Tightening a bolt based on torque values can be quite risky as the torque is directly related to the coefficient of friction and can vary greatly with the amount and type of lubricant used (or the amount of sand and grit in the threads). The best way to tighten a bolted joint is to determine the bolt load per bolt and then use that force to determine the elongation in the bolt and the rotation of the nut needed to seat the nut against the flange.
Ie Bolt stress / Strain = E (or Stress / E = Strain) therefor: change in bolt length = Length * (Stress / E)
Knowing the pitch of the threads used, you can determine the rotation of the nut needed.
Regards,
CreativeVessel