Hypothesis or Your Best Guess Page

The Real Life Can Crush

Contact: M. Garlick @(989)686-9272 Last update: 12/13/06

Date June 6th 2001 Tim Repp Railfan (or Ferroequinologist) Writes...

The shell didn't rupture nor was it over stressed -- the tube began collapasing at a very small imperfection in the cross-sectional circle (like a weld or bracket) that made it less than perfectly circular. As the non-circular imperfection became greater, the rate of collapse increased. As the longitudinal (cigar) shape was lost ( i.e., the cross-sectional moment of interia was reduced), it bent down under its own weight. In outer space, the tube would have just sucked in, without any bending. Neither has anything to do with the material strength of the steel. It's all geometry ratio's, what we call L/D (length/diameter).

I bet that car couldn't take -10 psig without some kind of yielding. The car should have had a negative pressure relief valve, but they cost money, and this kind of thing doesn't happen very often.

Date June 6th 2001 Ed Alley Writes...

Dr. Slime:

Atmospheric pressure is about one million dynes per square centimeter. That translates into about 2092 pounds per square foot, since there are 478. dynes/cm2 in 1 pound/sqft.

You said on your web page that the tank car is 55 ft long. I estimate by the picture that the diameter of the tank car is about 8 ft, maybe 7.5 ft?. That makes the surface area of the tank car (neglecting the ends) to be roughly: PI X D X H = 3.14 X 8 X 55 = 1380 sq ft.

If the tank depressurized by 1/2 atmosphere that would leave 1000 pounds per square foot negative pressure on the shell of the tank car. Result:

1380 sq ft X 1000 pounds per sq ft = 1380000 net pounds force working on the hull of the tank car. The tank is made to hold things in by the expansive strength of the hull as the pressure inside pushes out and expands the tank; however, a compressive load would be unstable; just as it is easy to crush a beer can with your hand.

The 1000 pounds per square foot that the atmosphere applies is more than enough.

Ed Alley

Many thanks to the fine viewers of these pages who point out my typo's and correct my Greek pluralization errors (Especially the rules of a third declension Greek Nouns), I do mean this, so if you spot an error please point it out, so I don't look like a bumpkin who lives 30 seconds from a corn field. which I do.

Write me, with yours I'd be glad to post any and all hypothesis, that I might receive.

Always Bewary of Chemicals! Wear Proper Saftey Equipment, Never Eat or Handle food before washing your Hands...

HAVE A BLAST!

Dr. SLIME

slime@alpha.delta.edu

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