Technical EngineeringJanuary 28, 20251 min read

Accurate PRV Sizing Prevents Production Shutdowns

#Process Safety #Relief Systems #PSV #Simulation

Problem

Relief valve undersizing causes frequent trips and production losses

Solution

Dynamic simulation-based sizing ensures adequate capacity

The Challenge

Undersized pressure relief valves (PRVs) are a common issue in offshore and onshore facilities. When relief capacity is inadequate for worst-case scenarios—like blocked outlet or fire cases—the system trips unnecessarily, causing production losses of $50,000+ per hour.

Traditional API 521 sizing methods often miss dynamic effects during transient upsets, leading to conservative oversizing or dangerous undersizing.

The Solution

Dynamic Process Simulation provides accurate relief loads:

  1. Transient Analysis: Model the actual pressure buildup rate during upset conditions
  2. Scenario Testing: Evaluate multiple credible scenarios (blocked outlet, cooling failure, fire)
  3. Integration Effects: Account for upstream/downstream system responses
  4. Validation: Verify against actual plant data where available

Using tools like HYSYS Dynamic or UniSim, we can determine precise relief requirements and avoid both undersizing risks and unnecessary capital costs from oversizing.

Impact

Proper PRV sizing ensures:

  • Reduced trips: 40% fewer false shutdowns
  • Safety compliance: Meet API 520/521 standards
  • Cost optimization: Right-sized relief systems save 15-20% on equipment costs

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