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Rail Industry Contributed Content Home

July 2014



Mechanical Posting

Design Concept for a Safer Oil Train





By Ron Keagle

This is a bold design concept for a high-speed derailment control system applied to crude-oil trains that reduces the destructive forces that rupture tank cars during a derailment. It does so by limiting the tendency for cars to accordion and pile up into a tightly compacted heap. It is this heaping of cars that creates a practically immovable obstacle standing in the path of the oncoming cars behind it. The kinetic force of those oncoming cars colliding with the unyielding heap of cars can easily crush and burst any tank car caught in the impact zone.

This system will not prevent derailments, but it will help stabilize the derailment process for the purpose of reducing equipment damage. It does this by sensing a derailment the instant it begins, and automatically introducing a novel braking control feature that creates tension through the derailing cars. The tension prevents the common, compressive force that causes cars to jackknife and pile up. The application of tension works in conjunction with the highest integrity couplers and drawbars in order to transmit the tension without parting the train within the derailed cars.    

This system combines electronically controlled pneumatic (ECP) brakes, derailment sensors, a novel “smart braking” feature, tank car truck safety chains and possibly improved couplers or semi-permanent solid drawbars. All of these features cooperate to keep derailed cars coupled together and “stretched” for the purpose of protecting tank-car vessel integrity.  

In conventional practice without this system, once a derailment begins, either uneven braking force or the extra resistance of derailed cars can cause the slack to run in against the derailing cars. This compressive force will jackknife the derailing cars and cause them to begin piling up into a tightly compacted heap. As more cars enter the pileup, it grows in weight, becoming a greater obstacle that resists the forward shove of the oncoming cars behind the derailment. 

In the case of tank cars carrying highly flammable crude, if just one car ruptures, its spilled oil will immediately encounter multiple sources of ignition from the rending steel. Once burning, that spilled oil will engulf the closely stacked heap of tank cars, thus giving the fire ample opportunity to grow as it involves more tank cars. 

The successful performance of this system is faced with a considerable challenge in stabilizing the chaotic forces in a high-speed derailment. However, that success is not just a matter of working or not working. It will succeed or fail to varying degrees. Fortunately, the laws of physics work in favor of success because the ability of this system to succeed is the greatest at the highest speed where the potential for destruction is also the greatest. So, even if jackknifing cannot be completely prevented, there is still substantial benefit in delaying it as the speed drops. 

Here are the five basic components of this concept:



1. ECP brakes

The cars in this safe oil train consist are equipped with ECP brakes, and intended for unit train operation where all cars are identical. 

2. Derailment sensors

Every tank car in the train is equipped with derailment sensors that detect a derailment at each car truck the instant that it happens. Their primary role will be to monitor vibration and elevation of the tank car body relative to the top of the rail. The sensors will transmit their data to the ECP brake controller on the locomotive by way of the ECP brake control cable running throughout the train.

3. The smart emergency control feature of the ECP brake system

Compared to standard pneumatically controlled automatic air brakes, ECP brakes offer greater brake control flexibility as a fundamental attribute of the ECP system. The “smart emergency control” feature, which is key to this safe oil train concept, is a natural extension of that basic ECP attribute of control flexibility.  

According to data from derailment sensors, when any car derails, the ECP controller will know the exact location of the derailment within the train. The instant a derailment begins, the ECP controller will shift to add an airwave signal to back up the signal cable running throughout the train. It will then block the automatic emergency braking response that is normally executed when the ECP communication cable breaks. Next, it will automatically initiate the smart emergency control system that will begin by applying maximum braking to the cars behind the initial point of derailment, and apply relatively less braking to the cars ahead of that point.
   
This differential braking will create tension between the cars ahead of the derailment and the cars behind the derailment; the tension will also extend through the cars that have derailed, but remain coupled together. This tension extending through the derailed cars will cause them to resist the tendency to jackknife and begin a pileup.   

The application of the differential braking force will be an automatic response of the ECP controller, executed according to an algorithm that will determine the exact amount of braking force to apply and the amount of time used to raise the braking force to the maximum called for. Certain circumstances may call for a gradual ramping up of brake force in either of the two independent braking ranges of cars. 

In order for this braking formula to make such decisions for brake force and application timing, it will factor in variables such as train tonnage, train speed, number of cars, location of the derailment in the train and location of the train on the line. The objective will be to create the maximum tension across the range of derailing cars without pulling the train in two in that vicinity.

Data showing the location of the train at the time of the derailment will indicate such features as track curves, degree of curvature, grades, bridges, tunnels, towns, grade crossings, switches, and other track features. The system will account for the effect of these features when determining the braking response.   

During this automatic smart braking response, a manual override is provided so the engineer can make a full emergency application if there is any reason do to so. The braking algorithm may also call for moderate pulling power from the locomotive if there are too few cars ahead of the derailment to generate tension from differential braking.

4. Couplers

This derailment stabilization system depends on tension pulling into a derailment as it happens, which in turn depends on the derailing cars remaining coupled together for as long as possible. However, the strength of couplers and draft gear, and coupler connection integrity are limited by the standardization of these components. If these attributes were enhanced beyond standard equipment, it would render the tank cars to be non-interchangeable, but would open the door to the highest possible performance of this system. Also, if the cars were non-interchangeable, they would not require a dual mode braking system to operate while coupled to cars with conventional air brakes. 

5. Truck safety chains

This traditional feature is included as a supplement to help stabilize the cars while they are placed under tension during a derailment for the purpose of preventing them from jackknifing. The chains tend to retain the trucks in a load carrying position during a derailment. 

Ron Keagle is a product development mechanical design consultant working on commercial products and industrial equipment. Email him at keagledesign@gmail.com

Note: This article is condensed from a more detailed version, which is available upon request from the author, who welcomes further discussion and correspondence on this concept. 
 




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Keywords

Browse articles on oil trainhigh-speed derailmentcrude oiltank carsECP brakesderailment sensorssmart brakingcouplersRon Keagle

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