At my last place, there were moulding machines with hot and cold water supplies for heating and cooling them. These got swapped/moved around from time to time as they needed overhaul or requirements changed. The plumbing tended to be in 22 or 28mm copper.I find that not overheating the fitting is essential.
One day I walked past and one of the fitters was struggling to get the solder to 'take' ... in a pipe and fitting that had long since turned blue/black with heat