Preparing for LNG by Rail Tank Car: A Readiness Review (2022)

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37 In 2020, the U.S. Department of Transportation (U.S. DOT), through the Pipeline and Hazardous Materials Safety Administration (PHMSA), ap- proved the DOT-113C120W9 tank car as a new member of the DOT-113 family of cryogenic tank cars. It was designed and approved specifically for transporting liquefied natural gas (LNG) by rail.1 This chapter begins with an overview of the key design features of common cryogenic containers, in- cluding the DOT-113 tank car and its upgraded specification for LNG. The discussion then considers hazard scenarios for LNG in a tank car involved in a derailment. In particular, consideration is given to the tank’s resistance to puncture and brittle fracture and to the performance of the insulation and pressure relief systems. DESIGN FEATURES OF CRYOGENIC PACKAGING AND TANK CARS In the United States, cryogenic cargoes have been transported by rail for decades in tank cars and portable tanks. The most commonly transported cryogens are argon and ethylene, followed by nitrogen and oxygen. As dis- cussed in Chapter 3, these commodities must be maintained at temperatures 1 “Hazardous Materials: Liquefied Natural Gas by Rail—Final Rule,” Federal Register, 85 FR 44994 (July 24, 2020). The final rule authorizing LNG transportation in the DOT- 113C120W9 tank car was subsequently revisited in a notice of proposed rulemaking that would suspend this authorization (“Hazardous Materials: Suspension of HMR Amendments Authorizing Transportation of Liquefied Natural Gas by Rail,” Federal Register, 86 FR 61731 (November 8, 2021)). 4 Cryogenic Tank Cars and Liquefied Natural Gas Hazards

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). The low temperatures must be maintained to keep the cargo in liquid form during transportation periods that can last for many days or weeks. These materials must be shipped in tank cars designed to minimize heat input so as to limit pressure rise to 3 pounds per square inch gauge (psig) (1.2 bar) per day.2 For example, ethylene is authorized to be offered for transportation at 20 psig and a corresponding temperature of −125°F (−87°C).3,4 Because the lading will continue to warm until delivery and the daily pressure rise of a DOT-113 tank car is 0.5 to 0.75 psig (1.05 to 1.07 bar), the temperature and pressure at the end of a 10-day trip is expected to be about −117°F (–83°C) and 27.5 psig (2.9 bar).5 Cryogenic packaging is therefore designed to maintain the low temper- atures of the liquid and to have systems that relieve pressure upon heating and evaporation. For temperature maintenance, the inner tank containing the cargo is surrounded by an outer tank (also referred to as an outer jacket6) separated by annular space maintained as a vacuum after filling it with insulation. The insulation limits all forms of heat transfer between the inner and outer tanks, while the vacuum limits conductive and convective heat transfer. In addition, the vacuum allows the insulation to meet design requirements, as the insulation’s thermal properties are pressure dependent and enhanced by the presence of a vacuum.7 The design of the support structure limits heat input through conduction. Piping and valves are in- stalled and set (based on the commodity) to allow for loading, unloading, pressure relief, and gauging of the contents. Cryogenic packaging is also designed to resist punctures that could re- lease cargo during an incident. The grade and thickness of the steel used for the shell and head of the outer tank are selected in part to achieve various levels of puncture resistance, as are the protections afforded the fittings on the openings on the outer tank. The following is a summary of key design fea- tures of the UN-T75 intermodal portable tank, DOT-113 cryogenic tank car, and the upgraded DOT-113C120W9, which is approved for LNG service. 2 49 CFR § 173.319, Cryogenic liquids in tank cars. 3 Ibid. 4 Carl L. Yaws and William Braker, Mathewson Gas Data Book, Appendix 10 (New York: McGraw-Hill Professional, 2001). 5 Ibid. 6 This report uses “outer tank” rather than “outer jacket” for the outermost section of cryogenic tanks because of the prevalence of the former term during the 2020 rulemaking and onward and by the Association of American Railroads. Although “outer jacket” is the term in common use and in regulatory text for the outermost vessel of the UN-T75 portable tank, this report uses “outer tank” for the portable tank for consistency. (See also the committee’s Phase 1 report, page 13, footnote 10.) 7 P. M. Sutheesh and Alex Chollackal, IOP Conference Series, Materials Science and Engi- neering, vol. 396, 2018, 012061, https://doi.org/10.1088/1757-899X/396/1/012061.

