question concerning stainless steel bolts and captured nuts (1 Viewer)

[billmc]

I've been wondering about this for a while now since I have a nice set of stainless steel bolts. Using s/s bolts with carbon steel nuts such as this in the frame or body panels would give an anodic series difference of 0.25 or 0.35, which means the captured nut rather than the bolt will be sacrificed, especially in humid conditions. Is this really an issue? Does anyone have an opinion based on science or experience?

 

[rkymtnflyfisher]

That's deep.

I've never even given a thought to something like that. I'm sure there are going to be some good opinions and valid arguments on this subject.

 

[Shark56]

Definitely use Never Seize type product on the stainless.

 

[steffan]

corrosion won't be an issue any more than standard fasteners but as Shark56 said, you definitely want anti-seize on there: stainless is sticky/ prone to galling

 

[dlzadl]

X2 on the anti seize. Your grandkids will appreciate it.....

 

[1969FJ]

I would like to give a one line answer , but, it is better to read and understand. Never use SS and carbon , anti seize will really not last for the real problem.


How to Prevent Galvanic Corrosion Between Carbon and Stainless Steel - https://www.appmfg.com/blog/how-to-prevent-galvanic-corrosion-between-carbon-and-stainless-steel

 

[Living in the Past]

That's deep.

I've never even given a thought to something like that. I'm sure there are going to be some good opinions and valid arguments on this subject.

I have never even given a thought into using stainless steel hardware. But I have never given any thought into aluminum or fiberglass parts. Anti seize in the threads is good enough for the desert. Dealt with many rusted bolts and nothing compared to a rusted body.

 

[DougAustinTx]

I used nickel anti-seize on all my stainless bolts in my 40 nine years ago. Nothing has gotten stuck or corroded yet. I'm in Texas. Maybe a different climate would pose problems.

 

[billmc]

I used nickel anti-seize on all my stainless bolts in my 40 nine years ago. Nothing has gotten stuck or corroded yet. I'm in Texas. Maybe a different climate would pose problems.

Hi Doug,

Yes, mine is a VT truck, so I need to consider these things.

 

[billmc]

1969FJ - Thanks for the link. It confirms my worries. I'd rather have to bolts rust than the nuts.

 

[Bear]

Opinion:

There are different "grades" of stainless steel, based on the alloys added and their percentages. Most stainless steel fasteners have less shear strength and "pull" strength than their similar carbon sisters. And used near salt water, or salted roads with regular sodium salt or magnesium salts and their brines, metals will corrode, some very much more rapidly than others.

Most car collectors simply don't drive their classic cars when they know their winter roads are salted, or drive along the beach or park outside in salty fog. Corrosion will occur not only on fasteners but body panels and any other metals in exposed seams or untreated areas. Galvanizing, powdercoating, painting, and various plating can help but not eliminate the chances of corrosion--preventative maintenance can help spot a developing problem. It seems in our oxygen environment, among other things, nothing is forever.

Used with various antiseize compounds, stainless fasteners in non-critical applications and when of smaller sizes, have been used by collectors for years, again in non-stressed areas. Anytime someone substitutes an original factory applied fastener, there is the risk of altering the specs engineered for its use. A wise restorer is someone who knows when it's safe to substitute a fastener; someone not so wise will change all kinds of things and likely only realize their error when something goes terribly wrong.

And for anyone having their original nuts and bolts replated, ask your plater what he does to protect your fasteners from hydrogen embrittlement.

Above is only opinion, not recommendation; we always should do our own research.

 

[kerplunk]

The theory, as explained to me in reference to boat maintenance, is that electrons will attempt to escape to the water, and using a metal, like zinc, that lets go of them faster, will prevent more "noble" metals from corroding.....

But, I think the zincs will corrode away regardless of being connected to another metal. Maybe a little faster? But those stainless screws aren't going to be large enough to make that kinda difference. If those captive nuts are in a corrosive environment, the entire steel body is going to rust. (If you had a fiberglass or aluminum body, you'd want to put a bit more thought into it.)

So, I use them. I'm going to use either stainless or zinc plated, not bare uncoated carbon steel.

They are not as strong, as @Bear mentioned. I'm sure they are fine holding the radiator in, front bib to the fenders, transmission tunnel to the tub, but I'm not using them on suspension, roll cage, seats and seat belts, or anything in the drive train (maybe to hold the rear axle inspection cover on?).

And, I've also been told they don't conduct electricity as well. (saw someone in a boat melt their battery post using stainless nuts and washers to attach the cable). So, you probably need to be careful using them anywhere that you might need things to ground (windshield hinges?).

The one place I used them that I'm still questioning is the thermostat housing. Those two M10 ( or M8?) bolts that never just unscrew and always seem more rusted than anything else. And I did use anti seize on them. Gimme a couple years, or so, or however long the thermostat and everything else lasts and maybe I'll remember to report back....

 

[billmc]

Thanks for the good posts Bear and Kerplunk. I've been living with rust for over sixty years up here in New England, so I'm pretty well acquainted with how it goes.
Kerplunk - I'd be pretty worried about the stainless bolts in the cast aluminum thermostat housing, because that will have an anodic difference of .40-.45, which is very high. It's the aluminum that corrodes and I believe that's what causes the bolts to jam and break.

 

[Splangy]

I would like to give a one line answer , but, it is better to read and understand. Never use SS and carbon , anti seize will really not last for the real problem.


How to Prevent Galvanic Corrosion Between Carbon and Stainless Steel - https://www.appmfg.com/blog/how-to-prevent-galvanic-corrosion-between-carbon-and-stainless-steel

Real facts.

Yes, there is a potential galvanic corrosion cell that can form between a stainless bolt and a carbon steel body panel. Fortunately, the anode/cathode surface ratio is in your favor in this application because the anode (sheet metal & nut) are much larger than the cathode (bolt), reducing the corrosion rate and chance of significant pitting of the carbon steel.

That said, the corrosion cell still exists and may lead to rust staining of body panels if repeatedly exposed to water, or worse if exposed to a lower resistivity and/or depolarizing electrolyte such as salt water. Making sure you preserve the paint in between the bolt head and the body panel can prevent the rust staining on the outside of the truck.

Material selection and coating selection for corrosion prevention all comes down to the intended use and environment the parts will be subject to. If the most moisture the truck is going to see is the occasional rain or car wash, you’ll be fine. If you’re going to drive the truck in New England winters, well, you wouldn’t do that.

Yes, antiseize is a good idea to prevent galling, but isn’t going to solve the corrosion issue.