So, I am doing some experimental welding for a company that I work frequently with. They do a significant amount of torch brazing for refrigeration and med gas. If you have ever done or witnessed torch brazing a 3 or 4" copper joint you know the insane amount of time and acetylene required to do this. That got me thinking why not use GTAW ? This company also employs a bunch of very proficient, qualified GTAW welders.
I've welded copper plenty of times with fantastic results both autogenously and with filler so I put together a typical copper socket joint and tried it. A 2" weld took me less than a minute and the structural integrity of the copper was much better than brazing. So I started looking in ASME Section IX at fillet welding procedure and performance qualifications (100% of the welding done would be fillet so no need to do a groove test to qualify for fillet).
Here's my question:

QW-462.4(d) Shows the test required for a pipe to pipe fillet weld. It requires a macro etch. I've performed macro etching plenty of times but never on anything as thin as .060" thickness (2" copper type L) How well would that work on something that thin? Would you be able to really see anything? Has anybody ever etched something so thin?

Am I looking at this incorrectly? Suggestions?
This is completely experimental on my part as I believe this could be an interesting alternative to brazing large diameter copper.

Thanks! -JJ