A bolted flange joint seals because the bolts squeeze the gasket hard enough to bed it into the flange faces and then hold that seating against the internal pressure trying to blow the joint apart. The bolt load must satisfy two conditions: enough to seat the gasket on assembly (W_m2), and enough to keep it seated under operating pressure once the hydrostatic end load tries to separate the flanges (W_m1). The larger requirement governs the bolting.

Calculation method & standards

• Gasket factors m and y from ASME BPVC VIII Div 1, Mandatory Appendix 2, Table 2-5.1 — the maintenance factor m and minimum design seating stress y for each gasket family (spiral-wound, RTJ, PTFE, graphite, elastomer, fibre).
• Operating load W_m1 = 0.785·G²·P + 2b·π·G·m·P and seating load W_m2 = π·b·G·y, with the effective seating width b and load-reaction diameter G from the gasket geometry (Table 2-5.2).
• Bolt area check: required A_m = max(W_m1/S_b, W_m2/S_a) compared against the available area of the flange's actual bolting (ASME B16.5 count & size), using bolt design stresses to ASME II-D.
• Assembly torque from T = K·F·d (short-form), cross-checked against the catalogue torque in the database.

Gasket dimensions, bolt counts and torques are taken from the governing standards; the m and y factors are the published ASME values, not assumed. Always verify against the flange rating and the gasket manufacturer's limits.