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 UN- T75 portable tank, a type of intermodal container approved by PHMSA for liquefied gases and designed in accordance with international (United Na- tions [UN]) guidance. They are used to transport LNG by ship and truck, and these portable tanks have been used on a limited basis for rail move- ments of LNG in Alaska and Florida. The container consists of cryogenic packaging within a container frame, and openings fitted with pressure relief devices and other closures and devices such as gauges.8 The inner tank is constructed from stainless steel, while the outer tank is constructed from either stainless steel or carbon steel. The UN guidance requires tank steels having a minimum thickness in accordance with yield and tensile strength performance standards for pressure ratings and puncture resistance. Special features added to protect against impact include metal bars installed across the frame and longitudinally along the outer tank’s length.9 DOT-113 Tank Car The most common tank car used for hazardous liquids that are not trans- ported under high pressure is the DOT-111. Its design consists of fewer up- graded and specialized safety features to contain pressure, resist punctures, and provide thermal protection of the cargo. Most recently the DOT-117 tank car was introduced to transport certain hazardous liquids that pose specific flammability hazards, such as ethanol and crude oil.10 For instance, these cars are insulated for thermal protection and include full-height head shields.11 Table 4-1 lists tank car families with examples of their corre- sponding commodities that PHMSA has approved for rail transportation. While the DOT-111 and DOT-117, as well as the DOT-113, are nonpres- sure tank cars, the DOT-105, DOT-112, and DOT-114 tank cars carry cargo under pressure. 8 U.S. Department of Transportation Pipeline and Hazardous Materials Safety Administra- tion, “Risk Assessment of Surface Transportation of Liquid Natural Gas,” March 20, 2019, p. 84, https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/docs/research-and-development/ hazmat/reports/71651/fr2-phmsa-hmtrns16-oncall-20mar2019-v3.pdf. 9 United Nations, ed., “Recommendations on the Transport of Dangerous Goods: Model Regulations, 22 Revised Edition, Vol. II” (New York and Geneva: United Nations, 2021), https://unece.org/sites/default/files/2021-09/ST-SG-AC10-1r22e_Vol2_WEB_0.pdf. 10 National Research Council, Ensuring Railroad Tank Car Safety: Special Report 243 (Washington, DC: National Academy Press, 1994), p. 49, https://doi.org/10.17226/11400. 11 Bureau of Transportation Statistics, “Tank Car Specifications & Terms,” April 18, 2018, https://www.bts.gov/surveys/annual-tank-car-facility-survey/tank-car-specifications-terms.

