Rusty rails

[Railcar]

Th sections of rail left in the 4ft or 6ft (presumably for fitting some time later) are brown with rust. Running rails are not rusty, they are steel-grey. Is there some treatment that the railing gangs apply? As the running rails are the earth return for electric traction, is that a factor?

 

[GardenRail]

Rails naturally go rusty when not used. Even on current running lines, like little used sidings and loops. It's the trains that keep them clear of rust. No traffic, they go rusty. The rails in the 4ft do not affect current.

 

[The exile]

In the right weather conditions, the contact surface can go rusty in less than a day.

 

[stuving]

I took the question to be not about the contact surface, but the rest, which means the sides really. In new rail the sides are, well, rust coloured. In rails in use they are dark, grey-brown or even black and often mucky.

I've always thought that was due to oil and grease escaping from trains' engines, axles, and other mechanical bits. But thinking about it, why would a modern electric train have that much oil and grease to chuck about? There's also de-icer and flange lubricant, which might spread away from their localised places of application to some extent. But is there anything else going on? Do rails now take longer to darken after being installed than they did more than 50 years ago?

 

[John Webb]

I took the question to be not about the contact surface, but the rest, which means the sides really. In new rail the sides are, well, rust coloured. In rails in use they are dark, grey-brown or even black and often mucky.

I've always through that was due to oil and grease escaping from trains' engines, axles, and other mechanical bits. But thinking about it, why would a modern electric train have that much oil and grease to chuck about? There's also de-icer and flange lubricant, which might spread away from their localised places of application to some extent. But is there anything else going on? Do rails now take longer to darken after being installed than they did more than 50 years ago?

Brake dust, perhaps? Or being so close to the ground heavy rain throws up anything deposited on it near the tracks? Or a combination of actions?

 

[Annetts key]

Th sections of rail left in the 4ft or 6ft (presumably for fitting some time later) are brown with rust. Running rails are not rusty, they are steel-grey.

All rails apart from certain parts of points (crossing or frog) or fixed diamond crossings and similar switch and crossing (S&C) / point work are made of mild steel. Hence left out in the British weather, will develop rust on the surface.

If the running surface (top or head) has sufficient rail traffic, the action of the steel rail wheels on the rails will keep that part of the rail clear of rust.

Note that new rails tend to have a different colour of rust compared to existing rails that have been in place for many, many years. The colour of the rust changes over time. New rust is a lighter brown colour. Over time the colour darkens towards a darker (blacker) brown. Yes, dirt may help with this, but even when in an area where there is not much dirt, the rust still becomes darker in colour as it ages.

Is there some treatment that the railing gangs apply?

No, not normally. And most definitely not routinely. If railhead contamination has been found, there are treatments to deal with this. But not for rust.

As the running rails are the earth return for electric traction, is that a factor?

No. On lines where electric trains run, generally there is sufficient trains to keep the running surface clear.

 

[AndrewE]

All rails apart from certain parts of points (crossing or frog) or fixed diamond crossings and similar switch and crossing (S&C) / point work are made of mild steel.

Not really... Rail is made from steel with one of the tightest specs there is...
https://www.metals4u.co.uk/blog/mild-steel-in-depth-guide says

Mild steel has a carbon content of between 0.16% and 0.29 % maximum

https://makeitfrommetal.com/what-grade-of-steel-is-railroad-track-uses-and-tips/ says (although it is from the USA)

Railroad track steel is typically 1084 or equivalent hot rolled steel. This is a medium carbon steel with 0.7% to 0.8% carbon and 0.7% to 1% manganese.
This type of steel is great for heat treating. It’s tough, through-hardening, and forgable.
One of the noticeable features of this steel is the high manganese content. This is a requirement for good reason – it allows for deeper heat treatment.

For railroad tracks to perform well in the long term, there are two really important qualities that the steel needs to have: high wear resistance and resistance to fracturing.

The deeper heat treatment allows the steel to have higher strength properties. Basically, it’s less likely that there would be surface cracks that would propagate over time.

reclaimed rail steel is a premium material for slitting and re-rolling. I read that at one time nearly all the bedframes in the USA were made from angle-iron re-rolled from rail!

 

[ChiefPlanner]

Certain trains were specially routed via little used relief lines / Loop lines , crossovers etc to relieve the "rusty rail" scenario. In fact - various London Underground working timetables used to show empty trains doing "odd" moves to achieve the same result. (e.g Queens Park to Kilburn High Road and back over the signalled crossover) - so if used in anger , there was a good chance it would work properly.

