Soldering or brazing copper pipes
CPU heat pipes are filled with low-boiling chemicals, such as water or alcohol. At 180°, likely above the critical temperature of the coolant, there would only be supercritical fluid in the tubes, and the heat pipes would no longer function. Further, they might burst, whether soldered or brazed.
Why not just add an auxiliary fan -- perhaps a squirrel-cage (centrifugal) blower, if there is high back-pressure? These blowers produce high airflow in limited area, and are used for cooling devices dissipating tens of thousands of Watts, such as transmitting valves (AKA &quot;tubes&quot;, to the US).