Horizontal vessels
Saddles are exclusively used with horizontal cylindrical vessels. The location parameter places each saddle relative to the nearest head weld.
Two-saddle rule
PSI always models a two-saddle configuration. Asymmetric placement (unequal
saddleLocation values) is handled by entering different values for each saddle instance.Parameters
Geometry
Height of the saddle web measured from the bottom of the base plate to the vessel shell centreline. Increasing saddle height raises the vessel clearance above the foundation.
Horizontal distance from the nearest head tangent weld line to the saddle centreline. Positioning saddles close to the heads (typically 0.2 × vessel length) reduces bending moments in the shell.
Arc of contact between the saddle and the vessel shell. Options: 120° or 150°.
A 120° contact angle is the minimum recommended for most vessels and produces higher local stresses at the saddle horn. A 150° contact angle distributes the load over a wider arc, reducing horn stresses and is preferred for thin-walled or large-diameter vessels. Select 150° when shell stress checks are marginal at 120°.
Web and Base Plate
Thickness of the saddle web plate that runs along the vessel axis. The web transfers shear from the vessel shell down to the base plate.
Width of the saddle base plate (dimension perpendicular to the vessel axis). Must be compatible with the foundation bolt pattern.
Length of the saddle base plate (dimension along the vessel axis). Longer base plates distribute the bearing load over a greater foundation area.
Rib Stiffeners
Rib parameters are only shown when the vessel type is Horizontal. Ribs are vertical stiffener plates welded between the web and base plate to prevent web buckling.
Number of rib stiffener plates per saddle. Options: 3, 5, or 7. A higher rib count increases out-of-plane stiffness and is required for wide saddles or heavy vessels.
Thickness of each rib plate (mm). Ribs are typically the same material and at least as thick as the web plate.
Friction
Friction condition at the sliding saddle. Options: Frictionless or High friction.
In a two-saddle configuration, one saddle is typically anchored (fixed) and the other is free to slide to accommodate thermal expansion. Setting the sliding saddle to Frictionless represents a PTFE or roller bearing interface. High friction represents a steel-on-steel contact without a slide plate, which transmits larger horizontal loads to the foundation.