right couple of pointers
get approval from the water supplier / board first as sometimes they class fire reels as cat 5
but what are you doing about backflow prevention ? if its class as 3/4
i wouldn't worry about expansion at that length its not going to be much 25mm at most (more like 10mm)
you have a few options depending on what steel beam you have
M10 Vertical Flange (1-5mm) Threaded Rod Hanger
Flange Clamps Lindapter & BTS
Heavy Duty Beam Clamp ( Pair)
25-30mm Surefix XL Rubber Lined Pipe Clamp -
i would press fit tbh
geberit 28mm press fit fittings
Copper | Pipekit
and you can hire the tool for about £150 a week (£ 40 a day) roughly
Sorry for going slightly off topic but why would exspansion be an issue if its mains cold water that won't be heated?