Grade 8 bolt corrosion resistance?

[mrblaine]

Are you doubting Damlier's superior knowledge Ive been told by numerous "bolt" suppliers" when in the Gov sector most all SS hardware you'll find at the local stores (TDH?? brand) is considered G5. Working at a coastal water plant I will say is if you plan on dismantling what ever you use them om and dont use anti seize they gall easily and will destroy threads.

The shit under the hood of a TJ started long before Daimler got aholt of them.

I almost always use a zinc plated nut on SS threaded fasteners due to the galling issue. If you really want to gall them faster, use an impact on them.

 

[Steel City 06]

Isn't is just easier to look at the examples of practical application we can see under the hood of a TJ and understand that theory is great, but we can do a lot of things that just work by following existing examples in application?

Underhood areas are generally less exposed to electrolytic fluids than elsewhere on the jeep, such as on the underbody.

During normal operation, even with moderate amounts of salt spray, large areas under the hood will remain dry or nearly dry due to the large amount of heat produced by the engine.

Even in cases where a small amount of salt spray reaches dissimilar metals, it may not start galvanic corrosion. In order for galvanic corrosion to begin, the electrolyte has to be continuous between the two metals. If there is a drop of salt water on a steel bolt and a drop of salt water on an attached stainless nut, no galvanic corrosion can occur unless the two drops are connected, or one drop spans between the two metals.

While I would say that the underhood array of dissimilar metals is not ideal, that particular environment is not as big of a deal as say the frame.

Automakers also rely on the principle of encapsulation (think paint/powdercoat) in a lot of cases to prevent corrosion (not just galvanic). Encapsulation stops galvanic corrosion because the material is not exposed to an electrolyte, and it also prevents other forms of corrosion, such as oxidation/rust from general oxidant exposure. That said, encapsulation is not perfect, and chips/scratches can pose a significant corrosion hazard.

Galvanization is a particularly unique type of corrosion protection, because it not only encapsulates the metal, but also provides galvanic protection to exposed portions.

Another example of where galvanic corrosion may not be such a big deal is in the interior of the jeep. Most keepers only rarely get their interior wet, if at all. And typically it is freshwater or rainwater rather than salt spray. So areas of dissimilar metal inside the cabin may generally not be prone to galvanic corrosion, even when dissimilar metals are coupled.

 

[freedom_in_4low]

I just replaced 8 rusty carbon steel windshield and door hinge bolts with stainless fasteners from Jeep Hardware. Like literally, yesterday lol.

I did use generous application of antiseize both on the threads and where the countersink taper meets.

 

[The shuggs]

Replace the bolts with the zinc coated ones. The black oxide & oil coatings will protect the bolts from rusting due to moisture in the air, but under a vehicle where there's spray that will wash off the oil in no time, and salt that the black oxide can't handle. The zinc coating will last a lot longer. Considering it's a recovery point, I'd prefer a stronger bolt anyways.

And before anyone says a grade 5 bolt is strong enough, that can only hold true as long as the bolt hasn't been compromised by accelerated corrosion due to inadequate coatings.

If you are going to get stainless, just bite the bullet and get 316, 304 is shit in salty conditions.

 

[sab]

Steel City 06:

Your treatise on galvanic corrosion is quite accurate, but there’s a lot more to to the “zinc plating” process (quotes because that’s just one step in the process) than you’ve shared, and what’s missing is vital to a full understanding of corrosion in modern fasteners. You are correct that the steel is zinc coated (zinc oxide, actually) and that the zinc oxide is sacrificial. However, those are the suspenders in a belt and suspenders approach to corrosion resistance.

The belt is the topcoat of chromate applied afterwards, which, as long as it remains intact, is highly non-corrosive. Today, trivalent chromium is used for the chromate tocoat, but years ago, and for decades, hexavalent chromium was the norm. Unfortunately, hexavalent chromium is a strong oxidizer and highly carcinogenic. Europe’s RoHS killed it. The chromate topcoat is the ticket to a long rust-free period for the steel. However, if it is compromised, the underlying steel would immediately begin corroding. Hence the zinc basecoat. When the zinc corrodes, it forms a barrier that buys the steel quite a bit of time. However, if the topcoat isn’t compromised, the zinc is protected from corrosion and doesn’t need to sacrifice itself at all. Belt and suspenders…

Also, with regards to stainless steel fasteners, most are passivated in a nitric acid bath. This allows the chromium (a key alloying element in stainless steels) in the base material to form a chromium oxide barrier (similar to the chromate topcoat mentioned above) on the surface. Additionally, and unlIke the chromate layer on steel fasteners, this passivated surface is self-repairing for small scratches because there is more chromium in the base material that reacts with oxygen in the atmosphere to repair the scratch. That is why stainless steel fasteners take longer to corrode. This passivation process is why - in theory - stainless steel fasteners shouldn’t work, but in reality, they do, as Mr. Blaine has attested.

And that, as Paul Harvey would say, is “the rest of the story”

 

[Atomicat]

Galvanic corrosion will generally occur between any pair of dissimilar metals. The rate at which it occurs depends upon the galvanic potential as described in a galvanic series. Stainless steels are generally far higher in a galvanic series than either carbon steel or aluminum, and will generally result in significant galvanic corrosion of either of the two materials.

Aluminum and carbon/plain steel are quite close in the galvanic series, and typically there is only small increase in the corrosion rate of the steel when the two metals are used together.

