Galvanic issues?

Status
Not open for further replies.

captainwireman

Senior Member
Location
USA, mostly.
Situation:
A four inch round aluminum traffic rail supported by stout thirty inch high aluminum stancions on a hydro-electric facility. The rail sections are to be bonded, every other stancion.
My concern is the use of bronze nuts and bolts for mounting the bonding wire to the stancion. The stancion was drilled out for the mounting bolts. I see the stancion being a big anode and the cathode being the bronze. Somewhere I recall some kind of elevated decay because of, in this case, there will be small scratches making contact at the bolt/stancion surface where the now occurring aluminum oxide is. For a reason I don't know, the article I read said this was an ideal condition for galvanic action if a conductive environment is present.
My assessment is the bronze bolts, being a higher noble, will eat away at the aluminum stancion.

Is this a legitimate concern?
 

FionaZuppa

Senior Member
Location
AZ
Occupation
Part Time Electrician (semi retired, old) - EE retired.
yes, always a reaction when two different metals touch, bronze will eat the AL. really need to know the species of each
can a yellow zinc or galvanized fitting be used, it plays nice with both Al and Cu. that would be my choice if you can find one that is UL listed

www.npfasteners.com/pdfs/galvanic-corrosion-chart.pdf


 
Last edited:

captainwireman

Senior Member
Location
USA, mostly.
Let's talk about a solution. I am thinking standard aluminum bolts and nuts slathered in noalox or other equivilant anti oxidant.
Any better ideas? The lug is a standard Burndy two hole which appears to be steel or tin, whatever they make the conductive surface out of.
 

FionaZuppa

Senior Member
Location
AZ
Occupation
Part Time Electrician (semi retired, old) - EE retired.
i would use yellow zinc hardware for its corrosion properties. Al will oxidize no matter what. if you use Al hardware will also oxidize, so you would have another layer of Al-oxide.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
i would use yellow zinc hardware for its corrosion properties. Al will oxidize no matter what. if you use Al hardware will also oxidize, so you would have another layer of Al-oxide.

It's not oxidation per se that is the issue. Standard Al oxidizes and then basically stops because the oxide layer has a lower bulk density than the base metal so it "piles up" and protects the base metal. Iron oxides on the other hand have lower bulk densities than pure iron so when they form they pull together, exposing more base metal. Think of a dry lake bed with the alligator cracking of the mud.

If you use Al nuts and bolts, all else being equal, this would be the best possible solution since in the presence of moisture, you won't get the anode/cathode reaction you see with dissimilar metals.
 

FionaZuppa

Senior Member
Location
AZ
Occupation
Part Time Electrician (semi retired, old) - EE retired.
Al oxide (Al2O3), a non-metal, general, 1x104 ohm-cm

so i might argue you want to minimize the Al oxide. having yellow zinc up against Al might keep Al oxide at bay, thus perhaps giving you a overall better electrical connection.

Aluminum oxide is an electrically insulating material

since threading is not the best place to make electrical contact, i assume here that its the lug pad to the Al that is making the connection.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
We solar guys bond aluminum outdoors every day.

Standard practice is stainless steel hardware separating the aluminum from a tin-plated-copper direct burial lay-in lug. Some products out there are all stainless steel. A star washer typically goes against the aluminum to dig into it and ensure that the oxidized or annodized layer doesn't insulate the material from the bond.

This is for copper bonding wires. If your bonding wire is aluminum then I guess all aluminum hardware would be fine, albeit probably harder to come by.
 

FionaZuppa

Senior Member
Location
AZ
Occupation
Part Time Electrician (semi retired, old) - EE retired.
We solar guys bond aluminum outdoors every day.

Standard practice is stainless steel hardware separating the aluminum from a tin-plated-copper direct burial lay-in lug. Some products out there are all stainless steel. A star washer typically goes against the aluminum to dig into it and ensure that the oxidized or anodized layer doesn't insulate the material from the bond.

hmmm, interesting, a star washer will do the initial cut. give it some time, Al oxide will form on the Al between the Al and washer (Al exposed to O will oxidize).

yellow zinc or galvanized is better than SS hardware on Al for corrosion of dissimilar metals. SS is also much more $$$.
 

big john

Senior Member
Location
Portland, ME
I've done a ton of hydroelectric work: I agree, stainless will work fine. Aluminum structure with stainless hardware is a very common thing to see and it lasts for decades.

I would through-bolt the stanchion and then secure my bonding lug on top of the stainless retaining nut.
 

FionaZuppa

Senior Member
Location
AZ
Occupation
Part Time Electrician (semi retired, old) - EE retired.
so, i originally thought it was a fitting by which a copper wire was affixed to. but this is a crimped lug (presumably tinned) that will be making the electrical contact with the Al. or is the lug to be sandwiched between two nuts?

if its lug on Al, then it seems it doesnt matter what bolt/nut hardware is used for the electrical component of the install, but the corrosion component says that yellow zinc is a better choice and less $$ than stainless.

that said, whatever is chosen, i would clean the Al prior to install, use some conductive anti-corrosion paste under the lug (just a light smear), .... done.
 

FionaZuppa

Senior Member
Location
AZ
Occupation
Part Time Electrician (semi retired, old) - EE retired.
acorn_copy.jpg
 

captainwireman

Senior Member
Location
USA, mostly.
The application approved is a Burndy two hole lug crimped on a bare copper tap wire. The stancion is drilled out to accept the silicone bronze bolt lockwasher and nut. The hole is oversized to accept the 3/8 bolt, no tap or threading. No prep or cleaning the aluminum, no antioxidant compound of any kind. I don't like this and I want to present a legitimate issue. I obtained all kinds of information on the web supporting my case.

