What causes tank car implosion

[litz]

To add to this ... remember, a tanker is not a pressure vessel. It's a liqiud container, not all that different from a milk jug or coke bottle.

If you remove the contents, and do not allow air in to replace the void, it will collapse from the outside air pressure.

- litz

[Allen Hazen]

Hot air exerts more pressure than cold air (Boyle's Law): I think if you rinse a plastic milk container in hot dishwater, drain it quickly and screw the cap on tight it will collapse a bit when the hot, steamy, air inside it cools down to room temperature.

So... Suppose a tank car is steam cleaned, and the valves then shut. Will the pressure differential when the interior temperature of the tank car falls be enough to collapse it?

[wis bang]

Hot air exerts more pressure than cold air (Boyle's Law): I think if you rinse a plastic milk container in hot dishwater, drain it quickly and screw the cap on tight it will collapse a bit when the hot, steamy, air inside it cools down to room temperature.

So... Suppose a tank car is steam cleaned, and the valves then shut. Will the pressure differential when the interior temperature of the tank car falls be enough to collapse it?

Yes...Steam and steam heated cleaning compounds plus steam heated rinse water raise the temp of the tank metal up over 180 degrees. This creates two problems if the tank is not vented; 1- condensation which may cause the tank to be rejected for excessive moisture at the next loading site which can be hundreds of miles away from the cleaning facility & 2- a potential implosion as the tank interior cools.

[wis bang]

To add to this ... remember, a tanker is not a pressure vessel. It's a liqiud container, not all that different from a milk jug or coke bottle.

If you remove the contents, and do not allow air in to replace the void, it will collapse from the outside air pressure.

- litz

Well it IS a pressure vessel with a pressure relief valve to protect it from over pressurization. We used air for alot of rail to truck transfers. The standard tankcar has a 'standpipe' from the valve sump up thru the top near the manway.

We used to transfer truckloads of plasticizer w/ one hose and air pressure by placing a 2" T fitting on top of the standpipe. One side was reduced to a 1" ball valve and a twist lock air hose connection while the other side was connected to a 2" hose that was handed to the driver on the tanker. We placed a 3" strainer into a 3" washout port on the tanker covered w/ a 3" X 2" reducing elbow and connected the hose. Pressurizing the tankcar and opening the standpipe valve let the product flow to the elbow while the driver stood by his trailer manway w/ a gauge stick measuring his innage until the needed amount of product was transferred. Once the correct amount was transferred we would close the standpipe valve and move the air hose to the fitting on the T and blow the hose empty.

This was alot easier than pumping off the bottom w/ the tractor pump which required at least three hoses and often left us figuring how to drain the hose.

DuPont sent us Titanium Dioxide Pigment slurry. It weighed 22lbs/gal and would settle out so they cut the standpipe and placed a T to run perforated pipe along the tank floor. We had to 'sparge' the railcar by placing an air hose onto the top of the standpipe and blow air down to sparge [re-mix the pigment into suspension in the water] for 10 min b/4 transferring the product by air pressure using the bottom outlet. The fitting also had a air connection so we could blow the hose empty.

Unless the product was flammable -or- somehow affected by the air, we preferred to use air pressure instead of a tractor pump. Less hoses and easier to clean the product from the hoses w/ air. Even a brand new pump wouldn't pump the hoses clean...