imploding railcar

[vulcanbomber]

 

apparently can't show GIFs

Edited August 20, 2019 by vulcanbomber

[Fat Controller]

We used to see examples of this at Marcroft's in Stoke, when we lived nearby. Presumably someone went to empty the tank without opening a breather to let air in to replace the contents.

[Andy Hayter]

A common event with tanks - whether rail, road mounted or indeed static.  As Brian says a blocked breather (either accidental or through someone forgetting to open an valve) will cause that.  The tanks are not designed to withstand a vacuum.

 

The most frightening case I came across was when having collapsed a tank, some bright spark decided to hide the fact by pressurising it with air.   The tanks are not designed for over pressure either.

[Wickham Green]

Bright sparks and tank wagons don't mix !

[kevinlms]

54 minutes ago, Andy Hayter said:

A common event with tanks - whether rail, road mounted or indeed static.  As Brian says a blocked breather (either accidental or through someone forgetting to open an valve) will cause that.  The tanks are not designed to withstand a vacuum.

 

The most frightening case I came across was when having collapsed a tank, some bright spark decided to hide the fact by pressurising it with air.   The tanks are not designed for over pressure either.

Well they won't be inflating this one!

 

 

[62613]

Did no-one do the collapsing can experiment in school science? The other thing, I suppose, is that tanks should be able to freely vent; indeed there are automatic pressure/vacuum valves manufactured just for this.

 

[Edwin_m]

1 hour ago, 62613 said:

Did no-one do the collapsing can experiment in school science? The other thing, I suppose, is that tanks should be able to freely vent; indeed there are automatic pressure/vacuum valves manufactured just for this.

 

Certainly they should vent on over-pressure - anyone remember the concern about BLEVEs (boiling liquid expanding vapour explosion) back in the 70s?  If the tank is exposed to an external heat source, venting of vapour even if it catches fire is probably preferable to the huge explosion (BLEVE closely followed by vapour-air) that could result if it was unvented and eventually failed.  

[kevinlms]

2 hours ago, 62613 said:

Did no-one do the collapsing can experiment in school science? The other thing, I suppose, is that tanks should be able to freely vent; indeed there are automatic pressure/vacuum valves manufactured just for this.

 

I don't remember doing that, but I do remember the opposite, i.e. expansion of water.

 

The science teacher put some water in a coffee tin and pushed the lid on a 'wee bit' (I lived in Scotland at the time).

So he lit the bunsen burner under it and we waited and waited and NOTHING.

 

So he moved forward to investigate & just before he got there, WHAM, up shoots the lid and puts a big dent in the ceiling, just missing the light fitting! Just as well he didn't move a bit quicker or he would have been hit in the face!

[Ian Morgan]

Spotted this one in Luxembourg, 2001

 

 

This goods yard was the place from which young Luxembourgers were deported and forced to join the german army, or act as forced labour, and where many Jews were deported to camps by the Nazis.

 

https://www.luxembourg-city.com/en/place/museum/deportation-memorial-luxembourg

 

 

[jonhall]

I wonder if the 'Mythbusters' tank car took more vacuum because it was 'frameless' and therefore the tan k body was more robustly constructed. I've photographed a tank in Hungary that appears to have imploded, but the lower half of the tank is still relatively intact (rather like Ian's example).

 

From a vacuum point of view, in the real world, these implosions must happen whilst there is still a fair amount of liquid in the tank, so perhaps a flattened top, and lower distortion of the sides is likely?

 

 

Jon

[rab]

7 hours ago, 62613 said:

Did no-one do the collapsing can experiment in school science? The other thing, I suppose, is that tanks should be able to freely vent; indeed there are automatic pressure/vacuum valves manufactured just for this.

 

Yes i still remember that one. Mine actually

'jumped' off the bench as it imploded.

[Edwin_m]

1 hour ago, jonhall said:

From a vacuum point of view, in the real world, these implosions must happen whilst there is still a fair amount of liquid in the tank, so perhaps a flattened top, and lower distortion of the sides is likely?

Yes, the weight of the liquid in the lower part of the tank would make the pressure lower down closer to atmospheric, so if the tank is of uniform thickness it will always "go" towards the top where the pressure is least.  

[Davexoc]

9 hours ago, 62613 said:

Did no-one do the collapsing can experiment in school science? The other thing, I suppose, is that tanks should be able to freely vent; indeed there are automatic pressure/vacuum valves manufactured just for this.

 

Did the small quantity of boiling water in an old 5 litre oil can and then refit the lid. It collapses as it cools, which is the same principle as the safety button on food jars. Fill hot, fit lid, contraction during cooling pulls the button down.

[melmerby]

6 minutes ago, Davexoc said:

Did the small quantity of boiling water in an old 5 litre oil can and then refit the lid. It collapses as it cools, which is the same principle as the safety button on food jars. Fill hot, fit lid, contraction during cooling pulls the button down.

Yours must have been a "poor" school, ours used new cans (from a hardware shop* iirc)

 

*remember them, where you could get useful things in proper quantities e.g a pound of nails, not 10 pre-packed in plastic!

[Davexoc]

2 minutes ago, melmerby said:

Yours must have been a "poor" school, ours used new cans (from a hardware shop* iirc)

 

*remember them, where you could get useful things in proper quantities e.g a pound of nails, not 10 pre-packed in plastic!

Nothing wrong with used Castrol GTX tins. We must have been at the forefront of recycling/re-use even back then in the 70s......

