Heat problems - long-term solution?

[Phil S]

It seems clear that at least some of the problems with at least some of the LD trains (especially 7/8) is slow orders due to heat. If so, what are the long-term options for solving this? Re-lay track at a higher neutral temperature? Clearly the "UP" Sunset line does just fine despite 110+ temps every year. But it doesn't get cold there in the winter.

Maybe this topic is better posted over at TO but I'd like to try here first.

Thanks.

Phil

 

[OlympianHiawatha]

While I am not an expert on metallurgy, heat and cold have been a problem that have plagued railroads since day one. Sure, advances have been made in tie and rail technology over the years, but when you get to extremes, problems are still going to happen, especially in heat where even the long stretches of ribbon rail need to expand.

 

[Phil S]

Yup, but, as best I understand it, a big part of the technology is simply picking the right "neutral temperature" at which to lay the track -- warm enough so that expansion doesn't buckle the rail. .The contraction due to cold is then handled by proper fastening of the rail so that it just stretches as it contracts. "Weather" we like it or not, the climate is warming and the rr's are going to have to deal with this. I'm just wondering if there's any alternative to re-laying miles and miles of track at a higher temperature.

 

[cirdan]

Yup, but, as best I understand it, a big part of the technology is simply picking the right "neutral temperature" at which to lay the track -- warm enough so that expansion doesn't buckle the rail. .The contraction due to cold is then handled by proper fastening of the rail so that it just stretches as it contracts. "Weather" we like it or not, the climate is warming and the rr's are going to have to deal with this. I'm just wondering if there's any alternative to re-laying miles and miles of track at a higher temperature.

Track has to be re-laid on a periodic basis anyway, especially on busy routes. Possibly there is no actual extra cost involved. It's just a question of chaning the specs.

 

[Devil's Advocate]

Track has to be re-laid on a periodic basis anyway, especially on busy routes. Possibly there is no actual extra cost involved. It's just a question of chaning the specs.

To my understanding, although modern track does require regular maintenance it does not generally require regular replacement. Most of the time when you see maintenance being performed it's related to relatively minor repairs such as tie replacement, ballast maintenance, geometric correction, etc. It's rare to just up and replace the rails themselves, which is a much more expensive and time consuming operation. Maybe in fifty years or so they'll replace the rails when they're approaching the end of their useful life. Sometimes it's much longer than that.

 

[John Bobinyec]

Yup, but, as best I understand it, a big part of the technology is simply picking the right "neutral temperature" at which to lay the track -- warm enough so that expansion doesn't buckle the rail. .The contraction due to cold is then handled by proper fastening of the rail so that it just stretches as it contracts. "Weather" we like it or not, the climate is warming and the rr's are going to have to deal with this. I'm just wondering if there's any alternative to re-laying miles and miles of track at a higher temperature.

If the climate is warming or cooling on average, track can be relayed at the proper new temperature. The problem is the variation of the high and low temperatures in the short term. If they are extreme, there will always be this problem.

Some possible solutions that I can dream up are:

1. Have some sort of expansion joint.

2. Super, super strong rail which can be layed in a very high neutral temperature and which is strong enough to withstand pull-aparts in cold weather.

3. Lay the rail at a high neutral temperature and then use heaters to warm the rails up to the minimum critical temperature, at least here and there along the track.

4. Have sections of jointed rail every once in a while. (This is an extended expansion joint).

jb

 

[cirdan]

Some possible solutions that I can dream up are:

1. Have some sort of expansion joint.

2. Super, super strong rail which can be layed in a very high neutral temperature and which is strong enough to withstand pull-aparts in cold weather.

3. Lay the rail at a high neutral temperature and then use heaters to warm the rails up to the minimum critical temperature, at least here and there along the track.

4. Have sections of jointed rail every once in a while. (This is an extended expansion joint).

jb

5) Use alloys with lower expansion coefficients.

 

[John Bobinyec]

Some possible solutions that I can dream up are:

1. Have some sort of expansion joint.

2. Super, super strong rail which can be layed in a very high neutral temperature and which is strong enough to withstand pull-aparts in cold weather.

3. Lay the rail at a high neutral temperature and then use heaters to warm the rails up to the minimum critical temperature, at least here and there along the track.

4. Have sections of jointed rail every once in a while. (This is an extended expansion joint).

jb

5) Use alloys with lower expansion coefficients.

