An insulated pressure vessel, such as a coke drum, having an insulation system installed thereon. The insulation system includes an insulation support system comprising either a floating ring type support system, or a cage type support system including a plurality of vertically spaced insulation support rings each having a diameter greater than the external diameter of the coke drum. A plurality of insulation panels are secured to the support rings, each panel including insulation material and an exterior metal jacket. The panels are secured to horizontally adjacent insulation panels with standing seams. Weather shields may be provided over the top of the seams. Tensioned insulation securing cables, corresponding in number to the insulation support rings, are routed through horizontally aligned eyelets in each standing seam.