"Sun Kink" and thermal expansion--WHY?

9766 views
16 replies
1 rating 2 rating 3 rating 4 rating 5 rating
  • Member since
    September, 2008
  • 1,060 posts
"Sun Kink" and thermal expansion--WHY?
Posted by aegrotatio on Sunday, December 21, 2008 10:11 PM

Routinely, our local Virginia Railway Express trains get slow orders due to thermal expansion of continuously-welded rail, which the jargon defines as "sun kink."

These trains can be reduced to 60% or less of their regular speed and the always informative VRE newsletter discusses it more than once during the summer months.  It even gets into the traffic reports on our local station.

 What I'd like to know is, why are there not any thermal expansion joints installed when a line installs continuously-welded rail?  Is this the reason for "sun kink" and hot summertime slow orders?  And if so, why do we tolerate slow orders due to "sun kink?"

 As an aside, the VRE newsletter is a very frank and candid window to the operations of a transit public/private partnership. For example, they frankly tell riders that commuter rail does not make money, and freely point out to commuters that VRE's fares only cover 50% of operating costs.  You can read it at http://www.vre.org/.

 

 

 

  • Member since
    November, 2007
  • 2,989 posts
Posted by Railway Man on Sunday, December 21, 2008 10:52 PM

 If there were expansion joints, it would not be continuously welded rail any longer.  It would be jointed rail.  Jointed rail was laid with some thermal expansion capacity at the joints, whereas welded rail absorbs all the thermal expansion by restraining the rail, compressing the steel itself, and transmitting the forces to the ties, and from the ties to the ballast section.  The entire idea of welded rail is to eliminate as many joints as possible.  Heat orders are placed on very hot days when the ability of the track structure to absorb the thermal expansion becomes less assured.

You're probably thinking, "So what?"  The drawback to jointed rail is much higher maintenance costs, and much higher maintenance time required on the track, which translates to a much higher access cost to operate the commuter trains, reduced capacity to run trains (in order to make time for maintenance-of-way), reduced reliability of passenger service, etc.  It's an economic trade-off, and in this case the railroad (CSX) is accepting the cost X of "heat orders" (with the agreement of VRE) on hot days and the resultant loss of train capacity and schedule reliability on those days versus the cost 10X of jointed rail, not to mention going back 50 years, technologically and economically speaking. It would be like substituting a horse-and-buggy for your car to eliminate the irritation of having to put up with taking the car in every 90-180 days for an oil change.

RWM

  • Member since
    February, 2005
  • From: Nebraska
  • 252 posts
Posted by PigFarmer1 on Sunday, December 21, 2008 11:01 PM

aegrotatio
And if so, why do we tolerate slow orders due to "sun kink?"

 

I'm not sure what you mean by "tolerating" slow orders due to sun kinks.  Kinks are a result of poor roadbed and tie condition.  Not enough ballast, mud holes, and poor anchoring all contribute to the instability which results in kinks.  It is a multi-faceted problem that requires spending large sums of money to repair.  Essentially when you have summer heating the rail will grow and if you don't have enough rock and anchors the ties will move as the rail expands because there is nothing to provide stability to the rail and/or the ties.  When you get enough growth the rail is going to kick out.

MoW employee
  • Member since
    October, 2006
  • From: Allentown, PA
  • 9,523 posts
Posted by Paul_D_North_Jr on Monday, December 22, 2008 8:46 AM

You've got two very good and comprehensive answers above.  To add just a little bit:

5 or 10 years ago CSX - which I understand is the line that VRE mostly runs on - had a couple of nasty derailments due to sun kinks.  At least 1 of those CSX sun kink wrecks involved an Amtrak train in Florida (if I recall correctly), which was discussed extensively on this forum about 1 or 1-1/2 years ago.  That particular one was caused more by improper maintenance practices - not tamping or allowing the track to "bed in" (my term) sufficiently before resuming full-speed traffic, etc., if I recall correctly - as opposed to overall poor track condition, such as ties, mud, ballast, etc. as mentioned above.

