v1.0.0 to v1.0.0

1 added, 0 removed. Audit A to A.

---

name: neqsim-relief-flare-network

version: "1.0.0"

description: "Relief and flare system design — PSV sizing per API 520 (gas/liquid/two-phase, fire case), API 521 fire heat input, flare load summation, flare-tip sizing, radiation contour (API 521 §6), header back-pressure & Mach, and the integrated TR3001 overpressure-protection study engine (multi-cause governing-case selection, fire-case relief, compliance check, disposal-load roll-up). USE WHEN: a task involves PSV sizing, relief contingency analysis, thermal relief for trapped liquid, flare network hydraulics, flare radiation/dispersion, PSV→flare integration, or a TR3001/API 521 overpressure study. Anchors on neqsim.process.util.fire.ReliefValveSizing, neqsim.process.safety.overpressure, neqsim.process.equipment.flare.{Flare, FlareStack}, neqsim.process.equipment.valve.SafetyValve."

last_verified: "2026-06-27"

requires:

java_packages: [neqsim.process.util.fire, neqsim.process.safety.overpressure, neqsim.process.equipment.flare, neqsim.process.equipment.valve]

---

# NeqSim Relief & Flare Network Skill

End-to-end relief design — from individual PSV sizing through plant-wide load

summation, flare-tip selection, and radiation/dispersion checks per **API 520**,

**API 521**, **API 537**.

## When to Use

- Sizing a single PSV (gas / liquid / two-phase / fire case)

- Checking whether a blocked-in liquid segment needs thermal relief or source-term

handoff after rupture screening

- API 521 fire heat input on wetted area

- Aggregating simultaneous relief loads to a flare header

- Flare tip diameter and stack height (radiation)

- Header hydraulics: back-pressure on PSVs, Mach < 0.7

- Sour-gas dispersion check (toxic clouds)

Standards: **API 520 Part I/II**, **API 521** (relief contingencies + radiation),

**API 537** (flare equipment), **NFPA 30**, **EN ISO 23251**.

## Pattern 1 — Gas-phase PSV (API 520)

```java

import neqsim.process.util.fire.ReliefValveSizing;

import neqsim.process.util.fire.ReliefValveSizing.PSVSizingResult;

PSVSizingResult psv = ReliefValveSizing.calculateRequiredArea(

massFlowRate_kgs,

setPressure_barg,

backPressure_barg,

T_K,

MW,

k_cpcv, // ratio of specific heats

Z_compressibility,

overpressure_frac, // 0.10 process, 0.21 fire

Kd // discharge coeff (0.975 typical)

);

double area_m2 = psv.getRequiredArea();

String orifice = psv.getRecommendedOrifice(); // API 526 letter

String issues = ReliefValveSizing.validateSizing(psv, /*fire*/ false);

```

## Pattern 2 — Fire Case (API 521)

```java

double Q_fire_W = ReliefValveSizing.calculateAPI521FireHeatInput(

wettedAreaM2,

/*hasDrainage*/ true,

/*hasFireProofInsulation*/ false

);

// Mass flow = Q_fire / latent heat at relieving conditions

double mdot = Q_fire_W / latentHeat_J_per_kg;

PSVSizingResult psv = ReliefValveSizing.calculateRequiredArea(

mdot, setP, backP, T_relief, MW, k, Z,

/*overpressure_frac*/ 0.21, // fire allows 21%

);

```

API 521 fire equation: **Q = C × F × A_wet^0.82** with credit factors for drainage / insulation.

## Pattern 3 — Liquid PSV (API 520 Part I §5.8)

```java

import neqsim.process.util.fire.ReliefValveSizing.LiquidPSVSizingResult;

LiquidPSVSizingResult lpsv = ReliefValveSizing.calculateLiquidReliefArea(

volumeFlowRate_m3s,

setPressure_barg,

backPressure_barg,

rho_kg_m3,

viscosity_cP,

);

```

## Pattern 4 — Two-Phase (Omega Method)

```java

double area = ReliefValveSizing.calculateTwoPhaseReliefArea(

massFlow_kgs, setP_barg, backP_barg, omega, rho_relief, Kd

);

