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Lug supports (also called bracket supports) are discrete attachment plates welded to the vessel shell that transfer loads to a structural steel framework or building structure. They are common in vertical vessels supported off a platform, heat exchangers supported from structural beams, and agitated reactors where the vessel must be elevated.

Discrete attachment

Lugs transfer concentrated loads at a small number of points, producing local shell stresses that must be evaluated per WRC 107/537 or finite element analysis.

Gusset and pad options

Stiffener gussets and pad plates are optional sub-configurations that reduce local shell stresses and improve weld fatigue life.

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Parameters

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Lug Layout

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lugQuantity
select
required
Number of lug supports distributed symmetrically around the vessel circumference. Options: 2 or 4. Two lugs are used for simple horizontal reactions; four lugs provide better load distribution and stability.
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lugElevation
number
required
Height of the lug centreline above the vessel datum (typically the vessel bottom tangent line). The elevation determines the moment arm for any horizontal force component acting at the lug.

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Lug Dimensions

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lugWidth
number
required
Width of the lug plate measured along the vessel circumference. A wider lug distributes the load over a longer arc of the vessel shell, reducing peak local stresses.
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lugLength
number
required
Radial projection length of the lug plate measured from the vessel shell OD. The length sets the lever arm for bending at the lug-to-shell weld.
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lugThickness
number
required
Thickness of the lug plate. The lug plate is checked for bending, shear, and bearing at the bolt hole.
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lugEccentricity
number
required
Horizontal offset between the bolt hole centreline and the vessel shell outside surface. A non-zero eccentricity introduces an additional moment at the lug base weld, which increases local shell stresses.
Eccentricity is the most significant geometric parameter governing local shell stress at the lug. Where possible, minimise eccentricity by positioning the bolt hole as close to the vessel shell as structural clearance allows.
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lugHoleDiameter
number
required
Diameter of the bolt or pin hole in the lug plate. The hole diameter is used to calculate the net section area of the lug and the bearing stress on the hole wall.

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Stiffener Gusset

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lugGusset
select
required
Whether a stiffener gusset plate is added to the lug. Options: Yes or No. Gussets are triangular or trapezoidal plates welded between the lug and the vessel shell to increase lug stiffness and reduce the bending moment transferred to the shell.
When Stiffener gusset is set to Yes, the following parameter appears:
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lugGussetThickness
number
Thickness of the gusset plate. The gusset is typically the same thickness as or slightly thinner than the lug plate.

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Pad Plate

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lugPadPlate
select
required
Whether a pad plate (reinforcing plate) is interposed between the lug and the vessel shell. Options: Yes or No. A pad plate spreads the lug attachment load over a larger shell area, reducing peak membrane stress and improving weld joint efficiency.
When Pad plate is set to Yes, the following parameters appear:
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lugPadWidth
number
Width of the pad plate measured along the vessel circumference. Should extend beyond the lug width by at least one shell thickness on each side.
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lugPadLength
number
Length of the pad plate measured along the vessel axis. Should extend beyond the lug length by at least one shell thickness at each end.
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lugPadThickness
number
Thickness of the pad plate. The pad plate thickness affects the local reinforcement area and must be compatible with the shell material for welding.
Adding a pad plate is the most cost-effective way to bring a marginal lug shell stress check into compliance. If stress results exceed allowables with no pad, enable Pad plate and increase lugPadWidth and lugPadLength before increasing vessel shell thickness.

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