Buckled rail repair

[MiniMax]

On a recent Sunset Limited trip (departed LAX on June 6) the heat was so intense that a rail buckled somewhere east of El Paso. The train was delayed 4 hours while a crew came to replace it. I'm puzzled as to how this was done. If the 2 adjacent rails had expanded to push the middle one into an S-type bend, did they replace it with a shorter rail to fit the smaller space? Or how did they fix it?

BTW, does this happen often? I don't want to think of a passenger train getting derailed, but those tin-can tanker cars are lately being shown to be extremely vulnerable to exploding.

 

[Ryan]

It happens from time to time.

CSX put the Auto Train on the ground because of a sun kink.

Usually the rails are put in under enough tension that you don't get buckles. Cracked rails in the winter are better (they trip the signals, so you know something is amiss).

 

[NW cannonball]

The railroads, and especially their engineering departments, plan for heat buckles, or sun kinks as they call them. Sometimes, they happen.

How - there's lots of finger-pointing - but - the best-laid plans --- yaah yaah.

For the tech details -- well - we all know google, and possibly a better resource - George - - - or - we could actually figure the risk factor our selves. but that would be Un American -- "I Don't know nuthin, but the bustards tricked me -- he he "

 

[xyzzy]

Ballast provides resistance to lateral movement, with the outcome that the rails remain in place but compression forces increase within the rails. In situations where a sun kink does develop, either the rail came loose from the ties or the ballast didn't prevent the ties from moving sideways. There are standards for track construction to keep that from happening. Also, it's a question of the temperature when the rail was originally installed. In the south and west where temperatures and insolations are likely to be high, the rail is installed at a higher "neutral temperature" -- which further reduces the likelihood of sun kinks, although it also increases (slightly) the likelihood of a pull-apart if temperatures get too cold in the winter.

 

[George Harris]

On a recent Sunset Limited trip (departed LAX on June 6) the heat was so intense that a rail buckled somewhere east of El Paso. The train was delayed 4 hours while a crew came to replace it. I'm puzzled as to how this was done. If the 2 adjacent rails had expanded to push the middle one into an S-type bend, did they replace it with a shorter rail to fit the smaller space? Or how did they fix it?

BTW, does this happen often? I don't want to think of a passenger train getting derailed, but those tin-can tanker cars are lately being shown to be extremely vulnerable to exploding.

First, for most of the main line tracks rail is no longer in a series of pieces as such. It is continuously welded. As tthe temperature goes up and down the rail does not move, but the internal force changes either increasing tension when cold or increasing compression when hot. Think the difference between a stretched rubber band and one slack. this may give you the idea that it is usually better for the rail to spend most of its time in tension. Thus the temperature at which the rail has no internal stress is set to be well above the average over a year's time. As Ryan said, if you are going to have failure, it is better for it to be a cold weather break than a hot weather kink. A break is detected by the signal system, a kink is not.

Normally when a kink does occur the rail is cut at some point along the length of the kink, a short piece cut out and the rail rewelded. Also, obviously, the track is lined back it to correct position and ballast added and tamped thoruoughly.

By the way, the high temperature in the calculation of what the neutral stress temperature ought to be is the temperature of the rail, not the air temperature. On a nice hot sunny day the rail can get quite a bit hotter than the surrounding air.

 

[neroden]

First, for most of the main line tracks rail is no longer in a series of pieces as such. It is continuously welded.

Well... they *say* that, but the fact is it's still a series of pieces (I did my research here).

What's been happening is that the pieces have been getting longer and longer (which is done by welding shorter pieces together). As someone said, "The expansion joints are still there, but they're further apart". On lines with track circuits, the frequency of joints may be determined entirely by the need for insulated joints for the track circuits. On lines with lots of switches, it may be welded from one switch to the next.

Each piece is typically a minimum of a quarter-mile long, usually several miles long, after welding.

Legally, it's considered "continuously welded" in the US if the pieces are more than 400 feet long. Which isn't really very long. You still have gaps in the rail for switches, bridges, all kinds of things.

You really shouldn't have 500-mile long continuous welding, you probably *would* get frequent track failures if you did that. But this sort of length of continuous welding doesn't happen much anyway because there are generally sidings, crossovers, and junctions far more often than that. In Australia, which has some of the longest stretches of plain line in the world, there are deliberate expansion joints every so often.

 

[George Harris]

First, for most of the main line tracks rail is no longer in a series of pieces as such. It is continuously welded.

Well... they *say* that, but the fact is it's still a series of pieces (I did my research here).

What's been happening is that the pieces have been getting longer and longer (which is done by welding shorter pieces together). As someone said, "The expansion joints are still there, but they're further apart". On lines with track circuits, the frequency of joints may be determined entirely by the need for insulated joints for the track circuits. On lines with lots of switches, it may be welded from one switch to the next.

Each piece is typically a minimum of a quarter-mile long, usually several miles long, after welding.

