Oil Train

[MidlandMike]

schlimm

...  

However, with oil price instability (generally lower) and thus declining Bakken production, this may all be a moot point.  ...

 

North Dakota production is up over 10% from this time last year when the oil prices started to drop.

www.dmr.nd.gov/oilgas/stats/historicaloilprodstats.pdf

 

[Euclid]

Midland Mike,

Can you explain how tank cars are typically loaded for unit trains regarding how much of the tank is filled with liquid, and how much is gas space?  I recall that it was brought up in the sloshing theory of oil train problems. 

Someone posted this information in a thread here on the general forum. The post may be in this thread, but I can’t easily find it. Can you confirm whether or not the information about the weight and empty space inside of the tank car is true?  This is quoted from the post:

“Bakken crude oil is a stratified multi constituent liquid. Its weight is such that something like 28,000 gallons are the weight limit for a 30,000 gallon tank car. Visualize the 2000 gallons as about 36 drums of 55 gallon capacity. That's quite a bit of empty space inside a tank car. It is about 269 cubic feet.”

[MidlandMike]

Euclid

Midland Mike,

Can you explain how tank cars are typically loaded for unit trains regarding how much of the tank is filled with liquid, and how much is gas space?  I recall that it was brought up in the sloshing theory of oil train problems. 

Someone posted this information in a thread here on the general forum. The post may be in this thread, but I can’t easily find it. Can you confirm whether or not the information about the weight and empty space inside of the tank car is true?  This is quoted from the post:

“Bakken crude oil is a stratified multi constituent liquid. Its weight is such that something like 28,000 gallons are the weight limit for a 30,000 gallon tank car. Visualize the 2000 gallons as about 36 drums of 55 gallon capacity. That's quite a bit of empty space inside a tank car. It is about 269 cubic feet.”

 

I retired before crude-by-rail was widespread, so I can only tell you what I know.  Crude oil comes in a wide range of densities, so it's not like you could design a perfect sized tank car for CBR.  Therefore, you would expect that they would use the next biggest volume sized tank car to contain the max weight load.  At approx 7 lb/gal, 200,000 pounds would be in the 28 to 29,000 gallon range, so there would be some leftover volume in a 30 to 33,000 gal tank car.  Vapors evolving off the crude, plus whatever fumes left over from the previous load, would fill the headspace.    One problem I have with the quote you cited is the ambiguous use of the word "stratified".  It would seem out of context when talking about CBR, as the Canadian report on the Lac Megantic wreck found that the crude in the uninvolved tank cars was not stratified.

[Euclid]

MAXIMUM FORCE POTENTIAL

 

I have mentioned the possibility of tank cars being trapped in a pileup and then being squeeze-burst from the impact from an oncoming string of cars still running on the rails.  As hard to believe as that may be, the point is only secondary to a larger point.  The larger point is that the force needed to squeeze-burst a tank car is available, and will be practically applied depending on the random dynamics of the derailment and where the derailment occurs in the train.  This maximum force potential comes from the cumulative kinetic energy of several cars running on the rails and coupled together. 

If the conditions do produce this maximum force, it will apply to all types of impact damage including punctures, crushing, crumple, and tears, although these types of damage can be caused by much less force than the maximum force potential that I am referring to.

I have seen a few references to tank car crash testing that seems to ignore this maximum force potential.  Instead, the tests show a rolling mass representing a single tank car, and it collides with an actual tank car from various angles.  Apparently, this type of testing result is what the newest puncture and tear resistance standards are based on.  Where are the tests that show what happens in the maximum force potential, say when 20 cars strike a tank car broadside when the car is trapped in a pile?    

This maximum force potential comes not just from one car striking another as seen in the crash tests.  Instead, it comes from the oncoming cars still on the rails behind the derailment.  The overall dynamics of this force depends on where the derailment occurs in the train.  If it occurs only a few cars up from the hind end, there may be little or no force from the trailing cars.  If it occurs near the head end, there will be maximum potential for the force from the trailing cars; however, there will be relatively little potential for the pileup to grow in its resistance to the force from the trailing cars.   