Also note that zinc is one of the most aggressively corroded metals in the chart, and that it will corrode long before the other metals. This is how zinc playing can protect a fastener or adjacent material, even if the coating is chipped. It is considered a sacrificial anode, meaning it corrodes in order to protect the surrounding metal. It works very well with carbon/plain steels, and to a lesser degree aluminum. It generally does not work well with stainless steels as the very large potential difference results in very rapid consumption of the zinc plating.

Zinc is often used as a sacrificial anode on boats and other metal underwater structures as its corrosion prevents the corrosion of surrounding metal.

Note that in order for galvanic corrosion to occur between two or more dissimilar metals, two conditions must be met. The dissimilar metals must be electrically connected, and also immersed in the same electrolyte. If either condition is broken, galvanic corrosion stops (however corrosion may continue in other forms).

In the case of most automobiles, they tend to operate above water, and not in it. The electrolyte can often be the air itself, which is not very conductive, though the presence of large amounts of moisture and salt particles can make it more conductive. Salt spray from the road can create a film of conductive electrolyte that vastly increases galvanic corrosion.

In automotive design (as well as many other engineering disciplines), great care is taken to electrically isolate dissimilar metals. This is why Ford and other manufacturers of aluminum-bodied steel-framed cars forbid anything that could electrically couple the body and the frame. If the two materials are properly isolated, no galvanic corrosion occurs (again, other types of corrosion can still take place).

Dielectric grease on the threads will isolate the dissimilar metals and break the galvanic reaction.

 

[Gollywomper]

I can’t tell you anything about the process or chemical make up of different bolts. I can tell you my experience with bolts of forklifts in a highly corrosive environment. I have worked on lifts at an olive plant for the last 23 years. They use a lot of salt water, lye and acids. These chemicals will eat aluminum hydraulic manifold within a few years. I have messed with lift manufacturers that have used black oxide, untreated and now our lifts use zinc coated fasteners. The zinc plated bolts out perform all others other than stainless. I would only use stainless when absolutely needed. Zinc plated will work just fine. Sitting on your bumper they will last a long time.
How many of you all replacing the Savvy hardware with stainless?

 

[Gollywomper]

Dielectric grease on the threads will isolate the dissimilar metals and break the galvanic reaction.

No it won’t. The threads will make contact.

 

[sab]

I can’t tell you anything about the process or chemical make up of different bolts. I can tell you my experience with bolts of forklifts in a highly corrosive environment. I have worked on lifts at an olive plant for the last 23 years. They use a lot of salt water, lye and acids. These chemicals will eat aluminum hydraulic manifold within a few years. I have messed with lift manufacturers that have used black oxide, untreated and now our lifts use zinc coated fasteners. The zinc plated bolts out perform all others other than stainless. I would only use stainless when absolutely needed. Zinc plated will work just fine. Sitting on your bumper they will last a long time.
How many of you all replacing the Savvy hardware with stainless?

Like Mr. Blaine said, getting stainless bolts with a tensile strength in the range of the Grade 8 spec is very expensive. For this reason, my Savvy bumper has Grade 8 steel fasteners. I do, however, use stainless fasteners when strength isn't important. They just look so purdy.

 

[Atomicat]

No it won’t. The threads will make contact.

Uh, not if you lightly coat the threads.

 

[Atomicat]

I've used it for years in outdoor environments for telecommunications. The entire industry uses it various ways to prevent the reaction between metals.

 

[NashvilleTJ]

Uh, not if you lightly coat the threads.

So think about that. Your saying that if you take a bolt and a nut, coat the surfaces with dialectric grease, tighten the bolt onto the nut, run a multi-meter from the bolt head to the nut - and you will get no continuity?

Golly’s right - it doesn’t work that way.

 

[sab]

What Atomicat is talking about is the galvanic corrosion that Steel City 06 discussed. In order for corrosion to occur, you need an electrolytic medium to propagate the corrosion via electrolysis. Coating the bolted joint with dielectric grease can prevent the electrolytic medium from allowing the electrolysis to occur by preventing water from making contact with both metals. However, I would consider that a fairly short-term solution because as soon as that grease washes off, it's no longer effective.

 

[Gollywomper]

What Atomicat is talking about is the galvanic corrosion that Steel City 06 discussed. In order for corrosion to occur, you need an electrolytic medium to propagate the corrosion via electrolysis. Coating the bolted joint with dielectric grease can prevent the electrolytic medium from allowing the electrolysis to occur by preventing water from making contact with both metals. However, I would consider that a fairly short-term solution because as soon as that grease washes off, it's no longer effective.

As soon as the bolt is properly torqued it will be in contact with what ever it is screwed into. Even if the head of the bolt was coated you still have the frame end of the bolt that is exposed.

 

[mrblaine]

This discussion reminds me of the ones about Co2 producing carbonic acid inside tires that will eat through your rim and kill you.

 

[DrDmoney]

This discussion reminds me of the ones about Co2 producing carbonic acid inside tires that will eat through your rim and kill you.

Those expensive ARP 12 point SS fasteners are sounding better.

 

[sab]

As soon as the bolt is properly torqued it will be in contact with what ever it is screwed into. Even if the head of the bolt was coated you still have the frame end of the bolt that is exposed.

I understand that. The point is that by greasing the bolt, you prevent it from being wetted. No water, no electrolysis. No electrolysis, no corrosion. (until the grease washes off)

 

[Artsifrtsi]

This discussion reminds me of the ones about Co2 producing carbonic acid inside tires that will eat through your rim and kill you.

https://www.dhmo.org/facts.html
Very dangerous stuff...

 

[DrDmoney]