49 C.F.R. § 180.203
As used in this section, the word "cylinder" includes UN pressure receptacles. In addition to the definitions contained in § 171.8 of this subchapter, the following definitions apply to this subpart:
Commercially free of corrosive components means a hazardous material having a moisture content less than 55 ppm and free of components that will adversely react with the cylinder (e.g., chemical stress corrosion).
Condemn means a determination that a cylinder is unserviceable for the continued transportation of hazardous materials in commerce and that the cylinder may not be restored by repair, rebuilding, requalification, or any other procedure.
Filled or charged means an introduction or presence of a hazardous material in a cylinder.
Mobile unit means a vehicle specifically authorized under a RIN to carry out requalification operations identified under the RIN within specified geographic areas away from the principle place of business. Mobile units must comply with the requirements outlined in the approval issuance letter from the Associate Administrator for Hazardous Materials Safety (see § 107.805 of subchapter A of this chapter).
Non-corrosive service means a hazardous material that, in the presence of moisture, is not corrosive to the materials of construction of a cylinder (including valve, pressure relief device, etc.).
Over-heated means a condition in which the temperature of any portion of an aluminum cylinder has reached 176 °C (350 °F) or higher, or in which the temperature of any portion of a steel or nickel cylinder has reached 343 °C (650 °F) or higher.
Over-pressurized means a condition in which the internal pressure applied to a cylinder has reached or exceeded the yield point of the cylinder.
Permanent expansion means a permanent increase in a cylinder's volume after the test pressure is released.
Proof pressure test means a liquid-based pressure test by interior pressurization without the determination of a cylinder's expansion.
Rebuild means the replacement of a pressure part (e.g. a wall, head, or pressure fitting) by welding.
Repair means a procedure for correction of a rejected cylinder that may involve welding.
Requalification means the completion of a visual inspection and/or the test(s) required to be performed on a cylinder to determine its suitability for continued service.
Requalification identification number or RIN means a code assigned by DOT to uniquely identify a cylinder requalification, repair, or rebuilding facility.
49 C.F.R. §180.203