This guide explains how FlangeTorque turns a flange and gasket into a defensible bolt-up plan, using the ASME VIII Appendix 2 load method with ASME PCC-1 assembly guidance.

How flange bolt torque is calculated

The chain is: find the load the joint needs, convert that into a bolt preload, then convert preload into a torque. The required load is the larger of the gasket seating load (Wm1) and the operating load (Wm2). The target preload comes from a chosen bolt stress, typically 40 to 75 percent of yield per PCC-1, and torque follows from T = K x F x D.

Gasket seating and operating loads

Wm1 = pi x b x G x y seats the gasket, where b is the effective seating width, G the gasket reaction diameter and y the seating stress. Wm2 = (pi/4) x G squared x P + 2 x pi x b x G x m x P keeps the joint sealed in service, combining the hydrostatic end force with the gasket compression needed under pressure P, where m is the gasket maintenance factor.

The nut factor and torque scatter

The nut factor K wraps all the friction in the threads and under the nut into one number. Because friction varies, a single torque value really represents a window, often plus or minus 20 to 30 percent of achieved preload. That scatter is why critical joints are frequently hydraulically tensioned, which applies load directly and far more repeatably.

Tightening sequence

Bolts are tightened in a cross or star pattern over several passes so the gasket compresses evenly. A common scheme is a snug pass, then roughly 30, 60 and 100 percent of target in the star order, finishing with a clockwise pass to recover relaxation. FlangeTorque draws the exact numbered order for your bolt count.

Turnaround planning and flange repair

For a shutdown, multiply bolts and flanges by realistic make-and-break times to get crew hours, then cost them out. Where a flange face is damaged, the repair module estimates weld-overlay volume, deposited weight, arc time and cost so the repair can be planned alongside the bolt-up.

Standards

Methodology follows ASME PCC-1 (assembly), ASME VIII Div.1 Appendix 2 (load method), ASME B16.5 / B16.47 (flanges), ASME B31.3 (piping), with reference to EN 1591-1, API 570 / 574 / 571 and ISO 898 / ASTM bolt material standards. FlangeTorque is a screening and planning aid; confirm against the governing code, gasket data and a qualified PCC-1 procedure before live work.