metal gurus....is putting a grade 5 titanium bolt (3mm) through Tethrd One stick's steel roll pin a galvanic disaster?

[raisins]

I'm not a fan of the roll pin.

I've sourced titanium bolts that you can put through them as "super back up"...I know not necessary....yeah, I know.....but I likie.

Anyways, if these get wet inside and you have that carbon steel roll pin sitting against a bare titanium bolt....is that a bad thing?

I've searched and searched and yeah, it will accelerate the corrosion of the carbon steel...maybe....but the amount is not known. Folks use titanium bolts all the time on motorcycles into steel though, it seems.

 

[thedutchtouch]

@Weldabeast would be the person on here that I'd send questions about metallurgy, though I'm guessing there's other knowledgeable people here as well...

 

[woodsdog2]

I know aluminum and steel combined together (e.g. an aluminum bike seat post in a steel chromoly bike frame seat stem) must be coated with a light film of grease to prevent corrosion if moisture or water infiltrate that union but with these sticks, I don't think they would be exposed enough on a long-term basis to have that level of corrosion, but you never know. I guess I'm saying I'd be much more concerned about it if you were leaving them up all the time. Not sure if Ti and CrMo (steel) have the same interaction issues or not.

 

[Weldabeast]

I don't have much Ti experience but anytime 2 dissimilar metals contact u can expect some galvanic reaction....Ti galls up easy like stainless so use antiseize....I don't remember exactly how those things are put together but I think the step sleeves over the tube and then a roll pin locks in place right? Why are u worried about the pin? Can u not drill out the roll pin hole and use a grade 8 bolt

 

[gcr0003]

Galvanic corrosion can occur when two dissimilar metals are in contact with each other. Dissimilar metals are those whose chemical composition are further away from one another (cathodic vs. anodic) which deals with the amount electrons the metal has. If you mix a metal that has less reactive electrons with a metal that has a lot of reactive electrons the more chance you have of the two reacting. Seawater (salt water) will speed this up since salt water does something weird (I am no chemist) with ions that allows electrons to transfer faster which in turn causes the material surfaces to react faster (corrode).

So yes it is best to avoid extremely dissimilar metals, especially if they will be exposed to salt water. That doesn't mean they can't be used in some situations. They will likely still react to one another if they get (and especially hold) moisture; however, if they aren't going to be exposed to that the chemical process will likely be slow and surface. I haven't looked up tethr'ds stick so I can't verify that it is a carbon steel, nickle plated, etc. You can use the chart below to help you determine the application. If they are carbon steel and you plan to use titanium it may corrode up and be difficult to remove. That said, the carbon steel is what is going to get ate up first so you may not want to risk it. How long that will take and to what extent will it corrode? I have no clue. Things like loc-tite or anti-seize (depending on the application) can aid in reducing corrosion both by creating a layer as well as sealing the application to some extent.

Crazy question, why not use a steel bolt that would be more similar to the base material? Surely it is not going to make that much of a weight difference. I assume weight is the main reason you're going with titanium? What is the size of the bolt? .125? .60? smaller?

I am no metallurgy expert, but generally speaking these are my thoughts. Good luck, let us know what you do and share pictures when you're done.

 

[enkriss]

For what?

The only thing you are going to fit in the pin is a 4-40 screw. You aren’t gaining any strength by doing that. The only thing it will do is stop the pin from walking out.

Why waste the money on titanium?

You are over thinking this!

 

[raisins]

Thanks for the replies. I'll probably just go with a steel bolt. I wanted titanium not because of weight but because the double shear strength of a 3 mm grade 5 (high strength) solid titanium bolt is probably much higher than a grade 8 slotted roll pin (what Tethrd is using here). I know the titanium has a sleeve over the tube that hopefully extends between the aluminum standoffs and the tube. However, the grade 8 carbon steel slotted roll pin is potentially in direct contact with both aluminum and titanium. I hope that Tethrd did their homework regarding long term durability of those metals in contact with each other.

The thing that very small titanium bolts have over steel bolts is that I have not found 7/64" (or 2.5 to 3 m range) bolts that are "high strength"/grade 8/whatever. So, the titanium small bolt in grade 5 I'm guessing is much stronger.

 

[Horn]

Is Ti, especially at a small diameter, rigid enough? I'm not familiar with the sticks but Ti is actually really easy to bend/flex. Great memory so it'll probably come back but does that fit the bill? I don't know.

 

[raisins]

Just going with a steel bolt and will coat the inside of the roll pin and outside of the bolt with 3 in 1 oil before pairing up.

 

[raisins]

For what?

The only thing you are going to fit in the pin is a 4-40 screw. You aren’t gaining any strength by doing that. The only thing it will do is stop the pin from walking out.

Why waste the money on titanium?

You are over thinking this!

true, not something you can turn off and on that easily, it usually serves me well though

 

[raisins]

Is Ti, especially at a small diameter, rigid enough? I'm not familiar with the sticks but Ti is actually really easy to bend/flex. Great memory so it'll probably come back but does that fit the bill? I don't know.

didn't even consider that, thanks

 

[Still Kicking]

I have complete confidence in the roll pin in this application. The shear strength of those things is remarkable. I worked on a lot of precision machinery with tons of force for many years and things had to go really bad to shear even a 1/16 inch pin.