During engineering possessions , some engineers would run a wagon / brakevan over a newly laid bit of track before handing the possession back , with the handbrakes applied (not fully !) - to knock off the new running rail rust.

 

[Rescars]

In the right weather conditions, the contact surface can go rusty in less than a day.

As you can see at your local station, the morning after a weekend engineering possession or similar shutdown.

 

[Keysan]

As you can see at your local station, the morning after a weekend engineering possession or similar shutdown.

They do rust quickly. I remember the WCML in the 80's after a strike the rails were really rusty after a few days.

 

[AndrewE]

They do rust quickly. I remember the WCML in the 80's after a strike the rails were really rusty after a few days.

Almost immediately, in fact. If you look at a usually-polished rail after no trains and even an hour's drizzle it starts to look orange.

 

[themiller]

A light coating of rust on the running surface of the rail won’t have a significant effect on train performance. The wheels of the first train over the line will scrub some and 25kV of the loco will see to the rest.

 

[samrammstein]

Would somebody be able to explain how the 25kV electrification gets rid of rust? I am no engineering expert, many thanks!

 

[bramling]

They do rust quickly. I remember the WCML in the 80's after a strike the rails were really rusty after a few days.

I remember similar on the ECML after both the Hatfield and Potters Bar derailments. In the aftermath WAGN operated a shuttle service as far north as Potters Bar and New Barnet respectively, using the slow lines only. It was rather surreal to see the fast lines completely rusted over during this time.

Rusting over can happen very quickly, and by the same token can disappear very quickly too.

 

[edwin_m]

Would somebody be able to explain how the 25kV electrification gets rid of rust? I am no engineering expert, many thanks!

Possibly the extra resistance of a rust film between the wheel and the rail would cause enough heat to burn off the rust? However, a reasonably frequent service is enough to keep the rust down even on non-electrified lines so I doubt electrification makes much difference for rust. It may have an effect on leaf film, which could explain why EMUs don't have Track Circuit Actuators despite sharing many common features which DMUs which do.

 

[AndrewE]

Would somebody be able to explain how the 25kV electrification gets rid of rust? I am no engineering expert, many thanks!

Possibly the extra resistance of a rust film between the wheel and the rail would cause enough heat to burn off the rust? However, a reasonably frequent service is enough to keep the rust down even on non-electrified lines so I doubt electrification makes much difference for rust. It may have an effect on leaf film, which could explain why EMUs don't have Track Circuit Actuators despite sharing many common features which DMUs which do.

Or maybe just (generally) faster, heavier, more frequent trains that you tend to find on electrified lines?

 

[edwin_m]

Or maybe just (generally) faster, heavier, more frequent trains that you tend to find on electrified lines?

Could be. Although the TCA works by circulating an electric current through the wheel-rail interface, and on an electric train the return current does the same thing.

 

[AndrewE]

Could be. Although the TCA works by circulating an electric current through the wheel-rail interface, and on an electric train the return current does the same thing.

yes, but isn't that only needed because of the absence of my suggested factors?
I thought the TCA was only needed because of relatively light vehicles not polishing either the rail or their treads, plus no tread braking which exacerbated the wheel tread grime and increased the resistance.
https://www.railengineer.co.uk/train-detection/ says

Where a thin film of contaminant insulates the wheel from the rail, this can often be pierced by a rough surface. The older style of tread brakes caused the tyres to be roughened at each brake application, whereas more modern disc-braked trains allow the tyres to be rolled into a very smooth surface condition. Therefore, older tread-braked trains provided better track circuit operation than modern disc-braked trains.


Similarly, the axle weight has an effect, as a heavy load will pierce a film more easily. Again, modern lightweight trains (and not-so modern ones, such as Pacers), designed to keep track wear down to a minimum, have more problems than old-style heavy freight trains.


One positive result from today’s crowded railway, however, is that busy lines have little chance to rust, reducing the problem. However, seldom-used branch lines, particularly those in coastal regions, are particularly at risk.


To assist vehicles to shunt track circuits, a device known as the ‘Track Circuit Assister’ (TCA) is fitted to modern trains to induce an electrical potential between the wheelset and the rail head. Typically, a TCA consists of a control unit and aerial with associated tuning unit, mounted between a pair of wheelsets close to the rails.

but I don't think that helps us non-electronics people understand it. I thought that the first TCAs were a big square ring of soldered copper pipe suspended over the rails which emitted a signal which somehow made the voltage or current through the wheelset enough to overcome the wheel/railresistance.

