Brake line is used for automobiles to transfer hydraulic pressure to the brake pads from cylinders. Usually brake system is designed to maintain a low or medium pressure, and the typical steel brake line tube called Bundy tube is used widely in the world.
Bundy tube is named by the name of whoever invented a special manufacture of steel tube: double wall copper brazed steel tube. By rolling steel sheets of copper coated double sides 720 degrees into a two layer pipe, heating it to melt the copper, and cooling it, the two layer steel sheet is “welded” into a round section tube. Its mechanical properties is quite idea to flare and bend, ensuring a safe burst pressure level also.
Bundy tube is used on brake system only after zinc plated to protect it from corrosion. Most tubes will be then treated by trivalent chromium to enhance the corrosion protection.