40 PREPARING FOR LNG BY RAIL TANK CAR TABLE 4-1 Examples of Rail Tank Car Families and Their PHMSA- Approved Commodities12 DOT-105/112/114 DOT-11113 DOT-11314 DOT-11715 Anhydrous Ammonia (flammable) Sodium Hydroxide (corrosive) Liquid Argon (cryogenic) Crude Oil (flammable) Liquefied Petroleum Gas (flammable) Sulfuric Acid (corrosive) Liquid Nitrogen (cryogenic) Ethanol (flammable) Chlorine Gas (reactive, toxic) Phenol (toxic) Liquid Oxygen (cryogenic) Ethylene Oxide (flammable) Diesel Fuel (combustible) Liquid Ethylene (cryogenic, flammable) For the transportation of cryogenic cargo, PHMSA requires use of the DOT-113 family of tank cars.16 This tank car family transports cryogenic commodities, such as argon, ethylene, oxygen, and nitrogen. All of the DOT-113 tank cars have inner and outer tanks, the former wrapped with insulation to maintain the low temperature of the cryogenic cargo. The pressure relief device (PRD) system is designed and set to activate when desired temperatures are not maintained. Figure 4-1 show the key safety features of a DOT-113 tank car. The DOT-113’s inner tank is supported within the outer tank to cre- ate an annular space of 6–8 inches that maintains a vacuum. Not pictured in Figure 4-1 is the multilayer insulation (MLI) that surrounds the inner tank. The MLI consists of alternating layers of aluminum foil and a non- conducting spacer material, such as fiberglass or ceramic fiber paper. Spe- cifically, the spacer material and the separation of the inner and outer tanks 12 U.S. Federal Emergency Management Agency, “Silhouettes of Rail Cars, Tank Trucks and Chemical Tanks,” 2004, https://www.hsdl.org/?abstract&did=445918. 13 National Research Council, Ensuring Railroad Tank Car Safety: Special Report 243 (Washington, DC: National Academy Press, 1994), p. 49, https://doi.org/10.17226/11400. 14 U.S. Department of Transportation Pipeline and Hazardous Materials Safety Administra- tion, “Risk Assessment of Surface Transportation of Liquid Natural Gas,” March 20, 2019, https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/docs/research-and-development/hazmat/ reports/71651/fr2-phmsa-hmtrns16-oncall-20mar2019-v3.pdf. 15 U.S. Department of Transportation, Bureau of Transportation Statistics, “Fleet Composi- tion of Rail Tank Cars Carrying Flammable Liquids: 2021 Report,” Washington, DC, 2021, https://doi.org/10.21949/1523084. 16 Although it is less and less common, some of this cryogenic material ships in AAR-204W tank cars. For an overview of the specification, see p. 92 in Association of American Rail- roads, “2017 Field Guide to Tank Cars,” February 6, 2017, https://www.aar.org/wp-content/ uploads/2017/12/AAR-2017-Field-Guide-for-Tank-Cars-BOE.pdf.

CRYOGENIC TANK CARS AND LNG HAZARDS 41 limits thermal conduction, the vacuum limits thermal conduction and con- vection, and the aluminum foil limits thermal radiation. Collectively, these features limit the cryogenic cargo’s pressure and temperature increase. The DOT-113 has a PRD system that consist of two types of pressure control devices. The first is a pressure relief valve sized and set to prevent the pressure in the inner tank from exceeding its test pressure17 if the vacuum is lost. The second is a frangible disc (rupture disc), or secondary relief valve, designed to prevent the pressure in the inner tank from exceed- ing its test pressure in the event of a fire and loss of vacuum. The industry standard for the past several decades is to have two sets of PRDs separated by a three-way valve, with only one set of the PRDs active at a time. These systems must function under high-temperature conditions in the event of an incident and must be made from materials suitable for the temperature of the cargo in liquid and vapor phases. For this purpose, the system is designed for a scenario in which the tank car is exposed to a temperature of 1200°F (648.9°C). The selection of the steel specifications for the inner and outer tanks has protective and practical purposes. Both tanks are composed of grades of high-strength steel to prevent puncture and cracking. While there is an appendix of approved steels for the outer tank of the DOT-113 tank car, the tank car industry reports that the standard for the outer tank material has generally been AAR TC-128 Grade B (TC-128B) normalized carbon 17 Per 49 CFR § 178.320, the test pressure is the pressure to which a tank is subjected to determine structural integrity. FIGURE 4-1 Schematic of DOT-113 tank car and some of its key safety features. SOURCE: PHMSA.

