Why don’t railroad tracks rust away?

I had a dream about this post last night.

My wife and I were picnicing by a small lake, and there was a pair of tracks that ended. I showed her that they were the end of the tracks evident by not just the tracks ending, but these signs of never having been used (in the last few feet of track): the tracks’ paint was still intact (?!?), and the crown of the tracks still came to a shallow point, not having been flattened by the weight of trains (!?!).


My two cents: As has been pointed out, the rust on the surface inhibits the further corrosion of the rail. So why not paint the rail at the factory and have no rust at all? It turns out there is a good reason to leave steel uncoated. Along with rail, couplers, wheels, and axles are left unpainted (actually painting is prohibited by the FAR) so that any structural defects that develop over time can be detected. The steel alloys used have a nice tight oxide that acts as a barrier, as has been mentioned.

Absimia mentioned the chunks left over from a rail grinding operation. I believe any sizable pieces were probably from the grinder taking off the burr that forms at the top inside corner of the rail’s cross-section. I have a piece of rail from the old Union Pacific branch line to Ketchum, Idaho that shows a burr about one eighth inch sticking out towards the inside of the rail. Steel can be pretty mushy under big loads.

And speaking of mushy, DougC mentioned the flattening of the rail under load. The tire and rail do flatten against each other under the load of a train. A fully loaded freight car puts around 10 tons on each wheel and produces a flattened area approximately 1/4 inch by 3 inches. That explains why most of the top surface of the rail is shiny, in spite of the fact that it is curved.

From Corrosion Engineering Mars G. Fontana

Actually only partly true. Rust takes a number of forms. What you’re describing is good old ‘red’ rust (Ferric Oxide) Under that, you’ll find another form, Magnetite, or ‘black’ rust, which forms a nice air-tight boundry.

The difference between the two is that (very basically), red rust requires more oxygen to form, which is why you’ll find it on the surface, while black rust forms with lower exposure to oxygen. Rails pick up both kinds of rust, but the high volume-to-surface ratios and the increasing presence of black rust inhibit massive wasting of the rails, while not competely preventing it.

Rusting is actually a fairly complex set of electrochemical oxidation-reduction reactions. Technically, the rail is undergoing a reaction similar to that producing fire.

Back in the day… they used to have rails that were WOODEN, with a thin strip of iron attached to the tops. These would come loose and sometimes pop up through the floor of the cars - this was called a ‘snakehead’, and was, as you have discerned, rather dangerous