 In this blog I will briefly present gasket design criteria and bolt torque calculation. For this purpose spreadsheet has been made, where yellow fields are required data that will be entered. All equations, units and description are given in the figures. Calculation is conducted for 4″ flanges class 300 having Flexitallic spiral wound gasket. Bolt torque calculation and checking gasket design criteria is accomplished in the five steps.
Step 1 Step 2
Calculate required bolt torque assuming that bolt preload tension stress is 0.65 of yield stress. Note that bolt torque must be in the range recommend by supplier. Sometimes bolt torque is given as percentage of yield stress (e.g bolt preload stress must be equal to 65% of yield stress). Step 3
Calculate equivalent pressure using Kellog’s method. Step 4
Calculate minimum required bolt load for gasket: seating condition (Wm2), operating condition (Wm1) and hydro test condition (Wmt).
Calculate: bolt preload tension force (Ft), bolt load for operating condition (Fm1) and bolt load for seating condition (Fm2).
Note that calculation is based on given design conditions: operating pressure is 150 Psi and design temperature is 350 degree F. Step 5  