API 650 dome roof storage tank design, which is a variation of fixed-roof tanks with a domed roof instead of a cone. These are often used when:

• Aesthetics, snow load, or wind considerations are important

• You want to reduce vapor losses (dome roofs are tighter)

• You're covering large-diameter tanks where cone roofs aren't practical without columns

Let’s dive into it!

🛢️ API 650 Dome Roof Storage Tank – Design Overview

📘 Standard Reference

• API 650 – Welded Tanks for Oil Storage

• Dome roof info is embedded in Section 5 and optional in Appendix G (for aluminum dome roofs)

• Applicable for aboveground, vertical, atmospheric storage tanks

📐 1. Tank Configuration

Feature Description

TypeFixed dome roof (steel or aluminum)

Shape Hemispherical, ellipsoidal, or geodesic dome

Orientation Vertical

Bottom Flat bottom

Roof Self-supporting or rafter-supported dome

Product Petroleum (diesel, crude, kerosene, etc.)

🔍 2. Key Design Inputs

Input Typical Values

Diameter10 m – 100 m+

Height Based on required volume

Design SG0.6 – 1.2 (fluid-specific)

Design Temp≤ 93°C

Wind, SeismicBased on site

Corrosion Allowance1.5 – 3 mm

Tank Capacity100 m³ to 100,000+ m³

🧮 3. Design Aspects

🔹 Shell Design

Same as cone-roof tanks, based on:

• Hydrostatic pressure

• Minimum shell thickness

• Wind and seismic loads (see Appendix E)

API 650 uses 1-ft method or Variable Design Point method

🔹 Roof Design

Steel Dome Roof:

• Hemispherical or elliptical shape

• Self-supporting or supported by rafters/girders

• Needs:

  • Compression ring at the periphery

  • Support ring or column (if not self-supporting)

• Designed for:

  • Dead load (roof weight)

  • Live load (maintenance, snow)

  • Internal pressure (small, per API limits)

Aluminum Dome Roof (Appendix G):

• Lightweight, corrosion-resistant

• Geodesic structure

• Suitable for large diameters

• Used on fixed-roof or floating-roof tanks (as covers)

📏 4. Dome Geometry Basics

For a hemispherical dome roof, the geometry is:

• Radius (R) of dome = half of tank diameter

• Crown height (h) can vary but usually between 1/10 to 1/5 of diameter

For example:

• Tank Diameter = 20 m → Dome radius = 10 m

• Crown height ≈ 2–4 m

🛠️ 5. Components & Appurtenances

Component Notes

Manways Roof manway for access

Nozzles Inlet, outlet, vapor recovery

Vent API 2000 compliant

Pressure relief Required if tank is sealed

Level gauge Float-type or radar

Roof Drainage Optional — rain drains off the dome naturally

Ladders & Platforms Shell-mounted, may include roof platform

🧪 6. Inspection & Testing

• Hydrotest (per API 650): Fill tank to operating height with water

• NDE of Welds:

  • Radiography (RT)

  • Magnetic Particle (MT)

  • Liquid Penetrant (PT)

  • Ultrasonic Testing (UT)

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