On Oct 5, 2011, at 4:08 PM, conrad geyser wrote:

> My experience on the Northeast coast(salty sometimes) is that the galvanizing helps protect all the metals in the system.  The zinc in the most anodic metal on the chart and will help protect anything.  On the contrary, the stainless and the aluminum do react and in the case of fasteners, often freeze.
>  
> Don't use zinc plated of course, just hot dipped.
>  
> Conrad
> Cotuit Solar
>  
> From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Kristopher Schmid
> Sent: Wednesday, October 05, 2011 12:45 PM
> To: RE-wrenches
> Subject: Re: [RE-wrenches] mixing aluminum and galvanized steel
>  
> This is an amazingly timely post for me!  I was just thinking of asking the same question since i have a couple of ground mount installs coming up with concrete pillars/galvanized anchor bolts/aluminum channel base.  I notice that DPW for example specs galvanized pipes to be attached with u-bolts to their aluminum racking in their LGM racks.  
> 
> Anxiously awaiting the collective wisdom...
> 
> On Wed, Oct 5, 2011 at 11:23 AM, Jeff Yago <jryago at dtisolar.com> wrote:
> For years we have used standard mounting racks like UniRac rails bolted together with stainless-steel hardware.  On larger arrays this usually means bolting their extruded aluminum module rails to galvanized 3” pipe supports for ground mounted arrays.
>  
> We have recently received several “flags” during the engineering review process of our design documents on state funded projects stating all bolted connections between aluminum and galvanized steel will require neoprene washers to prevent corrosion.
>  
> Any of you run into this requirement or have had any problems?  The only issues we ever see with corrosion is mixing copper and aluminum such as where somebody used wrong type module frame ground connectors.
>  
> Jeff Yago
> 
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> Kris Schmid
> Legacy Solar, LLC
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