Why don’t railroad tracks rust away?

They’re not made from stainless steel, are they? And I’ve never seen a painting crew on them. Yet they seem to last forever.

They do rust, if they’re not being run over by trains on a regular basis.

We had a few rail lines near our place where I grew up, and those tracks that weren’t used on a regular basis (say, once a day or more) would get slightly rusty across the top. The tracks that were used on a regular basis stayed shiny.

(I also remember seeing that item referred to in a western movie once. Two lost cowboys reached a set of railroad tracks, the first one thought they were saved, but the second one pointed out the rust on the tracks and claimed that this particular line couldn’t have been used more than once a week.)

Good question!

My father was in charge of track maintenance for the RF&P RR here in VA for nearly 40 years, and he told me that rails that begin to show signs of rust and wear are quickly replaced. There is simply too much liability exposure not to replace track when it begins to go bad. You don’t see rusted track because it is replaced before it ever gets to that point (at least on a line that is active).

Lots of the former New York Central tracks that are not used anymore (especially a lot of the sidings near North White Plains) are rusted over. The ones used for regular service are shiny. I presume that the friction of the trains rolling over them keeps them nice and smooth. Also, tracks which are used regularly are replaced fairly regularly when they wear down.

In addition, rust actually forms a barrier to further corrosion by blocking oxygen from reaching to the bare metal. Once something rusts a little, the rate of corrosion slows down, so a big solid chunk of rail is unlikely to rust to any large degree in just a few years.

Tranquilis is on the right track. Badom-tschhh!

People are used to rust as something that happens to their cars. But the rust you see is in the body–very thin steel. Rusting will actually go through it. But if you look at the underside of the car, there are other metal parts that are rusted, like axles. But they are thick, and a low surface area/volume ratio.

Rails also have a low ratio. But they do rust. It’s just slow.

Cracking of tracks from metal fatigue is more common. I think this happens before the rails have a chance to rust enough to be a problem.

      • The metal alloy that the rails are made out of is somewhat resistant to rust, and the tops of the rails stay clear from abrasion of the train wheels. Another point is that the top of the rail is normally curved, but flattens out undeneath the weight of a locomotive wheel. If you look at the sides of the rails, you can see the normal corrosion that forms as an initial barrier, as Tranq noted. That barrier does eventually give way to the familiar brown flaky stuff though.
  • They don’t just use stainless steel for the rails, mainly because it’s quite a bit more expensive than regular steel, but it’s also more difficult to cut and weld. - DougC

If a thin layer of rust helps insulate the track, why do I remember seeing a machine come by every now and again that seemed to scrape off the top layer on the top of the rails? (I lived by railroad tracks as a kid). This big old grinder thing would come by and afterwards the tracks (on top, but not on the sides where, as others have pointed out, they are rusty) were smooth and shiny and there were rusted metal shavings laying around the tracks (usually pretty big chunks of them).

Did they do that specifically to help the tracks be smooth? (and presumably cut down on friction?)

Responding to Absimia’s post, rail grinding is indeed used on heavily traveled main lines to smooth out the top of the railhead. Grinding is needed because over time, the top of the rail develops gouges and indentations, particularly if the wheels of a passing train lock up under emergency braking.

The problem with these low spots is not so much the rough ride or increased friction that result, but that the impacts of wheels hitting them at speed cause stresses on the rail that may result in premature failure.

There is also a need for a clean electrical contact between the rails and wheels to allow the signalling system to function, and on an electrified route, for the motive power itself.

This would be true, but rust is a soft and powdery substance, and seldom lasts long enough in one spot (due to weather, mechanical disturbance, etc.) to form a barrier. This is why things made of iron tend to rust out faster than things made of aluminum.

Umm, are you saying aluminum rusts? Going back to my HS chemistry rust is iron oxide. As Al has no iron in it, it cannot rust. It can corrode, don’t get me wrong, but no rust.

Train track rails are MASSIVE. Sure, they will rust. Even if the tops are polished regularly by passing trains (that also wear them down) they will rust from the sides and bottoms. It will just take a Hell of a long time before they are weakened by rust.

HS chemistry was a long time ago, then, was it? :smiley:

Rust is oxidation, but not necessarily oxidation of iron. Iron rust is iron oxide, aluminum rust is aluminum oxide, etc. The effect referred to above is that iron oxide is very brittle compared to iron, and will rapidly flake off and expose the iron underneath to the air. Aluminum oxide is not so, and tends to remain as a thin layer of rust on the surface of the aluminum, protecting the rest of the hunk of metal from exposure and further rusting.

      • Yea, I remember those things too. If it was at night, you could see the sparks from the grinding. I don’t know what it does, but it doesn’t do it very often. Where I live, clean mild steel will rust completely brown in a matter of a month or so if left outside, but the train tracks stay shiny… - DougC

re: Aluminum “rust”: It’s whitish and usually appears in little “blooms” rather than as an overall coating as in iron oxide rust. Aluminum corrosion causes pitting, which in turn can often result in cracks propigating from the pits, and then in failure of the aluminum part. Just like in a steel car body panel, you can have aluminum corrosion under the paint of an aircraft.

Total trivia: As I recall, corrosion in magnesium results in short little squiggles that look almost like the worm damage (wood borer insect, actually) one sees in old furniture, only smaller.

We had a branch line in town that was torn up about five years ago (southern Saskatchewan), and the rails that formed it were dated, most of them were from the early teens, and it was never a highly travelled branch (probably in the forties there were four or five trains a day), so that shows that the rails can last a long time. Of course when you are dealing with a six inch thick rail, its gonna take a long time for it to rust through…and the rails are also exposed to the air not sitting in water constantly so they do tend to dry off, which will slow the corrosion process.

JCHeckler - That squiggly corrossion is called “filiform” it forms under paint and can occur on any painted metal not just magnesium.

I read a book not too long ago (sorry, forgot the name) about the NYC subway system. Oddly, it said that the shiny, new-looking rails were actually old, worn rails that needed to be replaced, and the old, rusty-looking rails were actually the new ones they had just put in.

Also [/hijack?], I read in some book about the 19th century that worn-down railroad tracks in the American West used to split while the train was going over them and shoot up through the floor (over the wheels), often killing or injuring lots of passengers. Anyone know if that’s true?