The correct torque value is based upon the gasket material being used, the strength of the fasteners and the strength of the flanges. Do not rely upon bolt stress torque tables or torque tables found on the internet because these generic tables were not compiled with a specific application in mind.
A torque wrench is a precision instrument and requires a skilled craftsman to use it properly. Tightening bolted flange joints precisely to a predetermined torque setting requires a calibrated torque wrench to ensure that the job is performed correctly. Over-tightening or under-tightening any one or all of the fasteners can result in a leak. The only way to protect against either case with certainty is if a measurement of the torque is made when it is applied.
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