Issuing body
API
Latest edition
10th Edition (2020)
Region
USA, Global
Equipment items
2
Scope
Sizing methodology and device selection for pressure-relieving devices.
Key requirements (7)
- PRV sizing for gas, vapor, liquid, two-phase relief.
- Effective discharge coefficient Kd: 0.975 (gas, certified), 0.65 (liquid certified).
- Backpressure correction Kb (conventional vs balanced bellows).
- Two-phase via Omega method (HEM) or DIERS.
- Set pressure: ≤ MAWP. Allowable accumulation: 10% (single PRV), 16% (multiple), 21% (fire case).
- Inlet line: max 3% loss at rated flow (rule of thumb to prevent chatter).
- Outlet line: backpressure ≤ 10% set (conventional) or ≤ 50% (balanced bellows).