§ 154.524 Piping joints: Welded and screwed couplings.

Pipe lengths without flanges must be joined by one of the following: (a) A butt welded joint with complete penetration at the weld root except that for design temperatures colder than −10 °C (14 °F) the butt weld must be double welded or must be welded using: (1) A backing ring that for design pressures greater than 979 kPa gauge (142 psig) must be removed after the weld is completed; (2) A consumable insert; or (3) An inert gas back-up on the first weld pass. (b) A slip-on welded joint with sleeves and attachment welds is allowed for an open ended pipe with an external diameter of 50 mm (2 in.) or less and a design temperature of −55 °C (−67 °F), or warmer. (c) A socket weld fitting with attachment welds is allowed for pipe with an external diameter of 50 mm (2 in.) or less and a design temperature of −55 °C (−67 °F) or warmer. (d) Screwed couplings are allowed for instrumentation and control piping that meets § 56.30-20 and § 56.50-105 (a)(4) and (b)(4) of this chapter. (e) A method or fitting specially approved by the Commandant (CG-ENG).