Branch Connection Reinforcement (Area Replacement, ASME B31.1)
Whether a branch opening cut into a pressurized run needs a reinforcing pad: the area-replacement check of ASME B31.1 para 104.3.1 (and B31.3 304.3 for process). The metal removed, A_required = t_rh x d1 x (2 - sin beta), is made up by the excess wall in the run (A1) and branch (A2) within the reinforcement zone; a shortfall is the pad area to add. An NPS 6 Sch 40 run with an NPS 2 Sch 40 branch at t_rh 0.10 is adequate on run excess alone (A1 0.37 >= A_req 0.21); raise the required wall and the same opening flips to needing a repad. The required walls come from the pressure design (pipe-pressure-rating); the engineer of record and the AHJ govern. The area balance, not a stamped branch-connection design.
Formula and source
d1 = (branch_od - 2 x branch_wall) / sin(beta); A_required = run_treq x d1 x (2 - sin beta); d2 = max(d1, branch_wall + run_wall + d1/2); L4 = min(2.5 x run_wall, 2.5 x branch_wall); A1 = (2 d2 - d1)(run_wall - run_treq); A2 = 2 L4 (branch_wall - branch_treq); adequate when A1 + A2 >= A_required, else pad_area = A_required - (A1 + A2).
ASME B31.1 para 104.3.1 branch-connection reinforcement (and B31.3 304.3 for process piping), by name; the area-replacement relations are read from the code's figure.
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