So,
Is this something that really will not be any kind of problem for the next fifty years?
Will the bronze eventually compromise the electrical connection?
How long will it take? A year or one hundred years?
Will this application cause enough corrosion to eventually fatigue the aluminum enough so a person could grab the copper tap conductor and yank it right off the stancion?
 

mgookin

Senior Member
Location
Fort Myers, FL
The application approved is a Burndy two hole lug crimped on a bare copper tap wire. The stancion is drilled out to accept the silicone bronze bolt lockwasher and nut. The hole is oversized to accept the 3/8 bolt, no tap or threading. No prep or cleaning the aluminum, no antioxidant compound of any kind. I don't like this and I want to present a legitimate issue. I obtained all kinds of information on the web supporting my case.

So,
Is this something that really will not be any kind of problem for the next fifty years?
Will the bronze eventually compromise the electrical connection?
How long will it take? A year or one hundred years?
Will this application cause enough corrosion to eventually fatigue the aluminum enough so a person could grab the copper tap conductor and yank it right off the stancion?

The design of many engineered systems includes periodic inspection. You'd have to know the chemical composition of the water and air to make a prediction as to longevity. Your system sitting in an arid desert would last much longer than it would if it were sitting under the 7 mile bridge in the Florida Keys.
 

FionaZuppa

Senior Member
Location
AZ
Occupation
Part Time Electrician (semi retired, old) - EE retired.
in context of the electrical connection, bronze is not involved as the burndy is being held down to the AL. 3/8" bronze bolt should last a long time w/o eating through the AL. if there is no "warranty" or it says "warranted for 5yrs" then it will be fine and legally no obligations past 5yrs, etc. what do the legal docs say?

for a better connection i would
1) use yellow zinc hardware (may be less $$ than bronze)
2) use some conductive anti-corrosion under the lug

are you the owner of the legal docs or just the installer? if the latter, install as prescribed and dont worry about it.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
hmmm, interesting, a star washer will do the initial cut. give it some time, Al oxide will form on the Al between the Al and washer (Al exposed to O will oxidize).

yellow zinc or galvanized is better than SS hardware on Al for corrosion of dissimilar metals. SS is also much more $$$.

That's news to me. And I would never trust galvanized hardware in these situations, if I could even obtain it for such small parts.

Yellow zinc plated? Outdoors? You cannot be serious.
 

FionaZuppa

Senior Member
Location
AZ
Occupation
Part Time Electrician (semi retired, old) - EE retired.
That's news to me. And I would never trust galvanized hardware in these situations, if I could even obtain it for such small parts.

Yellow zinc plated? Outdoors? You cannot be serious.

zinc dichromate hardware should last a "lifetime". if it were salt env i would be ok with SS only, but then again, in this case (if it were salty env) why SS if the other parts would be destroyed, so cost of SS doesnt make sense to me.

3/8" hot dipped bolts you cant find ???

SS or zinc dichromate (or maybe zinc-cobalt alloy) ?? a choice that as of now needs a good use/cost analysis vs the prescribed bronze hardware. if bronze will last the period of "warranty" then so be it, install and be done with it.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
zinc dichromate hardware should last a "lifetime". if it were salt env i would be ok with SS only, but then again, in this case (if it were salty env) why SS if the other parts would be destroyed, so cost of SS doesnt make sense to me.

I've never seen any kind of zinc plated hardware touted for long term exposure to the elements. You'll have to cite some sources for me.

3/8" hot dipped bolts you cant find ???

Try 10/32 machine bolts and kep nuts. And star washers. Hot dipped #10 star washers? Yeah, I don't think those exist. Prove me wrong.

Also the stainless does much better than hot dipped galvi for the 3/8" stuff, after a couple years.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
This discussion is above my pay grade, but consider:

If the (large) aluminium surface is acting as a sacrificial anode for the (small) fasteners, then the fasteners themselves will be protected, and because of the relative size the corrosion of the aluminum may be negligible.

Stainless steel fasteners would be quite happy in this situation, but the aluminum material around those fasteners may be quite unhappy.

-Jom
 

FionaZuppa

Senior Member
Location
AZ
Occupation
Part Time Electrician (semi retired, old) - EE retired.
This discussion is above my pay grade, but consider:

If the (large) aluminium surface is acting as a sacrificial anode for the (small) fasteners, then the fasteners themselves will be protected, and because of the relative size the corrosion of the aluminum may be negligible.

Stainless steel fasteners would be quite happy in this situation, but the aluminum material around those fasteners may be quite unhappy.

-Jom

i think we all agree with ya. zinc-dichromate is much closer to Al than SS is.

hot galvanized zinc coated hardware is also good, many times thicker than zinc-dichromate plating, and is close to Al on the chart.

hot galvanized zinc coated hardware has been used on roadway structures for a long time and has proven to be a good coating to thward off corrosion. cheap and effective.

read about zinc use till your eyes burn
http://www.galvanizeit.org/sustaina...galvanizing/what-is-zinc/zinc-in-construction

http://www.finishing.com/421/40.shtml

SS is ok, not as good as zinc to Al on the chart, and SS costs a lot more.

post #17 ???? post #12 says 3/8" bolt, so where does #10 come into this? $$ for 3/8" SS bolt vs 3/8" hot zinc, is a big diff. SS is about 2.5x more $$.
 
Last edited:

mgookin

Senior Member
Location
Fort Myers, FL
We use hot dipped zinc bolts to build docks over salt water. As the tide rises and falls, the bolts are under water and out of the water. That's what I call exposed to the elements. Not sure if I read a previous post in the intended context.
 
Status
Not open for further replies.
Top