While supplying liquid, it may be the normal phenomenon for there being any condensation water or frosting in the vessel outer surface. While the increasing pressure being carried out by switching-on the pressure increasing valve, the liquid may flow through the pressurization coil and absorb heat from the outer cylinder for vaporization and realizing the goal of pressurization; there may be some spot-like frosting in the outer cylinder surface; while the pressure increasing valve being switched off, the spot-like frosting shall be disappeared slowly. While the pressure increasing valve being switched off and the supplying liquid being not carried out, there may be any condensation water or frosting in the vessel outer surface; as may indicate that the vessel vacuum has been destroyed and this vessel could not be used. You should turn to the specialized factory for maintenance or abandon it.