Hello Lim
There are published values in a number of publications. The 'Pressure Vessel Design Manual' 3rd edition by Dennis R Moss is one of them. There does not seem to be a definitive method for relating torque to bolt stress. There are other issues that affect the relationship between torque and stress. For example: Are the bolt Teflon coated? Is a lubricant used? Are washers employed? The may be other things that affect the stress of the bolt. This answer may not be satisfactory.
A method that has been used is to have a partially hollow bolt with a strain gauge installed in it. As the bolt is torqued up, the torque and the bolt stress can be correlated. That may be extreme, but I have seen this done at a flange seminar.
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Sincerely,
Ray Delaforce
CADWorx & Analysis Solutions
Hexagon PPM