For a design temperature colder than −10 °C (14 °F), an independent tank type C of:
(a) Carbon and carbon-manganese steel must be stress relieved by post-weld heat treatment under § 54.25-7 of this chapter or by mechanical stress relief under subpart 54.30 of this chapter; or
(b) Materials other than carbon and carbon manganese steel must be stress relieved as required under part 54 of this chapter. The procedure for stress relieving must be specially approved by the Commandant (CG-OES).