Even better.

jb

 

[George Harris]

Let's see if I can come up with a simplified version:

First, If there is a problem with the zero stress temperature being too low (or high), you do not have to relay the track to change it. What you do is knock off the anchors if standard wood ties and spikes, make a cut and stretch the rail, either vibrating and pulling or heating, vibrating and pulling, then re-welding and re-apply the anchors. If it is on concrete ties with spring clips, then you knock the clip loose, the go through the cut and stretch, re-weld and knock the clips back in. Ever heard the expression, "you can't push a rope?" You really can't push a rail, either. (An anchor is a device that clips around the base of the rail. It is applied tight against the side of the ties to keep the rail from "running", that is moving longitudinally. Normally in welded rail (CWR) they are applied on both sides of every other tie. Anchoring on both sides of a tie is called box anchoring.

Installing rail expansion joint or lengths of jointed rail at intervals should not be done. If in doubt, the answer is, DO NOT INSTALL RAIL EXPANSION JOINTS AT ANY LOCATION FOR ANY REASON EXCEPT IN THE APPROACH TO DRAWSPANS. Expansion joints are maintenance problems. The maintenance cost for jointed rail track is roughly double that of welded rail. (Somebody else may have a better ratio than that, but for sure it is significantly more.)

Beyond a few hundred feet it does not matter how long the welded rail section is. It will not move due to sliding friction between rail and fastening or anchoring system. So, whether the length of CWR is 600 feet or 6,000 feet, or 600 miles, the movement of the free end will be the same.

Also, beyond this length of a few hundred feet, the stress in the rail is not related to how long the section of rail is. The stress is solely based on the difference between actual rail temperature and zero stress temperature.

The tensile strenght of rail is sufficiently high that there is not real problem with overstressing the rail at low temperatures. Remember, "You can't push a rope?" If you try to push a rope, all it does is go off to the sides. The desire is to keep the rail in tension most of the time. It might be better to think of the rail more in terms of it being a rubber band. It sags when you hold the ends closer together than what it takes to make the rubber band straight. It will stay straight as you pull it up to the point at which it breaks.

In the AREMA Manual the recommended neutral stress temperature for welded rail is (2H+L)/3 + 15 to 25 degrees F. The “H” is the high temperature of the rail over a year. It can be up to 30 degrees or so higher than the air temperature due to heating by the sun. Let’s take an example:

High Air Temp, 105F, so take High Rail Temp, 140 Low Temp, -10F. Set no stress at (2H+L)/3+20

(2x140+(-10))/3 =90. 90+20=110. Therefore we want to stretch the rail so that it has no stress when the rail temperature is 110 degrees F.

Notice that with this setup, the difference between zero stress temperature and low rail temperature is four times the difference between zero stress temperature and high rail temperature. Since temperature difference and internal stress are directly related, the maximum tensile stress is four times the maximum compressive stress.

When the rail is in compression it is kept straight by the ballast shoulders and the friction and interlocking between the ties and the ballast. This second force, the friction and interlocking between tie and ballast is more important than is frequently considered. To improve that connection is the primary reason that many concrete ties are now molded with a pattern on their sides so that they key into the ballast better.

One of the main reasons that a buckle will frequently occur under a train is because the passage of the train will shake things loose thereby reducing the stabilizing forces. Also, once the track is at all out of line, there will be a lateral force from the wheels passing over the misalignment further making the track want to go sideways.

A break is a much better form of failure for a couple of other reasons.

In signaled track a rail break will drop the signals, so that unless the train is already in the block when the break occurs the signal system will tell him to stop before he gets to the break. A buckle in the track does not announce itself to the signal system because the rail remains continuous.

If the rail ends stay in line, and they usually will, and if the gap is not too wide, and usually it is not, the wheel will simply bounce across the break and keep going. In transit and other systems where trains are light and short the train will most likely survive a trip across the break. This is much less likely under heavy freight trains, because even if the first few axles bounce across, the heavy impact can cause another nearby break which will result in everything from there back derailing. Heavy impacts can also cause a broken wheel which can also result in a trip off into the cornfieds.

The coefficient of thermal expansion of steel is not as high as that of several other metals, and is only one of many properties of concern. Rail steel metallurgy has been experimented with in many ways over the years, and probably will be some more.

 

[railiner]

Thanks for that detailed and informative explanation of the problem.....

