Report shows pictures of various wheel failures. One item that is noted that there has been more rim failures since 1990. Reason not determined yet.
Wheel Failure Investigation Program: Phase I | FRA (dot.gov)
That seems like an extremely complex problem. It even gets into the idea of grinding wheel profiles and reducing the grinding on rail profiles because they affect each other.
Report seems to indicate that there is more trouble with wheels in the West as opposed to the Eastern carriers and that Covered Hoppers and Gondolas (remember todays ‘coal cars’ are frequently AAR designated gondolas). The recurring theme that was mentioned numerous times was ‘thin rim’.
Will be interesting if they can pin down some provable reasons.
Is it thin rim or sharp flanges*? Regardless, overly worn wheelsets that see so very few checks with AAR wheel gage templates… Lot fewer one-spot and car-knocker inspectors out there than there used to be.
(*) fun with switch point simple derailments, flanges sharp to the touch / hardly rounded edges and the cop-out is that the gage says it’s OK. (pegging the needle on the ol’ baloney-meter)… If it were not for the appearance of the new generation switch point protectors, we might see a lot more simple yard failures)
I was an observer to a yard derailment that was associated with a sharp flange and a switch protector, back in 1976.
Thuis was in Mt Newman’s port yard at Nelson Point, Port Hedland, in Western Australia.
I was sitting in the trailing cab of a three unit set of locomotives when I heard our train crew call the Yard Tower. “Has our train been cancelled?” Yard Tower “No, why?” Train Crew “Have you looked at the yard lately/” Yard Tower (expletive deleted).
A loaded train had derailed across the yard ladder taking out four switches, including the one between us and the main line, with 24 loaded 100 ton gondolas leaning at 45 degrees.
They worked out a path for us which involved backing the whole train through the car dumper and bypassing the derailment on the one remaining track. This was on a Friday and my train arrived back on Saturday night.
Since I’d been trained in investigating derailments, I spent my free time on Sunday morning trying to work out what had happened. (It was at least as interesting as anything else happening in town on a Sunday where we had one radio station and one TV station…)
I checked out the leading wheelset on the first derailed wagon and it did indeed have a very sharp flange which shouldn’t have been running. I then walked back
There has to be a standard somewhere. Your issue should be with the regulation - not the person holding the gage that is following that regulation.
According to this report, the wheel failure problem developed between 1990 and 2000. Does this coincide with the weight limits increase of rolling stock? It seems that the wheels in use before this failure phase began must have been just on the safe side of the “razor’s edge” of durability. Then it crossed over that edge and a vast array of consequent failures have ensued with many possible interrelated causes and effects.
Sorting this out and resolving the problem with just the adequate remedies must be the biggest technical challenge the industry has ever faced. It involves changing the mass of the various wheel features, changing the metallurgy, changing the manufacturing process, abandoning the single-use wheels, adopting wheel truing equipment and methods, evaluating rail grinding, balancing the wheel truing with rail grinding, evaluating the heat effect of braking, evaluating the effect of ambient temperature, and evaluating how the wheel, axle, and rail loading re-forms metal and adds residual stress.
It seems strange that with this wheel failure issue being a systemic problem with the wheel and rail standards, it is consistent, but the failure rate is extremely low. And this despite the fact that the conditions are standardized over such a high number of wheels in use. If wheel durability has reached a tipping point, I would expect the majority of wheels to be failing.
I think part of the implication he’s making is that the gage designed for one purpose isn’t picking up a critical condition affecting safety in another respect.
I had thought that sharp flanges were in themselves so important a safety consideration that they had their own regulation – so much so that I never looked in the CFR to see exactly how inspection and condemnation standards might have been worded. What exactly IS present Federal practice regarding sharp flanges?
Car loaded weight increases might also be relevant?
I suspect it is relevant. Were wheels and axles upgraded specifically for the weight increase, or did the increase fall within the existing wheel and axle capacities?
Somewhere there has to be a metallurgical analysis of the increased tendency to failure, and I have no doubt this would assist in finding causes. By analogy weight increases causing increased railhead problems could be expected to have some effect on the corresponding contact patch. Shock damage (for example at non-flange-bearing crossings or frogs) might be a factor with some approaches to providing hardened tread. I believe in this period we’ve seen much more intensive profile grinding to reduce running shock and noise, which might be conducive in some way to the ‘wrong’ kind of stress raising.
From the PDF:
As previously discussed, VSRs are extremely rare—if not non-existent—in domestic and international passenger wheels, and international freight wheels, including Australian mining railroads which operate at higher axle loads than the North American freights. The aforementioned railroads generally utilize multi-wear wheels and routinely turn their wheels. However, the North American freight railroads use single wear wheels which typically have zero or one turn before end of life. It appears that the U.S. freight railroads are an outlier in the world for not utilizing multi-wear wheels and routinely turning the wheels.
The loading of the wheel onto the rail cold forms and changes the profile of both the wheel tread and the rail. Much of this change is just the plastic flow of the metal being reshaped as though it were dough. It has been discovered that rail grinding to maintain its correct profile adds life to the rail. It seems counter intuitive because grinding removes metal, which seems equivalent to wearing the rail out. But re-truing the rail head profile adds life that exceeds the life lost by wear between re-truing operations.