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 tempera- tures.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) Field Guide to Tank Cars describes cryogenic tank cars, including the DOT-113 specification, as follows: Cryogenic liquid tank cars, Class DOT/TC-113 and Class AAR-204, are vacuum- insulated cars having an inner container (tank) and outer shell (tank, not a jacket (although referred to as an “outer jacket” in 49 CFR)). The inner tank is constructed of alloy (stainless) steel and the outer shell is constructed of carbon steel. Cryogenic tank cars are designed to transport refrigerated liquefied gases having a boiling point colder than minus 130°F [54.4°C] at atmospheric pressure; e.g., liquid hydrogen, ethylene, oxygen, nitrogen, and argon. The annular space between the inner and outer tanks has a vacuum drawn and is equipped with an insulation system using granular perlite or an alternating wrap of multiple layers of aluminum foil and paper. These tank cars are frequently referred to as Thermos® bottle tank cars. The insulation system (designed for the commodity being transported and meet- ing specified performance standards) and vacuum controls the rate of heat input for normal transportation time periods. Specification DOT/TC-113A60W tank cars have a design service temperature of minus 423°F [217.2°C], a minimum burst pressure of 240 psig, and a tank test pressure of 60 psig. Specification DOT/TC-113C120W tank cars have a design service temperature of minus 260°F [126.7°C], a minimum burst pressure of 300 psig, and a tank test pressure of 120 psig. Cryogenic liquid tank cars are required to have two liquid-level gauges. One gauge measures the liquid level in the inner tank (this gauge may be a portable gauge that does not move with the car) and the other gauge, a fixed-length dip tube set, indicates the maximum allowable liquid level for the allowable filling density. In addition, the car must be equipped with a vapor-phase pressure gauge to indicate the pressure within the inner tank. 18 A. D. McKisic (personal communication), July 6, 2022, http://onlinepubs.trb.org/online- pubs/C4rail/DOTShell13ShellSpec.pdf; Scott Nason (personal communication), July 5, 2022, http://onlinepubs.trb.org/onlinepubs/C4rail/AARTC128GrB.pdf. 19 49 CFR § 179.400-5, Materials. 20 Scott Nason, “DOT 113 Tank Cars for LNG,” September 20, 2021, http://onlinepubs. trb.org/onlinepubs/C4rail/NasonChartDOT113TankCars092121.pdf.

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. The discharge of the PRD must be directed away from operating personnel, the car structure, trucks, and safety appliances; e.g., steps, handholds/grab irons, and handrails. The inner tank must be equipped with at least one PRV [pressure relief valve] and at least one safety vent (rupture disc device), which may be replaced by an alternate PRV. The car may also be equipped with a pressure control device (regulator valve) and mixing device to control the routine release of vaporized lading during transportation. The outer jacket/tank must be equipped with a system to prevent buildup of pressure within the annular space. The loading/unloading valves and other fittings are required to be enclosed within a protective housing (not to be confused with protective housings on pressure tank cars), which appears to be a box or cabinet. The protective housing(s) is located on both sides, at one end or, in rare cases, on the top of the car. The housing(s) must be adequate to protect the fittings from direct solar radiation, mud, sand, adverse environmental exposure, and mechanical damage incident to normal operation. The protective housings for the fittings must be equipped with precautionary instructions for the safe operation of the equipment during storage and transfer operations, and must include a diagram of the tank and piping system with the various gauges, control valves, and PRDs clearly identified, and their location indicated. In addition, all valves and gauges must be clearly identified with corrosion-resistant nameplates. In addition to other stenciling, cryogenic liquid tank cars must be stenciled “DO NOT HUMP OR CUT OFF WHILE IN MOTION” and “VACUUM JACKETED” on both sides in lettering at least 1½ inches high. SOURCE: Excerpt from AAR, Field Guide to Tank Cars, Third Edition, 2017, pp. 91–93.21 21 Association of American Railroads, “Third Edition Field Guide to Tank Cars,” February 6, 2017, pp. 91–93, https://www.aar.org/wp-content/uploads/2017/12/AAR-2017-Field-Guide- for-Tank-Cars-BOE.pdf.

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 con- struct the DOT-113’s outer tank. As shown in Table 4-2, the upgraded specification, named the DOT-113C120W9, requires that the outer tank be made of a TC-128B normalized carbon steel plate to create a thicker shell and head when compared to the DOT-113C120W. The upgraded specifica- tions for shell and head thickness were intended to add greater protection from punctures and to reduce the severity of deformations that may occur when the tank is damaged in a derailment. No additional changes were made to the DOT-113 with regard to the insulation or PRD systems. HAZARD SCENARIOS WHEN TRANSPORTING LNG IN TANK CARS Among incident types, a high–kinetic energy train derailment is generally considered to be the main scenario that would pose a risk of tank dam- age and a fire event sufficient to cause a loss of LNG containment from TABLE 4-2 Upgraded Requirements of the DOT-113C120W9 Rail Tank Car22,23,24 DOT-113C120W DOT-113C120W9 Outer Tank Steel Any steel listed in AAR’s M-1002 Appendix M AAR TC-128, Grade B (TC-128B) normalized carbon steel Tank Shell, Minimum Wall Thickness 7/16 in. 9/16 in. Tank Head, Minimum Wall Thickness 1/2 in. 9/16 in. 22 49 CFR § 179.400-8, Thickness of Plates. 23 49 CFR § 179.400-5, Materials. 24 U.S. Department of Transportation Pipeline and Hazardous Materials Safety Adminis- tration, “Hazardous Materials: Liquefied Natural Gas by Rail,” July 24, 2020, https://www. regulations.gov/document/PHMSA-2018-0025-0480.

