Vessels that operate above atmospheric pressure — the second largest static group in the process industries. Vertical or horizontal cylindrical, spherical or special geometries; welded construction in carbon steel, low-alloy or stainless steel depending on service.
Usual types
- Process vessels — gas-liquid separators, reactors, distillation columns.
- Accumulators and surge drums — dampen pulsations and flow misalignment.
- Pressurized storage vessels — LPG, compressed air, industrial gases.
Reliability: internal corrosion (H₂S, CO₂, chlorides), stress cracking (SCC, HIC), creep in high-temperature service and fatigue from thermal or pressure cycling. Risk-based inspection (API 580/581) is the dominant practice.