I have copper on both cars. Easier to bend and no rust. The pipes on my saloon were renewed 5 years ago and other than discolouration are perfect. Similarly on the Traveller but three years ago. I did, however, have to replace both front "transfer" pipes on the saloon after the original copper pipe twisted with the union nut when removing the front wheel cylinders.
Any car I've had with steel pipes has eventually led to a MOT failure or advisory due to corrosion of usually front pipe(s) in the wheelarch area. The only exception was on a Maestro on which the steel pipes had a plastic covering.
The steel pipes on my Volvo had a plastic covering, but if it gets scratched they don't last long - the main front to rear pipe had to be replaced when it was 12 years old
Therefore far less durable than the Minor steel pipes that lasted 30 to 50 years - sometimes longer.
Copper brake pipes are fine, but make sure they're secured properly. Copper work hardens a lot quicker than steel. If the pipes move/flex too much, they can crack .
The problem pipe is the one that comes out of the master cylinder to the rear. It's well hidden until it appears out the end of the chassis rail. At least the others can be fairly easy to check.
I bought some fuel pipe here recently & it was steel with a slight copper coloured tinge to it, possibly some sort of anodised finish for protection .
eh? I have just had some steel billet wheel hubs from JLH and they are anodised (according to him). Like a yellow surface finish or is that some other method?
Could be a zinc plating using a yellow passivite as opposed to a clear passivate which give bolts etc their bluey tinge on the sliver. If it is yellow passivate then that's better as it is much more corrosion resistant.
Failing that it could be nickel plate but that would make them more expensive than zinc...
Suggest you use cupro-nickel (Kunifer) brake tubing. Stronger than copper and does not rust - bit more expensive, but how often do you need to replace them?