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. Exposure of its outer tank to LNG could cause embrittlement of the outer tank steel and risk the occurrence of circumferentially brittle fractures of the tank. An outer tank fracture that causes a loss of vacuum and degradation of the inner tank’s insulation could result in a thermal rupture or high-pressure release, especially if the tank car is exposed to fire. Figure 4-2 depicts potential outcomes in the case of a derailment sce- nario in which a tank car containing LNG derails and is in close proximity to other tank cars that are on fire. Three principal mechanisms that can jeopardize the integrity of the outer tank are illustrated: damage to safety features during the derailment event, thermal softening of the tank steel from exposure to an LNG fire, and embrittlement of the tank steel from exposure to LNG. Situations that result in LNG pooling, such as the pres- ence of trenches or a rollover resulting in release through the PRDs, may expose the outer tank to LNG and the possibility of embrittlement and brittle fracture. Brittle fractures that lead to vacuum loss and/or degrada- tion of the insulation will allow heating of the LNG in the inner tank and result in an increase in internal pressure. If the inner tank is exposed to fire and experiences thermal weakening, its failure pressure may drop below the pressure rating of the PRDs. The potential for these outcomes would be greater in case trains having multiple LNG tank cars. As shown in the diagram, the outcomes from such scenarios could range from the venting of vapors to a thermal rupture or high-pressure release. In considering such scenarios and informed by the result of recent testing and modeling by PHMSA and the Federal Railroad Administration (FRA), the committee took a closer look at the relevant design features of the DOT-113C120W9 that relate to survivability of a tank car in a derail- ment scenario: resistance to puncture and brittle fracture, PRD perfor- mance, and insulation performance. 25 National Academies of Sciences, Engineering, and Medicine, Preparing for LNG by Rail Tank Car: A Review of a U.S. DOT Safety Research, Testing, and Analysis Initiative (Washing- ton, DC: The National Academies Press, 2021), pp. 15–16, https://doi.org/10.17226/26221. See also the discussion about the Worst-Case Scenario Model task on p. 38, as well as its related tasks such as Punctures and Derailment Simulation Modeling. 26 U.S. Department of Transportation Pipeline and Hazardous Materials Safety Administra- tion, “Incident Statistics,” n.d., https://www.phmsa.dot.gov/hazmat-program-management- data-and-statistics/data-operations/incident-statistics.

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. C ar in iti al ly n ot o n fir e, bu t n ea r/n ex t t o bu rn in g ta nk c ar s Ta nk c ar in b ur ni ng po ol o f l iq ui d LN G Li ke ly b rit tle fr ac tu re an d lo ss o f v ac uu m V en tin g of v ap or s Th er m al ru pt ur e O th er p ro du ct Fi re s in fi tti ng s ca bi ne ts Lo ss o f v ac uu m du e to d am ag e to pr es su re re lie f de vi ce o n ou te r ja ck et V en tin g of v ap or s Ta nk c ar im pi ng ed by fi re fr om a dj ac en t ta nk c ar Fu lly e ng ul fe d Fi re s in fi tti ng ca bi ne ts Lo ss o f v ac uu m d ue to d am ag e to pr es su re re lie f de vi ce o n ou te r ja ck et O ve ra ll he at in g of ta nk c ar V en tin g of v ap or s Fi re o ut v en t s ta ck in cr ea si ng in in te ns ity S m al l a re a af fe ct ed Fi re s in fi tti ng s ca bi ne ts Lo ss o f v ac uu m d ue to d am ag e to pr es su re re lie f de vi ce o n ou te r ja ck et V en tin g of v ap or s Fi re o ut v en t s ta ck in cr ea si ng in in te ns ity Lo ca liz ed h ea tin g of ta nk c ar Ta nk c ar im pi ng ed by h ig h m om en tu m je t f ire fr om v en t st ac k of a dj ac en t LN G ta nk c ar V en tin g of v ap or s

