Nylon coated steel brake line tubes are used by many automakers. The tubes with nylon coating is also called NyGAL coated brake lines.
It is defined as zinc-aluminum alloy as described in GALFAN , with min coating thickness 3 micrometer, i.e. 50 g/m2 per ASTM A875, followed by a topcoat of Nylon 11 or 12.
Appearance: The topcoat shall be uniform in color and free from discontinuities such as flow lines, pin holes, craters, or abnormal roughness. The topcoat shall be black in color unless otherwise specified on the engineering drawing
Film Thickness: The Nylon PA11 or PA12 topcoat shall have a min thickness of 150 μm, average thickness 170 μm.
Salt Spray Testing (Normal): 1000 hr min before white rust shows, and 12000 hr min before red rust shows;
Salt Spray Testing (Gravel Impact): 2000 hr min before red rust.