(a) For the purposes of this section -
(1) Design pressure means the “MAWP” as used in Section VIII of the ASME Code (IBR, see § 171.7 of this subchapter), and is the gauge pressure at the top of the tank.
(2) Design service temperature means the coldest temperature for which the tank is suitable (see §§ 173.318 (a)(1) and (f) of this subchapter).
(b) Each cargo tank must consist of a suitably supported welded inner vessel enclosed within an outer shell or jacket, with insulation between the inner vessel and outer shell or jacket, and having piping, valves, supports and other appurtenances as specified in this subchapter. For the purpose of this specification, tank means inner vessel and jacket means either the outer shell or insulation cover.
(c) Each tank must be designed, constructed, certified, and stamped in accordance with Section VIII of the ASME Code.
(d) The exterior surface of the tank must be insulated with a material compatible with the lading.
(1) Each cargo tank must have an insulation system that will prevent the tank pressure from exceeding the pressure relief valve set pressure within the specified holding time when the tank is loaded with the specific cryogenic liquid at the design conditions of -
(i) The specified temperature and pressure of the cryogenic liquid, and
(ii) The exposure of the filled cargo tank to an average ambient temperature of 85 °F.
(2) For a cargo tank used to transport oxygen, the insulation may not sustain combustion in a 99.5 percent oxygen atmosphere at atmospheric pressure when contacted with a continuously heated glowing platinum wire. The cargo tank must be marked in accordance with § 178.338-18(b)(7).
(3) Each vacuum-insulated cargo tank must be provided with a connection for a vacuum gauge to indicate the absolute pressure within the insulation space.
(e) The insulation must be completely covered by a metal jacket. The jacket or the insulation must be so constructed and sealed as to prevent moisture from coming into contact with the insulation (see § 173.318(a)(3) of this subchapter). Minimum metal thicknesses are as follows:
| Type metal | Jacket evacuated | Jacket not evacuated | ||
|---|---|---|---|---|
| Gauge | Inches | Gauge | Inches | |
| Stainless steel | 18 | 0.0428 | 22 | 0.0269 |
| Low carbon mild steel | 12 | 0.0946 | 14 | 0.0677 |
| Aluminum | 0.125 | 0.1000 | ||
(f) An evacuated jacket must be in compliance with the following requirements:
(1) The jacket must be designed to sustain a minimum critical collapsing pressure of 30 psig.
(2) If the jacket also supports additional loads, such as the weight of the tank and lading, the combined stress, computed according to the formula in § 178.338-3(b), may not exceed 25 percent of the minimum specified tensile strength.
[Amdt. 178-77, 48 FR 27703, June 16, 1983, as amended at 49 FR 24316, June 12, 1984; Amdt. 178-104, 59 FR 49135, Sept. 26, 1994; 66 FR 45387, Aug. 28, 2001; 68 FR 75754, Dec. 31, 2003]