Bolt Tightening Stress Notes - CAESAR II - Help

CAESAR II Users Guide

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CAESAR II
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CAESAR II Version
12

This is a critical item for leakage determination and for computing stresses in the flange. The ASME Code bases its stress calculations on a predetermined, specified, fixed equation for the bolt stress. The resulting value is however often not related to the actual tightening stress that appears in the flange when the bolts are tightened. For this reason, Bolt Initial Tightening Stress, is used only for the flexibility/leakage determination. The value for the bolt tightening stress used in the ASME Flange Stress Calculations is as defined by the ASME Code:

Bolt Load = Hydrostatic End Force + Force for Leaktight Joint

If Bolt Initial Tightening Stress is left blank, CAESAR II uses the value

Where 45,000 psi is a constant and d is the nominal diameter of the bolt.

This is a rule of thumb tightening stress that will typically be applied by field personnel tightening the bolts. This computed value is printed in the output from the Flanges output. Compare this value to the bolt stress printed in the ASME stress report (also in the output). The “rule-of-thumb” tightening stress is frequently larger than the ASME required stress. When the ASME required stress is entered into the Bolt Initial Tightening Stress field, a comparison of the leakage safety factors can be made and the sensitivity of the joint to the tightening torque can be determined. You are strongly encouraged to adjust these numbers to get a feel for the relationship between all of the factors involved.