BaltACD Welded Rail is a technology that still has not been MASTERED.
Welded Rail is a technology that still has not been MASTERED.
cx500 BaltACD Welded Rail is a technology that still has not been MASTERED. Sun kinks can also occur on jointed rail, especially branch lines that see minimal maintenance. During the hot days of summer several lines are operated only at night or early morning. Experience is a great teacher.....
Never too old to have a happy childhood!
Two joints.
charlie hebdoTwo joints.
Initial Joint - 39 feet of rail - 2nd Joint - 39 feet of rail 3rd Joint + 22 feet to get to 100 feet.
A potentially important point that seems not to be quite realized yet is that jointed rail does not accommodate expansion or contraction unless the joints are sequentially loosened and retightened while the temperature is low or high. In the old days of roving section gangs this could be done regularly with the weather. When I first read about 'sun kink' the account (I think it was on the Burlington in Kansas) said that when the bolts were loosened the rail ends came together with a crack like a pistol shot, an indication of the strain built up in those rails... but also an indication the stress wouldn't 'relieve itself' at the joints without explicit action.
BaltACD charlie hebdo Two joints. Initial Joint - 39 feet of rail - 2nd Joint - 39 feet of rail 3rd Joint + 22 feet to get to 100 feet.
charlie hebdo Two joints.
But only two joints within the 100 foot span unless you count a joint to the rail preceding.
It would be 3 joints. 2 at the joints separating the 3 rails and then 1/2 of the joint on each end, since it would be shared with the adjoining rails. All this talk of joints makes me think of the Amtrak Tucson thread...
Ditto, but the shared (half) joints would be outside the aforementioned 200 foot span.
Given the strength of the product, joints are no longer used as in the other thread. One-hittters (pipes) or vapes are current.
charlie hebdoDitto, but the shared (half) joints would be outside the aforementioned 200 foot span.
Perhaps all you budding mathematicians can agree on '5/8" of expansion spread over an average of 2 and a fraction bolted joints per 100 feet' or something. And we can move on.
Overmod Perhaps all you budding mathematicians
Perhaps all you budding mathematicians
I see what you did there!!
rdamonI see what you did there!!
One key point is that rail expansion does not cause track buckling just because rail expansion is physically constrained. So just because heat elongation of rail runs out of space accommodation in rail joints, it will not necessarily cause rail/track buckling. If that it did, that would make continuous welded rail impossible for practical use. Instead, what makes CWR possible is that the rail being physically restrained will absorb further expansion by compressing the steel in the rail.
This is very close to the idea that if rail is constrained lengthwise, it will express its thermal expansion by bulging outward from its top, bottom, and sides. So it will grow fatter rather than longer.
However, it need not rely even on that option for physical expansion. It need not grow any larger at all when heated, if it is physically constrained form doing so. Then it will just internalize the expansion. But when doing so, it will exert a force on whatever is constraining its outward thermal expansion. The more expansion the rail internalizes, the greater its outward force against the constraints. The constraints are limited, and with CWR, when the constraints fail, the track buckles.
Euclid One key point is that rail expansion does not cause track buckling just because rail expansion is physically constrained. So just because heat elongation of rail runs out of space accommodation in rail joints, it will not necessarily cause rail/track buckling. If that it did, that would make continuous welded rail impossible for practical use. Instead, what makes CWR possible is that the rail being physically restrained will absorb further expansion by compressing the steel in the rail. This is very close to the idea that if rail is constrained lengthwise, it will express its thermal expansion by bulging outward from its top, bottom, and sides. So it will grow fatter rather than longer. However, it need not rely even on that option for physical expansion. It need not grow any larger at all when heated, if it is physically constrained form doing so. Then it will just internalize the expansion. But when doing so, it will exert a force on whatever is constraining its outward thermal expansion. The more expansion the rail internalizes, the greater its outward force against the constraints. The constraints are limited, and with CWR, when the constraints fail, the track buckles.
