Usually it depends on the specific job you are working on whether you are required to stamp you weld with your assigned welder I.D., but I think is and ASME requirement (B.31.3 or B.31.1, section- IX). Certain states (Massachusetts for example) requires anyone working on steam systems (over 750,000 btu-output) be licensed (journey pipe fitter) even if you are just the welder.
The contractor I work for requires that every weld be identified by the weldor's company I.D., no matter what the system is. However, it may not be tracked to the point where a year down the road someone wants to see who welded what joint as that requires alot more effort to produce traceability. Meaning, after a system is welded and tested (hydro-pressure tests or other tests) the system is then "signed-off" by the client, which means they "bought" the piping system as welded once these tests are approved by an authorized inspector. No further traceability needed as the system is bought.
Anything that is used in the production of drugs (pharmacuitical or bio-tech) is strictly monitered by the Food & Drug Administration (FDA) and any piping system (other than but may include drains) is stringently traced. All welds are documented. A typical system is isomectrically drawn where all welds are logged with information such as : welder I.D., weld number, date, heat numbers of the fitting and tubing used. Most welds are optically inspected and video-taped using a fiber-optic camera which will snake down in a system and show the weld (inside of the tubing at the joint). These sytems are most always stainless steel tubing .049 to .065 wall and thicker. These are usually orbital welded with an automatic fusion welder.
Every single part to be welded must have a MTR (material testing report) which tells you everything about the part: what the percentages of the elements used to produce that part, size, ovality (how round it is), exact length (center to end), smoothness (RA defined by the specifications), and whether the systen requires electro-polished tubing and fittings or it may be mechanically polished.
Needless to say, this type of work requires alot more expense to build and design and so companies that specialize in the bio-tech, pharmasuidical and electronic systems installation have to charge alot more to the client to build their required piping systems. Did I mention Slope???? Everything built has to have proper drainage as these systems are steam-cleaned to change from one product to the next so everything has to have pitch (usually a minimum of 1/8" per foot). The client will hire an out side QA/QC to verify weld logs and maps along with using their own personnel to contiuously double & triple check these systems, because if the is anything not up to par........the FDA will not approve the system and the whole project (multi-million dollar ventures) will be nothing but shiney scrap metal.
Sorry I got into this too much and if I bored you, but that IS the way it is. The risk is great and so are the profits , but you have to be able to work smart to make it work. If I didn't answer your question than atleast I gave you more information than you had before.
I know somewhere in D1.1 it specifies the identification of welders. I can't remember where exactly, and I also do not have the code book in my possetion. It probably is under the section listed as "fabrication" and I think there is a paragraph titled "identification", if my memory is correct.