When they refer to hollowed wheel threads, I understand that to be a result of the cold reshaping due to metal flow under pressure. This cold flow not only changes the profiles of wheel and rail, but it also induces stress areas that become prone to breaking out of the wheels. It also moves metal out of the rail/wheel contact and brings the rail contact deeper into the critical mass fiber of the wheel. Moving this load into that weaker area of the wheel causes stress cracking to begin. The cracking then lengthens deeper into the wheel toward the center, and further weakens the wheel.
Note: I have revised my understanding of the fracture process detailed here in green text, and the next post reflects that new understanding.
VSR WHEEL FAILURE
The focus seems to be on a type of wheel failure called VSR for “Vertical Split Rim.”
The fracture separation plane falls on a vertical reference plane that is perpendicular to the axle of the wheelset and parallel with the rail. This vertical reference plane falls within an inch or so from either the outside of the wheel or the flange side of it.
This vertical reference plane passes entirely through the wheel tread, although the fracture itself starts at one location on the thread where it intersects the reference plane and progresses around the tread circumference.
The fracture may ultimately pass through the tread over its entire circumference and thus break off a solid ring as part of the tread from the near outside of the wheel or from near the inside, in which the broken off portion would be essentially the entire flange as a solid ring.
Also, the fracture may not progress entirely around the wheel circumference and then release as s continuous ring. Instead it may progress only part way around the circumference, and break off as just an arc shape. The fracture may continue to propagate and break off additional arc shapes in succession.
This is my understanding of what causes this fracture: Wheels and rail a
How might this mechanism be affected by repeated passage through retarders?
I don’t know if retarders would have much effect. Some kinds of track impact may cause the actual breaking away of the wheel material, but the initiating cause is the development of the stress crack.
The basic fundamental cause is the development of the zones of tensile stress on each side of the zone of rail contact. That happens without impact. Eliminating those stress zones seems like it would be a major threading of the needle in the manufacturing process. As I understand it, the malleability of the steel wheel tread is apparently intended and quantified by specification. But the tensile stress zones are apparently undesired and unanticipated.
There is discussion about adopting the practice of periodic wheel truing by reshaping the treads by grinding. The grinding would cut deep enough to take the hollowness out of the tread face. So it would cut deepest into the outer edges of the zone “compacted” by running under load. So that would remove the most embedded tensile stress. Actually, I would think the entire wheel tread, including the flange, would have to be cut down while maintaining the proper form until the hollow zone of the tread is eliminated. But even doing that will leave the work-hardened loading zone completely intact at the center of the zone, and then diminishing toward its edges where more metal will be removed.
Interestingly, Rio Tinto in Australia runs higher wheel loads than U.S. practice, and they have no failing wheels. It is said that they run multiple use wheels and true their treads and flanges on a regular basis.
The issue is likely not the ‘work-hardened zone’ in the affected tread, but the material cold-flowing under it. Think of it as the counterpart to martensite breaking up into platelets on the railhead at 315K axle load… or induction of gauge-corner cracking and then propagation.
Yes, the reprofiling would have to extend out to the face, and yes, that might thin the rim.
Look up the theory of the ‘magic wear rate’, which in theory would just get rid of SCC and other micro cracking or platelet deformation before cracks could turn in/down and propagate. Some of the early rail-grinding discussions involved ‘realizing’ this rate by organized means.
The Australians also figured out you could get safer performance and longer life by using a shorter roller bearing… something I did not see coming. It would not surprise me to find they have done their HAL homework and understand the wheel/rail system better. I would not be surprised to find ECP involved somehow.
Well, brake friction heat is said to play a role in the VSR wheel failures. An air brake application must dissipate a specific amount of heat to the atmosphere. If all brakes, during an application, set up simultaneously, each wheel should reach the same temperature in the same amount of time. ECP brakes would set up simultaneously.
However, conventional airbrakes will set up sequentially, and the ones setting up first, will get hotter during the brake application than the ones setting up later. So, the earlier/hotter wheels will likely reach a temperature higher than the uniform wheel/braking temperature rise of the wheels braking with ECP.
I wonder if some type of relatively rare anomalies in the practice of setting up brake service applications might explain why these VSR failures occur consistently, but so infrequently compared to the number of wheels in service.
From reading that report it sounds like a triple failure. Improper metalurgy in the wheels. To much deferred maintance waiting until they are just at the minimum before doing anything to fix the issue. And the last one is not enough inspections to catch the problems before they fail. The railroads have gotten way to reliant on technology to catch problems. Wheel dynamic impact sensors to catch flat wheels hot box dectection by remote. So instead of having people look at things with the mark 1 eyeball they go by what the computer says is good. Doing things like that leads to massive problems down the line that tends to cost millions of dollars when they fail. We have all heard it that the carmen are under pressure to get the trains out of the yard. So instead of fixing them properly they say they are good and pray they make it to the next 1000 mile inspection point. You are just lucky that PSR hasn’t caused a major TIH spill in a major city yet. The odds will catch up to the penny pinchers in the Boardrooms sooner than later and when it does I do not want to be a shareholder in the company it happens to be with.
How many truck accidents are there yearly because of unsafe, under standatd maintenance are there vs. train derailments because of your perception of railroad maintenance?
The Mark I eyeball is not as good a hidden defect detector as you may think it is.
https://www.fmcsa.dot.gov/safety/data-and-statistics/large-truck-and-bus-crash-facts