Screen PSV atmospheric releases for jet-dominated dispersion per API Standard 521 Equation 55: determine if rigorous dispersion modeling is required or if the release passes prescreening criteria.
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What It Does
Enter your PSV rated capacity, discharge conditions, PSV tailpipe size, and atmospheric parameters. The calculator evaluates the API 521 (7th edition) Equation 55 jet dominance criteria: Reynolds number, fluid velocity, and jet-to-wind velocity ratio — to determine whether the atmospheric release is jet-dominated and safe to vent without further analysis.
If all criteria pass, no rigorous dispersion modeling is required. If any criterion fails, the tool flags the issue and indicates that a detailed study is warranted.
Prescreening Checks
Before running Equation 55, the calculator validates that the release is within the applicable range:
- Molecular weight ≤ 60 lb/lbmol
- H₂S concentration ≤ 20 ppm
- Tailpipe height ≥ 7 ft above grade
- No hazardous chemicals present
Releases outside these bounds require separate evaluation.
How It Works
Free tier: Run the screening calculation and view pass/fail results on screen for each API 521 criterion: jet dispersion Reynolds number, minimum fluid velocity, and jet-to-wind velocity ratio.
Paid report: Generate a professional PDF report with cover page, design basis, assumptions, detailed calculation results, prescreening validation, and an attachment section for equipment photos and reference documents, which are then ready for project files or regulatory documentation.
Why Use This
API 521 requires evaluation of atmospheric releases from pressure relief devices. If a PSV vents to atmosphere, you need to demonstrate that the discharge disperses safely. Running rigorous dispersion modeling (PHAST, AERMOD, SLAB) for every PSV is expensive and time-consuming. This screening tool lets you quickly determine which PSVs pass the jet dominance criteria and which ones actually need a detailed study.
The calculation evaluates discharge velocity at 25% of rated capacity for conservatism, consistent with standard industry practice for first-pass screening.
Typical Applications
Upstream and midstream facilities with PSVs venting to atmosphere. MOC evaluations where PSV capacity or tailpipe configuration changes. New facility design where atmospheric vents need dispersion justification. Audit and compliance reviews where existing atmospheric discharges need documentation.
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Need a rigorous dispersion study or PE-reviewed analysis? Contact Franc Engineering