FieldEngineersKitEngineering Reference & ASME Code Basis
1. Formula & conversion factors
ASME B31.3 (2022 Edition) · Process Piping — Paragraph 304.3.3 (branch reinforcement) · ASME B36.10M / B36.19M (NPS × schedule OD and wall thickness)
t = PD / (2(SEW + PY))
A1 = d1 th (2 − sin β)
Areq = max(0, A1 − (A2 + A3 + A4))
ASME B31.3 Para. 304.3.3 area replacement · mill tolerance on nominal wall
Screening calculator for welded branch reinforcement per ASME B31.3 Paragraph 304.3.3. Computes required area A₁ vs available excess wall A₂/A₃ and fillet-weld A₄ (leg²+leg²), then recommends pad OD/ID/thickness when A_req > 0. Nominal schedule walls are reduced by mill under-tolerance. Design temperature is recorded only — allowable stresses S_h/S_b/S_r are user inputs at temperature. No schematic: geometry limits d₂/L₄ and pad sizes appear in result tables.
- A₁ (Required reinforcement area) — d₁ · t_h · (2 − sin β) — area to be replaced at the branch opening.
- A₂ (Header excess area) — (2d₂ − d₁) · (T_H − t_h − c) when positive.
- A₃ (Branch excess area) — 2 L₄ (T_B − t_b − c) / sin β when positive.
- A₄ (Fillet weld area) — Approximation leg_h² + leg_b² for both fillet legs.
- d₂ (Reinforcement zone limit) — min(D_h, max(d₁, (T_B−c)+(T_H−c)+d₁/2)).
- L₄ (Effective branch length) — min(2.5(T_H−c), 2.5(T_B−c)) for initial pad screening.
2. Quick reference lookup table
| Header / branch | Pressure | Expected status |
|---|---|---|
| 10" STD / 6" STD | 500 psi | Adequate without pad |
| 16" STD / 10" STD | 800 psi | Pad required |
| DN250 / DN150 STD | 35 bar | Adequate without pad |
| DN400 / DN250 STD | 55 bar | Repad required |
| 8" STD / 4" STD | 600 psi @ 90° | Screen A₁ vs A₂–A₄ |
3. How to use this calculator
- 1
Select header and branch NPS × schedule
Branch NPS must be ≤ header NPS. STD maps to Sch 40 in the lookup tables.
- 2
Enter design pressure and allowable stresses
Use project design P and temperature-adjusted S values for header, branch, and pad material.
- 3
Review A₁ vs available area
Compare required A₁ against A₂ + A₃ + A₄. Positive A_req triggers pad sizing.
- 4
Confirm pad dimensions
Use recommended pad OD, ID (= branch OD), and T_pad as a screening start — verify with detailed calc.
4. Engineering FAQ
ASME B31.3 Para. 304.3 requires enough reinforcement area at branch connections. This tool applies the area replacement method: required area A₁ from the branch opening vs excess wall and weld areas A₂–A₄.
When A_req > 0, pad metal area is A_req_metal (stress-adjusted if S_r < S_h). Thickness T_pad ≈ A_req_metal / (2 W_pad) with W_pad = max(d₂ − D_b/2, 0.5 in) screening minimum.
Yes. Required thickness uses t = PD / (2(SEW + PY)) including W on both header and branch.