I believe that this maximum force potential vastly exceeds ability of thicker tank walls and stronger head shields to resist it.  That is why the car builders have said that it is impossible to make cars strong enough to resist breaching in a high speed or high energy derailment.   

This maximum force potential is basically the same force involved when a train runs into another train.  Consider a tank car that is pinned in position and hit by say 2,000 tons of loaded tank cars.  I would expect that pinned tank car to disintegrate.  It may be purely a squeeze-burst, or it may be combined with puncturing, tearing, or cracking of the bending and crumpling wall.  But in general, it seems like the force potential would be way out of proportion to what could be resisted by stronger head shields and tank walls. 

Here is a crash test video that gives a good feeling for the kind of force that would be involved in in a derailment where individual cars are struck by the incoming string of trailing cars.  The music is a little weird, but the video is quite graphic with a variety of impacts.  Notice how rubbery the equipment looks as it is impacted:   

https://www.youtube.com/watch?v=Q9gUFR8P0jQ

[MidlandMike]

I presume several following cars give more force than a single car, however, couplers/draft gear do not ridgidly transfer the momentum of an entire trainload of following cars, and in fact fail, and often give way to an accordian-like bunching of cars.

[Euclid]

Midland Mike,

Well, the process that I am referring to does include the accordion-like bunching of cars that you mention.  That is where each car entering the growing heap is forced to nestle into the heap, and become backed up by the mass of the other cars ahead of it in the heap.  That accordion heap of cars is directly within the derailment process. 

But the process also includes the string of cars that are rolling in and feeding cars into that accordion heap. As the heap grows larger, the zigzag jackknifing of the accordion process can suddenly cease, and therefore allow the incoming string of cars to punch directly into the mid-section of a tank car crosswise in the heap.  Maybe the next car in that string will bypass the car that has struck the mid-section of the crosswise car.  And then that bypassing car also strikes the mid-section side of the car struck by the previous car.  So, all of a sudden this process turns into a series of direct collisions between the incoming cars and the cars that are trapped in the heap with no way to deflect.

The couplers and draft gear of the incoming string of cars will be able to rigidly transfer the momentum forward because those cars are running on the rails of undamaged track.  So the incoming string of cars would act just like a colliding train as shown in the crash test video.         

[tree68]

Euclid

...the zigzag jackknifing of the accordion process can suddenly cease,...

And this would happen how?

[MidlandMike]

Euclid

...

The couplers and draft gear of the incoming string of cars will be able to rigidly transfer the momentum forward because those cars are running on the rails of undamaged track.  So the incoming string of cars would act just like a colliding train as shown in the crash test video.         

 

The only way the incoming cars could ridgidly transfer all their momentum, is if all those cars were welded together as a single car and were structurally ridgid so that they themselves would not crumple.  The couplers/draft gear do not accomplish that.  Additionally all the cars are identically constructed, and the following cars are no stronger than the cars already derailed.

[Euclid]

tree68

 

Euclid

...the zigzag jackknifing of the accordion process can suddenly cease,...

 

 

And this would happen how?

 

The derailment process is generally chaotic, but patterns can form amid the random action.  One classic pattern is the jackknifing, zigzag that forms an accordion pattern.  For as long as the forming accordion pattern continues, it can protect the pileup from a direct impact.

But the continuation can suspend at any point if random factors intervene and restore the chaos.  Generally, that could be caused by a parting at the joint of the first incoming car on the rails in the string of trailing cars and the next car ahead that is about to jackknife.  It could be influenced by the extent to which the zigzagging cars dig into the ground and resist.  It could also be influenced by cut banks along the roadbed, or by the presence of fills leaving the ends of the zigzagged cars unsupported.  It could also be influenced by a jackknifing car failing to fully fold up against the car ahead of it, thus changing the deflection angle for the next car coming in.

Generally, my only point is that the accordion process could continue until the train stops, or it can end at any point before the train stops.  It also might never form at all during the derailment.  Instead, the cars might pile up in a completely chaotic, random pattern.  That way, every incoming car might have the opportunity to strike other cars that are relatively anchored by the random pileup.