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 DOT- 113 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. Using these test data, subsequent modeling of the surrogate tank car indicated that a relative impact speed of nearly 19 mph would be needed for the ram car to puncture the outer tank.29 In May 2022, FRA conducted an additional side-impact test, but this time with an actual DOT-113C120W9 tank car, which was filled with liq- uid nitrogen, which is transported at −350°F (−196°C).30 This test provided additional validation of the modeling that predicted the tank car outer shell resists puncture up to at least 19 mph, as the ram car punctured the inner and outer tanks at 22 mph.31 It merits noting that, following the puncture, the outer tank of the tested DOT-113C120W9 tank car experienced brittle fracture, manifested by an initiating crack at the puncture site and a large, circumferential crack caused by cryogenic damage. Additional brittle fractures occurred over the next few days as the liquid nitrogen fully dissipated.32 For brittle fracture to occur, a load and/or a crack initiator must be present on the outer tank steel, and the temperature of the steel must be below the average nil-duc- tility transition (NDT) temperature when steel loses ductility. After a crack initiates, the main factors effecting propagation is hoop stress—tangential 27 National Academies of Sciences, Engineering, and Medicine, Preparing for LNG by Rail Tank Car: A Review of a U.S. DOT Safety Research, Testing, and Analysis Initiative (Wash- ington, DC: The National Academies Press, 2021), p. 31, https://doi.org/10.17226/26221. “The results from multiple tests on a range of tank car designs are used to establish the relative puncture resistance of different tank car designs. Test results also provide empirical data for the development and validation of impact and puncture finite element (FE) model capabilities. After validation, these capabilities are used to simulate the puncture resistance associated with various changes in impact conditions and tank design parameters.” 28 The surrogate tank car met the requirements of the 2020 regulations of a DOT- 113C120W9, with 9⁄16-inch TC-128B steel normalized for the outer tank and filled to ap- proximately 95% of its volume with liquid nitrogen. 29 Federal Railroad Administration, Side Impact Test and Analyses of a DOT-113 Surrogate Tank Car with Water, DOT/FRA/ORD-21/35, December 2021. 30 The DOT-113C120W9 was filled to approximately 97 percent of its volume with liquid nitrogen. 31 Federal Railroad Administration (personal communication), June 17, 2022. 32 Ibid.

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. The brittle fracture of the DOT-113C120W9 tank car loaded with liq- uid nitrogen warrants noting because LNG is transported at significantly warmer temperatures (−260°F [−162°C]) than liquid nitrogen (−320°F [−196°C]), which has a greater potential to cause embrittlement than LNG. Nevertheless, a reason to be concerned about a potential for LNG to cause brittle fracture of the DOT-113C120W9’s outer tank is that the NDT temperature of its specified steel grade, normalized TC-128B, is −59.8°F (−51°C), which is higher than the temperature of transported LNG.33,34 Pressure Relief Device Performance The DOT-113C120W9 design shares the same specifications as the standard DOT-113 tank car for pressure relief devices. As discussed above, a DOT- 113C120W9 tank car is required to have one set of PRDs and may have a second set serving as reserve PRDs. The primary pressure relief valves are set to discharge at 75 psi (6.2 bar); the secondary PRD could either be a pressure relief valve set to discharge at 90 psi (7.2 bar) or a rupture disc set to discharge at 120 psig (9.3 bar).35 Because LNG has a liquid-to-gas expansion ratio of 600 to 1, a container is susceptible to overpressurization if the pressure release valve is faulty or upon rapid heating. A matter that may be deserving of attention is that the PRDs on the DOT-113C120W9 have not been tested for a tank car engulfed in an LNG fire. Such testing could be valuable for assessing whether the systems are properly sized in light of an incident where the tank car heats and results in the evaporation of LNG. Insulation Performance The 2020 rule did not alter the DOT-113’s specification for the multilayer insulation that wraps the inner tank, presumably under the premise that the insulation system would likely be satisfactory in maintaining cryogenic 33 Normalized TC-128B steel has an NDT of −59.8°F (−51°C), which is above the −260°F (−162.2°C) temperature of LNG. 34 G. E. Hicho and J. H. Smith, “Determination of the NDT Temperature and Charpy V- notch Impact Properties of AAR TC128 Grade B Steel and A 8XX Grade B Steel,” National Institute of Standards and Technology, NISTIR 4300, Report No. 20, 1990. 35 49 CFR § 179.401-1, Individual Specification Requirements.

