Can Surface Rust Eventually Compromise A Frame?
 

How bad do spots of surface rust have to be, to threaten the integrity of a steel frame?

I have a vintage frame (SLX) with a few 1/4" wide spots of surface rust where the paint is chipped. But radiating out from some of these spots are squiggly black tracks which seem to be under the paint, and won't come off with Goof Off. I suspect those are rust tracks.

My plan has been to sand the rusty spots and touch up the paint, while leaving the black tracks alone. The bike will then be placed into duty as a high school boy's school bike including being locked up in the rain. I imagine any rust under the paint will continue to develop.

Will those rust tracks ever compromise the frame? If left untreated, would the spots of surface rust ever do so?

I'm basically wondering if we treat rusty chips simply for cosmetic reasons, or if there are functional reasons to do so?

Rust never sleeps.

therefore, eventually it will eat through and cause pin-holes.

If the frame is going to be used as highschool boys bike, it will be stolen long before the rust becomes a worry.

He'll lock the hell out of it. U lock + heavy chain. Almost all the bikes stolen off Portland streets were cable locked, per our police dept. I think there is a good chance he will take the bike to college, should he wish to. So the longer term longevity of the frame will, probably, matter.

Have we ever seen a quality (not gaspipe) steel frame that has been structurally compromised by rust? How bad did the rust look?

I would be more concerned about internal corrosion.

Potential fork assembly failures scare me far more than frame failures -- I have experienced three of the latter (one drive side chainstay, one bottom bracket shell, one downtube right behind the butting), and never felt my safety was compromised.

Yes

Ick! Was that caused by rust? Internal? I don't see any external.

I'll Framesaver the inside of this frame.

External - Frame was blasted and powder coated. I believe it spent a good share of it's life on a trainer getting sweat dripped on it.