I'm no physicist or metallurgical expert, but your post is loaded with what appear to be absurd contradictions.
charlie hebdo Euclid One key point is that rail expansion does not cause track buckling just because rail expansion is physically constrained. So just because heat elongation of rail runs out of space accommodation in rail joints, it will not necessarily cause rail/track buckling. If that it did, that would make continuous welded rail impossible for practical use. Instead, what makes CWR possible is that the rail being physically restrained will absorb further expansion by compressing the steel in the rail. This is very close to the idea that if rail is constrained lengthwise, it will express its thermal expansion by bulging outward from its top, bottom, and sides. So it will grow fatter rather than longer. However, it need not rely even on that option for physical expansion. It need not grow any larger at all when heated, if it is physically constrained form doing so. Then it will just internalize the expansion. But when doing so, it will exert a force on whatever is constraining its outward thermal expansion. The more expansion the rail internalizes, the greater its outward force against the constraints. The constraints are limited, and with CWR, when the constraints fail, the track buckles. I'm no physicist or metallurgical expert, but your post is loaded with what appear to be absurd contradictions.
If you google this topic, you will encounter an erroneous explanation that is the near universal popular misunderstanding of the principle. So the correct understanding needs to be stated in the starkest of terms. In so doing, it is not surprising that it might appear to be full of contradictions.
Here is an example of the widely held erroneous explanation. Notice that it assumes jointed rail with expansion gaps that allow the rail to expand and contract by giving it the space to do so:
“People also ask
What will happen if the rails are made without gaps?
The gap is left between the rails to provide a space for the iron metal to expand and contract during the summer and winter season due to the change in the temperatures. If the gap is not left in between then the rails will bend more and cause derailing of the trains.Dec 16, 2018”
The first problem with this explanation is that it ignores the question of how gapless rail can work; and it does that by ignoring the existence of gapless rail.
Here is the correct explanation, which matches my post above:
https://engineering.stackexchange.com/questions/23623/how-do-gapless-rails-deal-with-thermal-expansion
“To take it back to the basic engineering principle: a change in temperature of something changes its stress-free length. That is, the length it would be if there was no stress on it.
For gapless rails (I'd call them Continually Welded Rails or CWR in the UK), the position of the rail is restrained by the connection of the rail to the sleeper or the slab below it. So the length is unable to change.
If you change the stress-free length without changing the actual length, you create stress. If your rail has got colder, it wants to get shorter, and this causes tensile stress; if your rail gets hotter it wants to get longer, and this causes compressive stress.
Failure occurs when the rail supports can't provide enough restraint against this tensile or compressive stress. On curved track this will manifest itself as the curve radius decreasing under tensile stress / cold weather, or radius increasing under compressive stress / hot weather. For a straight section of track this usually only happens under compressive stress / hot weather, where the track will buckle, snaking left and right, which makes the path of the rail longer, hence relieving the compressive stress.”
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The erroneous explanation would have you believe that when rail is heated, it must expand in all directions including lengthwise. So when it expands lengthwise, it must have air gaps that allow it space to expand. And if it expands to the point that all air gaps are closed, the next tiny bit of expansive elongation will buckle the rail as an irresistible force.
In the first place this ignores the fact that CWR has no air gaps and yet, it does not buckle every time the temperature rises. In the second place, if the erroneous explanation were true, just an elongation of 1/16 inch would buckle the rail. That would form a sun kink that might not even be visible.
Yet experience has shown that sun kinks will often radically buckle and displace rail into sets of multiple wide, serpentine loops; and that this can happen in a very short time. How many inches of rail must that massive track displacement have required? It certainly was not 1/16 inch. More likely, it was a foot or two.
What has happened is that the sun kink has built up as internalized stress within the rail steel, which is compressed just like steam in a boiler. In track, the track structure acts like the boiler that confines and constrains the rising steam pressure. The track structure does this by its strength that resists buckling. If the track cannot buckle, where does the physical expansion go? It cannot make the rail longer.
