Why do unused railways rust and used ones do not?

[richieb1971]

I've been to several places where the amount of rust build up on a unused line has turned the whole rail to orange. This seems a bit of contrast compared to the exact same type of rail next to it, which is totally smooth even on the sides and has retained its smooth finish with absolutely no rust at all. I can see why the rail is shiny on top because of the traction but I don't know why the rest of the rail doesn't rust like the one next to it that is unused.

A prime example of this is at Nuneaton. They created a relief line (that has subsequently never been used to my knowledge).

 

[A-driver]

I would have thought that it's largely as unused railways are not maintained. Just left to rot and rust away.

 

[DaleCooper]

I did a bit of brainstorming and come up with the following ideas which may be complete nonsense:

Flange greasers
Vibration and friction shake off moisture and warm rail
Track on lines in use is replaced before rusting
Oil spray from various parts of the running gear
Cathodic protection due to track circuit currents

 

[L&Y Robert]

I would have thought that it's largely as unused railways are not maintained. Just left to rot and rust away.

This contrast was very noticeable last week where the disused Fleetwood branch peels off from the Preston - Blackpool North line. I too wondered about it.

 

[Harpers Tate]

I suspect that actually what you are seeing and comparing is
- an unused NEW piece of rail, such as you might find on a newly-laid piece of track yet to be used, or even a recently positioned length of new rail in the cess or 4ft awaiting installation
vs
- a piece of rail that has been in situ for some many months or more probably years.

New rust is orange. You'd find this on a fairly fresh piece of metal. Old rust is much much darker. You'd find this on something that has been in the open for many years.

In both cases, whether regularly used or not. See if you can find an old disused siding or mothballed track and you'll see dark rust on the sides and top. See if you can find a newly relaid rail that's in use and you'll see orange rust on the sides and a polished top.

 

[Peter Mugridge]

It's the train wheels - they act to polish the rails; they literally rub the rust off.

 

[L&Y Robert]

It's the train wheels - they act to polish the rails; they literally rub the rust off.

Well, yes, but not on the sides - the "web" of the rail. In the Fleetwood branch example the rail was more creamy coloured than orange. I thought at first it had been treated with something, and somewhere else - Preston I think - I saw pointwork where the web of the rail had been spray-painted white.

 

[WatcherZero]

Rails that have been painted are to counteract heat expansion, as they are a lighter colour they reflect more light and don't heat up as much.

 

[stockport1]

Rails that have been painted are to counteract heat expansion, as they are a lighter colour they reflect more light and don't heat up as much.

i have seen alot of this in italy.
--- old post above --- --- new post below ---
how long must rail be left rust before the pitting renders it useless?

 

[gazzak]

I'd have thought that it's the trains removing static water by the vibrations and shock of moving the rails.

 

[ASharpe]

My guess is that used rails are generally just covered in grime, oil, grease, muck, diesel(or coal) particulates, leaves, effluent, brake dust and so on. That stuff could get on the web and never be washed off by rain. Under all of that i'd expect to see a thin layer of rust.

 

[Mugby]

Many's the time an old piece of rail which has been lying on the cess for perhaps years and is excessively rusty has had to be plated or welded in as an emergency repair job.

It only needs a couple of trains over it to bring the rail head back to shiny again.

 

[Cliveblackpool]

Shiny mainline rails often (bit of light drizzle/ rain) soon turn yellow to orange during the Christmas/ Boxing day shutdown.

 

[GRALISTAIR]

I could go all technical and start talking about Pilling-Bedworth ratios and how stainless steel does not corrode because it it DOES corrode - and same for aluminium. I wil lawait some replies first.

 

[mbonwick]

Please do; I'll be able to see just how much of my metallurgy I have remembered correctly!

 

[edwin_m]

I could go all technical and start talking about Pilling-Bedworth ratios and how stainless steel does not corrode because it it DOES corrode - and same for aluminium. I wil lawait some replies first.

Are either of these materials actually used for rail, at least in anything larger than a ride-on miniature railway?

In my experience rails near where trains stop tend to be dark grey (on the non-shiny parts), probably because of the deposition of oil and, er, other matter. This fades to a mid-brown away from stopping places and unused but reasonably new rails tend to be more orangey.

 

[GRALISTAIR]

In my experience rails near where trains stop tend to be dark grey (on the non-shiny parts), probably because of the deposition of oil and, er, other matter. This fades to a mid-brown away from stopping places and unused but reasonably new rails tend to be more orangey.

These act as inhibitors.

 

[Dennis]

I could go all technical and start talking .....