But again, the point is not so much that these collision impacts can occur.  Instead, it is that the real world force potential is so vastly greater than just one moving car striking a stationary car; the simplistic model of collision which appears to be assumed in the crash testing of tank cars.    

[BaltACD]

The accordion process stops when the stresses on the coupling are not sufficient to break the coupling between cars in two.  The entire derailment procees is an exercise in depleting the kinetic energy in the moving train to zero.  It cannot be depleted to zero, instantly.

[CSSHEGEWISCH]

At last, somebody who understands the basic laws of physics, especially:  Energy neither be created nor destroyed.

[Euclid]

BaltACD

The accordion process stops when the stresses on the coupling are not sufficient to break the coupling between cars in two.  The entire derailment procees is an exercise in depleting the kinetic energy in the moving train to zero.  It cannot be depleted to zero, instantly.

 

I am not sure if you are intending to contradict what I said about the accordion process stopping during the derailment.  I agree that the depletion of kinetic energy will continue for as long as the train is in motion, as you say.  My point was that the accordion process can start or stop at any point during the derailment process while the train is in motion.  I did not mean to suggest that the depletion of kinetic energy can stop during that period.

My point was that if the accordion process suddenly stops during the derailment, the continuing depletion of the kinetic energy may cause incoming cars to increase their damage to the derailed stationary cars.    

[MidlandMike]

Euclid

...

But again, the point is not so much that these collision impacts can occur.  Instead, it is that the real world force potential is so vastly greater than just one moving car striking a stationary car; the simplistic model of collision which appears to be assumed in the crash testing of tank cars.    

 

You still have not demonstrated a mechanism by which the force of a following car is multiplied by the rest of the following cars.  Couplers are designed to fail before structural damage is done to a car.  Tank cars themselves are their own structural force, since the absence of center sills.  A following tank car will itself be crushed between the pile and the next following tank car, and so on.  The entire force of the train will never be concentrated at one spot, and the kenetic force will be disapated thru the entire pile-up process.

[Euclid]

MidlandMike

 

Euclid

...

But again, the point is not so much that these collision impacts can occur.  Instead, it is that the real world force potential is so vastly greater than just one moving car striking a stationary car; the simplistic model of collision which appears to be assumed in the crash testing of tank cars.    

 

 

 

 

You still have not demonstrated a mechanism by which the force of a following car is multiplied by the rest of the following cars.  Couplers are designed to fail before structural damage is done to a car.  Tank cars themselves are their own structural force, since the absence of center sills.  A following tank car will itself be crushed between the pile and the next following tank car, and so on.  The entire force of the train will never be concentrated at one spot, and the kenetic force will be disapated thru the entire pile-up process.

 

Midland Mike,

This in respose the your above quoted post and your post a few posts prior:

I agree that a small amount of the kinetic energy in string of cars coming into the derailment from behind is going to be absorbed in the draft gear.  Also, a fair amount will be dissipated by braking.  But every car will still retain a large amount of kinetic energy that will either require enough braking time to dissipate or; might get dissipated in a mass of collisions and friction during a derailment pileup, if there is not enough time for the brakes to stop the cars.   

So, I would say that the total energy of this line of incoming cars is indeed concentrated to one point.  Generally speaking, that force is directed through the drawbars and couplers to the head end.  Specifically, the force is concentrated to the point of impact if it runs into an obstacle.  

Say you have 20 cars on the rails, rolling forward, and feeding cars into the derailment zone.  The collective energy of those 20 cars is pushing one car at a time into the derailment pileup.  It is true than just one car at time is derailing, but that does not mean that the collision force is as if only a single car hit a stationary car.   On the contrary, the force that is directed into the collision point is the force of 20 cars acting as one, just like a giant battering ram.

Therefore, regarding the force that damages and ruptures tank cars in a pileup; the greater the number of cars behind the derailment, the higher that force rises.

[BaltACD]

Euclid

MidlandMike

Euclid

...

