I have have never had any issues with brake pipes on any of the Audi's, they seem to make them out of fairly corrosion resistant steel. Even if the coating (paint) on the pipes have gone they only get surface rust which is not really an issue. I have seen a lot of badly corroded pipes on Vauxhalls, Fords, Rover and Land Rover. They are usually corroded near the ends where the coating gets damaged from turning nut or at the mounting points where moisture stays in for longer under rubbers. Even had one fail and start to leak while driving on 1980 Opel Kadet which was my first car. Replaced the leaking rear pipe, slammed on brakes to test and burst front pipe
. That looked like too much job to replace so just soldered bigger pipe over it so seal and connect.
Nickel (or rather nickel alloy stainless steel) and copper pipes that Dezzy talks about are used in aftermarket repairs/replacements, factory pipes are usually carbon steel as the steel is cheaper for manufacturers to use. Copper is most popular in aftermarket repairs because it's soft and easy to work on, does not corrode to badly and is relatively cheap. Nickel alloys steel is more expensive and hard to work on, benefits are strength, corrosion resistance and some say harder feel on the pedal but I am not sure about that, mostly used as replacement on race cars.
Another thing to remember is that you do not necessarily need to replace whole pipe if only one end is corroded. I had Freelander fail MOT on corroded brake pipe and it was too involving to replace whole pipe running from the ABS pump in the engine bay to rear wheels. So i just replace corroded rear part and and joined the pipes with compression fitting similar to this:
http://www.ebay.co.uk/itm/Equal-Ende...item19fd4a9ef9
Was not sure what the MOT tester will think of it when I went for re-test but got thumbs up.