Legally, it's considered "continuously welded" in the US if the pieces are more than 400 feet long. Which isn't really very long. You still have gaps in the rail for switches, bridges, all kinds of things.

You really shouldn't have 500-mile long continuous welding, you probably *would* get frequent track failures if you did that. But this sort of length of continuous welding doesn't happen much anyway because there are generally sidings, crossovers, and junctions far more often than that. In Australia, which has some of the longest stretches of plain line in the world, there are deliberate expansion joints every so often.

Once you get over about 300 feet each way from a joint it does not matter how long the piece is. If you do the math to calculate the force required to make the thermal expansion to be zero you will find that length drops out of the equation. Rail is now commonly welded through turnouts. There is no reason whatsoever to have rail expansion joints unless you are dealing with such things as drawbridges where the slightest rail movement at the opening point cannot be tolerated or very long span bridges where you do not want the structure moving in relation to the rail. Note I said structure moving in relation to the rail. That is actually what is happening. Yes, I know that some systems still put in rail expansion joints at long intervals. That is engineering psychology not actual engineering need. Sometimes you have people in management that thinks they are needed, and sometimes it is simply because the engineer cannot get past having the need to allow for thermal movement drilled into him in college.

I do not know what you did in the way of research here. Yes, rail is still produced in a series of pieces bbut the pieces are then welded up into strings of about 1/4 mile and hauled by CWR train to teh point of installation and then welded together at the time of placement in track. Normally in transit work the strings that are being hauled around are shorter, commonly about 700 feet. Sometimes they are laid out in pieces and then welded up in place by a mobile welding plant. This is not research but job related.

 

[neroden]

Note I said structure moving in relation to the rail. That is actually what is happening.

Yep, that's the obvious failure mode for really really long continuous welded rail. Kind of an interesting failure mode.
I would not want to deal with a welded rail which is so long that it's crossing lots of fault lines and subject to differential movement of the earth. Trying to estimate the degree to which ballast will hold ties in place is... well, it's got large error bars on it, because ballast isn't a consistent product, it's a pile of rocks.

Frankly, it's not going to come up much, but if you keep extending the length of continuously welded rail long enough, you *will* start encountering issues which you don't consider in everyday practice, which will cause problems. Overlooking the new and unidentified problems is the classic engineer's mistake. Overbuilding with a safety factor, and preserving structural elements which you don't really know the full reasons for, is the classic engineer's method of trying to avoid this. But I'm sure you know that.

 

[NE933]

I'm reading Neoden's and George Harris' insightful missives on the physics on rail behavior in temperature changes.

Now say that tomorrow's forecast called for a high temp in one of the 150mph territories, like Rhode Island, to be one hundred ten degrees - well above the neutral temp, which would be a rapid increase to a severe level. Would Amtrak (or any railroad) with CWR deliberately cut a 'wound' to remove a foot or so of steel rail, to prevent it from kinking?

 

[George Harris]

I'm reading Neoden's and George Harris' insightful missives on the physics on rail behavior in temperature changes.

Now say that tomorrow's forecast called for a high temp in one of the 150mph territories, like Rhode Island, to be one hundred ten degrees - well above the neutral temp, which would be a rapid increase to a severe level. Would Amtrak (or any railroad) with CWR deliberately cut a 'wound' to remove a foot or so of steel rail, to prevent it from kinking?

NO.

They might put up a slow order and do additional inspections, but no more. With good wide ballast shoulders, tightly tamped ballast, and scalloped sided concrete ties the rail is unlikely to go anywhere. Generally when and where a buckle does occur it is because the shoulder is insufficient or the ballast has been recently disturbed or both and/or some work has been done on the track so that the zero stress temperature is lower than it is supposed to be.

 

[George Harris]

Note I said structure moving in relation to the rail. That is actually what is happening.

Yep, that's the obvious failure mode for really really long continuous welded rail. Kind of an interesting failure mode.
I would not want to deal with a welded rail which is so long that it's crossing lots of fault lines and subject to differential movement of the earth. Trying to estimate the degree to which ballast will hold ties in place is... well, it's got large error bars on it, because ballast isn't a consistent product, it's a pile of rocks.

Frankly, it's not going to come up much, but if you keep extending the length of continuously welded rail long enough, you *will* start encountering issues which you don't consider in everyday practice, which will cause problems. Overlooking the new and unidentified problems is the classic engineer's mistake. Overbuilding with a safety factor, and preserving structural elements which you don't really know the full reasons for, is the classic engineer's method of trying to avoid this. But I'm sure you know that.

What I was referring to in the line you quoted was relative movement, NOT a failure. Movement does not equal failure. Everything in track moves, just not much. If you think it does not, I strongly recommend getting out and standing as close as you safely can to a track and watch it as a train goes by.

