At one of my favorite train watch spots yesterday, a train with a lot of tank cars went by. Some of the cars appeared to be approximately 40 feet long, but others were much longer. Maybe 75 to 80 feet!
What accounts for the difference in the car lengths? Do the smaller cars, for example, tend to carry a different product than the larger cars? Or is this just one of those it is what it is things?
AAR FIELD GUIDE TO TANK CARS
https://www.aar.org/Documents/BOE/2017%20Field%20Guide%20for%20Tank%20Cars.pdf
As I understand it tank cars are designed to carry specific chemicals some of which are heavier than others but none of which can exceed the 286,000 pound limit on the rails. Heavier liquids demand shorter cars so they don’t exceed the axle load limits. Longer cars carry lighter liquids.
could it be that some product’s receivers do not need a big tank car of product at one time ? As well it may be some products have a short shelf life or half life ? Contamination if kept too long is another consideration ? H2O2 will certainly soak up water.
Major league transportation is based on cube and weight - no matter the vehicle. Heavy commodities reach the weight limits with smaller vehicles. Light commodities may not reach the weight limits even with the largest available vehicle.
Shippers don’t want to pay to ship air.
I think it’s tetraethyl lead, or something like that, has a really short tank car, due to the weight of the product.
It may be easier to consider certain dry cargos, like comparing iron ore/pellets with grains.
Hydrogen peroxide does not “soak up” water. It loses an Oxygen atom and BECOMES water
Larry, what use is there for tetraethyl lead nowadays since it is no longer put into gasoline?
It is still used in off road fuel. I’m paying $10 a gallon for 112 octane racing fuel with lead.
It’s also used in aviation gasolene, though currently available avgas has nowhere near the lead content of the “weapons grade” 115/145 avgas.
I’m not even sure it was tetraethyl lead, but whatever the liquid in that tank car was, it was much heavier than plain ol’ water.
Sam,
Two words “bulk density”, that is the weight per gallon or specific gravity which can be used to calculate weight per gallon or the product the car was designed to carry.
Before I elaborate you should know that I worked for the Bureau of Explosives for 5 years and Southern Pacific Hazardous Material Control for 8, so I lived and breathed tank cars for 13 years. The balance of this is based on 263,000 pound gross weight on rails which was the regulatory limit when I was working in the 1970s and 1980s. That limit was imposed after 6 axle and 8 axle cars got in trouble, but that is a separate story and before my time in the business.
That 263,000 pounds is utilized in one of two ways, tare weight and weight of product, or lading. A 263,000# car is said to be a “nominal 100 ton” car. Consider a grain car sized for wheat. It will have a tare weight of 60,000 - 63,000 pounds leaving a lading weight of 100 tons. At 60#/bu that is 3,333 bushels. Convert bu. to cubic feet, and add a bit for space not filled due to the slope of grain in the car, and you will find a lot of 4425 cuft grain cars in the system. If you want to also carry barley, which is a bit lighter you go to 4700 cubic feet, but wheat loaders have to be careful not to overload these cars.
Now lets consider two products at opposite ends of the density line, Liquefied Petroleum Gas (LPG) and Sulfuric Acid. Before we go any farther we must state the obvious, tank cars are built to carry one product or a specific range
Erik,
I don’t think “Purple Gas” has been seen since the heavy military bombers such as the B-36 last flew. There is still lead in avgas (No, I don’t mean Jet A or B) but 100LL is still very common for the recips of todays GA aircraft. Even “Green Gas” has not been available for quite some time.
PNWRMNM,
Thanks for your thoughtful explanation of tank car differences.
If the car is designed to carry a corrosive product, would it be lined with a material that would prevent the inside of the car from being eaten away?
I have seen various octane rated Sunoco race fuels with different dyes added so they can be differentiated. I have seen Blue, Purple, Green and Pink.
As a general matter yes, but not always. It depends on the nature of the product. The car builders are expert at this, but I did not have to be in the positions I occupied.
Hydrochloric Acid has its own Specification, DOT111A100W5, which by the definition of the spec included rubber lining.
Cars are often lined to protect the purity of the product as well.
Mac
Based on various articles on the big recips, “purple gas” seems to have been available until the early 1970’s. There were still a number of plans flying with Wasp Major’s and Turbo Compounds that could use purple gas for a bit extra manifold pressure.
They used to have 130 (Green) / 145 (Purple) or some variant at the CDF Forest Fire Airbase at Fox Field (Lancaster, CA) to support their “warbird” fleet. I think there still may be a few S-2As with the R-1820 radials, most have been converted to turbine engines.
Balt, thanks so much for that reference; I’ve now bookmarked it.
JPS1, I’m betting you saw a train on a western railroad, probably Union Pacific. The short cars may have been for the transportation of corn syrup and the larger ones (closer to 60 feet long) were probably for ethanol.