Torque Required for High Tensile Studs + Nuts

Not enough info...

1. What is the flanges' class (150, 300, 600, etc.)?

2. What is the bolt size?

(use ANSI B16.5)

Even if the OP provides the data noted in our colleague's subsequent post, there still wouldn't be enough data to determine what the torque requirement should be. We would still need to know:

• the friction between the nuts and spot faces at each hole
• the friction between washers on each fastener assembly
  
• the condition of the threads
• the spotface conditions
  
• the amount of lubricant applied on each fastener
  
• where the lubricant will be applied on each fastener
• the degree of contamination in the lubricant
  
• the rotation of the flange at each hole
• the temperature of the assembly

• etc

While admitedly tongue-in-cheek, the above serves to show that it's folly to try to predict that a certain applied torque will result in a defined pre-load. There are too many unknowns that will affect this end. Rather than hoping, guessing, praying and assuming that one's prediction will be correct, it's much better to actually measure the results after the fact. This way, one would be certain that a critical joint has been properly tightened.

Furthermore, actually measuring the effect of the torquing exercise enables "tuning" of each fastener for proper preload. In most cases this results in a different applied torque for each identical fastener within the fastener population of that flange.

* A good indication of potential problems is reading a report stating that each fastener has been tightened to the same "torque"