The answer is that the rail expansion is absorbed in the compression of the rail steel which acts like rubber. When the rail is restrained from expansion, its steel compresses like a spring, and that is what is referred to above as “compressive stress.” Just like rubber, rail can be compressed or stretched by its physical changes of thermal expansion and contraction. If this movement is physically constrained in rail, it compresses stress into the steel of the rail.
In the case of the large, multi-loop sun kind I mentioned, such large sun kinks can often develop in a matter of minutes as the sunk kink “runs,” which means suddenly experiencing the loss of constraint, and rereleasing it to form the actual track deforming sun kink.
This sudden release or “running” of the kink often isthe result of a train running over the overstress track. The vibratory and pressure waves of the rolling car wheels of the train reduces the transverse strength of the track bed ties and ballast. Yet that strength was necessary to resist buckling and force the rail to absorb the rail elongation as internalized compressive stress.
So the giant sun kink of multiple loops was not caused by the first 1/16 inch of expansion that demanded the rails buckle to accommodate the expansion. Instead a much greater amount of expansion was absorbed internally in the rail as compressive stress. Then when the train weakened the transverse strength of the track bed, it caused the sun kink to “run” or develop in one generally continuous action, until the foot or more of rail expansion (in each rail) was released by the failure of its track constraint—like the steam boiler that finally explodes when its pressure gets too high for it to resist.
Rail moving into a serpentine path that is not what was intended, and due to stress (heat or direct physical contact with an object with sufficient propulsion to cause the defect), can't be compared to something like an uncooked length of spaghetti noodle that will take some deformation and then finally snap. This is because the rail doesn't snap. Instead, it deforms, but only if its retainers move with it, meaning the ties must either move with the rails laterally in the ballast or the rails must be freed from the retainers, or the retainers are freed from the ties and they move with the rails ( I don't know how likely that is, probably not very).
A boiler, pressure cooker, concrete slab, noodle...they'll all break under sufficient stress, even if they don't largely change shape along their exposed and visible surfaces. They'll spawl, separate, tear, shear, whatever when they relent and change due to the excessive forces, but like the rails, they WILL change measurably up to the point where they do it. Strain gauges would show the strain, and pretty much everything would deform ever so slightly, maybe requiring an interferometric measurement to detect it (that's a guess).
Anyone who has pressurized a garden hose whose open end is stopped with a nozzle will see that the hose begins to straighten, and torsion, and otherwise exhibit life-like, snakey, behaviours. The rails do much the same thing. They swell radially in profile, they'll maybe elongate a whole bit of a mm or two, but they'll stay put, parallel, in gauge, and even at grade while the strains build. Then, zing, and the hose...err...rail does its thing.
When I first started looking into track mechanics in the engineering library, I was reading accounts of the German experiments with sprung track in the 1920s. They conducted experiments in which a length of track was fixed at both ends and electrically heated. This produced the result of upward-bowed rails that took the ties with them... a thing noted as never occurring in the field, probably because heating occurs there more slowly.
OvermodWhen I first started looking into track mechanics in the engineering library, I was reading accounts of the German experiments with sprung track in the 1920s. They conducted experiments in which a length of track was fixed at both ends and electrically heated. This produced the result of upward-bowed rails that took the ties with them... a thing noted as never occurring in the field, probably because heating occurs there more slowly.
The CSX rail expansion chart I have access to indicates that a 1800 foot length of rail, with a 80 degree change in temperature will have 11 5/8 change in length.
The reality of welded rail in the 21st Century is that the welded strings can be a mile or more in continuous length between required bolted (insulated or not) joints. While 80 degrees is a very extreme change for a short period of time - it can easily happen during the change of seasons and 90 degree Indian Summer day followed two days later by a Arctic Express dropping the mercury below Zero F.
While I was still working - that first COLD night of the Fall where temperatures would fall well below freezing - was the night nearly every train left track circuits on behind themselves. Send out the Signal Maintainers and MofW Personnel and in roll the reports of Broken Rails, pull aparts and broken joint bars. All of which happened under moving trains, moving at track speed. That first COLD night would normally be a temperature change of 40 to 50 degrees over a day to to span.
