Thanks for all the replies guys.

The only thing that makes me wonder about your answers suggesting it is stress related is that this is a brand new frame.

The crack appears directly in line with the rear side of the joint circled in the attached picture.

Hi All, On inspecting a few welds recently I've spotted some cracks on the back side of some T-joints. These are on the inside of a bicycle headtube, 6061, approx 2mm wall thickness. The joint is only welded on one side (It's actually tube to tube rather than a T-joint). When sanded, the cracks tend...

Hello,
I'm a materials science graduate with a grasp of the basic theory behind sticking metal together, starting m explorations into the practical side and looking to learn from the best!