Copper tubing MUST NEVER be used on any brake or hydraulic system. Copper work hardens, become brittle then cracks, then bleeds hydraulic fluid when fluid pressure is most needed.... as in crash or not crash panic stop.
Copper-Nickel alloy brake tubing is completely different than the common copper tubing. It is specifically designed for auto brake systems with corrosion resistance and ease to flare and bend while remaining soft and reliable in auto hydraulic systems. Alternative to this would be SAE steel brake tubing except this tubing tends to corrode. Even the plastic coated steel brake tubing has corrosion problems once the coating is damaged or cracked due to aging.
An alternative is annealed 302 or 316 seamless stainless steel tubing. Works ok, but required special flaring and bending and cutting tools due to the higher hardness of stainless steel.
Speaking of copper hydraulic tubing, Friend had a problem with a BIG DoAll band saw, the hydraulic system lost pressure. Turns out the OEM hydraulic tubing is copper. Over many years and pressure cycles, the copper tubing work hardened, cracked then failed. The fix was to remove and replace ALL that copper tubing with a proper tubing that is not the OEM copper.
Bernice