 

[Phil S]

Yes, thank you George. Your excellent posting got me to do some more Googling and this time I actually found useful info. Here's a July 16 Safety Advisory from FRA

http://www.ofr.gov/OFRUpload/OFRData/2012-17343_PI.pdf which tentatively attributes 4 recent derailments to the record heat.

So now that I understand a little more about the engineering and mechanics, I still wonder about the best way to deal with a changing climate, especially since all the predictions are for greater extremes in both temperature directions. Using higher neutral temps may help prevent kinks but might also trigger breaks, although I can see that breaks are easier to catch. Seems to me that the most cost effective immediate solution would involve better ways to monitor the actual in place rail neutral temperature, which apparently tends to decrease significantly as the track and roadbed experience wear and parts are replaced. That way only the sections whose RNT has degraded significantly need to be re-stretched.

A shorter version of the advisory is here http://ohsonline.com/articles/2012/07/16/extreme-heat-prompts-safety-advisory-on-track-buckling.aspx and also cites a 2010 research report about development of an acoustical (ultrasonic) method for measuring compressional stress in CWR in the field. I'll do some more reading on how this research is panning out but if anyone has the info at hand please consider posting it here. One good piece of news - BNSF collaborated with the UCSD research team that was developing the new method (acronym is SAFE).

 

[RampWidget]

Track has to be re-laid on a periodic basis anyway, especially on busy routes. Possibly there is no actual extra cost involved. It's just a question of chaning the specs.

To my understanding, although modern track does require regular maintenance it does not generally require regular replacement. Most of the time when you see maintenance being performed it's related to relatively minor repairs such as tie replacement, ballast maintenance, geometric correction, etc. It's rare to just up and replace the rails themselves, which is a much more expensive and time consuming operation. Maybe in fifty years or so they'll replace the rails when they're approaching the end of their useful life. Sometimes it's much longer than that.

It is true that rail on tangent track does not require frequent replacement, although it's not uncommon to see rail renewal on high-volume tangent track every five years or so, mostly for wear on the gage side that causes degradation of the wheel/rail relationship.

Curves are another matter; rail on the outside of curves on high-density freight lines is renewed as frequently as once a year.

The rails that are replaced can and are be reused (mostly in yard & secondary tracks) by re-laying the rail in the other direction (i.e., the outside "field" side is re-laid as the inside "gage" side).

 

[RampWidget]

So now that I understand a little more about the engineering and mechanics, I still wonder about the best way to deal with a changing climate, especially since all the predictions are for greater extremes in both temperature directions. Using higher neutral temps may help prevent kinks but might also trigger breaks, although I can see that breaks are easier to catch.

This is a really good discussion. You are correct that breaks are generally easier to catch than misalignments. It is for that reason that track inspections, both by hi-rail and on foot, are conducted more frequently in hot weather.

A broken rail, however, isn't always harmless if the break occurs under movement and is of other than a simple "straight break." Breaks can also be compound, where the break is jagged or actually has a piece of the ball of the rail break off or separate from the rail web. The good thing, if there is one, is that passenger trains rarely experience a rail break under themselves; the odds are much more likely that a break will occur under or behind a freight train due to the relatively light weight of passenger equipment.

As discussed, both heat and cold extremes are taken into consideration during track planning, engineering, and maintenance.

 

[RRUserious]

My natural question (since the entire world runs trains) is whether our derailments are the lowest and our conventional trains are the fastest in the world. If either of those is untrue, what rail technologies are other countries (that value passenger business more) using? Is there a site anywhere that ranks things like ontime performance internationally?

 

[ChillZZ]

... our conventional trains are the fastest in the world.

i can tell you, looking at the railroad type classes defined by the FRA (wiki link)

that mainland europe (netherlands, belgium, germany, france etc) have higher speeds for conventional passenger rail, minimum would be around class 3/4 around 120kph/74mph to class 7 ish. The Highspeed rail in Netherlands, Belgium, Germany and France would be comparable with class 8 and 9 speeds up to 330kph/205mph.

Most newer lines or the ones that are rebuild have concrete ties/sleepers with continuous welded rail, not much different then in the US i guess. Ofcourse the amount of at least double, tripple and even up to six paralel tracks would help the average speed of passenger trains, where local trains eventhough fast, will be passed by the limited trains.

