Supports for vertical vessels – understanding lug supports Which statement best characterizes lug supports for vertical vessels in comparison to skirt supports?

Introduction / Context:
Vertical vessels are commonly supported by skirts, legs/lugs, or brackets. The choice depends on vessel size, operating loads (pressure, wind, seismic), and nozzle locations. Proper selection prevents excessive shell stresses and simplifies foundation design.

Given Data / Assumptions:

• Vertical cylindrical vessel with typical nozzle penetrations.
• Comparison of common support types.
• Focus on relative applicability by size/height.

Concept / Approach:
Skirt supports transfer loads through a cylindrical shell to a base ring and foundation—best for tall, heavy, high-temperature pressure vessels. Lug (leg) supports weld pads or clips to the shell that bear on structural members; they are suited to small-to-medium, relatively short vessels where shell local stresses are manageable. Thus, lug-supported vessels are generally smaller and shorter than skirt-supported ones. Bracket supports are a broader category; while a lug is a type of bracket, “same as” is an imprecise equivalence and not universally true in design terminology. Thick, tall vessels are better on skirts, not lugs.

Step-by-Step Solution:

Verification / Alternative check:
Mechanical design guides show skirts preferred above certain diameter/height ratios and thermal conditions; lugs have allowable local stress limits.

Why Other Options Are Wrong:

• (a) Opposite of standard practice; thick/tall vessels use skirts.
• (b) Over-simplifies terminology; not strictly identical in application and geometry.
• (d) Includes incorrect (a) and (b).

Common Pitfalls:
Ignoring local shell stress checks under lug loads; even short vessels can require reinforcing pads or rings.

Final Answer:
Lug supports are usually provided for vessels of much smaller height than skirt-supported vessels.