Abstract: A penetration seal and its installation method for use with a pipe extending through an opening, or penetration, in a vessel, such as a boiler, containing fluid. A first collar surrounds the pipe adjacent the vessel and is in fluid communication with the opening in the vessel. A second collar has a sleeve portion engaging the exterior of the pipe and is spaced from the first collar. An insulation pillow substantially surrounds the pipe and is connected to the first and second collars. An expansion sleeve substantially surrounds the insulation pillow and is connected to the first and second collars, wherein the sleeve portion of the second collar is configured to compressively engage the exterior surface of the pipe sufficiently to frictionally fix the second sleeve against movement relative to the pipe.