But again, the point is not so much that these collision impacts can occur.  Instead, it is that the real world force potential is so vastly greater than just one moving car striking a stationary car; the simplistic model of collision which appears to be assumed in the crash testing of tank cars.    

 

 

 

 

You still have not demonstrated a mechanism by which the force of a following car is multiplied by the rest of the following cars.  Couplers are designed to fail before structural damage is done to a car.  Tank cars themselves are their own structural force, since the absence of center sills.  A following tank car will itself be crushed between the pile and the next following tank car, and so on.  The entire force of the train will never be concentrated at one spot, and the kenetic force will be disapated thru the entire pile-up process.

 

 

 

Midland Mike,

This in respose the your above quoted post and your post a few posts prior:

I agree that a small amount of the kinetic energy in string of cars coming into the derailment from behind is going to be absorbed in the draft gear.  Also, a fair amount will be dissipated by braking.  But every car will still retain a large amount of kinetic energy that will either require enough braking time to dissipate or; might get dissipated in a mass of collisions and friction during a derailment pileup, if there is not enough time for the brakes to stop the cars.   

So, I would say that the total energy of this line of incoming cars is indeed concentrated to one point.  Generally speaking, that force is directed through the drawbars and couplers to the head end.  Specifically, the force is concentrated to the point of impact if it runs into an obstacle.  

Say you have 20 cars on the rails, rolling forward, and feeding cars into the derailment zone.  The collective energy of those 20 cars is pushing one car at a time into the derailment pileup.  It is true than just one car at time is derailing, but that does not mean that the collision force is as if only a single car hit a stationary car.   On the contrary, the force that is directed into the collision point is the force of 20 cars acting as one, just like a giant battering ram.

Therefore, regarding the force that damages and ruptures tank cars in a pileup; the greater the number of cars behind the derailment, the higher that force rises.

The only way you are going to understand what actually happens in a derailment is ride one out in the middle of the derailing train.  What you learn there will have applicability to that unique set of circumstance.  Derailments do not conform to your simplistic rules of physics and train dynamics.

[Euclid]

There is not a complete set of rules for them, but they do conform to what said above. 

[Buslist]

BaltACD

 

 

Euclid

MidlandMike

Euclid

...

But again, the point is not so much that these collision impacts can occur.  Instead, it is that the real world force potential is so vastly greater than just one moving car striking a stationary car; the simplistic model of collision which appears to be assumed in the crash testing of tank cars.    

 

 

 

 

You still have not demonstrated a mechanism by which the force of a following car is multiplied by the rest of the following cars.  Couplers are designed to fail before structural damage is done to a car.  Tank cars themselves are their own structural force, since the absence of center sills.  A following tank car will itself be crushed between the pile and the next following tank car, and so on.  The entire force of the train will never be concentrated at one spot, and the kenetic force will be disapated thru the entire pile-up process.

 

 

 

Midland Mike,

This in respose the your above quoted post and your post a few posts prior:

I agree that a small amount of the kinetic energy in string of cars coming into the derailment from behind is going to be absorbed in the draft gear.  Also, a fair amount will be dissipated by braking.  But every car will still retain a large amount of kinetic energy that will either require enough braking time to dissipate or; might get dissipated in a mass of collisions and friction during a derailment pileup, if there is not enough time for the brakes to stop the cars.   

So, I would say that the total energy of this line of incoming cars is indeed concentrated to one point.  Generally speaking, that force is directed through the drawbars and couplers to the head end.  Specifically, the force is concentrated to the point of impact if it runs into an obstacle.  

Say you have 20 cars on the rails, rolling forward, and feeding cars into the derailment zone.  The collective energy of those 20 cars is pushing one car at a time into the derailment pileup.  It is true than just one car at time is derailing, but that does not mean that the collision force is as if only a single car hit a stationary car.   On the contrary, the force that is directed into the collision point is the force of 20 cars acting as one, just like a giant battering ram.

Therefore, regarding the force that damages and ruptures tank cars in a pileup; the greater the number of cars behind the derailment, the higher that force rises.

