Click Materials from the Setup tab:
Questions about applying settings?
Select the Pipe wall by left clicking on it:
Hide the pipe wall by middle clicking on it while holding Ctrl.
Hide the flow part by middle clicking on it while holding Ctrl:
Select the divider part by left clicking on it:
Open the Materials quick edit dialog in ONE of the following ways:
On the Material quick edit dialog, Type = Solid.
Name = Copper
Click Apply.