Having thus been "snake-bit", the immediate reaction by CSX - the "band-aid" fix, if you will - was to impose the hot weather slow orders, which CSX was far more aggressive in doing than any other railroad, resulting in far more delays for VRE and Amtrak on CSX's lines than anyplace else.  I believe that comparison remains valid today - for example, I'm not aware that BNSF places any restrictions (or at least nowheres near as limiting as CSX) - on BNSF's "TransCon" line across the southwestern US deserts, even though the temperatures there routinely exceed those to which CSX's tracks are exposed. 

My opinion - then and now - was that rash was primarily due to the underlying problem of poor or insufficient track maintenance in terms of money being spent and the resulting quality of track, and secondarily by insufficient training and/ or supervision of the maintenance-of-way crews that compounded the underlying track conditions by aggravating or mishandling the sun kink factors.  I also recall a report regarding CSX's official standard for the "neutral temperature" of the continuous welded rail ("CWR"), which struck me as being unusually low when compared to other railroads, esp. NS.  As a result, CSX's tracks would be more susceptible to sun kinks, all other things being equal. 

Another factor is that of technology - directly measuring the compressive stress building up in the rails that could result in a sun kink - is not a mature science.  It is usually done by measuring the rail temperature, and letting that temp. value act as a "surrogate" for the actual stress in the rails.  Accordingly, there is inherently a lot of uncertainty associated with determinations and judgments as to the risk of sun kinks, which naturally enough would lead a railroad to err on the side of caution. 

Finally, from a liability or risk management standpoint, CSX is taking the course that maximizes safety, though it also has the same effect in inconveniencing you.  Perhaps having had confidence in the reliability and integrity of both its track structure and M-O-W forces shattered by the sun kink derailments a decade ago, CSX may be responding with understandable institutional paranoia, and so might now be behaving by over-reacting - in comparison with other railroads - so as to absolutely preclude that from ever happening again.  Well and good, but I think it would be better to understand and fix the underlying track conditions problem - once and for all - than continuing to rely on the slow orders for protection against that hazard. 

Hope this is helpful.

- Paul North.

 

"This Fascinating Railroad Business" (title of 1943 book by Robert Selph Henry of the AAR)
  • Member since
    June, 2001
  • From: Lombard (west of Chicago), Illinois
  • 13,312 posts
Posted by CShaveRR on Monday, December 22, 2008 8:52 AM

aegrotatio
Routinely, our local Virginia Railway Express trains get slow orders due to thermal expansion of continuously-welded rail, which the jargon defines as "sun kink."

Had this problem recently, have you?  (He says, looking through frosted window panes into zubzero cold.)

Carl

Railroader Emeritus (practiced railroading for 46 years--and in 2010 I finally got it right!)

CAACSCOCOM--I don't want to behave improperly, so I just won't behave at all. (SM)

  • Member since
    May, 2003
  • From: US
  • 16,298 posts
Posted by BaltACD on Monday, December 22, 2008 10:05 AM

CSX (VRE & MARC) operates in the MOST POLITICALLY CHARGED environment in the country - the Greater Washington DC metro area.  Whenever a frog farts on the track there is a news report on radio and TV about it within the half hour.  CSX and it's legal staff take note of this.

Heat orders are issued when the anticipated high temperature will be 90 F or higher.  The heat order, when issued, applies to track having a timetable maximum speed of 40 MPH or higher and reduces those maximum speeds by 10 MPH.  Heat orders are in effect from 1300 to 1900 - through the hottest part of the day.  Heat orders are NOT issued because there ARE Sun Kinks, they are issued as a preventive measure.  Heat orders apply to ALL TRAINS, not just VRE.

The derailments that CSX has had with heat related track structure movement were where timetable speeds were restored after track work prematurely.  Whenever the track structure is disturbed (tie & surfacing gangs, rail laying gangs), the initial train over the disturbed track is limited to 10 MPH, subsequent to the initial train further trains are limited to 25 MPH for a period of time to, as has been previously mentioned, "bed in" the track.  Operation of trains settles the track structure to the point that ballast/tie work themselves into a sustainable configuration.

When Sun Kinks are discovered, then M of W personnel will physically cut out a segment of rail and either apply joint bars or re-weld the track joint.  If joint bars are applied the track will have a speed restriction until such time as those joints are re-welded.

