Pressure Relief System Design of Non-Reactive Systems
Pressure Safety Valve (PSV) design in non-reactive systems is based on evaluating credible overpressure scenarios where the process fluid does not undergo exothermic decomposition or runaway reactions. The goal is to ensure the valve relieves sufficient mass flow to prevent equipment pressure from exceeding the allowable accumulation limits per codes (ASME, API).
Full relief sizing for hydrocarbon, inert, and other non-reactive process streams:
Identification of credible overpressure scenarios (blocked discharge, thermal expansion, fire, relief from compressor or pump failure)
API 521 / API 520-compliant sizing calculations (liquid, gas, vapor) and PSV selection support
Liquid flashing analysis and two-phase decision logic when applicable
Valve metering and inlet piping recommendations to avoid chatter or blowdown issues
Frequently Asked Questions (FAQ)
1. Which standards do you follow for non-reactive relief sizing?
We follow industry practice and codes (example: API 520/521, ASME recommendations) for scenario identification and sizing methodology
2. What are the typical Non-Reactive Overpressure Scenarios?
- Blocked discharge / outlet isolation
- Fire case exposure
- Gas blowby through control valves
- Utility or inert gas overpressure (N2 entrainment, instrument gas)
- Tube rupture (shell & tube heat exchanger)
- Thermal expansion of trapped liquid
Each scenario is screened, and the worst-case relieving rate becomes the PSV design basis.
3. How do you select the PSV type?
Selection (conventional, balanced bellows, pilot-operated) depends on:
- Corrosive service
- Back pressure sensitivity
- Required tight sealing at normal conditions
- Dirty/wet service acceptance
4. How is this different from PSV sizing of reactive system?
Reactive PSV sizing requires chemical kinetic data and runaway modeling (DSC/ARC/VSP2). Non-reactive PSV sizing relies only on process conditions and thermophysical properties, making it simpler but still scenario driven.
5. Why is back pressure important?
Back pressure can affect valve stability and flow capacity. Systems tied into a flare header have fluctuating back pressure during contingency events, so this must be accounted for to avoid chatter and capacity losses.
6. Will the PSV be discharged to atmosphere, containment or flare?
Both are possible. Discharge routing depends on site philosophy, regulatory requirements, and risk tolerance. Hydrocarbon services typically route to flare for safe combustion and environmental compliance.