The longer I have been working with this stuff the more I have become convinced that rail expansion joints tend to be way overused, and question whether they should be used at all other than just before the mitre joints on the approach to the drawspan in drawbridges. Just by way of example, the owner of one of the major Mississippi River bridges removed the expansion joints in the rails on the bridge about 18 years ago, and so far as I know have had no difficulties with the track or bridge related to the track since that time.

Ballast is far more than just a pile of rocks. The American Railway Engineering and Maintenance of Way Association's Manual for Railway Engineering has 22 pages just on ballast materials and shape of cross sections, and that does not include the discussion on proper installation and maintenance.

You think the people that work with this stuff have not thought about and dealt with as much as practical with potential ground movements? Of course they have.

Let's try this one more time: Once you get beyond a few hundred feet it makes no difference how long your string of continuous rail is, whether 10 miles or 1,000 miles or coast to coast. The people that work with this stuff and have determined the practicalities of this did not fall off the turnip truck yesterday.

By the way, for the last 30 plus years insulated joints have been epoxy glued so that they do not move and therefore do not form a break in the mechanical continuity of the rail.

 

[neroden]

You're almost certainly correct that there are far too many joints in current practice. I still suspect that you're going to need breather switches intermittently for various weird stuff, or at least material breaks to avoid strange resonance effects, but there are way more joints than that right now.

There will never be a single continuous ribbon of rail from the Arctic to the tropics, if only because of switches, so the question of whether strange problems will come up is essentially theoretical.

 

[xyzzy]

Generally when and where a buckle does occur it is because the shoulder is insufficient or the ballast has been recently disturbed or both and/or some work has been done on the track so that the zero stress temperature is lower than it is supposed to be.

Yes, and the NTSB concluded that this was the cause of the 2002 Auto Train derailment.

 

[Ryan]

Yeah, that's the derailment I mentioned in post #2.

The NTSB has a lot of fascinating (to me, at least) detail about the mechanics of this.

 

[MiniMax]

Two questions: Do European trains have the same type of track structure that causes the rails to buckle in extreme heat?

Our train's on-board announcement was that we had to wait for a crew to come fix the buckled rail. In layman's language, how do they fix a buckled rail?

 

[Ryan]

Yes.

Cut out busted section, weld in new section.

 

[George Harris]

Two questions: Do European trains have the same type of track structure that causes the rails to buckle in extreme heat?

Our train's on-board announcement was that we had to wait for a crew to come fix the buckled rail. In layman's language, how do they fix a buckled rail?

Q1: In general, yes. There are a few major differences: Most of their tracks have cable troughes along each side which does add some more resisitance to lateral movement.They normally use heaped ballast shoulders which gives them some more rock on each side. My own opinion is that this provides no real benefit. The additional width of ballast shoulder this causes is beneficial. Their average weight of rail in track is lower there than here, being in no place above 60 kg/m (=120 lb/yd) and in many line 54 to 50 kg/m (108 to 100 lb/yd) while the US main line tracks are for the most part in 132 to 141 lb/yd, and in almost no place under 115 lb/yd. (Yes, the coversion ratio is almost exactly 2:1) Their daily and annual temperature swings tend to be smaller than much of the US experiences. The formula recommended in the UIC to calculated the rail neutral temperature results in a lower temperature in relation to the temperature swing than that recommended in AREMA. This I regard as a bad idea. The smaller temperature swings and cable troughes results in less problems from this lower temperature than you would otherwise expect. However, when you talk so some of their track people you get the impression that buckles are at least as common there than here. They appear to be far more concerned about pull aparts than we are here. There are several reasons for this which I will not detail. Lower strength rail steel is among them. You just do not hear as much about track failures, either buckles or pull-aparts since they happen in other countries on another continent. Also, a far greater portion of their lines are multiple track which enables track failures to be bypassed with less time lost.

Q2: They cut the rails, commonly a double cut so to take out a piece, line the track back to where it ought to be, stretch the rail so that the zer stress temperature will be up to what it ought to be, put in a new field weld, or install joint bars temporarily to be replaced with a weld later, and tamp the ballast up tight. When a joint bar is installed to be replaced with a weld later the hole nearest the rail end is not drilled so there will be no hole in the rail ain/near the heat affected zone from the new weld.

 

[xyzzy]

Only thing I'd add to the previous answer to Q2 is that there is likely to be a slow order for at least 24 hours after the repair is made.

In the UK it's called a rail buckle, and they definitely happen there. See http://www.arcc-cn.org.uk/wordpress/wp-content/pdfs/ARCADIA-09-buckling.pdf

 

[crescent2]

Yeah, that's the derailment I mentioned in post #2.

The NTSB has a lot of fascinating (to me, at least) detail about the mechanics of this.

Fascinating to me, too. I spent several hours yesterday reading NTSB reports on Amtrak accidents.

 

[MiniMax]

I never look at my watch when riding Amtrak. I move away from any person who is looking at their watch, but I've got to admit that taking only four hours to fix the buckled rail, out in the middle of nowhere, is pretty damn efficient. I'm so grateful that we weren't piled onto a bus.