Rivets or SS machine screws

[Steve L.]

Yowser! Touchy touchy. Dude! I’ve been trying to restrict my responses to my experiences without taking it personally that we have different experiences. I’ll take my dubious quality fasteners and go sit in the corner.

I will admit to not procuring aircraft quality fasteners for my marine (and trailer) usage. I buy my stainless fasteners at West Marine and I expect they reflect the usual cross section of quality that’s generally out there for most consumers not willing to search farther afield. I’m almost willing to grant that if I used aircraft quality stainless fasteners I might have had a different experience.

So, in the end I guess I’m confused. I don’t know if you’re telling me that my corrosion issues were due to my dubious quality (but commonly available) fasteners or you’re telling me that no aluminum alloy will corrode with any grade stainless steel.

[Jared J]

Originally Posted by Steve L.

Yowser! Touchy touchy. Dude! I’ve been trying to restrict my responses to my experiences without taking it personally that we have different experiences. I’ll take my dubious quality fasteners and go sit in the corner.

I will admit to not procuring aircraft quality fasteners for my marine (and trailer) usage. I buy my stainless fasteners at West Marine and I expect they reflect the usual cross section of quality that’s generally out there for most consumers not willing to search farther afield. I’m almost willing to grant that if I used aircraft quality stainless fasteners I might have had a different experience.

So, in the end I guess I’m confused. I don’t know if you’re telling me that my corrosion issues were due to my dubious quality (but commonly available) fasteners or you’re telling me that no aluminum alloy will corrode with any grade stainless steel.

I'm telling you something funny was going on, either by material of the screw, something used to install them, or something that was in your boat and got between the screw and aluminum.

We see it on planes…from the piss tube, or blue water. Planes get corrosion all the time, just not from the screws. When a plane with a big corrosion problem comes in that might lead to legal trouble,, samples are sent to a lab. It has never been the fastener.

I also use numerous stainless screws in aluminum and steel at home. I've never had a problem, and some of it sets outside.

I have a very hard time believing a stainless screw corroded enough to break. I can believe they were possibly installed improperly and galled, but I wasn't there.

Did you turn the nut or the screw? Did you put anything on the threads? What rpm were they installed at?

[Evan Friesen]

Originally Posted by Steve L.

Not my experience however. I've put stainless screws in aluminum spars on my sailboat and have had real problems removing the screws or breaking them (due to corrosion) while trying to remove them. And I sail in freshwater. I would expect even quicker corrosion in saltwater which is probably not a problem for most of us.

After a few lessons learned I used Tef-gel after and never had another problem.

I can back you up on this. I've been working on my father-in-law's sailboat and catamarans used in the San Francisco bay for a few years and have come across a handfull of SS bolts that have been eaten away half way through - one or two has snapped even when gently turning off the nut. I also have seen aluminum that has corroded extensively. I'm not an expert on dissimilar metals, fasteners or boats (or airplanes for that matter!)...but corrosion happens...or it doesn't! We use tef gel also on all dissimilar metal applications.

That said..to reply to the OP's original question... I used aluminum rivets on the aluminum windows and replaced the furniture rivets with SS fasteners, washers, neoprene washers (they were in the plumbing section at Home Depot) and a dab of Sikaflex.
My reason for this wasn't to avoid corrosion, because I don't think it'll happen all to quickly in a non-marine environment, but because it was quicker and cheaper to install a bunch of rivets in those windows. I chose SS fasteners on the furniture because I wanted to test it out, and had access to cheap SS fasteners. I haven't had any problem with cracking or flexing, but it's only been a couple years. When I redid all the rivets there was spider web cracks and chipped gel coat around almost every rivet. I spent a lot of time fixing and reinforcing with fiberglass and epoxy the bad ones.

[ruscal]

Originally Posted by Steve Hammel

Any experience with aluminum nuts and bolts? Is there such a thing? Several of the windows in my 19' had been removed and replaced with steel not stainless nuts/bolts. I couldn't figure why they liberally slathered each bolt/nut with silicone but now I'm begining to get an idea. I'm not too overly concerned with thread strength.

Steve
I have seen some aluminum bolts used for ornamental purposes. There are a couple of drawbacks with using them. First thing would be strength. An aluminum fastener would have to be larger in diameter to get the same tensile or shear strength. The stronger aluminum alloys also are not very malleable after heat treating. Another drawback is the galling you would expect when like metals are tightened together. Aluminum is bad in that respect compared to steel. Stainless steel also has the same drawback as aluminum, hence the sheared off bolts while removing. The two parts of the fastener sort of "trade" metal which fuses the joint. Anti seize compound will help prevent galling. I have sheared off cad plated steel hardware screwed into aluminum many times even though the electrical potential is very close for those metals. I have found stainless steel to be a better choice for architectural use in my city. The worst corrosion I have found is aluminum sliding door tracks installed directly on concrete. Some are badly perforated after 20 years. Nothing to do with the screws used to fasten them down. The same aluminum on the jambs which are screwed to the wood framing with cad plated screws are typically in good shape, with some surface pitting and oxidation. The plating on the screw heads is usually solid rust, as the plating has long gone.
Russ

[Steve L.]

From Boeing: Aero 07 - Design for Corrosion

From the Methods of Protection Control (Finish Selection):

"Stainless steel parts are cadmium plated and primed if they are attached to aluminum or alloy steel parts. This is to prevent the stainless steel from galvanically corroding the aluminum or alloy steel. For the same reason, titanium parts are primed if they are attached to aluminum or alloy steel parts.

The corrosion-inhibiting primers used are Skydrol-resistant epoxies formulated for general use, for resistance to fuel, or for use on exterior aerodynamic surfaces. In some areas, Skydrol-resistant epoxy or polyurethane topcoats are applied over the primer for functional reasons."

This would seem to make another case for use of aircraft grade fasteners (or an anti-sieze compound) when possible. My Casita is already 10 years old and I'd like to be able to use it another 10 years so I'm thinking mods I made when the trailer was new are falling into the long term range. Heck, my sailboat is a '77 so we're talking about 35+ years. Good Grief Charlie Brown!

What I don't know is what sort of practical time scale for corrosion we're talking about.

[David Tilston]

Not being a corrosion expert, I was a bit worried when I attached aluminum stair nose moulding to my outside stairs, I did not know what to use for screws. On the advice of some stranger, I used the brass screws. My dad was dubious about how long that would last.
Here we are four years of snow and salt later, and no signs of corrosion.
I never did look up the redox potential between them.