 

[NW cannonball]

Thanks, George -- really helpful info --

About drawbridges -- heat can make them fail --

about 6 years back my daughter waited in a heat wave in Portland, Oregon on the CS just out of the station there -- they waited more than 4 hours because the drawbridge was swelled up in the heat - and could not close properly - they were pumping river water on the bridge to cool and shrink it but only after the sun went down did the bridge shrink enough to close properly.

The drawbridge there over the Willamette is one of the longest spans in the world -- but a few inches of heat expansion took it out of service for hours.

 

[George Harris]

A broken rail, however, isn't always harmless if the break occurs under movement and is of other than a simple "straight break." Breaks can also be compound, where the break is jagged or actually has a piece of the ball of the rail break off or separate from the rail web. The good thing, if there is one, is that passenger trains rarely experience a rail break under themselves; the odds are much more likely that a break will

Did not say a pull-apart was harmless. Only that it was the lesser disaster and that a train was more far likely to pass over a break without derailing than over a track buckle.

 

[George Harris]

Thanks, George -- really helpful info --

About drawbridges -- heat can make them fail --

about 6 years back my daughter waited in a heat wave in Portland, Oregon on the CS just out of the station there -- they waited more than 4 hours because the drawbridge was swelled up in the heat - and could not close properly - they were pumping river water on the bridge to cool and shrink it but only after the sun went down did the bridge shrink enough to close properly.

The drawbridge there over the Willamette is one of the longest spans in the world -- but a few inches of heat expansion took it out of service for hours.

Have no idea of either the temeprature range or span length, but for a temperature range of 100 degrees F and a span length of 320 feet, the difference in length of bridge span would be 0.0000065*100*320*12 = 2.496 inches. Really should call it 2.50 inches at the finest slice. To go the extra decimal place or more would not be warranted by the information going into the calculation. (The calculation is coefficient of thermal expansion for steel times temeprature change in Fahrenheit degrees times length in feet times inches per foot.)

 

[NW cannonball]

Thanks, George -- really helpful info --

About drawbridges -- heat can make them fail --

about 6 years back my daughter waited in a heat wave in Portland, Oregon on the CS just out of the station there -- they waited more than 4 hours because the drawbridge was swelled up in the heat - and could not close properly - they were pumping river water on the bridge to cool and shrink it but only after the sun went down did the bridge shrink enough to close properly.

The drawbridge there over the Willamette is one of the longest spans in the world -- but a few inches of heat expansion took it out of service for hours.

Have no idea of either the temeprature range or span length, but for a temperature range of 100 degrees F and a span length of 320 feet, the difference in length of bridge span would be 0.0000065*100*320*12 = 2.496 inches. Really should call it 2.50 inches at the finest slice. To go the extra decimal place or more would not be warranted by the information going into the calculation. (The calculation is coefficient of thermal expansion for steel times temeprature change in Fahrenheit degrees times length in feet times inches per foot.)

The center lift span of this bridge - the Burlington Northern Railroad Bridge 5.1 is 516 feet . The overall length is 1,763 feet. - so it seems that the last 10 or 15 degrees Fahrenheit outside the design temperature could put the bridge out by a few inches if the air temp was above 100 degrees F.

Unfortunately can't see the actual way the rails lock in when the bridge is lowered for rail traffic. I'm guessing, but would expect the designers of the 1989 replacement of the lift span part allowed for low temps down to about freezing, but high temps above 100 F were not considered. Seems likeley?

I know my daughter experienced the delay a few years back (not to mention more delays on the UP on the rest of her trip)

 

[jis]

Handling such temp range is not exactly rocket science. It requires some design thought, even in existing bridges, mods can be made to deal with such. It is just a huge maintenance headache no matter which way you look at it. That is why people try to avoid moveable bridges if they can.

Even NJ Transit agreed to a higher gradient to get the movable component out of the design for the Portal South Bridge by simply raising it another 10 feet.

 

[trainviews]

My natural question (since the entire world runs trains) is whether our derailments are the lowest and our conventional trains are the fastest in the world. If either of those is untrue, what rail technologies are other countries (that value passenger business more) using? Is there a site anywhere that ranks things like ontime performance internationally?

While in no way a technical expert, I will chip in here from Denmark.

Standard speed on the main line here is 180 kph/approx. 110 mph. Lower on the side lines. The system is far from the best in Europe but a concerted upgrade is on the way and has largely eliminated heat related slow orders.

