Oil Trains & Lag Screws

[tdmidget]

Bucky, give it a rest. You have no idea what you are talking about. You don't know what a shear force is and you invent terms like "bowing range". They break as a result of single shear force and they break exactly as expected, right at the start of the thread engagement. Tension is not a factor, other than this fastener will not develop enough tension to prevent lateral movment.

[Euclid]

They have not given all of the details about the lag screw failure and rail movement in the Mosier wreck.  It may have only been a case of spreading rails as their graphic shows.  However, the CN wreck report gives a lot of detail, and it indicates that there was gradual gage widening that eventually culminated in the rail tipping over.  What they say about the gage widening appears to match what U.P. has indicated about gage widening at Mosier.  I perceive that the cause of the CN and UP wrecks was basically identical.  Both began with breaking lag screws.

What is less clear in this news is exactly how the forces break the lag screws.  It is said to be a combination of bending and shear stress.  Apparently, the shear force is applied right under the screw head between the bottom of the plate and the top of the tie.  Yet, the screws don’t break there.  So apparently, the term “shear” only refers to the nature of the force, and not to an actual shearing of the bolt.  What happens is that the shear force is applied under the head, and then it bends the descending shank along its length in a bowing fashion.

This bending along the shank causes fatigue that has its highest concentration around toward the bottom of the bowing range, which appears to be about 2-3” below the head of the screw.  At that point of concentrated bending stress, the bolt shank breaks. 

Therefore, the actual parting of the screw shank is not due to being sheared. Instead, the parting is caused by the fatigue cracking induced by repeated bending eventually causing the shank to break.   

Likewise, while bending force is involved in stressing the screw, there is no actual permanent set induced introduced to the screw shank by the bending force.  After the breaking, the shank appears to be straight as it was originally made. 

The repeated bowing action of the screw shank also crushes surrounding wood, thus compromising the thread engagement between the tie and the screw. Therefore, when the screw breaks, the few threads above the break are not sufficiently engaged with the wood to provide any significant holding power above the break. 

[AnthonyV]

tdmidget & Norm:

I agree, especially given that the tie is predrilled prior to driving the screw.  Here is the recommendation from the Lewis Bolt & Nut Company:

For screws going into wood there should always be a pre-drilled hole. Without a hole the difficulty installing a screw gets much worse, the holding power decreases and the danger of splitting the wood increases. A good rule of thumb is that the pre-drill should be slightly smaller than the root diameter of the thread. It is best if it is a little larger in very hard wood and a little smaller in soft wood. Some adjustment may be required depending on the particular conditions. Some common recommended sizes are listed below.

Evergrip ® Spike: 11/16”
Permagrip ® Spike 7/16”
15/16” Screw spike 11/16”
5/8” Recessed Head timber Screws: 3/8”
3/4” Recessed Head timber Screws: 1/2”

Here's the link: http://lewisbolt.com/about/faq/index.html

 

[Norm48327]

AnthonyV

I wonder how many lag screws get overstressed during tightening.  It would be interesting to investigate the condition of the screws on tangent track.

 

One would like to think they are made of a grade of steel sufficient to prevent breakage while inserting in an oak tie and have enough corrosion resistance to last the required time till replacement. Looking at the screws in the photo, that does not appear to be the case. Quality steel should strip the threads in the tie long before breaking.

[tdmidget]

AnthonyV

I wonder how many lag screws get overstressed during tightening.  It would be interesting to investigate the condition of the screws on tangent track.

As I have previously pointed out, it would be very difficult "overtighten" a steel screw in wood, even with 4 diameters of engagement, unless it was an exotic wood like Azobe. Even harder with a 2 start thread and also hard for it to stay tight. Multiple start threads are used for rapid movement, not for tension.

[tdmidget]

AnthonyV

 I almost made the same mistake. Notice that the drawing calls for the "root" or gullet of the thread to be a 1/16" flat. If you use the theoretical gullet of a 4 pitch thread you would be correct. BUT you made me check my numbers and I had an error. To get the 1/16 flat at the gullet you would have a minor diameter of .75. This gives a cross section of .442". I some how figured the minor 1/16" too large. Thanks for questioning it. It makes the difference between the screw and a slightly larger cut spike even more dramatic.

