Storage tank design: Which roof type is most commonly provided on cylindrical storage tanks for general service?

Introduction / Context:
Fixed-roof cylindrical tanks are widespread for liquids such as water, light hydrocarbons (when not requiring floating roofs), and chemicals. Roof geometry affects structural behavior, rainwater shedding, fabrication simplicity, and cost.

Given Data / Assumptions:

• Atmospheric or low-pressure fixed-roof tanks for general liquid service.
• No special internal pressure demanding domed roofs.

Concept / Approach:
Conical roofs are simple to fabricate with plate segments, provide efficient drainage, and achieve adequate strength with rafters and columns where needed. Flat roofs are uncommon for outdoor service due to poor drainage. Domed (spherical segment) roofs are used on low-pressure tanks and larger diameters but entail more complex fabrication; “umbrella” is a descriptive variant but not the standard choice for general service.

Step-by-Step Solution:

Verification / Alternative check:
Tank standards and vendor catalogs show conical roofs as the default for many fixed-roof designs, with options for self-supporting or supported configurations.

Why Other Options Are Wrong:

• Flat: drainage and ponding issues.
• Dome: often used for low-pressure/vapor-tight tanks but not the most common across general services.
• Umbrella: not the prevalent standard term/choice in typical specifications.

Common Pitfalls:
Assuming floating roofs (used for volatile products) fit the question; those are different from fixed roofs addressed here.

Final Answer:
Conical roof