Rail and road transportation of hazardous materials in the United States are recognized to be the safest methods of moving large quantities of chemicals over long distances.
These cars and trailers are designed in various shapes, sizes, and maximum load capacities according to the needs of the nation’s freight shippers.
RAIL CAR TYPES
Modern rail cars have a gross capacity of 286,000 pounds and feature numerous common markings, such as reporting marks and car numbers, empty weight, placards, tank qualification, and pressure relief device information, car specifications, and the names of the commodities they’re carrying.
NORTH AMERICAN TANK CAR FLEET BY CAR CLASS
Source Railcar supply institute As of 12/31/2019
Rail cars come in a few different types:
- Pressure Tank Cars
- Non-Pressure/Low-Pressure Tank Cars
- Non-Pressure/Low-Pressure Tank Cars (TC117, DOT117)
- Box Cars
- Hopper Cars
Pressure Tank Cars and Non-Pressure/Low-Pressure Tank Cars
More cylindrical than other rail cars, tank cars are designed to carry between 6,500 gallons and more than 31,000 gallons of various kinds of liquids, including water, diesel fuel, chemicals, and food products. Effective loading arm systems and safe loading platforms are essential in the transfer of corrosive or flammable liquids from tank cars to the destined storage location.
There are a few variations of tank cars to assure fuel transport safety:
Non-Pressure/Low-Pressure Tank Cars (DOT-111)
Known as general service tank cars, these cars typically have fittings and valves visible at the top, and can also feature a bottom outlet valve. They carry a variety of hazardous and non-hazardous materials at pressures normally below 25 psi.
A non-pressurized tank car is similar to the DOT-111 rail tank cars. There are very few of these tank cars actively operating in the ﬂeet carrying Class 3 ﬂammable liquids.
A pressurized tank car that has additional safety features than what is required on DOT-111 class non-pressurized tank cars.
Non-Pressure/Low-Pressure Tank Cars (TC117, DOT117)
With a bottom outlet valve and protective housing separate from the manway, these cars carry petroleum crude oil, ethanol, and other flammable liquids typically below 25 psi.
Announced in 2015 by the United States Federal Railroad Administration (FRA) and Canada’s Transport Canada (TC), the DOT-117 (TC-117 in Canada) is an unpressurized tank car used on North American railroads. It was developed in the aftermath of the Lac-Mégantic rail disaster of 2013 in an effort to upgrade the specifications of the then-common DOT-111 and CPC-1232 designs.
Specifications require that the tank shells be made from 9/16″ steel with 11-gauge sheet metal jackets, 1/2″ thick head shields on the ends of the tanks, and improved valves. Per the new DOT-117 standard, the FRA and TC required that all tank cars constructed after October 1, 2015 be built to these specifications. The agencies also imposed a retrofit schedule to bring in-service cars up to DOT-117 standards.
Depending on the volatility of the cargo carried, DOT-111 and CPC-1232 cars would be banned in certain services per a series of cut-off dates, with all out of service or rebuilt by May 1, 2025.
This pressurized tank car has additional safety features than what is required on DOT-111 class non-pressurized tank cars.
Pressure Tank Cars
These cars feature protective housing and carry flammable, non-flammable, toxic, and/or liquefied compressed gases at pressures typically above 40 psi. Leaks can be life-threatening for this type, that is why we prepared the best practices in handling leak prevention when tank carloading and unloading.
Fully enclosed to protect cargo from the elements, these cars can have single or double sliding doors on the sides and/or ends. They can transport a wide variety of general freight, including lumber, packaged goods, paper, and beverages. They may also carry hazardous materials or dangerous goods in small totes.
Hopper cars are produced in two varieties: open-top and covered. Both are loaded through an opening at the top and feature a sloped floor for unloading. Covered hopper cars feature tops that protect the contents inside. They haul free-flowing dry bulk freight like sand, corn, wheat, sugar, rice, barley, fertilizer, cement, and roofing granules. Open-top hopper cars carry cargo that can withstand the elements, like coal, petroleum, coke, ore, rock, and copper concentrate.
