49 CFR §178.33a-6

1. (a)By appliances and methods that will assure uniformity of completed containers; dirt and scale to be removed as necessary; no defect acceptable that is likely to weaken the finished container appreciably; reasonably smooth and uniform surface finish required.
2. (b)Seams when used must be as follows:
   1. (1)Circumferential seams. By welding, swedging, brazing, soldering, or double seaming.
   2. (2)Side seams. By welding, brazing or soldering.
3. (c)Ends. The ends shall be of pressure design.