Ok people...
Here is how it goes... No matter who you are, as a fabricator, you are going to have some discrepancy in your product, somewhere along the line. You have to think about where they get their materials from, the quality of that material, and how its handled as well.
I agree that they are atleast looking at the parts that are broken, to learn how to rectify any weaknesses, or issues.
And yes, heat does weaken metal, so think about your science class folks... when heated molecules expand, when cooling they contract.... now, think about it in thousands of cycles.... anything, if not prepped properly will give in/crack/break.
My suggestion to Megan would be to use 16 or 14 gauge piping, they may have to increase the pipe diameter to offset the gauge thickness, and allow the same flow. DC from my understanding and research uses 16 gauge pipes.
As for the welds.... maybe they should test them in an environment that exceeds its natural habitat... In other words, get a Camry/Solara/ES300, install their components to it, and run this vehicle hard... Im talking autocross hard. Then, do a spot check on the components to see how they stood up to that abuse.
Anyway, enough of my ranting... I will consider Megan when I decide to get headers for my Solara. All depending on price, and how the final product turns out.
Sorry for the long post, Im ex-military, and did a lot of quality control, still do...

Geeks get it done, while Nerds whimper and call for mommie.