TRUCK TRAILER TYPES
Road trailers and cargo transport units carry similar silhouettes to rail cars with varying maximum legal load weights. Here are the most general types of road trailers and cargo transport units:
MC331, TC331, SCT331
These trailers feature rounded heads and are used to transport pressurized and liquefied compressed gases like LPG and ammonia. They have a design pressure between 100 and 500 psi.
MC338, TC338, SCT338, TC341, CGA341
Similar to a “giant thermo-bottle,” these trailers haul refrigerated liquefied gases (cryogenic liquids). They feature fitting compartments in cabinets at the rear, and have a MAWP between 25 and 500 psi.
DOT406, TC406, SCT306, MC306, TC306
With a minimum MAWP of 25 psi, these trailers feature a circle cross-section and are designed to carry toxic, corrosive, and flammable liquids.
DOT412, TC412, SCT312, MC312, TC312
The diameter of these circular cross-section tank trailers is relatively small. They feature external ring stiffeners and are typically used to transport corrosive liquids with a MAWP of at least 15 psi.
With a hopper-style configuration, these trailers transport emulsion and water-gel explosives and carry a MAWP between 5 and 15 psi.
Compressed Gas/Tube Trailer
These trailers carry between four and 36 cluster high-pressure gaseous hydrogen tanks — or “tubes” — varying in length from 20 feet for small tubes to 53 feet on jumbo tube trailers. The hydrogen is compressed to pressures of 180 bar (~2,600 psig) to a maximum of 250 bar by DOT regulations. Steel tube trailers are most commonly employed, with DOT weight limitations for on-road vehicles resulting in a limited carrying capacity of approximately 280 kg due to the heavy weight of the steel tubes.
Dry Bulk Cargo Trailer
Dry bulk cargo (or tank) trailers feature an aluminum cylinder with one or more compartments. Each compartment features a cone-shaped hopper at the bottom and openings (or “manholes”) at the top and back for safer dry bulk loading. These trailers are available with two or four axles, or a B-train, and have capacities ranging from 550 cu.ft. to 2,800 cu.ft. Since they transport non-hazardous goods like sand, cement, flour, and plastic pellets, they are considered non-code tankers.
Vacuum tank trailers safely store and transport residential or caustic waste, chemicals, liquids, solids, slurries, or sludge. Each tanker features a vacuum breaker attachments that pneumatically loads and unloads content. Vacuum tankers have capacities ranging from 4,800 gal to 5,500 gal, and safely and efficiently exceed DOT specifications for transporting hazardous materials in commerce.
Enclosed mixed cargo trailers range from 48 to 53 feet long, with weight limits of 42,000 pounds to 45,000 pounds. Some can be loaded from the front, while others can be loaded from the sides. These trailers transport items like bags, boxes, tools, and drums, and protect them from the elements and security threats.
Intermodal Freight Container
Also known as shipping containers, intermodal freight containers are designed and built to be used on cargo ships, trains, or trucks without unloading and reloading their contents.vv
While these containers are available in numerous designs and sizes, roughly 90 percent used in the global container fleet are so-called dry freight or general purpose containers, typically measuring 8 feet wide by either 20 or 40 feet standard length. They are usually 8 feet 6 inches or 9 feet 6 inches high, with the taller variety known as “High Cube” or “Hi-Cube” containers.
Intermodal tank containers — or tanktainers — are used for transporting hazardous and non-hazardous liquids, gases, and powders as bulk cargo via different modes of transportation. They must meet a variety of regulations, like IMDG, ADR, RID, US DOT, and more. Tank containers, also known as isotainers, are stainless steel vessels surrounded by insulation and a protective layer, typically consisting of polyurethane and aluminum to assure safety in handling intermodal-type of containers. The vessels in each are held in the middle of a steel frame, which is constructed per ISO standards and is 19.8556 feet long, 7.874 feet wide, and 7.874 feet or 8.374 feet high. The contents of the tank range from 3,800 to 5,700 imp gal or 4,600 to 6,900 U.S. gal.