Hot duct esp. for steam has insulation jacket - of double-walled metal casing resting on shoulder of duct with freedom to expand

摘要

Vertical duct for a hot medium, typically gas or steam consists of a pipe with external insulation in an annular space of a double walled metal casing surrounding the pipe coaxially. Top and bottom closures of the casing are both formed of conical plates (with upward conical taper); the lower conical plate rests of a shoulder formed by the junction with the main pipe of an additional, outer pipe in the region below the conical insulating casing. The close fit of the conical tapered plate on this shoulder forms a seal to the small annular gap between outer face of pipe and inner face of insulating casing. In a pref. embodiment the lower conical plate is welded to the inner and outer walls of the insulating casing and also welded to the shoulder; the upper conical plate is welded only to the inner casing wall and forms a sliding fit with the outer casing wall. In this region, the cylindrical part of the upper conical plate may be coated to prevent friction welding at this joint. For any hot vertical duct, typically a gas or steam duct, esp. in a nuclear plant. The insulating jacket can be completely prefabricated and is easily mounted by pushing it onto the duct. The insulating effect is not adversely influenced by "chimney convection", because the lower end of the gap between casing and pipe is sealed by the conical plate. Uses include in steam generators of conventional or nuclear power plants, esp. as a live steam duct. The duct would be mounted on the top closure (or double closure) of the vessel.