Go ahead, I love a bit of technical stuff

 

[Trog]

In part new rails are more orangey because the steel used is not the same as it used to be. Most new rails are now Wear Resisting A grade as opposed to the Normal grade used in the past. Wear resisting A rail stays the new orange colour for much longer than normal grade rail, often years longer.

There are two reasons to paint rails, heat reduction and corrosion. Rails painted to help reduce eat build up are usually white, corrosion resistance generally involves a more glossy and slightly magnolia coloured paint containing glass.

As for unused rails it is true that if you put two rails in track and use one and not the other, the unused rail will rust faster than the one in use. To the extent that you often see chairs in unused sidings that appear to have had the jaw pushed off by the build up of rust and scale between rail and chair. I think maybe the vibration of use shakes the surface rust off leaving the rail cleaner, so it stays drier and thus rusts less.

 

[dgl]

Roughly (although there probably are a few errors in it)......

the reason why aluminium rusts but doesn't rust is that the rust (aluminium oxide) that forms on aluminium (signified by a dulling/tarnishing of the metal) quickly and therefor in a thin hard layer (due to the high reactivity of aluminium) . this thin layer essentially then forms a barrier stopping any further rusting. The fact that the layer is so thin and that it prevents any more rust forming means that essentially the aluminium has it's own rust-preventative coating.

The lower reactivity of iron prevents such a layer being formed and therefore the water can penetrate and such more rust forms and this then starts to become a problem as it reduces the structural integrity of the iron.

 

[GRALISTAIR]

Roughly (although there probably are a few errors in it)......

the reason why aluminium rusts but doesn't rust is that the rust (aluminium oxide) that forms on aluminium (signified by a dulling/tarnishing of the metal) quickly and therefor in a thin hard layer (due to the high reactivity of aluminium) . this thin layer essentially then forms a barrier stopping any further rusting. The fact that the layer is so thin and that it prevents any more rust forming means that essentially the aluminium has it's own rust-preventative coating.

The lower reactivity of iron prevents such a layer being formed and therefore the water can penetrate and such more rust forms and this then starts to become a problem as it reduces the structural integrity of the iron.

Pretty damned good start. With stainless steel (like aluminium) it is the Chromium Oxide which forms which is tough, adherent and extremely corrosion resistant. It needs oxygen!!!! to stay that way.

Iron Oxide (forms when iron/steel oxidizes) because of the unfavourable Pilling-Bedworth ratio, has a higher volume, is not adherent and spalls off. Various Iron Oxides are black, brown, red, orange etc.

 

[snowball]

the reason why aluminium rusts but doesn't rust is that the rust (aluminium oxide) that forms on aluminium (signified by a dulling/tarnishing of the metal) quickly and therefor in a thin hard layer (due to the high reactivity of aluminium) . this thin layer essentially then forms a barrier stopping any further rusting. The fact that the layer is so thin and that it prevents any more rust forming means that essentially the aluminium has it's own rust-preventative coating.

The lower reactivity of iron prevents such a layer being formed and therefore the water can penetrate and such more rust forms and this then starts to become a problem as it reduces the structural integrity of the iron.

However, weathering steel, used for some bridges and (under names like Corten) for some buildings, operates on the same principle that you've described for aluminium.

 

[DownSouth]

I did a bit of brainstorming and come up with the following ideas which ...

are mostly fairly reasonable guesses and not nonsense

Flange greasers ... Oil spray from various parts of the running gear

It is true that the general grime which accumulates on a railway does a decent job of providing barrier protection from rusting - but this only applies to the parts of the rail not contacted by train wheels.

Track on lines in use is replaced before rusting

Surface rust is not a problem, it just needs a train to run over it and scuff off the rust before the line can be brought back into normal use.

This is absolutely normal for many of the rural branch lines in Australia where poor crops will see trains running for as little as three months before lying dormant until the next harvest. When the next season rolls around, the operator simply runs the first empty train of the new season out to the end of the line at low speed and with a couple of ballasted flatcars (i.e. loaded with concrete sleepers) included in the consist to enhance the cleaning effect.

Vibration and friction shake off moisture and warm rail

It's more that the wheels scuff off the rust each time a train runs over it, in the same way that you can remove dullness from a kitchen knife using a honing steel. If you looked at a rail right after you would still see droplets on the non-contacted parts of the rail.

Oxidation is actually fastest when a rail is warm, and during wet weather the moisture in the air will be enough to assist it even if there are no droplets on the surface.

Even railways in the middle of deserts (e.g. the Trans-Australian Railway or Central Australian Railway) don't escape the problem of moisture as the overnight temperatures are cold enough for dew to form on the rails.

Cathodic protection due to track circuit currents

No.

AC track circuits don't provide cathodic protection, and the current runs through the middle of the rail with DC track circuits.