Reactor heating to achieve minimum pressurization temperature

Systems and methods are provided for performing the initial heating phase for a thick wall reactor, such as a hydroprocessing reactor, by using heat tracing to heat the exterior walls of the reactor. Instead of attempting to initially heat the reactor by passing a low pressure heat transfer gas through the interior of the reactor, external heater(s) placed under the reactor insulation can be used to heat the exterior of the reactor. An example of a suitable external heater is a heat tracing blanket, where heat is provided by passing steam through pipes in contact with the external surface or by electrical heaters in contact with the external surface. This can allow for more rapid heating of the reactor, so that a target temperature can be achieved in a time of 5.0 hours or less.