As a corollary, when temperatures dive, there is also stresses applied to the track structure in the opposite direction and as a result there becomes a relatively high incidence of broken rails, some at the weakest welds and some at points of internal rail defects.  The cold induced broken rails have been decreasing over the years as increasing amounts of new welded rail have been installed.

  • Member since
    February, 2002
  • From: Muncie, Indiana...Orig. from Pennsylvania
  • 13,456 posts
Posted by Modelcar on Monday, December 22, 2008 10:55 AM

....Sun Kinks:  Doesn't the engineering community have the instruments  currently that they could install strain gauges at periodic locations in known troubled heat / cold spots to give a better indea of looming trouble...?

If so....couldn't engineering then establish "charts" of performance over time and temp and perhaps sneak up on trouble spots with slow orders and whatever else could be done.

Quentin

  • Member since
    September, 2008
  • 1,060 posts
Posted by aegrotatio on Monday, December 22, 2008 1:33 PM

 Thanks for the very informative answers.

What I was getting at was that is "sun kink" a normally accepted phenomenon or does it happen when the state of the track gets bad?  Sounds like it is the latter combined with generally over-protective CSX policy due to past experience.

If I remember correctly, also, this year they did mention on the radio that the track was recently replaced and needed to 'settle.'  They didn't say that last year.

 For what it's worth, I never hear about speed restrcitions on MARC's Penn Line which is AMTRAK.  Those lucky commuters rival Metro-North in high speeds.

 

 

  • Member since
    May, 2003
  • From: US
  • 16,298 posts
Posted by BaltACD on Monday, December 22, 2008 2:47 PM

aegrotatio

 What I was getting at was that is "sun kink" a normally accepted phenomenon or does it happen when the state of the track gets bad?  Sounds like it is the latter combined with generally over-protective CSX policy due to past experience.

If I remember correctly, also, this year they did mention on the radio that the track was recently replaced and needed to 'settle.'  They didn't say that last year.

 

Sun kinks are an accepted phenomenon, they will occur more frequently when maintenance gets deferred on a line.  Over the past 5 years, the RF&P S/D from Fredericksburg to Washington has received some of the most extensive maintenance of any sub division on CSX, including new welded rail and an extensive tie and surfacing program as well as installation of new Control Points and signaling changes not to mention eliminating the single track operation over the Quantico Creek bridge.  Additional changes and enhancements for this line are being worked on.

  • Member since
    September, 2008
  • 1,060 posts
Posted by aegrotatio on Monday, December 22, 2008 3:33 PM

 Slightly off-topic, I think it's notable that the bridge and track work along VRE's Fredericksburg line is being paid for by Virginia and the VRE.

  • Member since
    May, 2003
  • From: US
  • 2,441 posts
Posted by PNWRMNM on Monday, December 22, 2008 5:32 PM

If VRE wants to run more trains it is only right and fair that they should pay for the capacity.  Or do you think CSX should?

 Mac

  • Member since
    February, 2005
  • 115 posts
Posted by bartman-tn on Monday, December 22, 2008 7:06 PM

A bit more info on sun kinks.  As discussed, they are fairly common where you have wide temperature ranges, such as where you have cold winters and hot summers.  While the railroad can install additional ballast, better condition ties and fasteners, and other items such as anchors, the rail will still expand.  The hope is that the rail grows vertically instead of lengthwise.

Sunkinks are not limited to welded rail.  Jointed rail can have them jsut as easily, especially since joints typically pump a bit leading to a less structurally contained track structure.

 

A final comment.  The FRA in their welded rail rules (49 CFR Part 213) requires that railroads develop procedures to respond to wide ranging temperature changes by using slow orders, additional inspections, etc.  The railroad industry has been testing many automated inspection systems at the AAR test track and better physical track designs, but kinks are still a problem that railroads have to respond to.

 

Bart Jennings

 

  • Member since
    October, 2006
  • From: Allentown, PA
  • 9,523 posts
Posted by Paul_D_North_Jr on Tuesday, December 23, 2008 10:22 AM

bartman-tn
[clip] While the railroad can install additional ballast, better condition ties and fasteners, and other items such as anchors, the rail will still expand.  The hope is that the rail grows vertically instead of lengthwise.

