It would seem that they have little wear, but they do rust, and hence, must wear out.
Are they required to be replaced, like every 25 years or so?
I once read that the NY Central RR once had their rails on a 100-year replacement schedule-that seems a tad long.
How long can they be servicable for?
I don’t have the precise answer, but I do know that railroads use(d) date nails for record keeping purposes.
Mainlines do wear and require maintenance or re-routing. Rails are reused, although I suspect most re-uses go to secondary routes and sidings.
I’ve personally photographed rails as old as 100 years still in use on sidings. Joiner plates and other parts are also reused if still in good condition.
Date nails were actually used to document the age of the wooden tie (sleeper) rather than the rails themselves. Generally ties have a shorter life than rails and have to be replaced more frequently.
As others have noted, rails can last a long time, especially in low-humidity areas where rust is not much of a problem. I’ve seen rails, on sidings and low-use branch lines that are nearly 100 years old (most rails have a date of manufacture stamped or welded on them). OTOH, mainline rails see constant heavy use can wear out in just a few years - I’ve heard anecdotally that some have to be replaced every 2-3 years. Wear is especially severe on curves, and particularly on the outside rail.
It should be understood that rails do not simply wear down to nothing, what happens is that the profile of the railhead gets worn and misshapen to the point that it impacts train operation. Most of the large railroads have rail-grinding machinery that can grind the profile back into shape and get a few more years of use from the rail before replacement is required.
SS
Here’s a tid-bit from a small Wisconsin railroad’s website…
So 100 years old is certainly not out of the ordinary for lightly used tracks, but certainly not on mainline routes! The rest of the webpage discusses how they rebuilt the tracks they own over the years they’ve been in business.
Many of the older rails were made using open hearth steel which is prone to internal flaws. Rails are inspected for internal defects on a regular basis, using what is called a Sperry car. Internal defects usually result in replacement of that section of rail.
The commuter line I use (heavy rail cars) started in 1918 and by 1990 had come to the end of its useful life. Over three summers, 1992-1995 everything, stations, ties, rails, catenaries, and cars were replaced. The revised line has been so successful that they are now buying new double-deck cars.