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Steel AN fittings on firewall?

amaris

Well Known Member
I'm not sure where to post this, so I'll put it in my model type, but applies to all.

I'm concerned about using aluminum AN fittings (or any important aluminum components) in FF so people recommend steel. I've not seen stainless steel fittings, just steel. Is there not concern about galvanic corrosion between the stainless and the steel? Or does the benefit of steel on FF outweigh the risk of corrosion?

Thanks.
 
steel

I used all steel FWF and it is black with some kind of anti-corrosion coating. Seems to be the standard.
 
Another never ending debate---Vans uses aluminum in some cases, and steel in others. We like stainless, but its a bunch costlier (?).
Personally I thinkn that if you had a fire hot enough to melt 2024T3 aluminum, then a lot of other things would go first.

Tom
 
The primary purpose for steel fittings FWF is for fatigue resistance in vibration environments. I use steel (or stainless) exclusively on the engine. On anything mounted firmly to the firewall, I will still use aluminum for large-size fittings.

Fire will likely burn through thin aluminum items (like a firewall-mounted cabin heat control valve) but in the time it would take to melt an AN fitting? A lot of other bad things will happen long before that happens.

One caution of using stainless fittings -- a stainless B-nut on a stainless flare fitting can seize and gall. Use a very light coating of nickel anti-seize.
 
Allen,

Stainless fittings are available at Anplumbing.com among other places. They are more expensive, but I went ahead. I have my brake and fuel line bulkhead fittings in stainless. No aluminum passthrough of any type on my firewall.
 
Thanks, everyone.

I think I'll go steel. It's a bit more but at least it's one less thing to be concerned with. Though as Tom points out, if it gets bad enough to worry about melting the fittings, I'm sure there will be many other issues to deal with too.
 
Use stainless rather than an oxide finish or plated steel. We want bulletproof fuel systems, so corrosion performance is notable. I've done one AOG call with rusty fittings. I don't know what got into the tanks, but a lot of steel parts looked like Brillo pads.
 
Steel and stainless steel JIC fittings can be purchased locally at just about any hydraulic shop. Most even carry braided SS teflon hose.
 
I did look at the JIC but they were essentially the same price as the AN versions. All look to be about $35-45 regardless.
 
Probably goes without saying, but just a reminder to make sure you get AN (or JIC) fittings, not SAE. That is to say, 37 degree flares, not 45.
 
It was probably overkill, but I used steel bulkhead fittings on my plane. It seemed like a good idea at the time. If I had it to do over again, I would use aluminum fittings. One word of caution, though: Whichever material you decide to use, be sure you orient them so you can get a backup wrench on the bulkhead fitting so it won't spin when you check the torque on the attached tubing B-nut each annual (You do that, don't you?), If you can't get a backup wrench on the bulkhead fitting, it will spin. The cockpit side of my firewall has 1" of sound insulation on it, making access impossible. Poor planning on my part...
 
Steel and stainless steel JIC fittings can be purchased locally at just about any hydraulic shop. Most even carry braided SS teflon hose.

A few words of caution here.

JIC fittings are slightly different than AN fittings, primarily in the tolerances. AN should be preferred when available. Certain styles of fittings don't seem to be available in AN which are available in JIC, and those can be very useful.

As for braided SS teflon hose that you might buy at a hydraulics shop - DON'T - !
Aircraft teflon hose has tiny carbon filaments in it that conduct any static charge to the ends where the charge can be dissipated to ground. Teflon hose from a hydraulics shop may or may not have that. I know of one catastrophic failure of an oxygen line because hydraulic shop hose was used. It caused fire damage and shrapnel damage to the glider, but fortunately no injury except for some ringing in his ears.
 
Why wouldn?t you use aluminum AN fittings on your firewall? Steel fittings on a shaking/vibrating engine might be a good idea, usually, but why would you need them on the firewall? Aluminum firings are lighter, less expensive, and are usually compatible with whatever you?re attaching to them.
 
Why wouldn?t you use aluminum AN fittings on your firewall? Steel fittings on a shaking/vibrating engine might be a good idea, usually, but why would you need them on the firewall? Aluminum firings are lighter, less expensive, and are usually compatible with whatever you?re attaching to them.

It's just a question of how much aluminum do I feel confident having in the engine compartment. Maybe going SS is overkill and as Tom points out if the aluminum AN fittings melt because of the temperatures of the fire, I've probably got many other issues to contend with.

Peace of mind for an extra $20? Probably worth it for me.
 
steve, do you know the part number or description of the teflon hose that hydraulic shops sell we shouldn't buy? and what kind of designation on the teflon that is ok?
thanks.
 
Will you tell us why you'd use aluminum?
Scott said it in the post below yours: "Aluminum firings are lighter, less expensive, and are usually compatible with whatever you’re attaching to them.". They're cheaper, too.
 
Not supposed to use

Just curious I understand we want to be as safe as reasonably possible (considering that we're taking to the skies in a contraption that we built ourselves) , but what about all the engines that have rubber,tygon,polyurethane, none conductive fuel lines? I'm unaware of any spontaneous combustion of these types of fuel lines unless too close to the exhaust system or an exhaust leak. So how can Teflon none conductive line be more dangerous than the other none conductive types that are sold specially as fuel lines?
 
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