Bobo,
The IVA road test requirement that we have to meet in the UK requires that the brake components need to be 'suitable to withstand the stresses, vibration and corrosion and ageing to which they may be subject' and typically, in the UK, brake lines are run in copper or kunifer. I am not aware of reported issues of crystallisation in the brake fluid assuming it is changed at regular intervals.
Thasnks
Ian