| name | pressure-vessel-nozzle |
| description | Pressure vessel nozzle design — area replacement method (ASME VIII UG-37), nozzle reinforcement, opening limits, local loads (WRC-107/WRC-297), hillside nozzles, trunnion loads. |
| metadata | {"priority":7,"promptSignals":{"phrases":["pressure vessel nozzle","nozzle reinforcement","area replacement","UG-37","WRC-107","nozzle local load","nozzle pad"],"minScore":3}} |
Pressure Vessel Nozzle Design — Complete Skill
Nozzle Reinforcement — ASME VIII UG-37
Area Replacement Method
When a hole is cut in a shell, the removed area must be compensated (replaced) within the "zone of reinforcement"
Required area (A_required):
A_req = d × t_r × F + 2 t_n × t_r × F × (1 - f_r1)
d = finished diameter of opening (corroded bore)
t_r = required shell thickness (from ASME UG-27, pressure only)
F = correction factor (1.0 for radial nozzles; 0.5 for nozzles at angles to axis)
t_n = nozzle wall thickness; f_r1 = S_n/S_s (ratio of nozzle to shell allowable stress)
Available reinforcement area (A_available):
A₁ = (t_s - t_r) × d [excess shell thickness]
A₂ = (t_n - t_rn) × 2h [excess nozzle wall; h = ±2.5t_n inward + outward projection]
A₄₃ = reinforcing pad area A₃ = (W_pad × t_pad) (add pad if A₁ + A₂ < A_req)
Acceptance: A₁ + A₂ + A₃ ≥ A_req
Zone of reinforcement:
Width = max(d, r_n + t_s + t_n)
Height = max(2.5 t_s, 2.5 t_n + t_pad)
Large Opening Exceptions (> half shell OD)
UG-36(b)(1): may require WRC bulletin analysis or FEA
UG-37 not valid for openings > 1/2 shell OD (separate methods apply)
Nozzle Wall Thickness (UG-45)
Minimum nozzle neck thickness (for pressure):
t_n,min = max(t_rn, t_n,structural)
t_rn = P r_n / (S_n E - 0.6P) (same as shell formula but for nozzle)
t_n,structural = minimum structural per UG-45(b): 0.875 × standard wall for pipe nozzle
Standard Nozzle Loadings (ASME and Vendor)
Internal pressure only → UG-37 area replacement
External loads → WRC-107 or WRC-297 (stress in shell at nozzle junction)
WRC-107 (Wichman-Hopper-Mershon):
Charts for local stresses due to radial force, circumferential moment, longitudinal moment, torsion
Stress at 4 locations: top/bottom/left/right of nozzle junction
Input: D_m/T_shell (shell parameter), d/D_m (nozzle-to-shell ratio)
Output: dimensionless stress coefficients → multiply by F_p, M_c, M_L, M_T
WRC-297:
More accurate for d/D_m up to 0.5; extended range
Combined stress check:
σ_combined = P×D_m/(2T) + σ_local (from WRC) vs. allowable (ASME Section VIII App. L)
For fatigue: peak stress range from WRC analysis → number of cycles (Div. 2)
Nozzle Flexibility
API 610 (pump standards) and API 650 (storage tanks) specify maximum nozzle loads
API 610 allowable loads (per Table 5):
F_r = allowable radial force; F_a = allowable axial; M_a, M_b = allowable moments
Typically scale with nozzle size; e.g., 6" nozzle: F_r ≈ 2700 N, M_a ≈ 3050 N·m
When loads exceed API 610: provide secondary support or redesign piping for lower reaction
Hillside (Offset) Nozzles
Nozzle axis does not pass through vessel centerline
F-factor modification for angle to meridian: F = sin(θ_angle) approximately
Hillside increases structural loads at one side of nozzle → asymmetric reinforcement
WRC-107 conservative for hillside → use FEA for accuracy
Nozzle-to-Shell Welding (ASME IX / D1.1)
Full penetration weld (Set-in or Set-on, per UW-16):
Set-in nozzle (inserted through shell): inside corner weld + outside fillet/partial pen
Set-on nozzle (abutting shell OD): full or partial penetration weld
Minimum weld size: per UW-16(d); full pen preferred for elevated temperature / cyclic
AWS D1.1 / ASME Section IX weld procedure qualification required
Trunnion and Lifting Lug Loads
Trunnion: cylindrical protrusion welded to vessel for support/transport
Local loads from trunnion: FEA preferred; WRC-107 conservative approximation
Minimize: use wide trunnion base; reinforce shell locally; check shell at attachment
Lifting lug: ASME PCC-1 / vendor guidance; check lug and attachment weld
Lug design: shear + bearing + out-of-plane bending from dynamic factor (DAF = 2.0 typical)
ASME Code References
UG-27: Shell thickness under internal pressure
UG-28: Shell under external pressure
UG-36: Openings and their reinforcement (general)
UG-37: Reinforcement required; area replacement
UG-45: Nozzle wall thickness
Appendix 1: Supplementary rules
Appendix L: Fatigue of vessels
Output
Provide: A_req [mm²], A₁ + A₂ + A₃ [mm²] (adequacy check), pad dimensions (if required), nozzle wall thickness t_n [mm] vs. t_n,min, WRC-107 stress results [MPa] at critical location, comparison to ASME allowable, nozzle external loads vs. API 610 limits.
