I can't speak for all the instructors that teach AWS and other commercial training programs, but to my knowledge the difference between piping porosity and spherical porosity is covered during the discussion of the different types of porosity, i.e., aligned, uniform, elongated, etc.
I would assume (very dangerous) that like any training program, the basics are covered during the fundamentals portion of the seminars and code specific requirements would be addresses in that portion of the program. I've sat through several CWI seminars over the years and I seem to remember the instructors differentiating between the various types of porosity. The fundamentals portion of the seminars is general and not code specific.
I just checked three different recent welding codes, D1.1, D1.5, D1.6 and each addresses piping porosity and provides limitations for acceptance. I even went back in time and checked D1.1-83. Even then the three categories of welds, static, cyclic, and tubular, addressed the issue of how much piping porosity was permitted. There is no mention or limitations imposed on spherical porosity under visual examination . As I looked through the book I noticed there were a lot of notes and highlighted passages. The section on piping porosity is highlighted. I bet someone pointed it out to me and told me it was important or I used it in one of the courses I taught for the local AWS section and I thought it was important enough to note.
Evidently, it has been some time that the criteria for porosity has been limited to piping porosity in the structural welding codes.
Just a quick question, have you rejected structural welds that have to meet D1.1 because of spherical porosity? And if you have, what was your criteria based on? :( Once again, the in-house QC/QA program can be as stringent as you want to the point that none of the welds pass visual examination, but the third party inspector has to stick to the criteria that was agreed to by the owner, EOR, and fabricator.
Best regards - Al