But to answer your question. you have to document that you have welded with each "process" that you are certified to at least every six months starting from the date you took your original test.
Generally this is done by the QC department, or the QC inspector at each project to keep " your papers active".  But this could be done by a foreman, onwer, supervisor, basically anyone who has the authority to document that you welded with that process and sign a paper.

In my compnay, I test and qualify all our welders, so I keep track and record when they are coming up for requalification and when that date comes around, I run down and watch them make a weld, inspect it and make sure it meets visual inspecection, and then document the date, position, wire, piece, job number and type of weld on a form and put it in the file.  Then in six months go back and so all over again, haven't had a problem in years.
Chris