Galvanic Corrosion

Hi I wonder if somebody can help me please?

I'm installing solar panels onto a campervan roof, and on one side it has T Bolts sticking out of the roof, I'm therefore going to fit stainless steel slotted channel directly to these T Bolts, however on the other side it has an Awning fitted, and they've already used the T Bolts by fitting aluminium slotted channels.

Therefore on the Awning side, I was planning on fitting a Stainless Steel Angle Bracket to the existing Aluminium Channel, with Stainless Steel M6 bolts into Stainless Steel slotted channel nuts, directly into the Aluminum channel....

The problem is Galvanic Corrosion?

Would I need to try and source some aluminium channel nuts, bolts, and angle bracket?

If so I'm worried about the force on the aluminium bolts, as wind force will. Be getting under the solar panels and could break them?

Or would it be OK to use the stainless steel hardware into the aluminium but smother it in loads of grease? How long would this work for on the roof of a van subjected to the weather in Scotland constantly?

You would probably be OK for the first 15 years and after that I would start to worry! I would be more worried if you were on a ship, but even some of them are made from aluminium alloys.

Bob

Hi Tyrone, I used to service submersible pumps with aluminium castings, which were used in acidic ground water, these used A4 stainless nuts, bolts and studs, never had any issues with corrosion between the ally and the stainless with them, so I would think A2 or A4 stainless should be OK, but do use a little oil om the threads, as they have a tendency to seize up when they are dry, when tightening.

Regards Nick.

Hi Tyrone I was involved in in potholing and we did work on rock anchors and galvanic corrosion and we cane to the main result that alloy anchors and steel bolts were not very good as they would eat each other but stainless steel bolts and aluminium anchors were acceptable and had little effect evan under running water. As as Nicholas says use a grease on the thread to prevent seizing up, I use copper slip, if you want to unscrew in the future or you may have to cut of the bolts.

David

Try this

Duralac paste

I have seen some real howlers where unprotected stainless steel has been used against aluminium, particularly in yacht masts.(I get involved in yacht rigging for our club). Of course salt water is a more difficult environment, but it will accelerate corrosion in a surprisingly short time- By that I mean as little as 18 months, sometimes less

Edited By Sam Longley 1 on 02/02/2022 08:19:53

Atom by atom , the aluminium channel will try to become part of the iron/steel campervan roof..

In reality , this will probably not be a problem during your ownership.

That sounds like a common phrase used in our village which has a high elderly population content

"Well it will see me out"

Most depressing & i am sure the Op will appreciate your prophecy.

I bet you will be trying to sell him an excellent  Sun Life life insurance policy next?

Edited By Sam Longley 1 on 02/02/2022 09:23:02

I would definitely use a jointing compound when assembling, my compound of choice would be Duralac, my background is in aircraft engineering and jointing compounds were used extensively when bolting together dissimilar metals. I can give an example of how quickly dissimilar metal corrosion will take hold, We have a Ring Doorbell at our front door, the first unit I purchased failed, out of guarantee, when water penetrated into the electrical internals and the unit shut down. This was replaced about 18 months ago with another unit, when I removed it recently to recharge the battery I noticed that there was corrosion festering around the bolts that secure the backplate of the unit, obviously dissimilar metal corrosion from the stainless bolts being in contact with aluminium and water being present every time it rains. This has taken hold in less than 18 months, again conveniently for Ring outside of the guarantee period, wonder how long this unit will last before it fails completely. For the cost of a jointing compound you will have peace of mind about the integrity of the assembly and could use stainless bolts. Dave W

Insulating flat mating surfaces to prevent galvanic corrosion is easy by coating the surfaces or placing an insulation material between them but more difficult to prevent it between bolts and the side of the bolt holes because painted on type insulation is easily worn off.

A better option is to use a flanges shoulder washer. Use a steel washer on the outside of the flange and a steel bolt,  ( 2 shoulder washers are normally used, 1 in each of the mating parts.)

Edited By Paul Lousick on 02/02/2022 12:00:45

As a long time Landrover owner, electrolytic/galvanic corrosion between stainless steel and aluminium can be a problem in less than the 10 years mentioned above.

I've not tried Duralac paste, though have heard good reports.
As far as the stainless angle is concerned, there's nothing to stop you insulating one side of the angle where it abuts the alloy channel; several layers of insulating tape, or a long sliver of builder's damp proof course spring to mind initially.

Stainless channel nuts might be a bigger problem inside an aluminium channel.

Why not just use BZP bolts and channel nuts, well lubricated with copperslip or similar; If you want to maintain a nice clean appearance on the visible part outside, use BZP channel nut and studs (or BZP T-Nuts), but with stainless dome nuts and washers on the outside.
That way the BZP steel will be in contact with the alloy, and the stainless contact will only be with more stainless.

Bill