Pipe Pressure Rating and Required Wall (ASME B31.1)

ScopeMaximum 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 -> ~1,636 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 or tableallowable: P = 2 S E W (t_avail - A) / (D - 2 y (t_avail - A)), t_avail = wall x (1 - mill_tol). required wall: t = P D / (2 (S E W + P y)) + A, ordered nominal >= t / (1 - mill_tol). W = weld joint strength reduction factor (1.0 seamless or below the creep range). ASME B31.1 / B31.3 internal-pressure design.

Source and editionASME 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.

Free accessThe internal-pressure design equation (Barlow for the first cut, the B31.1 form for the real one) is public; the material allowable stress, joint factor, and y-coefficient are read from the applicable code tables.

What governsEstimate. AHJ and licensed professional govern.

API field namesod_in, wall_in, allow_stress, joint_factor, y_coeff, mill_tol_frac, mode, p_allow

• Allowable stress S is read from the applicable code edition's allowable-stress table for the material at temperature (user-supplied)ASME B31.1
• Joint factor weld-joint efficiency E (seamless = 1.0) from the codeASME B31.1
• y-coefficient temperature coefficient y (ferritic <= 900F = 0.4) from the code tableASME B31.1