Q. Calculate flange stresses?
Step 1: Calculate flange stresses for system design conditions using existing gasket dimensions. The minimum width of the gasket should equal or exceed [Ab * Sb / (2 * 3.14 * y * G)] to prevent crushing, where values of Sb and ‘y' are either the ASME values for the allowable bolt stress and gasket seating stress, or the largest Sb / y ratio in all 5 calculation steps.
If the flange is overstressed, or gasket crushed, substitute ASME values of ‘y' in lieu of COLT's.
If stresses are still too high, adjust gasket dimensions to:
- Reduce flange stress below ASME Code allowable.
- Reduce bolt stress to acceptable values.
- Achieve optimum diameter for gasket load reaction.
Step 2: Using conditions in Step 1, vary the value of ‘y' to give maximum allowable flange stress. The value of ‘y' should not exceed the maximum limit.
Step 3: Recalculate flange stresses, bolt loads and torques for the hydrotest conditions, using the gasket dimensions, ‘y' and ‘m' values in Step 1. Maximum flange stress shall be limited to 90% of the minimum yield strength by adjusting ‘y' downward, if necessary, but in no case lower than ASME Code value.
Step 4: Using the design pressure, increase the value of ‘y' until the same bolt load from Step 3 is reached. If flange stresses are substantially greater than Code allowables, recalculate Step 3 using lower COLT ‘y' values to obtain a lower bolt load. Repeat calculation in Step 4.
Step 5: Using the hydrotest pressure, increase the value of ‘y' until the same bolt load from Step 2 is reached. If maximum flange stresses exceed 90% of the minimum yield strength, recalculate Step 2 using lower COLT ‘y' values to obtain a lower bolt load. Repeat calculation in Step 5.