There is extensive reference to rail transport facing a sun kink crisis caused by the global warming of climate change. It predicts that rail sun kinks will become more severe and more frequent. This suggests that the sun kink problem needs a real solution rather than just the resolve to live with it by repairing the damage and picking up the occasional train wrecks.
Track has to be built robust enough to carry the load of trains and last an acceptable time between rebuilds. But, sun kinks have the potential to impose extra loading on track systems that far exceeds the strength requirements of train operation. To resist sun kinks, track needs a stronger bedding that will absolutely prevent transverse or vertical movement of rail and/or rail with ties. Sun kinks often move rail, fastening hardware, ties, and ballast all at once. These components need to be absolutely anchored in place well enough to resist buckling should the rail temperature cause compressive stress in the rails to rise into the danger zone.
The track bed that this requirement implies is a, very thick reinforced concrete slab set in the ground below the frost line, and with its top above the ground grade. The supporting soil would be well engineered for drainage and support capacity. The rails would have to be mechanically fastened directly to the slab. With a robust enough version of this anchoring foundation, rails could expand internally and never reach the pressure level that would buckle the track.
This would be the so called “Ballastless Track” or “Slab Track” which has its pros and cons. Cost and inability to adjust track alignment are to drawbacks, but fundamentally the system should never need alignment adjustment.
However, I wonder if ballastless track would be necessary to prevent sun kinks if the concrete slab was built as a trough to hold typical crushed rock ballast. The sides of the concrete trough would prevent the ballast from moving with transverse rail buckling force. The trough sides would contain the ballast to prevent it from moving sideways; and since ballast can withstand high compressive loading of trains, it may also withstand being displaced by the tie ends under the pressure of transverse tie shifting; that is if the ballast itself is constrained by by side walls of the concrete trough.
This still leaves the possibility of the track being lifted by the excess rail stress cause by heat expansion. To address that, there would need to be a mechanical connection of the track to the floor of the concrete trough.
In any case, the greater anchoring potential of ballastless track is the logical extension of the quest for better track anchoring to combat sun kinks.
Here is a link that covers extensive detail of ballastless track:
https://railtec.illinois.edu/wp/wp-content/uploads/Tayabji-and-Bilow-2001-Concrete-Slab-Track-State-of-the-Practice.pdf
Here is an excellent technical reference to sun kinks, including a video of a serpentine sun kink “running” when it reaches the point of track buckling transverse stress:
https://pwayblog.com/2015/11/04/buckling-prevention/
Many years ago I visited the Yellow River bridge in China. The Chinese were very proud of this bridge they built as Russian and East German teams said it was impossible to build. At each end of the bridge the rails were cut on a diagonal of about 50 feet. This allowed the rails to slide as they expanded or contracted. No sun kinks here. Doubtful if such a thing would be practical for on land lines.
rdamon Noticing in today’s practice that the insulated joints are made offsite and seem to be coated with some form of epoxy. They are then welded in place. Do these have less flexibility for expansion and contraction than the ones made onsite?
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
Electroliner 1935 I still wonder if the two rails as shown in the photo being spread apart like ( ) which means they left the restraint of the ties has any significance?
It could have significance to finding the cause of the derailment, but it would have to be looked at closely along with all other details at the site that were related to the derailment. Certainly the derailment caused a lot of track damage, but if was caused by a sun kink, that too would have damaged track to some extent. But if there was a sun kink that left damage, that damage may have been obliterated by the derailment damage.
If there was sun kink, I doubt that it was visible ahead of the approaching train, so that would mean that it was in its latent form of overstressed rail compression, but not yet have “run,” thus pushing the track out of alignment. The news reported that investigators looked at forward facing video from the locomotive. They did not report what was seen in the video. I would bet they saw no sun kink.
So if there was a sun kink, it “ran” and took visible form after the locomotive passed over the latent, overstressed rail. So the sun kink began to form as the train passed over it. At that point the sun kink became visible and represented a threat to derailing the train.
