Old 01-11-19, 11:06 PM
  #19  
repechage
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Originally Posted by Doug Fattic View Post
The situations I was referring to looks just like the yellow frame Merziac posted. Where the rusting-from-the-inside-out is most common is the very underside of top and down tubes and chain stays. If a person doesn't clean their bikes often the problem can go unnoticed. Sweat induced rust is usually found on the top of the top tube - especially around top mounted brake cable guides. I've done many repaints where that was the only issue. In these cases because the rust is starting on the outside early damage is visible and not as likely to be as destructive before corrective measures are taken.

Where inside rust creates holes is most common is when lighter heat treated steels (like Tange Prestige) began to be used. I don't remember seeing this nearly so often on heavier Reynolds or Columbus tubes from the 80's and before. Partly this is due to older frames having thicker walls. However different steels rust at different rates. One of my framebuilding class students had his shop flooded with hurricane Sandy so his inventory of various brands of tubes were immersed in a salty sewage brine. Some of some of those tubes rusted a lot and others not at all. Of course what kind of oily protection played a part too.

I made myself a fancy lugged frame back in the 80's. It was for a contest that Bicycling magazine did in conjunction with Shimano to market their Sante brand of components so I kind of went all out doing extra stuff. For the seat post binder I used the concept of a Cinelli 1R stem that had a push plate to secure the seat post so the seat lug did not have a visible binder bolt and the whole lug could be carved. While the concept worked okay to hold the seat post it also let moisture in the crack between the lug and post allowing water into the top tube. Eventually because I rode the bike a lot and sometimes in the rain, rust with small pin holes developed on the very underside of the top tube. When I repainted the frame to save it I used a kind of stuff that turns rust into primer (inside the top tube). After that I used a combination of silver and body putty to patch the holes and it still is working fine today. I remember rushing like crazy to get the bicycle together so it could meet the contest deadline and I didn't spray the insides with rust preventative.
I did have a DeRosa that was a replacement for a failed frame, the original looked good, most likely the problem started with an incomplete or skipped rinsing step in the chrome plating process. pinholes from the inside out within 24 months of purchase. Stored indoors, no rain riding, southern california... De Rosa replaced it no questions asked.
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