neqsim-depressurization-screening

name	neqsim-depressurization-screening
calculation_basis	screening
version	0.1.0
description	Educational blowdown and depressurization screening with time-to-target and low-temperature flags. USE WHEN: a task needs a public, screening-level blowdown time indicator and auto-refrigeration low-temperature triage without proprietary blowdown design methods.
last_verified	2026-05-31
requires	{"python_packages":[],"java_packages":[],"env":[],"network":[]}

Depressurization Screening

Use this skill for public, educational emergency depressurization (blowdown) screening examples. It provides a simple time-to-target indicator and an auto-refrigeration low-temperature flag that help agents structure early blowdown questions before moving to a validated transient depressurization model and material low-temperature review.

When to Use

• When a user asks for a quick, public blowdown time triage example.
• When an agent needs a placeholder estimate of cold-end temperature for a low-temperature flag.
• When examples must run without confidential vessel data, valve sizing, or company blowdown bases.

Inputs

• initial_pressure: starting pressure in bara.
• target_pressure: target depressurization pressure in bara.
• inventory: vessel gas inventory in kg.
• vent_mass_rate: representative blowdown mass rate in kg/h.
• relieving_temperature: starting fluid temperature in C.
• mdmt: minimum design metal temperature in C, default -20.

Outputs

• blowdown_time_indicator: dimensionless ratio of estimated blowdown time to a configurable public target time.
• estimated_blowdown_time_min: estimated time to reach the target pressure, in minutes.
• estimated_min_temperature_C: simplified isentropic cold-end temperature estimate.
• low_temperature_flag: True when the cold-end estimate is below the MDMT.
• depressurization_warning: ok, watch, or high.
• assumptions: public assumptions used by the placeholder model.

Engineering Method

The Python class DepressurizationModel uses open placeholder calculations only:

• the vented mass to reach the target pressure is scaled from inventory using a linear pressure-fraction placeholder.
• blowdown time is the vented mass divided by the representative blowdown rate.
• the cold-end temperature uses a simplified isentropic expansion relation with a public isentropic exponent.
• warnings combine a too-slow blowdown indicator with the low-temperature flag.

This is educational and screening-only logic. It is not a transient depressurization standard, a valve sizing method, a vendor method, or a replacement for a validated NeqSim blowdown model and materials review.

Python Usage Pattern

from depressurization_screening import DepressurizationModel

model = DepressurizationModel()
result = model.evaluate(
    initial_pressure=100.0,
    target_pressure=7.0,
    inventory=2000.0,
    vent_mass_rate=12000.0,
    relieving_temperature=30.0,
    mdmt=-46.0,
)

print(result.depressurization_warning)
print(result.estimated_blowdown_time_min)
print(result.estimated_min_temperature_C)
print(result.low_temperature_flag)

If the optional neqsim Python package is available, the result records that fact so an agent can recommend moving to a validated NeqSim transient depressurization model for cold-end temperature and time profiles. If it is not installed, the example still runs with public placeholder logic.

Validation Checklist

• Pressures are positive and the target pressure is below the initial pressure.
• Example inputs are public and synthetic.
• Tests cover normal, warning, and invalid-input cases.
• Results are described as educational screening indicators.
• Real blowdown design is redirected to validated NeqSim transient models, API 521, and qualified review.

Common Mistakes

Symptom	Cause	Fix
Treating estimated_min_temperature_C as a design cold-end	Placeholder isentropic relation ignores heat input and real fluid behavior	Use a validated NeqSim transient depressurization model for design
Optimistic blowdown time	Representative vent rate held constant instead of decaying with pressure	Use transient simulation with valve characteristics
Missing low-temperature risk	MDMT not provided at the correct case	Confirm MDMT against the controlling depressurization case

Limitations

• No proprietary valve data, vessel geometry, or project blowdown bases are included.
• No transient pressure or temperature profile, heat input, or two-phase behavior is modeled.
• No reaction force, flare back-pressure, or downstream network effects are included.
• 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.depressurization.DepressurizationSimulator — transient blowdown inventory and time-to-target-pressure.
• neqsim.process.equipment.valve.SafetyValve — relief/blowdown valve model inside a process flowsheet.

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 depressurization references such as API Standard 521 for general blowdown concepts.