Western Railroad Discussion > Rail neutral temperature

I was speaking with someone in CPKC's MOW department last week, and we got to wondering about the "rail neutral temperature" for CWR. He said that CP had adjusted it by 5 degrees recently, but couldn't remember if their current number is 90 or 95 degrees.

What number do the other class ones use, and are there regional differences? CP's number is apparently system-wide, but I'd think that lines further south should theoretically use a higher temperature (eg, BNSF northern TransCon vs the ex-ATSF)

Posted from Android

Darren Boes
Lethbridge, AB
Southern Alberta Railfan

BNSF has several rail neutral temperatures, higher across the Mojave than in Montana for example. I do not know the current temps they use.

Posted from iPhone

There are two aspects of Rail Neutral Temperature (RNT).
First is the decision by the Engineering department as to what the number is to be, often varied by obvious differences in local temperature extremes.
Generally a high RNT means you are less likely to develop sunkinks but will put more stress on the joints and rail during low temperatures.  Thermal contraction is a large factor in the stress on rails, which is especially bad for internal defects.  They seem to grow faster in cold weather.  You can see that when the first cold snap comes in the late fall, track gangs are chasing broken rails and stripped joint until all the weakened components get replaced.
The second aspect is the maintenence discipline to closely follow and document rail temperatures.  Track gangs know their RNTs and with a rail thermometer they know how far off the RNT the local condition is.  To actually accomplish track repairs someone is going to have to get their hands dirty and work outdoors in any weather.  No software can actually do this work (but it can help keep your records and make your rail stress calculations.)
To make a replacement rail have the same RNT is often not possible due to the pressures to get traffic moving.  To document this on paper and by painting information of the welds and joints involved is critical to getting the RNT adjusted before temperatures increase in the spring.  In some cases the rail can be heated by burning, or it can be adusted by pulling with hydraulic jacks to stretch the rail, either way can get the rail back to the RNT specified. Example:  A rail breaks at a detail fracture and the ends pull back say 5".  In the dark of night and in a hurry the only thing to do is to install a piece of rail that is 5" longer than what used to be there.  OK so far.  But by inserting that slightly longer rail the repair crew has changed the local RNT from the desired number (maybe 90 degrees) to the temperature then and there (maybe way below zero).  So on a warm spring day at 70 degrees with the sun shining on the rail and no wind you can find yourself at an actual rail temperature of almost 100.  The track, in good condition, can withstand the thermal expansion forces of about a 45 to 55 degree above the RNT.  That winter repair is just waiting for an opportunity to jump out in a sunkink.  What holds it back is the fact that usually the second rail still has the right RNT.
The FRA has requirements for all track owners to establish sound thermal rail maintenance plus to train and qualify people responsible to do the work.

You don't carry diesel soaked ropes in a 5gal bucket to get the adjcent rail temps up to close the gap in the rail?

Ted Curphey
Ontario, OR

funnelfan Wrote:
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> You don't carry diesel soaked ropes in a 5gal
> bucket to get the adjcent rail temps up to close
> the gap in the rail?

They use rail snakes on CSX where I am....

I have heard of some welded rail being as much as 8 miles long.  Does extreme length make repair more difficult?

No, the resistance to movement provided by the first several hundred feet of rail anchors or clips will confine the changed RNT to the area near the new change (or added rail), so several miles of CWR does not matter for this discussion.
No, the opposite rail is presumed to be at the target RNT, so no need to heat it, it is already where it needs to be.  The broken end of the rail pulls back through the track fasteners, see above.

Thanks for the explanation Railstiesballast. Interesting how much goes into keeping the rail on the ties. Here is a photo of a weld that broke a week after it was done when bitter cold weather hit. The tempature was about -15' with a wind chill around -40'. These guys would work for 10 minutes then go warm up in the truck. The video is a break when temps were in the teens. Looks like internal defect finally made itself known. They ran two more trains over the break before getting track time to fix it.

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How close can two welds be on the same rail? Is there a minimum distance between welds?

I am slowly unloading my brain cells post retirement, not less than 15 feet was what we did as a plug rail (minimum distance between any two welds).



Edited 1 time(s). Last edit at 11/19/24 08:09 by train1275.

That weld break picture looks like a weld flaw that was created by not properly heating the rail ends when the thermite weld was made.  We just had one of those happen in 40 degree weather.

The video of the second break appeared to be adjacent to a weld. It makes me wonder if this is possibly in the heat affected zone where the grain had changed from heating and cooling, resulting in a reduction of the modulus of elasticity.

abyler Wrote:
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> That weld break picture looks like a weld flaw
> that was created by not properly heating the rail
> ends when the thermite weld was made.  We just
> had one of those happen in 40 degree weather.

PHall Wrote:
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> How close can two welds be on the same rail? Is
> there a minimum distance between welds?

On BNSF, do not thermite weld closer than 2 feet of an electric flash butt weld and do not thermite weld closer than 14 feet of another thermite weld.  There is an exception to allow a thermite weld no closer than 4 feet from another thermite weld, but there must not be any bolt holes in that 4 feet..