If there was a sun kink: once the derailment began, it may have destroyed all or most of the evidence of the sun kink.
However, if there was a sun kink that became an alignment hazard under the train, there is a possibility that some of the train passed over misalignment hazard without derailing. In that case, the sun kink would be visibly obvious as evidence for being the cause of the derailment.
So there may have been a range of track that showed the sun kink evidence prior to reaching the range of track that was subjected to the derailment. But that sun kink range may have been very short, such as 100 feet or less. And in that range, the sun kink damage may have been very subtle because it was just beginning to form into its visible misalignment.
So it would be critically important for investigators to find the pinpoint of the start of the derailment. Any misalignment whatsoever prior to reaching that pinpoint would strongly indicate that the derailment was caused by a sun kink.
But that evidence could be easily overlooked unless the point of derailment was exactly located within a couple feet. Once such an exact point of derailment is found, it may be deemed unnecessary to look closely at the track prior to that point. Yet that is a most critical requirement to finding the cause if the cause was a sun kink.
EuclidThe constraints are limited, and with CWR, when the constraints fail, the track buckles.
This does contradict what you stated in the first part of your post. I think what your trying to say is that constraints sometimes counteract the heat kink but not always.
There is a youtube video on a derailment caused by a heat kink. Safety inspectors asked why the heat kink at that location. Turns out that a track maintenence gang replaced a section of CWR in the winter, releasing the existing tension in the rail and the rail contracted by several inches. The replacement section of rail was measured to be several inches longer than the cut-out section of rail which should have been a red flag to the track maintence crew but was not. They welded the longer replacement section in place and left. The next summer the summer was extraordinarily hot and the rail reached a temperature of 112 degrees heated by the sun (yeah I know that sounds high but it is what the YouTube video said). The expansion of the rail forces were so much because now there was additional rail that the contraints had to hold back.........the constraints failed and the gauge widened to a heat kink.
Goes to show that with CWR care must be taken in replacement and maintenence.
I believe what the track maintence crew should have done with a winter replacement is measure the replacement section of rail to be same as what was cutout minus the cut steel. Then artificially heat the in place rail to expand back to what length it was at prior to the cut.......then recreate the joint. I think that was the proper procedure to restore tension but I am just guessing.
CMStPnP Euclid The constraints are limited, and with CWR, when the constraints fail, the track buckles. This does contradict what you stated in the first part of your post. I think what your trying to say is that constraints sometimes counteract the heat kink but not always. There is a youtube video on a derailment caused by a heat kink. Safety inspectors asked why the heat kink at that location. Turns out that a track maintenence gang replaced a section of CWR in the winter, releasing the existing tension in the rail and the rail contracted by several inches. The replacement section of rail was measured to be several inches longer than the cut-out section of rail which should have been a red flag to the track maintence crew but was not. They welded the longer replacement section in place and left. The next summer the summer was extraordinarily hot and the rail reached a temperature of 112 degrees heated by the sun (yeah I know that sounds high but it is what the YouTube video said). The expansion of the rail forces were so much because now there was additional rail that the contraints had to hold back.........the constraints failed and the gauge widened to a heat kink. Goes to show that with CWR care must be taken in replacement and maintenence. I believe what the track maintence crew should have done with a winter replacement is measure the replacement section of rail to be same as what was cutout minus the cut steel. Then artificially heat the in place rail to expand back to what length it was at prior to the cut.......then recreate the joint. I think that was the proper procedure to restore tension but I am just guessing.
Euclid The constraints are limited, and with CWR, when the constraints fail, the track buckles.
EuclidI think you are right about cutting the replacement rail to the same length as the rail it replaces and then heating it to fit, but I am not familiar with the details of that process.
An apparently common procedure I've seen is to soak ropes in something like diesel fuel, put them up against a length of rail, and light them until the extension is right or rail thermometers indicate the right neutral temperature. Perhaps one of the forum participants with real-world experience in welded-rail management can comment on this; I've never thought much of it (other than it's expedient).
