Mythbusters Tank Car Episode

[Blazeman]

http://www.progressiverailroading.com/mechanical/article/AllTranstek-tackles-imploding-tank-car-legend-on-MythBusters-TV-show--47621

Different situation than not venting cars when discharging lading. That will crumple a car or tank trailer.

[nkalanaga]

Filling it with HOT steam, then leaving it sealed will also collapse it, as there was a training video from a car cleaning company online several years ago.  It may have been an earlier, and possibly less substantial car, or it could have had flaws, or it could simply have used hotter, and thus higher pressure, steam, meaning a greater pressure difference when it condensed.

[Steve S]

Here's the implosion.  They had to dent it in order for it to implode.

https://www.youtube.com/watch?v=UpWeU2fvFGs

Steve S

[Steve S]

Here's the small scale tests they did.

https://www.youtube.com/watch?v=E5pljUJ6b1k

Steve S

[jagged ben]

Cool vid, but I wonder:  does the 'legend' derive from a modern tank car, or from some three dome thing from the 40s?

[nkalanaga]

The one I remember probably predated the public Internet, but wasn't "ancient", so I'd say it was a 1970s/80s car.  Certainly not one of today's reinforced versions.  A quick Google search doesn't find it, which isn't surprising, given how long ago it was.  The entire site is probably gone by now!

Here's one that might have started the current interest, by confusion, as it does NOT involve steam, but improper unloading of a car, in this case a relatively modern European design.

https://www.youtube.com/watch?v=Zz95_VvTxZM

One of the more intelligent comments:
"Kris Rehberg 3 months ago
This is a demonstration because this more often happens after steam cleaning and closing the valves.  When the pressure release valves fail, the tank implodes as the gas inside cools.  Using a vaccuum pump is used to simulate this kind of accident." 

[John]

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This is why I never served on submarines ..

[Steve S]

This is why I never served on submarines ..

A submarine implosion would be even more violent.  Here on the surface the largest pressure differential you can reach is one atmosphere.  But under water, you hit a pressure difference of one atmosphere at just 10 meters below the surface.  Forty meters below gets you a difference of 4 atmospheres.

Steve S

[C855B]

Cool vid, but I wonder:  does the 'legend' derive from a modern tank car, or from some three dome thing from the 40s?

Early tank cars couldn't do this. As soon as something started to deform from the vacuum, even slightly, a riveted seam would be compromised and that would be the end of the fun. This is only possible with modern, unitized welded construction and modern steel alloys.

Besides, this principle as a significant force has been known for centuries. You guys forget your steam engine history - the first walking beam stationary engine worked this way. The Newcomen engine injected low pressure steam into a cylinder and then cooled it off with a water spray, creating a vacuum which then moved a piston.

[nkalanaga]

I've seen models of the Newcomen engine, although not working models.  I'll bet that was as alien to the people then as some of our high-tech gadgets are to the non-geeks today.