Which standard does FieldEngineersKit follow?

API RP 520 Part II §4.2 for open-discharge vapor/gas reaction forces, with ASME VIII-1 Appendix M guidance. Momentum matches the Part II US customary term when converted to SI.

Why is DLF often 2.0?

For sudden popping on open vent elbows, API 520 Part II allows a dynamic load factor up to 2.0 as a screening amplification of the steady thrust.

Can I use this for liquid relief?

No. Liquid, two-phase, and water-hammer cases need dedicated transient piping analysis — not this vapor/gas screen.

Safety Relief Valve (PSV) Reaction Force Calculator (API 520 Part II) — CO₂ · 25 000 kg/h · NPS 4

Parameter	Value
Nominal pipe size (NPS)	4"
Schedule	Sch 40
Test gas	Co2
Outside diameter (OD)	114.30 mm (4.500 in)
Wall thickness (t)	6.02 mm
Inside diameter (ID)	102.26 mm

Engineering Reference & ASME Code Basis

1. Core Formula & Variable Definitions

API Recommended Practice 520 Part II (6th Ed., 2015) §4.2 Reaction Forces · ASME BPVC Section VIII Division 1 Appendix M (Para. M-14) · ASME B31.1 Appendix II (safety valve installation guidance) · ASME B36.10M outlet pipe inside diameter

v = √[ 2k/(k+1) · (R/M) · T ] · F_mom = (W/3600)·v

F_press = max(0, P_e − P_atm)·A_exit · F_total = (F_mom + F_press)·DLF

API RP 520 Part II §4.2 open-discharge vapor/gas screen · ASME VIII-1 Appendix M guidance · R = 8314 J/(kmol·K)

Default duty CO₂ · 25 000 kg/h · NPS 4F_total 5.98 kN (DLF 2.0)F_steady 2.99 kNDLF 1.0 – 2.0

Sonic exit velocity from stagnation temperature matches the API 520 Part II US customary momentum term when converted to SI. Exit static pressure uses continuity at T_e = T·2/(k+1). Outlet area from ASME B36.10 pipe ID. Base bending moment assumes a 1.5 m (4.92 ft) vent-elbow lever arm for screening only.

F_total (Peak dynamic reaction force) — Steady reaction scaled by DLF for sudden popping (N or lbf).
W (Nameplate relieving capacity) — Mass flow rate on the PSV nameplate (kg/h or lb/h).
v (Exit velocity) — Sonic exit velocity from isentropic critical flow at relieving temperature.
P_e (Exit static pressure) — Absolute static pressure at the sonic exit plane from mass continuity.
A_exit (Outlet pipe flow area) — π/4 · ID² from selected NPS and schedule (B36.10).
DLF (Dynamic load factor) — Popping amplification (typically 1.1–2.0 for open vent elbows).

2. Screening Assumptions

Vapor/gas open-discharge reaction screen with optional closed-header momentum-only mode. Not a substitute for transient piping analysis.

Default duty25 000 kg/h CO₂ · 180 °C · NPS 4 Sch 40 · DLF 2.0

Hero F_total = 5.98 kN; F_steady = 2.99 kN (momentum + exit pressure).

Outlet areaASME B36.10 ID for selected NPS / schedule

A_exit = π/4 · ID². Sch 10 / 40 / 80 supported in Phase-1.

Base moment arm1.5 m (4.92 ft) screening offset

M_bending = F_total · 1.5 m for open vent elbow. Adjust in detailed layout.

Out of scopeLiquid · two-phase · water hammer · full closed-header P₁/P₂ layout

Use Caesar II / equivalent dynamic piping analysis for those cases.

Quick Reference Lookup Table

Open-discharge screening — CO₂ at 180 °C, DLF 2.0, Sch 40 outlet
W (kg/h)	NPS	F_steady (kN)	F_total (kN)	v (m/s)
10 000	3	1.05	2.09	311
25 000	4	2.99	5.98	311
25 000	6	2.16	4.32	311
50 000	6	5.76	11.51	311
50 000	8	4.37	8.75	311
100 000	8	12.02	24.04	311

Forces scale with W; exit velocity depends on T, M, and k (not NPS). Larger NPS reduces exit pressure thrust. Confirm project fluid data and piping dynamics for design.

3. Applicability & Fluid Limits

API 520 Part II reaction-force screening applies to single-phase vapor/gas relieving through an open vent or simplified closed header.

Group / Regime	Range / Condition	Limit / Criterion	Engineering Notes
Vapor / gas (ideal-gas screen)	−50 to 600 °C input band	—	Uses MW and k from API 520–style presets (CO₂, air, steam, N₂, methane, light HC) or custom entries.
Open discharge vent elbow	Same	—	Includes exit pressure thrust above atmosphere and DLF up to 2.0 for popping.
Closed discharge header	Same	—	Momentum-only screen — layout-specific pressure terms are not modeled.
Liquid / two-phase / flashing	N/A	—	Out of scope — requires multiphase transient analysis.

Code Applicability & Safety Boundaries

Screening only — not a certified piping support design
Confirm nameplate capacity units (kg/h vs lb/h) before applying DLF

4. Step-by-Step Worked Example

Field VerificationShow

Worked example — CO₂ · 25 000 kg/h · NPS 4 Sch 40

Open-discharge PSV relieving carbon dioxide at 25 000 kg/h and 180 °C through an NPS 4 Schedule 40 vent (ID 102.26 mm), DLF = 2.0, P_atm = 1.013 barA.

W:25 000 kg/hT:180 °C (453.15 K)Gas:CO₂ · M = 44.01 · k = 1.30Outlet:NPS 4 Sch 40

Sonic exit velocity

v = √[2k/(k+1)·(R/M)·T]

Result:v ≈ 311 m/s

Momentum and pressure thrust

F_mom = (W/3600)·v; P_e from continuity; F_press = (P_e−P_atm)·A

Result:F_mom ≈ 2.16 kN; F_press ≈ 0.83 kN; F_steady ≈ 2.99 kN

Apply DLF

F_total = F_steady · 2.0

Result:F_total ≈ 5.98 kN

Conclusion: Peak screening reaction is F_total = 5.98 kN (F_steady = 2.99 kN). Use this thrust with the project support/layout model; liquid or two-phase relief is out of scope.

5. How to screen PSV open-discharge reaction force

1
Enter nameplate capacity and temperature
Use the PSV nameplate relieving rate W and relieving temperature in the active unit system.
2
Select gas and outlet pipe
Pick a preset gas (or custom MW/k) and the discharge NPS / schedule for A_exit.
3
Set DLF and discharge mode
Open discharge includes exit pressure thrust; closed header uses momentum only. DLF 2.0 is typical for open vent popping screens.
4
Read F_total and export
Hero shows F_total. Badges show F_steady and DLF. Export CSV/PDF or carry NPS/temperature to related pipe and nozzle tools.

6. Frequently Asked Questions & Technical References

Show

A field screen of the thrust on discharge piping when a safety valve pops — momentum of the vapor jet plus exit pressure above atmosphere, often multiplied by a dynamic load factor (DLF).