 

tdmidget

A 5/8 cut spike has a cross section of .3906 square inches. The BNSF screw, which is probably typical, has a cross section of.5050 in the minor diameter, which is where every example shown has broken. A 3/4 cut spike would have a cross section of .5625 square inch and likely be cheaper. It would not cost much to put smll grooves on it like a ring shank nail, which are a mofo to pull out.

The stress riser of the threads cannot be disregarded, as cannot the obvious corrosion.

 

 

 

 

tdmidget:

What did you use for a minor diameter for the lag screw?

I used 11/16" for the root diameter (from the drawing in the link above) and got 0.371 sq in cross section.

 

[AnthonyV]

I wonder how many lag screws get overstressed during tightening.  It would be interesting to investigate the condition of the screws on tangent track.

[AnthonyV]

tdmidget

A 5/8 cut spike has a cross section of .3906 square inches. The BNSF screw, which is probably typical, has a cross section of.5050 in the minor diameter, which is where every example shown has broken. A 3/4 cut spike would have a cross section of .5625 square inch and likely be cheaper. It would not cost much to put smll grooves on it like a ring shank nail, which are a mofo to pull out.

The stress riser of the threads cannot be disregarded, as cannot the obvious corrosion.

 

tdmidget:

What did you use for a minor diameter for the lag screw?

I used 11/16" for the root diameter (from the drawing in the link above) and got 0.371 sq in cross section.

[tdmidget]

A 5/8 cut spike has a cross section of .3906 square inches. The BNSF screw, which is probably typical, has a cross section of.5050 in the minor diameter, which is where every example shown has broken. A 3/4 cut spike would have a cross section of .5625 square inch and likely be cheaper. It would not cost much to put smll grooves on it like a ring shank nail, which are a mofo to pull out.

The stress riser of the threads cannot be disregarded, as cannot the obvious corrosion.

[blue streak 1]

What was the weight of an overloaded car ? 

Many of the home improvements shows often state that some woods do better with nails than screws.  Screw holes drilled sometimes are better.  So are screw spikes drilled or just run into the crosstie ?  Would expect that type of wood for cross tie might have different results ?

 

 

[Buslist]

Euclid

 

 

 

 

 

 

 

 

 

 

Here is what the article says about the basic reason to prefer lag screws over cut spikes on curves in the first place:

Rail consultant and former industry regulator Steven Ditmeyer said a series of Burlington Northern derailments in the 1990s in Washington state all involved sheared off railroad spikes. Investigators eventually determined overloaded cars, a lack of lubrication between the wheel assembly and the body of the tanker cars, and not enough gravel in the railroad bed combined to put strain on the track along curves.

That strain loosened the spikes holding the rails to the rail ties and pushed the rails apart, much like the recent Oregon derailment, he said.

 

For the record Steve Ditmeyer was never a federal "regulator". He did work for FRA but was head of their research group. His major focus was PTC related work. The Aries system at BN was his baby, he was quite bitter when the BN did not implement it. His tenure at FRA was short.

[Electroliner 1935]

Nice to see the Made In America since 1927 line.

[AnthonyV]

tdmidget

Does anyone know the dimensions of these lagscrews?

 

Here is some info on what they call BNSF-style lag screws.

www.lewisbolt.com/products/Square_Head_Timber_Screw_BNSF_Style/index.html

 

[tdmidget]

Does anyone know the dimensions of these lagscrews?

[Euclid]

BaltACD

           Euclid said:  Well if reducing inspections to minimize work leads to train wrecks, it seems penny wise and pound foolish.

 

Balt ACD said:  Who is reducing inspections?  FRA sets the required inspection standards for the various classes of track and the carriers either meet or exceed these inspection standards already.  If the inspection item (lag screws) now creates more work in their inspection than a competing technology - the lag screws will shortly be replace by the competing technology.

