Neqsim Vacuum Collapse Screening

Vacuum Collapse Screening

Use this skill for public, educational vacuum-collapse (external-pressure implosion) screening examples. When a vessel is blocked in and cools down, the trapped vapour contracts and any condensable vapour (for example steam) condenses, so the internal pressure can fall below atmospheric and pull a vacuum. This skill provides a simple final-pressure estimate, a vacuum-depth indicator, and an external-rating flag that help agents structure early reverse-pressure questions before moving to a validated NeqSim constant-volume cooldown model and a vessel external-pressure (buckling) review.

When to Use

• When a user asks for a quick, public vacuum-collapse triage for a blocked-in vessel.
• When an agent needs a placeholder estimate of how deep a cooldown or condensation vacuum could be.
• When examples must run without confidential vessel geometry, external-pressure ratings, or company vacuum design bases.

Inputs

• initial_pressure: starting pressure in bara.
• initial_temperature: starting temperature in C.
• cold_end_temperature: final cooled temperature in C (must be below the initial temperature).
• condensable_fraction: fraction of the initial vapour that condenses on cooldown, 0.0 to 1.0, default 0.0.
• external_pressure_rating: vessel external-pressure (vacuum) rating in bara, default 0.0 for full vacuum.
• atmospheric_pressure: atmospheric pressure in bara, default 1.01325.

Outputs

• estimated_final_pressure_bara: ideal-gas constant-volume final pressure after cooldown and condensation.
• vacuum_depth_bar: amount the final pressure sits below atmospheric, in bar (0.0 when no vacuum).
• margin_to_rating_bar: final pressure minus the external-pressure rating; negative means the rating is exceeded.
• vacuum_present: True when the final pressure is below atmospheric.
• exceeds_rating: True when the final pressure falls below the external-pressure rating.
• verdict: no_vacuum, vacuum_within_rating, or vacuum_exceeds_rating.
• collapse_warning: ok, watch, or high.
• assumptions: public assumptions used by the placeholder model.

Engineering Method

The Python class VacuumCollapseModel uses open placeholder calculations only:

• the non-condensing pressure drop uses the ideal-gas constant-volume relation P2 = P1 * (T2 / T1) for a rigid, blocked-in vessel.
• any condensable_fraction is removed from the vapour, scaling the final pressure by (1 - condensable_fraction) as a screening proxy for steam or vapour condensation.
• the vacuum depth is the atmospheric pressure minus the final pressure, floored at zero.
• the rating margin is the final pressure minus the external-pressure rating, and a negative margin sets the exceeds-rating flag.
• warnings combine a vacuum-present indicator with the exceeds-rating flag.

This is educational and screening-only logic. It is not an external-pressure (buckling) standard, a vessel design method, a vendor method, or a replacement for a validated NeqSim constant-volume cooldown model and a code external-pressure review (for example ASME BPVC Section VIII external pressure).

Python Usage Pattern

from vacuum_collapse_screening import VacuumCollapseModel

model = VacuumCollapseModel()
result = model.evaluate(
    initial_pressure=1.8,
    initial_temperature=120.0,
    cold_end_temperature=20.0,
    condensable_fraction=0.85,
    external_pressure_rating=0.5,
)

print(result.verdict)
print(result.estimated_final_pressure_bara)
print(result.vacuum_depth_bar)
print(result.margin_to_rating_bar)
print(result.collapse_warning)

If the optional neqsim Python package is available, the result records that fact so an agent can recommend moving to the validated NeqSim VacuumCollapseAnalyzer, which performs a real constant-volume (TVflash) cooldown of the actual fluid, tracks condensation, and reports a cooling curve and make-up gas requirement. If it is not installed, the example still runs with public placeholder logic.

Validation Checklist

• Pressures and temperatures are positive and the cold-end temperature is below the initial temperature.
• The condensable fraction is between 0.0 and 1.0.
• Example inputs are public and synthetic.
• Tests cover normal, vacuum, exceeds-rating, and invalid-input cases.
• Results are described as educational screening indicators.
• Real vacuum-collapse design is redirected to a validated NeqSim constant-volume cooldown model and a code external-pressure review.

Common Mistakes

Limitations

• No proprietary vessel geometry, external-pressure rating, or project vacuum design bases are included.
• No real-fluid condensation, multi-phase behaviour, or make-up gas flow is modelled.
• No shell buckling, stiffener, or out-of-roundness external-pressure calculation is performed.
• Not suitable for safety-critical, design, guarantee, or standards-compliance work.

Related NeqSim Functionality

This educational screening corresponds to validated, rigorous functionality in the NeqSim Java library that a qualified engineer should use for design-grade work:

• neqsim.process.safety.vacuum.VacuumCollapseAnalyzer — constant-volume (TVflash) cooldown of a blocked-in vessel, vacuum-depth versus external rating, cooling curve, and make-up gas requirement.
• neqsim.process.safety.vacuum.VacuumCollapseResult — structured result with the cooling curve, verdict, and JSON export.

In Python the same classes are reachable through the neqsim package (for example from neqsim import jneqsim).

References

• NeqSim repository: https://github.com/equinor/neqsim
• NeqSim Skills Guide: https://github.com/equinor/neqsim/blob/master/docs/integration/skills_guide.md
• Public external-pressure references such as ASME BPVC Section VIII Division 1 (external pressure / vacuum) for general vacuum-collapse concepts.