CRYOGENIC TANK CARS AND LNG HAZARDS 49 temperatures in the inner tank in the aftermath of a derailment under ther- mal load. DOT-113 tank cars are not required to meet federal regulations (49 CFR § 179, Appendix B) that require that thermal insulation be tested under simulated conditions representing a pool fire for 100 minutes and a torch fire for 30 minutes.36,37 However, plate tests have been conducted in which an insulated steel plate of a representative tank car thickness is ex- posed to simulated fires, typically carried out with propane torches. While the specified insulation meets federal standards, it merits pointing out that the test temperatures in the standard are significantly lower than temperatures expected during an LNG pool fire or natural gas torch fire. The temperatures used during testing versus the temperatures of an LNG pool fire and natural gas torch fire can be seen in Table 4-3. It is conceivable, therefore, that the insulation may fail when subject to the intense heat flux of an LNG fire (~270 kW/m2). Indeed, the use of propane as the fuel for a fire test of a UN-T75 portable tank (commissioned by FRA) demonstrated that a heat flux lower than LNG can degrade similar insulation.38 The tests indicated that insulator performance can vary significantly with pressure or temperature changes and that maintaining the vacuum is critical to performance. TABLE 4-3 Temperatures of Testing Under Federal Regulations Versus LNG and Natural Gas Fires Testing Scenario LNG39 Natural Gas40,41 Temperature of Pool Fire in °F (°C) 1600°F ± 100°F (871°C ± 55.6°C) 2303.6°F–2912°F (1262°C–1600°C) — Temperature of Torch Fire in °F (°C) 2199°F ± 100°F (1204°C ± 55.6°C) — Up to 2732°F (1500°C) 36 49 CFR § 173.31, Use of tank cars. 37 The torch fire has a velocity of 64.4 ± 16 km/h. 38 Pipeline and Hazardous Materials Safety Administration and Federal Railroad Ad- ministration, “Portable Tank Fire-Testing Task Resource,” August 13, 2020, p. 67, http:// onlinepubs.trb.org/onlinepubs/dvb/LNGrail/UNT75_Fire_Test.pdf. In addition, the committee offered its advice on this study during its Phase 1 report, Preparing for LNG by Rail Tank Car: A Review of a U.S. DOT Safety Research, Testing, and Analysis Initiative (Washington, DC: The National Academies Press, 2021), https://doi.org/10.17226/26221. 39 A. Luketa and T. Blanchat, “The Phoenix Series Large-Scale Methane Gas Burner Experi- ments and Liquid Methane Pool Fires Experiments on Water,” Combustion and Flame, vol. 162, 2015, pp. 4497–4545. 40 B. J. Lowesmith et al., “An Overview of the Nature of Hydrocarbon Jet Fire Hazards in the Oil and Gas Industry and a Simplified Approach to Assessing the Hazards,” Transactions of the Institute of Chemical Engineers, Part B, May 2007. 41 This temperature is for a natural gas torch fire with flowrates of 3–10 kg/s.

