Running a Server at Freezing Temperatures?
I'm not the expert on heat pipes but I do know something about soldering copper pipes and you're better off soldering a cap on one end and a threaded adapter to the other, then filling with water, heating, and screw a brass cap on the threaded adapter.
You don't have to spend much time soldering even wet pipes to get a good illustration of the differences in the boiling point of water and the melting point of solder. Soldering anything but bone dry pipes is a non-starter.
Also, you want a brass cap instead of galvanized with the copper since galvanized will create a small electrical charge that will corrode the steel and the copper.