 

 

The only way you are going to understand what actually happens in a derailment is ride one out in the middle of the derailing train.  What you learn there will have applicability to that unique set of circumstance.  Derailments do not conform to your simplistic rules of physics and train dynamics.

 

 

That is why actual physical derailment/impact (the term FRA prefers) tests are carried out at TTC.

[tree68]

Euclid

Therefore, regarding the force that damages and ruptures tank cars in a pileup; the greater the number of cars behind the derailment, the higher that force rises.

And, the more cars "behind" the derailment, the greater the combined retarding force of their brakes, which are now in emergency.  The oncoming cars (which are not getting a head start - they are right behind the derailing cars) are not free rolling, unless you have a situation where the engineer has p!ssed away the brakes on a downgrade.  And that could happen with ECP, too...

So far we've heard lots of theory on how this battering ram phenomenon is supposed to happen.  It's time for some incident reports documenting same.  Just because it "could" happen doesn't mean it ever has, or ever will.

[Euclid]

I did mention above that the brakes will dissipate some of the kinetic energy.  They would dissipate all of it if there were enough time to stop the train.  A derailment does not often give the brakes time to stop the train before cars collide.  Obviously there is a lot energy remaining when then happens.  Otherwise, what causes the pileup?  I cannot imagine how the battering ram analogy can be doubted.  It is the essence of trains.  If two trains hit head on, are we to conclude that the energy directed to the point of collision was just the force of the two knuckles hitting each other because they were the first to contact?

[dehusman]

In order to "squeeze" a tank car hard enough to cause it to "burst" from internal pressure the car has to have enough compression pressure placed on it that it compresses the inside without exceeding the tensile strength of the shell. 

That's why I say "bursting" is unlikely.  I think that in the collision the pressure is so rapid and so concentrated that the shell is punctured or torn before it has a chance to compress the internal pressure to the failure point and rupture from the inside.

While the TTC cab surviveability videos posted by Euclid are a poor example none of the cars involved were tank cars and all the strikes were end to end or cornering blows, it is clearly seen that in all cases the sheet metal of the car sides rends and tears almost immediately on impact. 

[Euclid]

Dave,

You say that bursting requires raise the internal pressure without exceeding the tensile strength of the shell.

I don’t understand your point.  Raising the internal pressure to the point of exceeding the tensile strength of the shell is precisely what bursting is.

[Wizlish]

Euclid

Dave,

You say that bursting requires raise the internal pressure without exceeding the tensile strength of the shell.

I don’t understand your point.  Raising the internal pressure to the point of exceeding the tensile strength of the shell is precisely what bursting is.

 

What he means is that, in order to have a tank car fail by your mechanism, you have to maintain the hydrostatic pressure inside an 'intact' shell (in other words, capable of holding the full hydrostatic pressure being developed) up to the point that some part of that shell fails entirely due to the force exerted by the hydrostatic pressure.

 

At least one of his points being that, in an accident, something else is likely to bend, puncture or compromise the shell (and incidentally relieve at least some of the hydrostatic-pressure force) before that state is reached.

 

It's the mechanism up to the moment of bursting he's discussing, not the actual "bursting" itself.

[Euclid]

Well, yes I agree that in order for the tank to burst from squeeze pressure collapse, there cannot be any openings in the tank wall.  If there are openings, there will be no internal pressure increase due to collapsing, and therefore no bursting from an internal pressure increase.

Perhaps Dave meant to say, “In order to "squeeze" a tank car hard enough to cause it to "burst" from internal pressure the car has to have enough compression pressure placed on it that it compresses the inside without to the point of exceeding the tensile strength of the shell.”  

Just to clarify, if we go back to the beginning of this topic, I said that I believe that squeeze bursting can happen and does happen sometimes.  So I don’t see the basis for all the rejection focused on the premise that it does happen all of the time in every derailment.  Nobody ever said it does. 

