It’s preferrable not to bend connecting pipes and use the appropriate elbows to install the piping with the desired layout.
If necessary it’s possible to bend the pipes if the correct bending radiuses are chosen (minimum is 4x the pipe diameter) and the correct tools are used (the correct tools do not alter the cross section of the pipes).
Bending of stainless steel is allowed only in case of heat-annealed pipes.
Wet sprinkler systems are always filled with water in pressure. In case of fire a thermal-activated sprinkler nozzle sprays water over the flames to cool the area. Dry systems act similarly but the pipes are constantly filled with pressurized air instead of water.