 

By “reducing inspections” I am also referring to withholding new inspections needed to address newly discovered dangers.

In this case, the technology that competes with lag screws are cut spikes.  Lag screws were chosen as a substitute for spikes on curves because they were thought to reduce maintenance cost.  Now we learn that the lag screws have a hidden cost to cover the inspections needed to reveal their developing failure.  So what to do?

You either pay the added cost for inspecting lag screws while enjoying the reduced cost of their better reliability–or—you revert back to the less reliable spikes and live the extra cost of their unreliability while enjoying the lower cost arising from a lower requirement for inspection. 

I have a feeling that neither one is the wise choice.    

Here is what the article says about the basic reason to prefer lag screws over cut spikes on curves in the first place:

Rail consultant and former industry regulator Steven Ditmeyer said a series of Burlington Northern derailments in the 1990s in Washington state all involved sheared off railroad spikes. Investigators eventually determined overloaded cars, a lack of lubrication between the wheel assembly and the body of the tanker cars, and not enough gravel in the railroad bed combined to put strain on the track along curves.

That strain loosened the spikes holding the rails to the rail ties and pushed the rails apart, much like the recent Oregon derailment, he said.

[schlimm]

Norm48327

 

 

Euclid

I see no reason why these lag screw installations could not be reliably inspected.

 

 

Care to tell us what "experience" you have in inspecting them? If you have a plan that works please make it public so the railroads can learn from it.

 

And what is your "experience" with this topic?

[Euclid]

Norm48327

 

Euclid

I see no reason why these lag screw installations could not be reliably inspected.

 

 

Care to tell us what "experience" you have in inspecting them? If you have a plan that works please make it public so the railroads can learn from it.

 

Norm,

The plan has been public since the TSB of Canada published in shortly after investigating the CN Fabyan Bridge derailment in 2012.  Here it is:

 

When conducting inspections of curves, turnouts, and bridge decks with screw spikes, please be governed by the following:

 

• Walk the entire curve inspecting both the high rail and low rail.
• Look for signs of plate movement.
• Use the geometry car printouts to identify areas of concern. Inspect all areas where the test car reports show a combination of wide gauge and alignment defects on either rail.
• Observe the washer head and look for shiny marks on the plate as evidence of possible broken screw spikes.
• Take a steel rod (lining bar) and strike every tie plate, noting any loose or bouncing screw spikes, which would indicate breakage.
• Hand inspect every 10th tie by physically attempting to pull on all the screw spikes on that plate to see if they can be pulled out of the tie by hand.
• At transition areas (wood ties territory going from cut spike to screw spikes and wood ties territory with screw spikes going to concrete ties) hand inspect every tie on both rails for 10 ties beyond the transition point.
• Additional inspection of screw spikes will be required, by unscrewing them from the tie. The Inspection intervals will be as follows:

1. curves 1/2 degree to 6 degrees - Every 100 feet on the high rail remove the screw spike from the tie and inspect. At a 50 foot offset from the high rail, remove and inspect the screw spikes every 100 feet on the low rail as well.
2. above 6 degrees curves - Every 50 feet on the high rail remove the screw spike from the tie and inspect. At a 25 foot offset from the high rail, remove and inspect the screw spikes every 50 feet on the low rail as well.

• Once the screw spike has been removed from the tie inspect it for cracks and other obvious signs of wear.
• Observe the unthreaded area of the screw spike. If this area shows 1/8″ reduction in diameter continue to monitor the curve closely. If the area shows 1/4″ reduction in diameter, the screw spikes should be incorporated into a planned program for replacement.
• When a broken screw spike is found, check the surrounding area to determine the extent of the broken screw spikes.
• Areas where ballast has been left over the plates should be cleared to enable inspection of the screw spikes.
• Limit operating speeds over areas of concern until repairs can be made.

[BaltACD]

Euclid

Well if reducing inspections to minimize work leads to train wrecks, it seems penny wise and pound foolish.