If a tank car is punctured or torn open, that precludes any possibility of squeeze bursting.  If a car is subjected enough force to collapse and burst it, but is not adequately restrained to resist that force, then no squeeze burst will be possible.  Or if a car is adequately restrained, but not subjected to a sufficient squeeze pressure, no squeeze burst will be possible.  I have offered the theory of squeeze bursting as just one more mode of breaching.  And as I originally said, I believe squeeze bursting is often facilitated by the tank collapse folding and cracking the steel.

However, aside from all of this, my larger point petains to the variations of train force that damages tank cars in a derailment; depending on how long the train is and where the derailment is located in the train; and how great these forces can be.  Unless you design head shields and tank walls to withstand these highest possible levels of compression, you are only working around the edges of the problem.         

[Wizlish]

Euclid

Just to clarify, if we go back to the beginning of this topic, I said that I believe that squeeze bursting can happen and does happen sometimes. So I don’t see the basis for all the rejection focused on the premise that it does happen all of the time in every derailment. Nobody ever said it does.

Just to clarify, Dave (and I) don't really believe it happens, but perhaps it does.  However, we are not just going to take your word that it does.  We have been asking, and will continue to be asking, for some proof, either photographic or reported, that 'squeeze bursting' exists as an actual cause of an actual failure ... even one ... and not just a hypothetical occurrence.

The 'rejection' is not based on any 'premise that it does happen all of the time in every derailment'.  I am not sure where you got the idea anyone was claiming that - except that a few posts ago you were trying to claim it was the predominant way in which tank cars were failing in these accidents.  That's neither here nor there.  We want to see proof that it happens in ANY derailment. 

Proof, that is.  Not more 'yes, but' assertions that it maybe, kinda, sorta, could be happening. 

[Euclid]

Wizlish

 

Euclid

Just to clarify, if we go back to the beginning of this topic, I said that I believe that squeeze bursting can happen and does happen sometimes. So I don’t see the basis for all the rejection focused on the premise that it does happen all of the time in every derailment. Nobody ever said it does.

 

 

Just to clarify, Dave (and I) don't really believe it happens, but perhaps it does.  However, we are not just going to take your word that it does.  We have been asking, and will continue to be asking, for some proof, either photographic or reported, that 'squeeze bursting' exists as an actual cause of an actual failure ... even one ... and not just a hypothetical occurrence.

The 'rejection' is not based on any 'premise that it does happen all of the time in every derailment'.  I am not sure where you got the idea anyone was claiming that - except that a few posts ago you were trying to claim it was the predominant way in which tank cars were failing in these accidents.  That's neither here nor there.  We want to see proof that it happens in ANY derailment. 

Proof, that is.  Not more 'yes, but' assertions that it maybe, kinda, sorta, could be happening. 

 

Wizlish,

I cannot prove that it happens.  All I claimed is that I believe it happens, and I explained why.  Others have not proved it does not happen, but they say they don’t believe it happens, and they have explained why.  You and others are free to believe or disbelieve whatever you want.  At this point, from both sides, all we have is the logic our reasoning.      

Several times it has been implied that I say it does happen very often.  Obviously that is not the case and I never said or implied it. It is the typical tactic of exaggerating something to an absurd level in order to discredit it. 

Now you say this: “except that a few posts ago you were trying to claim it was the predominant way in which tank cars were failing in these accidents.”

That is not true.  I never said anything of the sort.  Please show me exactly where I said that.  You say it was a few posts ago.  Which one?

[Paul of Covington]

    I'm still trying to figure out why it is important to know that a tank car might fail by being compressed till the pressure of the liquid blows it out.   Personally, it seems much more likely that the metal fails by being punctured or torn by an edge or corner of another car or a solid structure.   If the pressure caused the metal to fail, it seems to me that the metal would be pushed out at the edges of the break, and investigators would have recognized this as the cause of failure.   If it can be shown that the pressure caused the failure, how would you design the cars differently?

[Wizlish]

Euclid

Now you say this: “except that a few posts ago you were trying to claim it was the predominant way in which tank cars were failing in these accidents.” That is not true. I never said anything of the sort. Please show me exactly where I said that. You say it was a few posts ago. Which one?

