Here's a few pics form a couple of sites that we have installed full liquid recirc Co2 systems in supermarkets. One plant is R134a/Co2 cascade with water cooled hi stage and screw compressors, the other R404a/Co2 and air cooled. All field pipework is copper pipe with steel pipe on the rack on the larger diameter pipes.
Site #1 R404a/Co2
Co2 vessel and low stage Co2 rack
Co2 pipework back of house
Co2 Coolroom evaporator with hand expansion valve