[emphasis added - PDN]

Well, not quite - perhaps you meant to post instead that "the rail may still expand".  In an ideal world - which is often achieved on the well-maintained lines - the ballast, ties, fasteners, and anchors, etc. would work together so well that the rail doesn't move at all as it heats up.  What happens to the rail is that it experiences thermally induced compression stress - it is pushing against itself, but not going anyplace.  As an analogy, think of an isometric exercise where you push against a solid wall.  If you do it perfectly, neither you nor any of your appendages move at all, but you can sure feel the load / pressure /stress in your hands, arms, and muscles.  It's the same with the rail.  The trouble starts when the rail expands - then it starts to move longitudinally.  That motion - often called "running" - can be fairly harmless if it is small in magnitude and remains in the same direction as the track.  But if the movement starts to or wants to get large in magnitude, and then is or becomes constrained in both directions - such as by a grade crossing, a turnout (switch), bridge, or even the weight (mass) of the adjoining length of track - then the rail and track will take the "path of least resistance" to relieve that stress.  In this context, the concern is that would be buckling into a sun kink at an (in)opportune location.

Next, technically, the rail will grow vertically when under such heat-induced stress, but only on a microscopic scale, per Poisson's Ratio (typically around 0.3 for steel, I recall).  Without getting into all of the aspects of the theory of elasticity that pertain here ( a very difficult 3rd year spring course at Lafayette College, thanks to the challenging but enjoyable now-retired Dr. B. Vincent Viscomi !), that means that for every unit of deformation in the longitudinal direction, a corresponding ratio of deformation occurs in the other orthogonal directions - think of how a chunk of Jello would respond under similar pressures.  To illustrate this with a very exaggerated example, if a very large chunk of steel is compressed by 1" in a certain direction (say, the X axis), it will typically expand in both of the other directions (Y axis and Z axis) by an amount equal to Poisson's Ratio x the amount of the deformation in the X axis direction, which is 0.3 x 1" = 0.3 inch.

To more clearly illustrate this, the pertinent length of rail would be 1 inch long.  For a change in the rail's temperature ("/\ T" or "Delta T") from the "neutral temperature" that the rail should have been laid at - say 90 degrees F, to a typical maximum temperature - say, 150 degrees F, the /\ T would be 60 degrees F.  Per the formula (see the excerpt from Railway Man's post below), the change in length would be:

Length of rail (in inches) x Coefficient of Thermal Expansion for Steel x /\ T (in degrees F), or here:

1" x 0.00000645in/in/degree Fahrenheit x 60 degrees F = 0.000387 inch, which is a little less than 4 / 10,000 of an inch, per inch of length of rail.

Multiplying this dimension by Poisson's Ratio gives the change in dimension of a 1" cube of steel in the other 2 directions/ dimensions/ axes, or:

0.000387 in. x 0.3 = 0.000116 in. per inch of distance, which is a little more than 1 / 10,000 of an inch, per inch of height or width of the rail section.

Since we're talking mainline here, let's use the height of 141AB rail, which is 7-7/16" = 7.44".  So the amount of vertical "growth" (expansion) would be the "strain" in that direction per Poisson''s Ratio (above), times the rail's length or dimension in that direction, or:

0.000116 in. / in. x 7.44 in. = 0.000863 inch - a little less than 1 / 1,000 of an inch of vertical growth.  So yes, technically the rail does grow vertically under heat-induced constrained expansive stress, but not by amounts that anyone would care about, I think. 

Alternatively, the track could buckle upwards instead of sideways - that's rare, but I believe it has happened from time to time in odd places. I doubt if that's what you meant either, though.

Also, the following illustrative example is from Railway Man's post of 12-19-2008 at 12:41 AM to the thread  "Re: Thermal Expansion and its Effects on Train Lengths" at - http://cs.trains.com/trccs/forums/t/143682.aspx - the distances, changes, analysis, and comments are the same for rails and track, except that the "neutral temperature" for adjusting the length and the residual thermal stress in Continuous Welded Rail ("CWR") is not 70 degrees - more often, it is a specific value in the range of 85 to 95 degrees Fahrenheit - which varies by railroad, territory, and the official making the determination:

"The thermal expansion coefficient of steel is 0.00000645in/in/degree Fahrenheit.

