Atmospheric storage tank design: For tanks of diameter ≤ 15 m, what is the typical minimum shell plate thickness specified for elastic stability?

Introduction / Context:
Atmospheric storage tanks must resist wind loads, handling damage, local buckling, and fabrication tolerances. Even when internal pressure is negligible, a minimum shell thickness is imposed for elastic stability and practical fabrication.

Given Data / Assumptions:

• Cylindrical vertical tank with diameter ≤ 15 m.
• Design pressure near atmospheric; hydrostatic head due to stored liquid applies.
• Common industry practice and standards guide minimum gage selection.

Concept / Approach:
Thin shells are susceptible to elastic instability (local buckling or wrinkling) during construction, lifting, or service. A nominal minimum thickness (often around 5 mm) provides stiffness, allows welding without burn-through, and tolerates corrosion allowances and out-of-roundness within reasonable limits.

Step-by-Step Solution:

Verification / Alternative check:
Industry guides and many company standards specify a lower bound of about 5 mm (exclusive of additional corrosion allowance) for small-to-medium atmospheric tanks.

Why Other Options Are Wrong:

• 2 mm: too thin for handling/welding and prone to buckling.
• 10 or 15 mm: possible in special cases but not the minimum; adds unnecessary cost for small tanks.

Common Pitfalls:
Ignoring local shell buckling near nozzles; neglecting corrosion allowance; underestimating wind loads and required stiffening rings.

Final Answer:
5 mm