49 CFR §195.222

1. (a)Each welder or welding operator must be qualified in accordance with section 6, section 12, Appendix A or Appendix B of API Std 1104 (incorporated by reference, see § 195.3), or section IX of the ASME Boiler and Pressure Vessel Code (ASME BPVC), (incorporated by reference, see § 195.3) except that a welder or welding operator qualified under an earlier edition than listed in § 195.3, may weld but may not requalify under that earlier edition.
2. (b)No welder or welding operator may weld with a welding process unless, within the preceding 6 calendar months, the welder or welding operator has—
   1. (1)Engaged in welding with that process; and
   2. (2)Had one weld tested and found acceptable under section 9 or Appendix A of API Std 1104 (incorporated by reference, see § 195.3).