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. The test steel plate was nearly twice the thickness of the specification for the DOT-113C120W9’s outer tank. The unexposed side of the tested plate reached temperatures high enough to significantly weaken the tensile strength of TC-128B steel.42,43 Temperatures of the tested plate reached 1832°F (1000°C), yet testing on TC-128B steel indicates that the ultimate tensile strength is reduced by about a factor of 6 when raised to a temperature of 800°C (1472°F).44 As noted earlier, the MLI of a DOT-113 tank car consists of alternat- ing layers of aluminum foil and a non-conducting spacer material, such as fiberglass or ceramic fiber paper.45 Aluminum’s melting temperature is 1221°F (660.3°C), while fiberglass will begin to soften and degrade around 400°F (204.4°C).46 Both of these temperatures are below the temperature of an LNG pool fire (see Table 4-3).47 On the other hand, there are ceramic fibers that have degradation temperatures greater than the temperatures of an LNG pool fire.48 SUMMARY The DOT-113 tank car family transports cryogenic commodities. All of the tank cars in this family have inner and outer tanks, the former wrapped with insulation to maintain the low temperature of its cryogenic cargo. The 42 U.S. Department of Energy, “Liquefied Natural Gas Safety Research,” Report to Con- gress, May 2012, https://www.energy.gov/sites/default/files/2013/03/f0/DOE_LNG_Safety_ Research_Report_To_Congre.pdf. 43 On the unexposed side of the outer steel plate, temperatures reached 1832°F (1000°C) after approximately 20 minutes of exposure, and then subsequently increased to 2012°F (1100°C) after an additional 5 minutes. 44 J. McKinley et al., “Strength, Creep, and Toughness of Two Tank Car Steels TC128B and A516-70,” Submitted to Transport Canada, GCDOCS Workflow ID 38647561, April 2019. 45 Pipeline and Hazardous Materials Safety Administration, “Hazardous Materials: Lique- fied Natural Gas by Rail—Final Rule,” Federal Register, 85 FR 44994 (2020), https://www. federalregister.gov/documents/2020/07/24/2020-13604/hazardous-materials-liquefied-natural- gas-by-rail. 46 J. L. Thomason, U. Nagel, L. Yang, and D. Bryce, “A Study of the Thermal Degrada- tion of Glass Fibre Sizings at Composite Processing Temperatures,” Composites Part A: Ap- plied Science and Manufacturing, vol. 121, June 2019, pp. 56–63, https://doi.org/10.1016/j. compositesa.2019.03.013. 47 A. Luketa and T. Blanchat, “The Phoenix Series Large-Scale Methane Gas Burner Experi- ments and Liquid Methane Pool Fires Experiments on Water,” Combustion and Flame, vol. 162, 2015, pp. 4497–4545. 48 J. Weinstein, “An Overview of Refractory Ceramic Fibers,” Thermal Processing, March 15, 2021, https://thermalprocessing.com/an-overview-of-refractory-ceramic-fibers.

CRYOGENIC TANK CARS AND LNG HAZARDS 51 inner tank is constructed of stainless steel to withstand cryogenic tempera- tures, 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. The annular space between the wrapped inner tank and outer tank is main- tained as a vacuum, which is a key part of the insulation system. A PRD system is designed and set to activate when desired temperatures are not maintained. These systems must function under high-temperature condi- tions in the event of an incident and must be made from materials suitable for the temperature of the cargo in liquid and vapor phases. In authorizing the LNG’s shipment by tank car, PHMSA established new requirements for a DOT-113C120W9 tank car design that specified an outer tank made with a stronger and thicker carbon steel. The new design did not include changes to the requirements for insulation materials or the PRD system. The upgrades to the DOT-113’s outer tank were intended to make it more resistant to impact damage. The results of impact tests con- ducted by PHMSA and FRA suggest that the DOT-113C120W9’s outer tank is more resistant to puncture than the outer tank of a standard DOT- 113 tank car. However, questions remain about the resistance of the outer tank’s steel to brittle fracture from a potential exposure to cryogenic LNG. A matter that warrants consideration is that the temperature of cryogenic LNG is lower than the temperature at which the outer tank steel can be- come embrittled. Uncertainties also remain about the PRD’s capacity to re- lease sufficient product when the tank car is engulfed in a high-temperature LNG fire and whether the materials used for insulating the inner tank can withstand the intense heat flux of the fire.