Decades of deferred maintenance resulted in a "summer of horror" about 10 years ago with everything being slow ordered and a rail actually breaking on the main line. That finally made the government to throw in the (substantial) required funds to bring things up to standard, and the slow orders are now a thing of the past. Replacing the whole signalling system (much of it 1912 technology!) is up next.

So granted, the challenges are greater in much of the US as the temperatures are much more extreme (we have pretty mild winters and not too hot summers often), but as George laid out in his detailed post, it is largely a matter of the quality of the technical solutions and the quality of the maintenance.

This leaves the ball with the owners of the rail and whether they have the funds and the will to keep the tracks up to standard. In the US I guess the answer is as manyfold as there are subdivisions. The class I's are spending a lot of money these years on their main lines and it might result in fewer heat related slow orders - more correctly exactly to the standard it pays for the RR to maintain the tracks to in relation to their freight customers on any given stretch. Higher standards will need a government co-financing.

 

[George Harris]

Thanks, George -- really helpful info --

About drawbridges -- heat can make them fail --

about 6 years back my daughter waited in a heat wave in Portland, Oregon on the CS just out of the station there -- they waited more than 4 hours because the drawbridge was swelled up in the heat - and could not close properly - they were pumping river water on the bridge to cool and shrink it but only after the sun went down did the bridge shrink enough to close properly.

The drawbridge there over the Willamette is one of the longest spans in the world -- but a few inches of heat expansion took it out of service for hours.

Have no idea of either the temeprature range or span length, but for a temperature range of 100 degrees F and a span length of 320 feet, the difference in length of bridge span would be 0.0000065*100*320*12 = 2.496 inches. Really should call it 2.50 inches at the finest slice. To go the extra decimal place or more would not be warranted by the information going into the calculation. (The calculation is coefficient of thermal expansion for steel times temeprature change in Fahrenheit degrees times length in feet times inches per foot.)

The center lift span of this bridge - the Burlington Northern Railroad Bridge 5.1 is 516 feet . The overall length is 1,763 feet. - so it seems that the last 10 or 15 degrees Fahrenheit outside the design temperature could put the bridge out by a few inches if the air temp was above 100 degrees F.

Unfortunately can't see the actual way the rails lock in when the bridge is lowered for rail traffic. I'm guessing, but would expect the designers of the 1989 replacement of the lift span part allowed for low temps down to about freezing, but high temps above 100 F were not considered. Seems likeley?

I know my daughter experienced the delay a few years back (not to mention more delays on the UP on the rest of her trip)

OK, if we take 516 feet span and say 120 degrees between high and low, we would get a length change of 4.83 inches between high and low. Taht would be then difference in length that the locking devices in the rail would have to deal with. Actually more like 2.5 inches each, because there should be a set on both ends fo the draaw span. It does not really matter how long the bridge is in total, only span lengths and location of fixed bearing points.

 

[George Harris]

It is true that rail on tangent track does not require frequent replacement, although it's not uncommon to see rail renewal on high-volume tangent track every five years or so, mostly for wear on the gage side that causes degradation of the wheel/rail relationship.
Curves are another matter; rail on the outside of curves on high-density freight lines is renewed as frequently as once a year.

The rails that are replaced can and are be reused (mostly in yard & secondary tracks) by re-laying the rail in the other direction (i.e., the outside "field" side is re-laid as the inside "gage" side).

RampWidget, I do not know where you are getting your numbers. Rail life is normally measured in million gross tons of traffic passing over it. For the 136 lb to 141 lb sections normally installed in high volume tracks, this will be somewhere above one billion gross tons. Few tracks carry more than 30 to 50 million gross tons per year. Therefore, you will have at the least about 20 years of life in a heavily used main line. Yes, for curves it will be less, but if a curve is small enugh in radius to have severe wear, the gage face fo the rail will be lubricated. Also, on a line where the majority of the traffic will be at about the same speed, the track will be superelevated for slightly less than that which would balance the average train speed, up to not more than 4 inches. When done properly there will be very little gage face wear on the curves. There has been a considerable amount of study and experimentation over the last 20 odd years on rail metallurgy, rail head shapes, wheel tread shapes and rail grinding programs, all to reduce wear, frequency of defects and failures and to provide better centering on the track. If you look at the mill marks on the web of the rail, you will find a lot of rail out there that is 30 to 50 years old, and even more. And: much of this older rail was put in track before some long before a lot of the metallurgy and shape studies were done.