Why are most industrial storage vessels and tanks designed as right circular cylinders?

Introduction / Context:
Tanks and pressure vessels in chemical plants store liquids and gases and must withstand internal pressure and external loads. Shape selection affects stress distribution, fabrication complexity, and cost.

Given Data / Assumptions:

• Thin-wall pressure vessel theory applies for many tanks.
• Fabrication uses rolling, welding, and standard head geometries.
• Cost and safety drive geometry choices.

Concept / Approach:
A cylinder distributes hoop stress uniformly under internal pressure and avoids stress concentrations typical of corners. Cylinders are also straightforward to roll from plate and to weld with standard heads (ellipsoidal, torispherical), enabling efficient, repeatable fabrication.

Step-by-Step Solution:
Step 1: Relate shape to stress: cylinders minimize peak stress vs prismatic shapes.Step 2: Relate shape to construction: rolling plates into shells and welding longitudinal and circumferential seams is standard practice.Step 3: Recognize cost and safety benefits: predictable stress distribution reduces required thickness for a given pressure, and standardization lowers fabrication cost.Step 4: Conclude both strength and fabrication advantages are decisive.

Verification / Alternative check:
Compare with rectangular tanks: corner regions would need heavy reinforcement; fabrication becomes complex and expensive for pressure service.

Why Other Options Are Wrong:
Only strength or only fabrication misses the full rationale.Neither: contradicts well-established design practice.Less floor area: not a primary governing reason.

Common Pitfalls:
Assuming spheres are always better: spheres minimize surface area but are far more difficult and costly to fabricate at large sizes; cylinders are the practical compromise.

Final Answer:
Both (a) and (b).