LittleInch - We can't replace it simply, since spare valve is not availalbe and threads that got ripped are in valve body.
geesamand - Yes, the preload shall increase on all remaining studs and more specifically to adjacent nearbuy studs. This is 8"x600 # butterfly valve with four threaded holes (two each on top and bottom) for alignment with piping flanges. Screws are tightened with adjacent piping flange and rest seating force is applied by eight studs of the adjace piping flanges. During torqueing, threads of one of the holes inside the valve body got ripped off and hence that side of the valve is left with three screws + eight studs.
racookpe1978 - I wouldn't have asked if we could have replace that damaged valve that easily. Damaged threads inside the valve body is beyond repair. We need to continue with the situation for a while until we get spare valve and the purpose is to understand hazards with such operation with one missing fastener. Final torque value for this size of the stud per our internal spec is 630 Ft-Lbs and manual, calibrated torque wrench was used for torqueing. Torqueing was carried out in three passes, first at 30%, second at 60% and final pass at 100%. Torqueing is done in legacy pattern per ASME PCC-1 and after the third pass, fourth pass in circular pattern is carried out at the same final torque value, i.e. 630 Ft-Lbs. Threads got damaged during final pass of the torqueing. 3.2 mm thick SS 316 Spiral wound gasket with grafoil filler is being used and stud-bolt/nut is A 193 Gr7 with A194 Gr 2H heavy hex nuts. Jet lube nikal paste is used as thread lubricant on studs for torqueing (friction factor - 0.15)