 

That'll be the hardware shop the sells Os and four candles I take it?

[melmerby]

1 hour ago, Davexoc said:

Nothing wrong with used Castrol GTX tins. We must have been at the forefront of recycling/re-use even back then in the 70s......

 

That'll be the hardware shop the sells Os and four candles I take it?

70s? This was the late 50s, when engine oil was engine oil and didn't have funny names.

Imploding cans - All to do with Boyles law I think, (if I'm right that's the first time it's cropped up in 50+ years)

 

Plugs? Barf, Basin?

No - firteen amp.

 

 

Edited August 20, 2019 by melmerby

[Andy Hayter]

2 hours ago, Edwin_m said:

Yes, the weight of the liquid in the lower part of the tank would make the pressure lower down closer to atmospheric, so if the tank is of uniform thickness it will always "go" towards the top where the pressure is least.  

 

 

Actually no.  The pressure in the tank is essentially the same all the way through*.  Liquids however do not expand or contract as the pressure changes.  So in essence the liquid in the bottom of a tank is like a solid block when the pressure drops and it is that solid block that helps to protect the bottom of the tank.

 

*  If you had a very high tank with a lot of liquid in it then the pressure at the bottom of the liquid would be higher, but in the context of a railcar - probably carrying a petroleum based liquid the effect is very small.  If the tank contained water, you would need a depth of around 10m (32 feet) for the bottom to be around one atmosphere higher than the gas space.  Petroleum products might need up to 30% higher liquid head to give the same result depending on their density.

[JeffP]

22 hours ago, melmerby said:

70s? This was the late 50s, when engine oil was engine oil and didn't have funny names.

Imploding cans - All to do with Boyles law I think, (if I'm right that's the first time it's cropped up in 50+ years)

 

Plugs? Barf, Basin?

No - firteen amp.

 

 

Not really. It's to do with the water boiling, producing a vapour which drives out the air.

But said vapour occupies a VERY small volume once condensed, so if the lid is on, and the can allowed to cool, no air can get in and a vacuum is the result.

The imbalance in pressure, (none inside and air pressure outside, crushes the can.

[Edwin_m]

21 hours ago, Andy Hayter said:

 

 

Actually no.  The pressure in the tank is essentially the same all the way through*.  Liquids however do not expand or contract as the pressure changes.  So in essence the liquid in the bottom of a tank is like a solid block when the pressure drops and it is that solid block that helps to protect the bottom of the tank.

 

*  If you had a very high tank with a lot of liquid in it then the pressure at the bottom of the liquid would be higher, but in the context of a railcar - probably carrying a petroleum based liquid the effect is very small.  If the tank contained water, you would need a depth of around 10m (32 feet) for the bottom to be around one atmosphere higher than the gas space.  Petroleum products might need up to 30% higher liquid head to give the same result depending on their density.

There's still be some pressure difference though, even if it's less than a tenth of an atmosphere for a metre depth of fuel.  The pressure differential between inside and the gas space will be less than one atmosphere as the upper part will contain some air (the tank wouldn't be completely full before unloading) and vapour (lower boiling point at low pressure!) so the difference between top and bottom could be perhaps 20% or more.  This strikes me as enough to make the top significantly more likely to cave in.  

[melmerby]

1 hour ago, JeffP said:

Not really. It's to do with the water boiling, producing a vapour which drives out the air.

 

It is still a relationship between pressure, volume & temperature (Maybe a different person's law?)

A gas contained in a fixed volume will reduce in pressure as the temperature drops, so even if you had a gas (say nitrogen) in a vented vessel, heat it up so that it expands, the surplus will escape.

Seal the vent, cool the vessel and the pressure inside will drop, it is now below atmospheric and the outside pressure can cause the vessel to collapse.

[RLWP]

5 minutes ago, melmerby said:

It is still a relationship between pressure, volume & temperature (Maybe a different person's law?)

A gas contained in a fixed volume will reduce in pressure as the temperature drops, so even if you had a gas (say nitrogen) in a vented vessel, heat it up so that it expands, the surplus will escape.

Seal the vent, cool the vessel and the pressure inside will drop, it is now below atmospheric and the outside pressure can cause the vessel to collapse.

 

With the addition that as the water vapour cools, it goes through a phase transition from gas to liquid. The can that was full of steam is now full of - well, almost nothing. This leads to a dramatic pressure change and an impressive demonstration of air pressure for a classroom full of kids

 

Richard

[kevinlms]

2 hours ago, RLWP said:

 

With the addition that as the water vapour cools, it goes through a phase transition from gas to liquid. The can that was full of steam is now full of - well, almost nothing. This leads to a dramatic pressure change and an impressive demonstration of air pressure for a classroom full of kids

 

Richard

Like this one. 

 

Sadly, the cameraman claims he captured the moment of collapse, it's not actually shown.

 

[eastglosmog]

8 hours ago, RLWP said:

 

With the addition that as the water vapour cools, it goes through a phase transition from gas to liquid. The can that was full of steam is now full of - well, almost nothing. This leads to a dramatic pressure change and an impressive demonstration of air pressure for a classroom full of kids

 

Richard

And how Newcomen and Watt steam engines worked!

[melmerby]

It's also how fridges work.

Compression produces heat which is dissipated in the radiator, it then expands inside the pipes in the fridge and absorbs heat cooling the fridge interior.

[PatB]

Interesting though this thread is, I'm mildly disappointed that it didn't turn out to be about entertaining things to do with a life expired Pacer.