Large-diameter vessels operating at atmospheric pressure (or near) — the backbone of liquid storage in refineries, terminals and chemical plants. Designed to API 650 and maintained per API 653 (risk-based inspection).
Usual types
- Fixed roof — cone or dome; low-volatility products and heavy oils.
- External floating roof (EFR) — floats in contact with the product; reduces vapor emissions.
- Internal floating roof (IFR) — floats under a fixed roof; combines protection and emissions control.
Reliability: bottom corrosion (plate in contact with soil/accumulated water), CUI (corrosion under insulation) on the shell, fatigue of nozzles from foundation differential settlement. Typical internal inspection every 10–20 years (API 653, adjusted by RBI).