Final answer:
To safely remove propane from a mounted ASME tank, ensure it is depressurized, close the service valve, transfer the propane to another tank, and relieve pressure before the fill valve replacement.
Step-by-step explanation:
To safely remove propane from a mounted ASME tank in order to change the fill valve, you should follow proper safety protocols which include ensuring that the tank is depressurized before beginning any work. The specific steps may include closing the service valve to prevent more gas from entering the tank, connecting a withdrawal hose to the liquid withdrawal valve, and transferring the propane to another certified tank or safely flaring it off using appropriate equipment. Always wear protective gear and ensure that no sources of ignition are present. After the propane has been completely removed, the pressure inside the tank can be relieved, and then the tank is safe for maintenance or valve replacement.