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Cracked weld?

Old 03-14-16, 06:59 PM
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Seizedpost
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Cracked weld?

I have an old steel mountain bike frame with some cracks in the paint at the weld between the seatstays and the seat tube. I am trying to determine if the weld is cracked or if it is just the paint.
The left side has some missing paint because I scraped some away to try to figure this out. Notice that above the scraped out area there is a red line of rust, a crack in the paint.
Can you guys tell from the photos? If not, how should I figure it out? Penetrant dye?
Thanks!

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Old 03-14-16, 07:46 PM
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Is there a vet hole in the stay? you could spray some penetrating oil in the stay and see if any bleeds out at the possible crack. There's a good chance the paint is failing from differences of flexibility between the weld and the tube. Andy.
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Old 03-14-16, 08:37 PM
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It does not look bad.

The welds are not all that nice; some spots are kinda lumpy and I would not be surprised if they were done a little cold so the toes are not too well fused. What Andy says about the paint cracking makes sense, and the poorly fused toes would be a good spot for rust to take after the paint cracked.

You might think about hitting the rusty spots with some sand paper and a small precision file, focusing on the weld metal, doing your best to avoid gouging the tube. The lumpy, convex parts of the weld are not contributing to the strength of the joint, given that they are in excess of the weld's effective throat. You could then do a little poor-man's penetrating fluid test -- with some penetrating oil and corn starch, IIRC -- once you expose some sound metal around the problem area.

I doubt that the damage goes deep at all.
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