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Horizontal Pressure Vessel on Two Saddles
Verification of saddle-horn localized shell bending stresses, vacuum buckling, and ASME Section VIII compliance for a horizontal pressure vessel.
Horizontal process vessels supported on twin saddles experience severe localized circumferential bending stresses (saddle-horn stresses) that frequently dictate shell plate thickness. Under combined internal operating pressure, hydrostatic liquid head, and external piping loads, thin-walled shells can suffer localized buckling near support horns. The WebCAE model accurately couples MITC4 cylindrical shell patches with stiffened saddle webs and ring frames to evaluate full stress states and buckling factors.
1. Geometry & FEA Mesh
- •Cylindrical vessel shell Ø3.2 m (R = 1.6 m), shell length 12.0 m (t = 18 mm), axis elevation z = 2.2 m
- •Two end heads: conical transitions (t = 20 mm), bolting flanges (t = 28 mm), and stiffened manway covers (t = 30 mm)
- •Two reinforced saddle supports at x = 2.0 m and 10.0 m with trapezoidal web plates (t = 24 mm), base plates (t = 30 mm), and tee gussets
- •Mesh comprising 1,380 MITC4 quadrilateral shell elements and 382 Timoshenko beam stiffener elements (8,279 DOFs)
2. Loads & Boundary Conditions
- •Pinned and sliding foundation boundary conditions at the base plates of fixed and expansion saddle supports (z = 0)
- •Internal gauge operating pressure p = 1.2 MPa (12 bar) applied uniformly over the interior shell and head patches
- •Axial compressive thrust 2.5 MN representing extreme piping reaction loads combined with full liquid self-weight
3. Simulation Results & Findings
- ✓Critical shell buckling factor λ₁ = 28.84 provides high safety margin against compressive wrinkling near the saddle horns
- ✓Fundamental breathing / beam bending vibration frequency f₁ = 22.52 Hz confirms high structural rigidity
- ✓Ring stiffeners effectively redistribute saddle-horn peak bending moments into membrane hoop tension
Process equipment design offices use WebCAE to verify horizontal vessels against LP Zick criteria and ASME Section VIII rules without cumbersome external meshing workflows. Direct browser-based simulation of combined shell and saddle framing accelerates vessel certification and optimizes ring stiffener spacing.
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