neqsim: Skill for Claude Code

NeqSim Depressurization & MDMT Skill

Transient blowdown / depressurization for inventory release on fire or controlled emergency, plus the minimum design metal temperature (MDMT) check that drives material selection. The two are linked: blowdown end-temperatures (often −80 to −120 °C for hydrocarbon gas) usually drive MDMT, which in turn drives whether LTCS, low-temperature carbon-Mn, 3.5 % Ni or 9 % Ni / 304L is required.

When to Use

• Sizing a blowdown / depressurization valve to reach 50 % pressure in 15 min (API 521 §5.20 fire case) or 7 bar in some operator standards
• Generating P(t), T(t), m(t) curves for the relief / flare load case
• Screening MDMT against end-of-blowdown vessel-wall temperature
• Producing source terms for the flare network (neqsim-relief-flare-network)
• Distinguishing depressurization cases from blocked-in liquid fire rupture cases, where neqsim-trapped-liquid-fire-rupture is the primary workflow

Distinct from neqsim-relief-flare-network (steady-state PSV sizing) and neqsim-dynamic-simulation (continuous-process transients) — this skill is the specific blowdown + MDMT pair.

Standards

• API 521 7th ed. — Pressure-relieving and depressuring systems (§5.20 blowdown)
• API STD 520 — PSV sizing, used for choke check at the BDV
• ASME UCS-66 / UCS-66.1 — MDMT impact-test exemption curves (carbon steel)
• ASME UHA-51 — austenitic stainless steel low-temperature service
• API 579 / FFS-1 §3 — fitness-for-service, MDMT for in-service vessels
• EN 13445-2 Annex B — European MDMT and impact-test approach
• NORSOK L-002 — piping system design (low-temperature operation)

Method 1 — Blowdown Simulation (VU-flash)

import neqsim.thermo.system.SystemSrkEos;
import neqsim.thermo.system.SystemInterface;
import neqsim.process.safety.depressurization.DepressurizationSimulator;

SystemInterface gas = new SystemSrkEos(273.15 + 50.0, 100.0);
gas.addComponent("methane", 0.92);
gas.addComponent("ethane",  0.05);
gas.addComponent("propane", 0.03);
gas.setMixingRule("classic");
gas.setTotalNumberOfMoles(5000.0); // mol — representative of vessel inventory

DepressurizationSimulator sim = new DepressurizationSimulator(gas);
sim.setVesselVolume(50.0);     // m³
sim.setOrificeArea(5.0e-4);    // m² — BDV equivalent area
sim.setBackPressure(1.5);      // bara — flare KO drum
sim.setHeatInput(0.0);         // adiabatic; > 0 for fire case
sim.run(900.0, 1.0);           // 15 min, 1 s timestep

double[] t = sim.timeSeries();
double[] p = sim.pressureSeries();
double[] T = sim.temperatureSeries();
double[] m = sim.massFlowSeries();
double pEnd = p[p.length - 1];
double tEnd = T[T.length - 1];
double t50  = sim.timeToPressure(50.0);  // s, time to 50 bar