Section 173.338 - Tungsten hexafluoride(a) Tungsten hexafluoride must be packaged in specification 3A, 3AA, 3BN, or 3E (§§ 178.36 , 178.37 , 178.39 , 178.42 of this subchapter) cylinders. Cylinders must be equipped with a valve protection cap or be packed in a strong outer packaging meeting the provisions of § 173.40 . Outlets of any valves must be capped or plugged. As an alternative, the cylinder opening may be closed by the use of a metal plug. Specification 3E cylinders must be shipped in an overpack that meets the provisions of § 173.40 .(b) In place of the volumetric expansion test, DOT 3BN cylinders used in exclusive service may be given a complete external visual inspection in conformance with part 180, subpart C, of this subchapter, at the time such periodic requalification becomes due. Cylinders that undergo a complete external visual inspection, in place of the volumetric expansion test, must be condemned if removed from tungsten hexafluoride service. 74 FR 16143 , Apr. 9, 2009, as amended at 75 FR 5395 , Feb. 2, 2010