Hello,

I have bought a 1997 Bianchi Mega Titanium frame about 4 months ago. Recently, I have discovered a tiny scratch or crack on the upper right side seat-stay.
It is right below the seatpost bolt. The "crack" extends a little into the weld. As it does look like a typical crack, I was about to find a titanium welder. But before that, I want to make sure...

The frame was brush-finished, so the titanium was never really smooth and shiny to begin with. Since the "crack" looked more shallow than the crack on my previously cracked carbon bike, I decided to sand it a tiny bit with my dremel. To my surprise, the more shallow side of the crack has disappeared. I was thinking the titanium dust may had filled the crack, but it remained the same after I cleaned it with a wire brush, water and windex. Now I am really not sure.



The orange circle is the entire "crack", while the red circle is the part that I haven't sanded with my dremel.
The bike has no change in handling after the crack was found.

This Bianchi is a later production that does not crack as often as the earlier units. I am 160lb and the previous owner was below 120lb.

Many thanks!

One more question - do welders usually just fill in a crack like this, or a tube-replacement is needed?

That "crack" may indeed be a scratch. It's direction makes me think it isn't a crack since cracks would usually be circumferential and parallel to the weld line, not about 45° to it. I'd just ride the bike and observe it occasionally for signs of spreading but I think the frame is fine.

Thanks, I will keep riding it, unless the "crack" expands or something else happens.

NB: Ti will, stress riser, crack, starting from scratches..

Since there's nothing you can do about it anyway, best to ride and observe. Use nail polish or touch up paint to fill the crack via the apply and wipe technique. Then you can quickly know if/when the crack begins to grow beyond where you've filled it.

BTW- there's no danger in riding it because it'll grow quite a bit before it breaks, and seatstay breaks are just about the least consequential.

So will any other material. What's your point?

steel much less of an issue .. Ti is less subject than aluminum ,

but is much more subject than steel.

You need a oxygen purged welding situation with TI and so a specialist welder need be found.

if that scratch becomes a crack and grows.

Can't speak to his point, but Ti is more prone to notch failure than other materials (depending on the alloy, temper and depth of notch). But this scratch's orientation is favorable compared to one running along the weld line.

Either way, it barely matters because there's not anything the OP can do about propagation or potential notch failure. What will happen will happen, if it'll happen, but it could be years out so the OP can cross that bridge if/when he comes to it.

Absolutely correct. If it is indeed a crack and propagates, the OP will have to find a welder completely familiar with the preparations (cleanliness, inert gas purge on both sides of the weld, etc.)needed to weld Ti. The welder guy at Joe's Body Shop won't do.

A final thought. The location of that "crack" is under compression when the bike is ridden so, even if it truly is a crack it is unlikely to see stresses that make it propagate.

That is not a very good weld in Ti. A good Ti. weld is small with ine ripples.
It looks more like an Aluminum weld.

I agree. The Italians were probably not very experienced at welding ti, especially back in the 90s.
My next titanium frame will be a Serotta or Moots.

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Knowing the titanium tubing is quite thick, I ended up sanding the rest of the "crack" away with my dremel.
The steel tip is not very effective at grinding titanium, but I did manage to remove the entire "crack". The "crack" looked deeper than it really was, I could observe very little titanium dust.

Since the titanium is undamaged underneath, I think this is just a deeper scratch. That part of seat stay should not take much stress.

The steel grinding tip may have left iron residue on the Ti so you may find rust stains if it gets wet. A wash with a mild acid (citric for example) will avoid this and won't hurt the Ti at all. This is why boat owners use bronze wool (not steel wool) to clean bright work.