Section 180.212 - Repair of seamless DOT 3-series specification cylinders and seamless UN pressure receptacles(a)General requirements for repair of DOT 3-series cylinders and UN pressure receptacles.(1) No person may repair a DOT 3-series cylinder or a seamless UN pressure receptacle unless- (i) The repair facility holds an approval issued under the provisions in § 107.805 of this chapter; and(ii) Except as provided in paragraph (b) of this section, the repair and the inspection is performed under the provisions of an approval issued under subpart H of part 107 of this chapter or by a facility registered by Transport Canada in accordance with the Transport Canada TDG Regulations (IBR; see § 171.7 of this subchapter) and conform to the applicable cylinder specification or ISO standard contained in part 178 of this subchapter.(2) The person performing the repair must prepare a report containing, at a minimum, the results prescribed in § 180.215 .(3) If grinding is performed on a DOT 3-series cylinder or a seamless UN pressure receptacle, the following conditions apply after grinding has been completed. Grinding must not be used to remove arc burns from a cylinder, as such a cylinder must be condemned: (i) Ultrasonic examination must be conducted to ensure that the wall thickness is not less than the minimum design requirement. The wall thickness must be measured in at least 3 different areas for every 10 square inches of grinding area.(ii) The cylinder must be requalified in conformance with § 180.205 .(iii) The cylinder must be marked in accordance with § 180.213(f)(10) to indicate compliance with this paragraph (a)(3).(4) DOT 3-series seamless steel tubes with an outside diameter greater than 95/8 in (244.5 mm) may be processed by a repair facility for derating the marked service pressure in accordance with CGA C-27 (IBR, see § 171.7 of this subchapter).(b)Repairs not requiring prior approval. Approval is not required for the following specific repairs:(1) The removal and replacement of a neck ring or foot ring on a DOT 3A, 3AA or 3B cylinder or a UN pressure receptacle that does not affect a pressure part of the cylinder when the repair is performed by a repair facility or a cylinder manufacturer of these types of cylinders. The repair may be made by welding or brazing in conformance with the original specification. After removal and before replacement, the cylinder must be visually inspected and any defective cylinder must be rejected. The heat treatment, testing and inspection of the repair must be performed under the supervision of an inspector and must be performed in accordance with the original specification.(2) External rethreading of a DOT 3AX, 3AAX, or 3T specification cylinder or a UN pressure receptacle, and external threading of a seamless DOT 3AX, 3AAX, or 3T specification cylinder or seamless UN pressure receptacle originally manufactured without external threads; or the internal rethreading of a DOT-3 series cylinder or a seamless UN pressure receptacle when performed by a cylinder manufacturer of these types of cylinders. The repair work must be performed under the supervision of an independent inspection agency. Upon completion of the rethreading or post-manufacture threading, the threads must be gauged in accordance with Federal Standard H-28 or an equivalent standard containing the same specification limits. The rethreaded cylinder or UN pressure receptacle must be stamped clearly and legibly with the words "RETHREAD" and a post-manufacture threaded cylinder or UN pressure receptacle must be stamped clearly and legibly with the words "POST-THREAD", on the shoulder, top head, or neck. No DOT specification cylinder or UN pressure receptacle may be rethreaded more than one time without approval of the Associate Administrator. 71 FR 33895 , June 12, 2006, as amended at 71 FR 54398 , Sept. 14, 2006; 72 FR 55697 , Oct. 1, 2007; 82 FR 15897 , Mar. 30, 2017; 85 FR 85435 , Dec. 28, 2020; 89 FR 15668 , Mar. 4, 2024 82 FR 15897, 3/30/2017; 85 FR 85435, 12/28/2020; 89 FR 15668, 4/3/2024