pipe ends 34 and 36 apparatus not shown can now be inserted through the passageway 32 in flange fitting 30 to cap off the ends 34 and 36 of pipe 10 and thereby close fluid flow after repair or maintenance has been done the mechanism for capping off the ends of the pipe are removed and it then becomes necessary to provide a permanent closure of the containment housing specifically to complete the job of temporarily terminating fluid flow through pipe 10 the passageway 32 in flange fitting 30 must be closed the invention herein provides a system of achieving permanent high temperature closure of passageway 32 by means of a completion plug assembly generally indicated by the numeral 38 before describing the details of completion plug assembly 38 and flange fitting 30 further reference to fig1 shows systems by which completion plug assembly 38 can be installed into flange fitting 30 secured to the top surface 40 of flange fitting 30 is a valve bottom flange 42 which is a lower portion of a valve generally indicated by the numeral 44 valve 44 has a top flange 46 which receives the bottom flange 48 of a hydraulic cylinder 50 valve 44 has a vertical passageway 52 therethrough that is of internal diameter equal to or greater than the passageway 32 in flange 30 opening 52 in valve 44.