The world's railways provide millions of people with a fast way to get to work and visit their friends. They also transport tons of goods from the manufacturers out to depots for delivery to the shops and to the ports for sale to other countries. There are many different types of engineering jobs to provide services to keep all of this working.
The trains run on steel rails that carry the weight and guide the trains through the towns and cities at increasing speeds for a fast and safe journey. The railway is an extremely safe way to travel, but one engineering job is to keep the railroad safe by constantly checking the track.
Steel is Strong but can Still Crack
The rails must be checked to see that they are fixed solidly in place and that they are not developing cracks. Steel is very strong and the rails can last for a hundred years or more – but sometimes small cracks develop and if they are not found they can grow into big cracks.
Train wrecks not only kill people but they can cause massive environmental issues like the Canadian National disaster in 1999 [1] in which two crew died but also "approximately 2.7 million litres of hydrocarbons spilled and caught fire, damaging private property, public property and the environment."
The cracks sometimes start from the corners but the majority grow from inside the steel. Engineers have to design systems to look into the steel while the test system is travelling along the track.
The First Rail Crack Detector
Back in the early 1900s the railroads found that many of their rails were cracking and there were some tragic rail disasters where many people died. A dreadful example is the Manchester NY train Wreck of 1911 [2] in which 29 people died and 62 were injured. The railroads approached an engineer and inventor by the name of Elmer Sperry to develop a way of finding the cracks while they were small and before the rail broke.
Elmer successfully created a system that could be run over a rail and look inside to find flaws in the steel. The system worked by running a very high current through the rail and monitoring the magnetic field it produced. If the steel was good the current went straight through but if the steel had a crack then the current had to go round the defect and this produced detectable changes in the magnetic field.
This system is still in use on Sperry Rail inspection trains in North America today alongside many new techniques.
Engineers Design Ultrasonic Inspection of Rail
The electro-magnetic systems are excellent at saying that there is a crack in the rail but a method was needed that could give more information about the size and shape of the feature the system could see. There are many holes and shapes in the rail that are not defects.
The engineers designed a system that uses high frequency sound [3] to give a picture of the inside of the rail steel. The image can be built up in the same way as an ultrasonic scan of a baby inside it's mother womb.
The Ultrasonic Echo
The way the ultrasonic systems work can be compared to an echo system sounder on a submarine or fish-finder. The system transmits a "blip" and then listens for an echo. The time it takes for the sound to come back tells the system how far away the "reflector" is.
For the submarine, the sound reflector is the bottom of the sea as it needs to know how much room it has to maneuver. For the rail inspection system the reflector is normally the bottom of the rail. If an echo comes back early then there is something in the center of the steel. The time between the "blip" and the echo indicates how deep the feature is.
Future Work for Design Engineers
The inspection systems work very well but there are still some weaknesses that engineers are working on. The rail track is a very harsh environment to inspect in and the temperatures can vary between minus 40 degrees and plus 140 degrees Fahrenheit. There are massive pieces of metal required for what is a delicate operation as well as water; grease and dirt everywhere.
All railroads want to keep their track clear so that freight and passenger trains can get through on time. They do not want test vehicles in the way and so the inspection systems have to be able to test at the speed of the traffic.
A Major Limiting Factor – The Speed of Sound
One thing that is always going to limit how an inspection system can be designed by engineers is the speed at which the sound travels down through the rail to the bottom and reflects back up.
In fact the time it takes is too long for a system that wants to travel at very high speed. If travelling fast, the test system will send a "blip" but may not be there to hear the echo!
Engineering Jobs in Rail Inspection
The design and build of these test systems require engineers with particular skills but then other engineers are needed to run the systems out on the railroad in almost every country of the world; in summer and winter; in the forests and out in the desert.
These are just a few examples of the types of job that engineers do every day on the railway to keep it safe for us to travel on.
[1] Major train wreck Transportation Safety Board of Canada - Rail Report Dec 1999.
[2] Early train disaster Manchester NY train Wreck of 1911.
[3] Non Destructive Testing - Basic Principles of Ultrasonic Testing
Resource: Brotherhood of Locomotive Engineers and Trainmen - Becoming an Engineer
Resource: University of Connecticut - Railroad History Archive
Dave Corby - Dave Corby is Director of Engineering Software for a large American inspection company.
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