Category
Pressure Vessels & Reactors
Subcategory
Separator
Applicable standards
3
Issuing bodies
2
Description
Vertical or horizontal vessel for liquid-vapor (and liquid-liquid) separation.
Applicable Standards (3)
API — 2 standards
API 12J / API Spec 12J
Specification for Oil and Gas Separators
Sizing, design and rating of oil & gas separators (2-phase, 3-phase).
Key requirements (8)
- Specification for oil and gas separators (2-phase, 3-phase).
- Sizing methods: settling theory + experience factors.
- Liquid retention time: typically 1–3 minutes for 2-phase; 5+ for 3-phase.
- Mist eliminator: wire mesh ≥ 6" thick; design velocity ≤ 0.1·(ρL−ρV)/ρV)^0.5 m/s.
- Vapor velocity: typically ≤ 0.107·(ρL−ρV)/ρV)^0.5 m/s through mist eliminator.
- L/D ratio: 3–5 typical for horizontal; 3–5 for vertical.
- Inlet diverter, weir/baffle plate for liquid-liquid separation.
- Companion to API RP 14C for safety system integration.
API 521
Pressure-relieving and Depressuring Systems
Causes of overpressure, relief load determination, depressuring, flare/disposal system design.
Key requirements (6)
- Sizing and design of pressure relief and depressuring systems.
- Relief scenarios: blocked outlet, fire, control valve failure, tube rupture, power failure, thermal expansion, runaway reaction, abnormal heat input.
- Fire heat input: Q = 21,000·F·A^0.82 BTU/hr (vapor space < 25 ft elevation; F = environment factor 0.3–1.0).
- Depressuring: typically blowdown to 50 % of design pressure or 100 psig (whichever lower) within 15 minutes for vessels exposed to fire.
- Flare radiation: max permissible 1.58 kW/m² (continuous), 4.73 kW/m² (limited exposure), 6.31 kW/m² (emergency).
- Disposal system sizing: must handle simultaneous events — 'global event' analysis.
ASME — 1 standard
ASME BPVC Sec VIII Div 1
Rules for Construction of Pressure Vessels
Mandatory rules for design, fabrication, inspection, testing and certification of pressure vessels operating above 15 psig (~1 barg).
Key requirements (12)
- Applies to vessels with internal pressure > 15 psig (1.03 barg) up to ~3000 psi (Div 1 sweet spot).
- Joint efficiency E: 1.0 (full radiography), 0.85 (spot RT), 0.70 (no RT) for Type 1 butt joints.
- Shell thickness: t = P·R/(S·E – 0.6·P) for circumferential stress (UG-27).
- Head thickness: t = P·D/(2·S·E – 0.2·P) for 2:1 ellipsoidal heads (UG-32).
- Hydrostatic test pressure: 1.3 × MAWP × (S_test/S_design) — UG-99.
- Pneumatic test (when hydro impractical): 1.1 × MAWP — UG-100.
- Corrosion allowance is added to calculated thickness (not included in S formula).
- MDMT and impact testing per UCS-66 / Figure UCS-66; below the curve, Charpy V-notch impacts are required.
- PWHT thresholds per UCS-56 — generally required above 19 mm thickness for P-No. 1 carbon steels.
- Nozzle reinforcement: area replacement method (UG-37) within reinforcement zone.
- Maximum allowable stress S: from ASME II Part D, Table 1A/1B/3 — temperature dependent.
- Flanges per ASME VIII-1 Appendix 2 (or B16.5 for standard sizes).
Note: Most widely used pressure vessel code worldwide.