Who is reducing inspections?  FRA sets the required inspection standards for the various classes of track and the carriers either meet or exceed these inspection standards already.  If the inspection item (lag screws) now creates more work in their inspection than a competing technology - the lag screws will shortly be replace by the competing technology.

[Norm48327]

Euclid

I see no reason why these lag screw installations could not be reliably inspected.

Care to tell us what "experience" you have in inspecting them? If you have a plan that works please make it public so the railroads can learn from it.

[Euclid]

Well if reducing inspections to minimize work leads to train wrecks, it seems penny wise and pound foolish. 

[BaltACD]

Euclid

BaltACD

Euclid

I would think the better approach would be a combination of improving the strength of the screws, determining their lifespan based on use, and replacing them within that time span.  They could also couple that with periodic inspection to see if their lifespan is on course with its prediction. 

If you can't reliabilly inspect something to determine failure, it makes no difference what it's life span before failure is - especially if the life span before failure is different than the rest of the inspectable track structure.

I see no reason why these lag screw installations could not be reliably inspected.  That alone would prevent failure.  After learning what happened in the CN Fabyan Bridge derailment, the TSB developed specfic instructions for how to inspect the lag screw systems. It is additional work, but it is effective and necessary. 

Then with what is learned in the inspections, they could determine the life of such lag screw installations.  Knowing that lifespan would then be used to give further insurance in addition to the direct inspection for lag screw condition.  This all should have been obvious after the CN wreck in 2012.

Remember you are dealing with railroads - additional work is verbotten!  Maintenance items are adopted as standard to decrease work, not increase it.

[Euclid]

BaltACD

 

Euclid

I would think the better approach would be a combination of improving the strength of the screws, determining their lifespan based on use, and replacing them within that time span.  They could also couple that with periodic inspection to see if their lifespan is on course with its prediction.  

 

 

If you can't reliabilly inspect something to determine failure, it makes no difference what it's life span before failure is - especially if the life span before failure is different than the rest of the inspectable track structure.

 

I see no reason why these lag screw installations could not be reliably inspected.  That alone would prevent failure.  After learning what happened in the CN Fabyan Bridge derailment, the TSB developed specfic instructions for how to inspect the lag screw systems.  It is additional work, but it is effective and necessary. 

Then with what is learned in the inspections, they could determine the life of such lag screw installations.  Knowing that lifespan would then be used to give further insurance in addition to the direct inspection for lag screw condition.  This all should have been obvious after the CN wreck in 2012.

[BaltACD]

Euclid

I would think the better approach would be a combination of improving the strength of the screws, determining their lifespan based on use, and replacing them within that time span.  They could also couple that with periodic inspection to see if their lifespan is on course with its prediction.  

If you can't reliabilly inspect something to determine failure, it makes no difference what it's life span before failure is - especially if the life span before failure is different than the rest of the inspectable track structure.

[Euclid]

tdmidget,

I meant to refer to the article saying U.P. is replacing their screws with spikes, and have edited my post accordingly.  I am somewhat mystified by their reasoning for the change.  Screws were adopted because their superior holding power is an advantage on curves compared to using spikes. 

I am guessing that the reason for changing back to spikes is that their progressive failure is visually predicted by seeing them somewhat backed out of their holes.  Whereas spikes with the better holding power do not back out, but rather, they break with no visual indication. 

I would think the better approach would be a combination of improving the strength of the screws, determining their lifespan based on use, and replacing them within that time span.  They could also couple that with periodic inspection to see if their lifespan is on course with its prediction.   

[tdmidget]

UP is replacing screws with spikes, not BNSF.

ECP brakes would have made no difference. An emergency application would have been exactly the same.

Without having dimensions of the screw I can't say for sure but if the shank Diameter of the screw is the same as the cross section of a cut spike then the minor diameter has a less than half of the area of the cut spike. I would have thought that going to a round fastener would mean maintaining that area, which is where the shear strength of the fastener comes from.

