Preparing for LNG by Rail Tank Car: A Readiness Review (2022) / Chapter Skim
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37 In 2020, the U.S. Department of Transportation (U.S.
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38 PREPARING FOR LNG BY RAIL TANK CAR below their boiling points, which range from −155°F to −321°F (−104°C to −196°C)
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CRYOGENIC TANK CARS AND LNG HAZARDS 39 UN-T75 Intermodal Portable Tanks As noted in Chapter 2, LNG has been transported for decades in the UNT75 portable tank, a type of intermodal container approved by PHMSA for liquefied gases and designed in accordance with international (United Nations [UN]
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40 PREPARING FOR LNG BY RAIL TANK CAR TABLE 4-1 Examples of Rail Tank Car Families and Their PHMSAApproved Commodities12 DOT-105/112/114 DOT-11113 DOT-11314 DOT-11715 Anhydrous Ammonia (flammable) Sodium Hydroxide (corrosive)
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CRYOGENIC TANK CARS AND LNG HAZARDS 41 limits thermal conduction, the vacuum limits thermal conduction and convection, and the aluminum foil limits thermal radiation. Collectively, these features limit the cryogenic cargo's pressure and temperature increase.
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42 PREPARING FOR LNG BY RAIL TANK CAR steel plate.18 In accordance with PHMSA requirements, the inner tank is made from either ASTM A240/240M Type 304 or Type 304L high-strength stainless steel.19 These grades of stainless steel are required for the inner tank because they are more ductile than carbon steel at cryogenic temperatures.20 A more complete description of a DOT-113 tank car can be found in Box 4-1. BOX 4-1 Main Features of Cryogenic Tank Cars The Association of American Railroads' (AAR's)
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CRYOGENIC TANK CARS AND LNG HAZARDS 43 The cars must be equipped with various PRDs [pressure relief devices] for the protection of the tank assembly and piping system.
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44 PREPARING FOR LNG BY RAIL TANK CAR UPGRADES TO THE DOT-113 FOR LNG PHMSA amended the design for the standard DOT-113 cryogenic tank car to account for the combined cryogenic and flammable properties of LNG. Specifically, to make the outer tank more resistant to damage, PHMSA modified the specified grade and thickness of the steel plates used to construct the DOT-113's outer tank.
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CRYOGENIC TANK CARS AND LNG HAZARDS 45 a tank car.25 Although the vast majority of derailed cryogenic tank cars successfully contain their cargo during a derailment,26 the means by which containment could be lost when transporting LNG need to be accounted for. While a main concern during a derailment is a puncture of a tank car's outer and inner tanks to cause the release of product, another concern is that a tank car that has successfully contained its product may be exposed to cryogenic LNG released from the PRD or other tank cars damaged in the derailment.
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46 FI G U R E 4 -2 E ve nt t re e of a t an k ca r ad ja ce nt t o bu rn in g ta nk c ar s.
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CRYOGENIC TANK CARS AND LNG HAZARDS 47 Resistance to Puncture and Brittle Fracture PHMSA and FRA have commissioned a series of side-impact tests on DOT113 tank cars.27 The first test conducted in 2019 using a ram car showed that the inner and outer tank of the standard DOT-113C120W punctured at 16.7 mph. Because an upgraded DOT-113C120W9 was not available in 2020 for the second test, a surrogate tank car was custom built with the thicker 9⁄16-inch TC-128B steel plate substituted for the outer tank of the standard DOT-113.28 When struck, the outer tank of the surrogate was deformed but not punctured when struck by a ram car moving at 17.3 mph.
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48 PREPARING FOR LNG BY RAIL TANK CAR stress around the circumference of a structure due to a pressure gradient -- and transmission of the weight of the inner tank through the support system to the outer tank. Initiators can arise from cracks, such as those associated with dents and buckles, as well as from thinning of the tank steel from scores, gouges, and wheel burns.
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CRYOGENIC TANK CARS AND LNG HAZARDS 49 temperatures in the inner tank in the aftermath of a derailment under thermal load. DOT-113 tank cars are not required to meet federal regulations (49 CFR § 179, Appendix B)
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50 PREPARING FOR LNG BY RAIL TANK CAR The committee is also aware of experiments performed on marine vessels to assess insulation performance when transporting LNG. In these tests, an at-scale vessel cross section was exposed to heat flux representative of an LNG fire.
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From page 51... ...
CRYOGENIC TANK CARS AND LNG HAZARDS 51 inner tank is constructed of stainless steel to withstand cryogenic temperatures, while the outer tank is constructed of carbon steel. The insulation around the inner tank consists of alternating layers of aluminum foil and a non-conducting spacer material, such as fiberglass or ceramic fiber paper.
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