You are correct -- I looked back at the recent history of this thread and you did not say that (directly or otherwise).  What you were doing was returning to the idea that it was frequently observed as a failure mode in these accidents.

In science, if you are going to promote a hypothesis, it is YOUR responsibility to establish evidence for it.  It is not permissible to claim that we have to disprove that it ever, ever happens when yes, yes, it sertaily could happen.  You have repeatedly stated that you think it occurs in many situations, not that it 'could' happen under some circumstances.  That does not give it scientific standing, any more than coining terms like "maximal force potential" somehow makes them real phenomena that we then bear the onus of refuting.

[dehusman]

Euclid

Several times it has been implied that I say it does happen very often. Obviously that is not the case and I never said or implied it. It is the typical tactic of exaggerating something to an absurd level in order to discredit it.

Lets see:

 

5/28 10:14 pm

Euclid

I also said that I believe that in many cases, the tanks are subjected to extreme compression that sometimes raises the internal pressure high enough to burst the vessel.  I know that you have insisted many times that this is impossible and has never happened.  I have explained why I think it can and does happen.

  

5/29 1:59 pm

Euclid

You raise good points.  All I am saying is that I believe this happens often.  If it can be proven otherwise, so be it.  If I could procure examples, I would, but how can I do that?  But in the meantime, I don’t see why it would be considered to be an extraordinary claim. 

 

 

[MidlandMike]

Euclid

 

MidlandMike

 

Euclid

...

But again, the point is not so much that these collision impacts can occur.  Instead, it is that the real world force potential is so vastly greater than just one moving car striking a stationary car; the simplistic model of collision which appears to be assumed in the crash testing of tank cars.    

 

 

 

 

You still have not demonstrated a mechanism by which the force of a following car is multiplied by the rest of the following cars.  Couplers are designed to fail before structural damage is done to a car.  Tank cars themselves are their own structural force, since the absence of center sills.  A following tank car will itself be crushed between the pile and the next following tank car, and so on.  The entire force of the train will never be concentrated at one spot, and the kenetic force will be disapated thru the entire pile-up process.

 

 

 

Midland Mike,

This in respose the your above quoted post and your post a few posts prior:

I agree that a small amount of the kinetic energy in string of cars coming into the derailment from behind is going to be absorbed in the draft gear.  Also, a fair amount will be dissipated by braking.  But every car will still retain a large amount of kinetic energy that will either require enough braking time to dissipate or; might get dissipated in a mass of collisions and friction during a derailment pileup, if there is not enough time for the brakes to stop the cars.   

So, I would say that the total energy of this line of incoming cars is indeed concentrated to one point.  Generally speaking, that force is directed through the drawbars and couplers to the head end.  Specifically, the force is concentrated to the point of impact if it runs into an obstacle.  

Say you have 20 cars on the rails, rolling forward, and feeding cars into the derailment zone.  The collective energy of those 20 cars is pushing one car at a time into the derailment pileup.  It is true than just one car at time is derailing, but that does not mean that the collision force is as if only a single car hit a stationary car.   On the contrary, the force that is directed into the collision point is the force of 20 cars acting as one, just like a giant battering ram.

Therefore, regarding the force that damages and ruptures tank cars in a pileup; the greater the number of cars behind the derailment, the higher that force rises.

 

I didn't say the draft gear would absorb some energy, I said theat the draft gear/couplers will fail.  You have not disputed that they are made to fail in extreme forces, you just keep repeating that the total force is directed thru the couplers.

A train of tank cars is not like an line of impenetrable billiard balls, but instead are elastic, which is indesputable as evidenced by the crumpled pile of tank cars in the wake of a wreck.  You have no basis in physics for saying that the total force of the following cars is transferred to the pile "like a giant battering ram".

[MidlandMike]

Euclid

Dave,

You say that bursting requires raise the internal pressure without exceeding the tensile strength of the shell.

I don’t understand your point.  Raising the internal pressure to the point of exceeding the tensile strength of the shell is precisely what bursting is.

 

You evidently don't know the difference between tensile strength and burst pressure.