[Euclid]

Now we know what "one or more" broken lag bolts looks like.

Here is the link again from the above post:

http://www.thedalleschronicle.com/news/2016/jun/25/railroad-replace-bolts-after-mosier-derailment/

As Norm says, some of the bolts, do indeed appear to have been broken for a long time.  Overall, they appear to be woefully inadequate for the task unless their service life were known and were conscientiously limited to its length.  That service life would also include the life of the ties as the bolts damage the threaded bores in the wood.  There is not much good in inspecting the track every couple days when you have this kind of mass failure underway.

Interestingly, the article mentions ECP brakes and Sarah Feinberg contenting that they could have reduced the number of cars involved, and also limited the breaching. 

I would say, that from what we know about the derail cars dragging in line for 3/8 mile prior to the pileup, derailment sensors on each car would have prevented the pileup, the punctures, and the fire altogether. 

The article says this:

There was little prior focus on failed lag bolts, and there appears to be only one other instance in which they caused a derailment, in Canada’s Alberta Province in 2012, Gard said, adding a further look is needed.

This is the CN Fabyan Bridge derailment that we have been discussing here.  In my opinion, there should have been a lot of focus on the potential failure of lag bolts after that wreck.  It was fully investigated and it should have been a wakeup call to the railroad industry.

What is most amazingly strange is the U.P. response that on 530 miles of track curves using lag bolts, they will replace those bolts with spikes.     

[Norm48327]

Judging by the corrosion, those bolts have been broken for some time.

[ORNHOO]

for the "after" picture: http://www.thedalleschronicle.com/news/2016/jun/25/railroad-replace-bolts-after-mosier-derailment/

zugmann

Can I point out that Norm just screwed the whole thread?

 

Sorry.. I couldn't resist any longer.

 

 

Norm48327

 

 

 

 

 

[ORNHOO]

for the "after" picture: http//:www.thedalleschronicle.com/news/2016/jun/25/railroad-replace-bolts-after-mosier-derailment/

zugmann

Can I point out that Norm just screwed the whole thread?

 

Sorry.. I couldn't resist any longer.

 

 

Norm48327

 

 

 

 

 

[Overmod]

NDG

Safety First.

Apparently not as First as it ought to be to Ackman, Harrison & Co.  Especially since I don't think it's dawned on some railroads that there is an enormous potential problem with lag-screw fixation and detection of some common problems with it... problems that may not have a good answer other than people ON the tracks with test equipment they know how to use.

There is also this, from Transport Canada (linked from the report NDG provided, but you have to read down past the newsworker tolerance limit to get there)

https://www.documentcloud.org/documents/2906493-TRANSPORTCANADASTATEMENTSTOCBC.html

Having established the point that it's ill-advised and 'not in the interests of Safety First, Last, and Always' to cut these trackwork positions arbitrarily ... I got angrier and angrier at the newsworker spin on this story as I got further into it.

"For the last 10 years in a row, CP has been the safest Class 1 railroad in North America, measured by train-accident frequency," Martin Cej, the railway's assistant vice-president of public affairs, said in a statement emailed to CBC.  "The recently announced temporary layoffs are the result of lower car volumes and softening demand in a lacklustre North American economy — factors that are affecting all railroads, not just CP."

And then, the story starts discussing all the recent derailments ... complete with de rigueur flaming oil-train picture ... on CN, which last I looked was a different railroad run by different people.  Then they mention that only two of their thirteen (horrors! how unsafe!) derailments were on  CP after all...

And then it starts quoting people who think the answer is more and more regulation and oversight by TC and other regulators, as if more bureaucracy was the common-sense answer to safety problems on the railroads.  I was waiting for a comment on Lac Megantic, and sure enough it provided some of that, too (as if, perhaps, CP's track maintenance had contributed to that accident?)

In short: very important message, delivered in an increasingly reprehensible way.  It'll be interesting to see if CP changes its tune on the 500 layoffs as the evolving story of the lag-bolt fixation problems gets better detailed...