Storage tanks: why must any shell opening larger than about 5 cm be reinforced around the nozzle location?

Introduction / Context:
Nozzles and manways cut into thin shells remove load-bearing metal and create stress concentrations. Codes require reinforcement to replace the metal removed and maintain shell strength under internal pressure, wind, and other loads.

Given Data / Assumptions:

• Atmospheric or low-pressure storage tanks.
• Shell openings greater than about 50 mm diameter.
• Standard nozzle neck plus reinforcement pad or integrally reinforced design.

Concept / Approach:
The primary reason for reinforcement is structural: removal of shell material reduces the area that carries membrane stresses. A properly sized reinforcement pad (or added neck thickness) compensates for this loss and spreads stresses to limit peak values around the opening. While good geometry and sealing matter, they are secondary to restoring strength.

Step-by-Step Solution:
Recognize that a hole removes load-bearing shell metal.Apply code principle: replace the lost area with reinforcement to prevent local overstress.Select the option aligning with structural intent.

Verification / Alternative check:
Design standards (e.g., storage tank codes) present area-replacement calculations and limits on reinforcement placement to ensure adequate strength.

Why Other Options Are Wrong:
Reducing discontinuity helps, but the core requirement is strength, not merely shape smoothing.Leak-proofing is achieved by welding and gaskets; reinforcement is not primarily for sealing.

Common Pitfalls:
Undersizing the pad by ignoring corrosion allowance; omitting tell-tale holes for leak detection between shell and pad.

Final Answer:
To prevent local overstressing of the shell around the opening