Abstract: An unheading device for removable attachment onto a lower flanged opening of a vertically-oriented vessel such as a coking drum, the unheading device being controllably supported by multiple elongated vertically-extendable actuators such as hydraulic cylinders which extend between a lifting frame unit holding a head unit and the vessel support structure. The multiple vertically-extendable actuators are each pivotably attached at its lower end to the lifting frame unit, and are each pivotably attached at its upper end to the separate stationary support structure for the vessel. The unheading device is adapted for lowering the head unit and moving it laterally aside to a parking position on a platform portion of the vessel support structure, then raising the lifting frame unit with its attached decoking chute unit to contact the vessel lower flanged opening for coke removal therefrom.