I work at a factory. That looks like expulsion from a weld. Leaving some "weld-flash" that was not cleaned-up. Hard to tell from the photos, but are the dimples from the welds "not-flat", and look angled from the surface of the metal? That would be from welder tip misalignment. I program and repair spot welding robots, so I might know a few things about this. If the spot welds look like a half-moon, and not a perfect circle, that is mis-alignment. That can cause a small ridge of weld-expulsion on the "light-side" of the weld. This would also cause poor, to no, adhesion of the priming process to this surface. Pretty much, just trying to paint weld-slag.
The difference between genius and stupidity, is that genius has it's limits. A. Einstein
Last edited by Lazarus Truck; 02-21-2014 at 11:46 PM.