Steel Storage Tanks: API 650, AWWA D100 and NFPA 22 Basics
An overview of above-ground steel storage tank standards and design: API 650 for oil and water, AWWA D100 for water, NFPA 22 for fire water, materials, foundations, testing and coatings.
Saudi Steel Work Editorial Team · · 3 min read
Short answer: Large welded steel storage tanks are usually designed to API 650 (oil and also water storage), AWWA D100 (welded water tanks) or, for fire water, NFPA 22 together with a structural design standard. The design defines shell thickness by course, bottom and roof type, nozzles, wind and seismic checks, materials, welding, NDT and hydrostatic testing.
Steel tanks store water, fire reserves, fuel, chemicals and process fluids across Saudi industry, agriculture and utilities.
Main standards
| Standard | Scope |
|---|---|
| API 650 | Welded tanks for oil storage (and widely used for water), atmospheric pressure |
| AWWA D100 | Welded carbon steel tanks for water storage |
| AWWA D103 | Factory-coated bolted steel tanks for water |
| NFPA 22 | Water tanks for private fire protection |
| API 620 | Low-pressure large tanks |
Key design elements
Shell: made of courses; thickness decreases with height. Determined by hydrostatic head, product density, allowable stress and corrosion allowance.
Bottom: usually lap- or butt-welded plates on a prepared foundation, often sloped for drainage.
Roof: fixed cone or dome roofs; floating roofs for volatile products.
Wind and seismic: checked for overturning, sliding and shell buckling under SBC loads.
Nozzles and appurtenances: inlets, outlets, drains, overflows, manways, vents, ladders, platforms.
Materials
Common plate grades include ASTM A36, A283, A516 and EN equivalents, as permitted by the standard (steel plate grades). Stainless and duplex for corrosive products.
Fabrication and testing
- Qualified welding procedures (WPS and PQR)
- Radiography or UT of shell welds per standard
- Vacuum box testing of bottom welds
- Hydrostatic testing of the completed tank
Coatings
- Internal: linings suitable for product (potable water approvals where needed)
- External: paint systems for the environment (corrosion protection)
- Cathodic protection for tank bottoms where specified
Foundations
Ring wall or slab foundations designed for tank loads and settlement. Coordinate anchor bolts early.
Welded vs bolted
Bolted galvanized or glass-fused tanks install quickly at remote sites; welded tanks suit large capacities and long life.
See our steel storage tanks service and fire fighting pipes.