49 CFR § 173.319 - Cryogenic liquids in tank cars.
(a) General requirements.
(2) The amount of flammable cryogenic liquid loaded into a tank car must be determined, either by direct measurement or by calculation based on weight, to verify that the tank has not been filled to a level in excess of the limits specified in paragraph (d)(2) of this section. The weight of any flammable cryogenic liquid loaded, except hydrogen, must be checked by use of scales after disconnecting the loading line.
(3) The shipper must notify the Federal Railroad Administration whenever a tank car containing any flammable cryogenic liquid is not received by the consignee within 20 days from the date of shipment. Notification to the Federal Railroad Administration may be made by email to HMassist@dot.gov or telephone call to (202) 493-6245.
(4) A tank car may not be loaded with any flammable cryogenic liquid:
(ii) That is colder than the design service temperature of the tank,
(1) At least 0.5 percent outage must be provided below the inlet of the pressure relief or pressure control valve at the start-to-discharge pressure setting of the valve, with the tank car in a level attitude, and
(2) The absolute pressure in the annular space must be less than 75 microns of mercury.
(c) Temperature. A flammable cryogenic liquid must be loaded into a tank car at such a temperature that the average daily pressure rise during transportation will not exceed 3 psig (see paragraph (a)(4)(iii) of this section).
(1) For purposes of this section, “filling density” is defined as the percent ratio of the weight of lading in the tank to the weight of water that the tank will hold at the design service temperature (one pound of water = 27.737 cubic inches at 60 °F., or one gallon of water = 231 cubic inches at 60 °F. and weighs 8.32828 pounds).
(2) Ethylene, and hydrogen (minimum 95 percent parahydrogen), cryogenic liquids must be loaded and shipped in accordance with the following table:
Pressure Control Valve Setting or Relief Valve Setting
|Maximum start-to-discharge pressure
|Maximum permitted filling density
(percent by weight)
|Maximum pressure when offered for transportation||10 psig||20 psig||20 psig|
|Design service temperature||Minus 260 °F||Minus 260 °F||Minus 155 °F||Minus 423 °F.|
|Specification (see § 180.507(b)(3) of this subchapter)||113D60W, 113C60W||113C120W||113D120W||113A175W, 113A60W.|
(e) Special requirements for class DOT 113 tank cars - (1) A class DOT-113 tank car need not be periodically pressure tested; however, each shipment must be monitored to determine the average daily pressure rise in the tank car. If the average daily pressure rise during any shipment exceeds 0.2 Bar (3 psig) per day, the tank must be tested for thermal integrity prior to any subsequent shipment.
(2) Thermal integrity test. When required by paragraph (e)(1) of this section, either of the following thermal integrity tests may be used:
(i) Pressure rise test. The pressure rise in the tank may not exceed 0.34 Bar (5 psig) in 24 hours. When the pressure rise test is performed, the absolute pressure in the annular space of the loaded tank car may not exceed 75 microns of mercury at the beginning of the test and may not increase more than 25 microns during the 24-hour period; or
(ii) Calculated heat transfer rate test. The insulation system must be performance tested as prescribed in § 179.400-4 of this subchapter. When the calculated heat transfer rate test is performed, the absolute pressure in the annular space of the loaded tank car may not exceed 75 microns of mercury at the beginning of the test and may not increase more than 25 microns during the 24-hour period. The calculated heat transfer rate in 24 hours may not exceed:
(3) A tank car that fails a test prescribed in paragraph (e)(2) of this section must be removed from hazardous materials service. A tank car removed from hazardous materials service because it failed a test prescribed in paragraph (e)(2) of this section may not be used to transport a hazardous material unless the tank car conforms to all applicable requirements of this subchapter.
(4) Each rupture disc must be replaced every 12 months, and the replacement date must be marked on the car near the pressure relief valve information.
(5) Pressure relief valves and alternate pressure relief valves must be tested every five years. The start-to-discharge pressure and vapor tight pressure requirements for the pressure relief valves must be as specified in § 179.401-1 of this subchapter. The alternate pressure relief device values specified in § 179.401-1 of this subchapter for a DOT-113C120W tank car apply to a DOT-113D120W tank car.