Pipe Pressure Rating and Required Wall (ASME B31.1)
The ASME B31.1 internal-pressure relation both directions: maximum allowable pressure from a wall thickness, or the minimum wall a design pressure demands - tying OD, wall, allowable stress S, weld-joint factor E, and the y-coefficient together (4 in Sch 40 A106-B -> ~1,637 psi). The allowable stress, joint factor, and y-coefficient are read from the applicable code edition's tables; a design screen, not a stamped calculation. The engineer of record and the AHJ govern.
Formula and source
allowable: P = 2 S E (t_avail - A) / (D - 2 y (t_avail - A)), t_avail = wall x (1 - mill_tol). required wall: t = P D / (2 (S E + P y)) + A. ASME B31.1 internal-pressure design.
ASME B31.1 Power Piping pressure-design relation, by name (B31.3 Process Piping uses the same form with its own allowables). The allowable stress S, joint factor E, and y-coefficient are read from the code edition's tables.
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