 For a 10,000 foot train, the difference between -30 degrees in North Dakota in January and +120 degrees in Arizona in August is 150 degrees x 12 x 10,0000 x 0.00000645 =  116" = 9.675'

But "nominal lengths" of cars over pulling faces are not measured in North Dakota in January at -30, they're measured on a ~70 degree F day at the car builder, so the difference is only ~ 50 degrees or 3.225' between the average day and the hottest possible day.  And this is for a 10,000-foot train.  Few trains are of that length."

Finally, you're right about the railroad industry's efforts at finding automated or better methods to monitor levels of heat compression in rails/ track to detect and provide a warning before it gets severe enough to cause a sun kink.  Although I'm not real familiar with that, it seems to be making some progress.  While simply installing a "strain gage" type of approach may seem to be enough, I understand that a very big challenge with that - since all it really measures is the change in length / strain / stress - is accurately defining and measuring the inital state or starting value of the compressive stress in the rails.  Without knowing that, you don't have the actual absolute value of that stress, so you can't know how much of a margin of safety is left before the risk of buckling becomes unacceptable.  And that depends on defining and measuring the stability and stiffness of the track structure, which is a whole 'nother discussion for a later time.

- Paul North.

"This Fascinating Railroad Business" (title of 1943 book by Robert Selph Henry of the AAR)
  • Member since
    October, 2006
  • From: Allentown, PA
  • 9,523 posts
Posted by Paul_D_North_Jr on Tuesday, December 23, 2008 11:26 AM

CShaveRR
Had this problem recently, have you?  (He says, looking through frosted window panes into zubzero cold.)

Laugh Bow Laugh Bow Laugh

That was pretty funny - thanks !

And, it must really be chilly out there - or still susceptible to sunkinks ? - too, if it's "zubzero cold", eh ?

- Paul North.

"This Fascinating Railroad Business" (title of 1943 book by Robert Selph Henry of the AAR)
  • Member since
    June, 2001
  • From: Lombard (west of Chicago), Illinois
  • 13,312 posts
Posted by CShaveRR on Tuesday, December 23, 2008 1:41 PM

Well, Paul, my computer is next to a north window (with frosted panes).  Perhaps I should be like Mookie and wear gloves for this.  However, I suspect that that would be the equivalent of being "all thumbs."

Fortunately, we've moved up to double-digit positive territory here.  It's warm enough to snow again.

Carl

Railroader Emeritus (practiced railroading for 46 years--and in 2010 I finally got it right!)

CAACSCOCOM--I don't want to behave improperly, so I just won't behave at all. (SM)

  • Member since
    September, 2008
  • 1,060 posts
Posted by aegrotatio on Tuesday, December 23, 2008 2:35 PM

 Comment wasn't so much about capacity but it was in response to the comment that the line that VRE uses happens to be getting the most maintenance attention in the entire CSX system.

 

  • Member since
    January, 2003
  • From: Kenosha, WI
  • 6,353 posts
Posted by zardoz on Tuesday, December 23, 2008 2:56 PM

BaltACD

As a corollary, when temperatures dive, there is also stresses applied to the track structure in the opposite direction and as a result there becomes a relatively high incidence of broken rails, some at the weakest welds and some at points of internal rail defects.  The cold-induced broken rails have been decreasing over the years as increasing amounts of new welded rail have been installed.

AKA: pull-aparts.

If you've got a scanner, listen in during very cold weather.  You'll hear about lots of "broken rails".  Sometimes the rails pull so strongly that the anglebar bolts are sheared completely in half, and sometimes the anglebar itself will seperate at the holes. I've seen pull-aparts that the rails were 3" apart.

Where's mudchicken? We need his expert advice here.

   23 17 46 11

Join our Community!

Our community is FREE to join. To participate you must either login or register for an account.

Search the Community

Newsletter Sign-Up

By signing up you may also receive occasional reader surveys and special offers from Trains magazine.Please view our privacy policy