Abstract: A casing for a high pressure steam turbine is provided which is adapted to be stocked for subsequent customization. The casing is made as an incomplete casing with a closed chamber between an inner and outer wall and extending axially along a significant length of the casing. Taps for extraction or admission are subsequently provided by locating the axial locations which provide the desired pressures, machining a slot through the inner wall and an opening through the outer wall, and securing a fluid tight barrier between the walls adjacent the slot to separate the chamber in an additional chamber. Other aspects of the invention include providing for a controlled extraction with control means in the upper portion of the casing and extraction out of the lower portion. Additional features include axial ribs to abut and support the barrier, and provisions for making connections to the interior of the turbine casing.