They don't build em like they used to.....

Friends,

A little rail related video <[video]http://www.cabrillo.edu/~jmccullough/Videos/SWF/tank_implosion.swf[/video]>

ns

Steam cleaned then immediately sealed. As the steam cools and condenses it creates and vacuum - the atmospheric pressure does the rest.

I think a vent should have been opened. Tankers like this should have vacuum breakers installed. I would think that's a code requirement!

Thanks for sharing mjolnir.

It appears that many forms of cylindrical construction are far less "over-engineered" than in years gone by.

I can remember the days when it was impossible to crush a beer can with one hand!

US railroads have been on a campaign to reduce the amount of tare in the loaded weight of freight cars for some years now. It costs as much to move a ton of a freight car's empty weight as it does to move a ton of its payload. So, reduce the tare and increase the revenue. The results are the pictures of hopper cars crumpled like paper and the "crushing beer can" video we've been treated to. Neat video, mjolnir.

Bernie

I never have seen a tank car collapse that fast. Are tank cars supposed to have vents?

frogpipe said:

Steam cleaned then immediately sealed. As the steam cools and condenses it creates and vacuum - the atmospheric pressure does the rest.

Click to expand...

It was a staged educational demonstration of what happens when you gravity(or pump) off-load without first opening a vent or hatch. It happens to highway tanker trailers all the time, when people get careless or impatient...or just forgetful.

-as an aside, it has nothing to do with under, or over-engineering, as it is a situation beyond the normal use and operation of the railcar. To engineer a tanker to witstand those kind of negative pressure forces, one would need sidewalls over 2 inches thick...much like navy submarines...very inappropriate for the intended usage.

jeffmorris said:

I never have seen a tank car collapse that fast. Are tank cars supposed to have vents?

Click to expand...

It depends on the intended cargo. Food Grade products do not, and can not (in the US) have any kind of atmospheric contact..ie, no vents, and access hatches must be sealed (tamper evident seals, not just closed).

Hot, cold or otherwise "known to expansion", AND non-hazardous products DO get vented tankers...Hazardous materials must also be sealed, like food-grade.

Another way that tank cars collapse like that is as a result of steam cleaning. The car is cleaned with steam, and the cleaner(s) neglect to leave the car unvented while the steam condenses, and pressure drops. And yes, they can collapse just that fast; as soon as the pressure differential drops below the correct threshold. You can reproduce the effect in miniature. Open a jar of your favorite salsa (I specify salsa because in my part of the world it's all still packed in glass) and heat the contents. Close the jar securely using the original lid. Let the salsa cool, and if you wait long enough, the "tamper evident" seal will pop to the sealed state.

ns