 

[DustyBin]

Almost immediately, in fact. If you look at a usually-polished rail after no trains and even an hour's drizzle it starts to look orange.

Just like brake discs. On my cars I give the outer faces of the discs a spray with “magic” liquid if I know they’re going to be stood for any length of time.

 

[edwin_m]

yes, but isn't that only needed because of the absence of my suggested factors?
I thought the TCA was only needed because of relatively light vehicles not polishing either the rail or their treads, plus no tread braking which exacerbated the wheel tread grime and increased the resistance.
https://www.railengineer.co.uk/train-detection/ says

but I don't think that helps us non-electronics people understand it. I thought that the first TCAs were a big square ring of soldered copper pipe suspended over the rails which emitted a signal which somehow made the voltage or current through the wheelset enough to overcome the wheel/railresistance.

Having been tangentially involved with the team developing TCA on several occasions, perhaps I can explain a little.

I would say it's not the weight of the vehicles on its own, as the first generation DMUs didn't have significant problems with detection on train circuits. Their power cars were similar weight to a Class 150 car and the trailers were lighter. The main difference with the Sprinter fleets was better vehicle dynamics leading to smoother travel of the wheels over the rails.

Lack of tread brakes did also make a difference, as the detection issue really became serious with the advent of Class 158 which was the first DMU class to have disc brakes. But when the TCA was developed it was rapidly retrofitted to classes 142-156 too.

EMUs with very similar weight and running gear to Sprinters, and also disc brakes, had been running for 10 years or so without significant detection issues and have never been fitted with TCA. It's open to debate how much this was due to return current and how much to electrified routes just having more and longer trains.

The TCA is exactly as you describe. There's actually a small gap in the square and a voltage is applied at 165kHz across this gap, so the current circulates through the pipe. This acts as a single-turn transformer, inducing a current at the same frequency that circulates through the circuit formed by the two axles and the two rails.

I don't think the physics was ever fully understood but it was clearly something to do with the circulating current at high frequency reducing the resistance for the low-frequency track circuit current. This would overcome the resistance of moderate leaf film but not a really heavy one. A trackside device known as TCAID was developed to be fitted in the really bad spots, that would detect the current induced in the rails by the TCA and connect them electrically so the track circuit would show occupied.

 

[Annetts key]

Okay, track circuits and rusty or contaminated rail head. This is a bit of a complex subject.

There are lots of different types of track circuit equipment in use. Each follows the same basic principles, but exactly how they work depends on the equipment and technology used.

They range from simple primary (non-rechargeable) cell (battery) DC types all the way through to Digital EBI Track 400 Audio Frequency (“jointless” - meaning no IRJs are normally needed) Track Circuits that can be monitored remotely.

With rust, which is a mineral (iron oxide), like various other mineral oxides, it’s an electrical insulator. Similarly, plant (leaf) oils and various other contaminants are also often electrical insulators.

Note that crushed rust may not be damaged enough for the track circuit to work correctly. If a rail head is badly rusted, it may take five to ten trains (depending on the type of train) to clean the rail head enough.

However, if the coating or film is thin enough, the insulation can be “punched through” if a sufficiently high enough voltage is applied.

Unfortunately, some (but not all) track circuits operate at relatively low voltages. This is especially true for cell (battery) fed DC types that use a shelf type relay (the first “standardised” series of relays used by the railways for signalling purposes). These typically operate at between 0.25V and 1.2V DC.

Even the current standard DC type operates at around 4V to 6V.

Some types of track circuits operate at a higher voltage. Some AC types can have an open circuit voltage of as much as 20V. Added into the design of the equipment (transformers), this can actually make swarf glow. Hence this type is less susceptible to rail head contamination. Note that this particular design is not compatible with AC OHL. There are other types of AC track circuits that I’m not familiar with.

Hence, if you have a high voltage supply for electric traction, the high voltage will tend to “punch through” the insulation. Once the insulation is compromised, the lower voltage track circuit current can flow. The process continuously repeats as the wheel rotates.

TCA aid track circuits by artificially adding a relatively high voltage, high current feed between the wheel sets and hence between each wheel and the rail.