Overmod An apparently common procedure I've seen is to soak ropes in something like diesel fuel, put them up against a length of rail, and light them until the extension is right or rail thermometers indicate the right neutral temperature. Perhaps one of the forum participants with real-world experience in welded-rail management can comment on this; I've never thought much of it (other than it's expedient).
In my experience it is very rare that anyone heats the rail when repairing broken rails or rail defects. Yes, that flammable rope (sold under the brand name "Firesnake") is out there, so it's used for something (probably derailments. I've only ever seen it sitting on the shelf in the section house.
Rail relay production gangs will have an on-track machine that burns propane to generate hot flame / exhaust to heat the rails. This is in the gang consist in front of the machines that apply the rail anchors.
But for everyday repairs such as cutting out rail defects, replacing failed IJ plugs, fixing service-failed rail, or "destressing" longer segments of rail (i.e. adding or removing rail to bring it's neutral temperature to the desired value), the tool of choice is the hydraulic rail puller. You leave a gap (of a size calculated according to the current rail temps and various other factors) between the ends of the two rails that are to be welded or jointed together, then you apply the puller. It's basically just a frame that clamps onto the two rails and pulls them together to make the gap disappear. With the puller still in place, you shoot or weld (or drill holes and apply joint bars).
If it's cold enough, or if you have to get the track back in service ASAP, you can "add rail" (use a smaller gap than what you really wanted). All of the information about the situation, including the amount of added rail, goes into the computer for tracking purposes, and you make plans to come back and take care of it when it's a little warmer, but before it gets to be a lot warmer.
Dan
dpeltier Overmod An apparently common procedure I've seen is to soak ropes in something like diesel fuel, put them up against a length of rail, and light them until the extension is right or rail thermometers indicate the right neutral temperature. Perhaps one of the forum participants with real-world experience in welded-rail management can comment on this; I've never thought much of it (other than it's expedient). In my experience it is very rare that anyone heats the rail when repairing broken rails or rail defects. Yes, that flammable rope (sold under the brand name "Firesnake") is out there, so it's used for something (probably derailments. I've only ever seen it sitting on the shelf in the section house. Rail relay production gangs will have an on-track machine that burns propane to generate hot flame / exhaust to heat the rails. This is in the gang consist in front of the machines that apply the rail anchors. But for everyday repairs such as cutting out rail defects, replacing failed IJ plugs, fixing service-failed rail, or "destressing" longer segments of rail (i.e. adding or removing rail to bring it's neutral temperature to the desired value), the tool of choice is the hydraulic rail puller. You leave a gap (of a size calculated according to the current rail temps and various other factors) between the ends of the two rails that are to be welded or jointed together, then you apply the puller. It's basically just a frame that clamps onto the two rails and pulls them together to make the gap disappear. With the puller still in place, you shoot or weld (or drill holes and apply joint bars). If it's cold enough, or if you have to get the track back in service ASAP, you can "add rail" (use a smaller gap than what you really wanted). All of the information about the situation, including the amount of added rail, goes into the computer for tracking purposes, and you make plans to come back and take care of it when it's a little warmer, but before it gets to be a lot warmer. Dan
FireSnake and similar products are normally used to fix pulled apart rail joint situations, rather than out right broken rail situations. Breaks in welded rail rarely leave the rail ends in a condition to be rewelded as a repair. The repair is to cut out a defined segement of the total rail - 10 feet, 20 feet or so and weld in a 'plug' rail that fits the amount cut out of the existing rail.
https://www.youtube.com/watch?v=Es5FbG8qotw
Euclid Most railroad accidents immediately present strong evidence of their cause, if not the total explanation. Often the primary component of cause is apparent such as a train rolling over on a curve from overspeed. Yet it may never be known what caused the speeding. The news of this Montana derailment has assured us that the NTSB will find the cause and tell us how to prevent it in the future. What happens if the NTSB cannot determine the cause? Will they just give their opinion as to the most probable cause? What if it was caused by a sun kink, but there is no evidence left to show that cause, and nobody actually saw the kink?
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