Re: HO Tank Car Lid

Charles Peck

Now if you were to have a tank car built to the minimum required standards, you 
might be tempted to fill it full of some heavy but free flowing liquid. Something with a 
suitably low viscosity, like clipper oil.
And then, if you were to open a drain valve at the bottom of the tank, some of that 
liquid would drain out.  BUT!  What if in doing so, it sucked in some bubbles of air,
like my ketchup bottle sometimes does?  Then more such liquid could pour out the
 bottom.  And you would have a mess between the rails that your track cleaning 
car probably wouldn't be able to clean up.
BUT! If you put a hose on that drain, and ran a long hose down into a deep hole, 
like maybe the Grand Canyon,  and put a check valve on it so the bubbles couldn't 
get back up the hose, then you could maybe get yourself a mess of scrap iron out of it.
Better, if you used a sharp file to create some stress points in vulnerable places, 
you could maybe use less hose. 
Presto!  You have demonstrated why most model RR tank cars are plastic and not steel.
Chuck Peck (enjoying some wine and a few laughs)

On Mon, Nov 23, 2020 at 8:00 PM mopacfirst <ron.merrick@...> wrote:
There are formulas in ASME Section VIII of the Boiler and Pressure Vessel Code that will allow you to calculate, or at least read off a set of curves, the expected maximum external pressure a steel fabricated vessel (say, a tank car) can withstand without collapsing.  Suffice it to say that the maximum possible external pressure a vessel in free air can see is 14.7 psi absolute (psia).  This would be less, say, if you assume this tank car is on Tennessee Pass or somewhere like that.

Some of the factors in the calculation are the ratio of the wall thickness to the diameter, and any reinforcement and the distance between reinforcements.  The tank heads count.  

I think the most common way you can get a vessel like a tank car to collapse is to fill it with steam and then close the vents while it's hot.  These guys who sucked a vacuum in one with a vacuum truck were probably doing this demonstration for the purposes of showing what could happen if you didn't have a vent open, and I'd say this is not surprising, that it would collapse at -7 psig or so (about 7 or so psia).  Notice that, in the video, they taped all the couplings on their hose to prevent air from leaking inward.  My best guess is that, if you did start to drain a tank car full of oil without opening a vent, a lot of it would run out by gravity but at some point it probably would collapse before it was fully drained.

A riveted 8k or 10 tank during the period of this list could have been slightly stiffer than a modern welded one, but probably not by much.  Or maybe not.

Ron Merrick

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