If you notice that your brake pipe is leaking, do not drive your vehicle. Inspect the brake pipes for corrosion or other potential causes of leaks. If the pipes are corroded the best thing to do is replace all of them at the same time. Partial repairs frequently result in multiple failures, often within a year of the initial failure, and can be more dangerous and more costly over the life of the vehicle. Check with your manufacturer to see if it offers a prefabricated brake pipe assembly kit, which can reduce the time and cost of repairs.
When replacing the steel brake pipes, always use double walled steer piping which is designed to withstand high pressure and resist corrosion. Also, it is important to make sure that the pipe is of the same size to assure both a proper fit and proper brake operation.
Do not bugg*r about with brake pipe spanners trying to take old brake pipes off. Cut the pipe with a decent pair of side cutters and get a tight fitting socket onto the end. You are going to be replacing the pipe anyway so why preserve it? If you are removing a pipe that you will need to refit then use a brake pipe/flare nut spanner. Most cars have metric fittings nowadays but if you end up having to do this job a lot it might be worth kitting yourself out with a set of AF spanners too. As they are all slightly larger/smaller than the metric ones it comes in handy if you are removing stubborn or heavily corroded brake pipe ends