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Also have a look at 'An Introduction to the Design and Behavior of Bolted Joints' by John Bickford which also explains some of the background into how bolt torques are derived.
ASME B16.5 flanges can usually be flogged up to some pretty high torques and are robust. I would be more concerned with bigger flanges or custom designed ones.
There are two torque equations given in Bickford's book, the "long form" and "short form" equation. The long form factors more things in, the short one uses a nut factor as a sort of summation of all the variables. The short form is easy to use, however quite inaccurate. A bolted joint has, by my own count about 90 variables in it, so equations for bolted joints are not too accurate.
If you're dealing with bolted flanged joint, he goes into two methods, the VDI and ASME method. The ASME method is not really intended to get bolt loads for installation, however that is what its used for, like it or not.
ASME PCC-1 is also for flanged connections, it offers torque based on the size of the bolts. The new 2010 update is very significant, I only advise reading that one.
Please know that torque is a poor indicator of bolt tension. Even with a torque wrench, a scatter of 25% in bolt tension between bolts is likely.
Re-tightening afer 4-24 hours is always recommended in bolting texts, I would say it is absolutely necessary.