```

## Pattern 4b — Integrated Overpressure Study (TR3001 / API 521)

For a full overpressure-protection study on one protected item — enumerate

credible relief contingencies, pick the governing case, size the PSV, and check

acceptance — use `neqsim.process.safety.overpressure`. Each cause calculator is

fluent and returns an immutable `ReliefScenario`; the engine selects the

maximum-rate credible scenario and sizes accordingly (vapour via `ReliefValveSizing`

API 520; liquid via the API 520 liquid method; two-phase via the omega method).

```java

import neqsim.process.safety.overpressure.*;

// 1. Cause scenarios (fluent → ReliefScenario)

ReliefScenario blocked = new BlockedOutletRelief().setName("Blocked gas outlet")

.setInflowRateKgPerHr(36000.0).setReliefPressureBara(50.0)

.setReliefTemperatureC(20.0).setFluid(gas).calculate();

ReliefScenario fire = new FireCaseRelief().setName("Pool fire")

.setVesselDiameterM(2.0).setWettedHeightM(3.0) // or setWettedAreaM2(..)

.setHasDrainage(true).setHasFireFighting(true)

.setLatentHeatJPerKg(350000.0).setReliefPressureBara(60.0)

.setReliefTemperatureC(120.0).setFluid(gas).calculate();

// 2. Engine: governing case + sizing + acceptance

ProtectedItem item = new ProtectedItem("V-100", 100.0) // tag, MAWP [bara]

.setReliefSetPressureBara(100.0).setBackPressureBara(1.5);

OverpressureStudyResult result = new OverpressureProtectionStudy(item)

.addScenario(blocked).addScenario(fire).evaluate();

result.getGoverningScenario().getName(); // worst credible case

result.getRequiredAreaIn2(); // API 526 required orifice area

result.getRecommendedOrifice(); // orifice letter

result.isCapacityAdequate(); // area-based adequacy

result.getAcceptance().getAccumulationFraction(); // vs 1.10 / 1.16 / 1.21

// 3. TR3001 compliance findings (PASS/FAIL/NEEDS_REVIEW)

List<ComplianceFinding> findings = new TR3001ComplianceChecker().check(result);

boolean compliant = new TR3001ComplianceChecker().isCompliant(findings);

// 4. Roll relief loads up to a disposal header (API 521 §5.3)

ReliefDisposalResult disposal = new ReliefDisposalNetwork("Fire zone 1")

.addRelief(resultA, true).addRelief(resultB, true).calculate();

disposal.getTotalSimultaneousKgPerS(); // simultaneous header load

disposal.getPeakSingleKgPerS(); // largest single contributor

disposal.getGoverningContributor();

```

- Cause calculators: `BlockedOutletRelief`, `CheckValveLeakRelief`,

`ControlValveFailureRelief`, `TubeRuptureRelief`, `FireCaseRelief`.

- Set `ReliefScenario` phase to `LIQUID` (with `densityKgPerM3`/`viscosityPaS`)

or `TWO_PHASE` (with `gasMassFraction`, `gasDensityKgPerM3`,

`liquidDensityKgPerM3`, `latentHeatJPerKg`, `liquidHeatCapacityJPerKgK`) to

trigger the matching sizing path; missing two-phase inputs are reported as warnings.

- Accumulation limits: 1.10 single non-fire, 1.16 multiple, 1.21 fire (ASME VIII Div 1).

- Verified by `OverpressureProtectionStudyTest` + `OverpressureExtensionsTest`.

> **Adequacy is judged by AREA**, not by re-plugging the selected area into the

> nozzle equation: `calculateRequiredArea` (API 520 empirical) and the nozzle

> capacity formula use different coefficient bases and are not inverses.

## Pattern 5 — Flare Tip & Stack (API 537 + 521 §6)

```java

import neqsim.process.equipment.flare.Flare;

Flare flare = new Flare("MainFlare");

flare.setInletStream(reliefStream);

flare.setRadiantFraction(0.30); // typical 0.20–0.40

flare.setTipDiameter(0.5); // m

flare.setDesignHeatDutyCapacity(150.0, "MW");

flare.run(UUID.randomUUID());

// Radiation at ground distance

double q_Wm2 = flare.estimateRadiationHeatFlux(75.0); // 75 m

double dSafe = flare.radiationDistanceForFlux(4730.0); // K = 1.5 kW/m² × 4 hr exposure

```

API 521 §6.4 radiation criteria:

| Receiver | Allowable flux (kW/m²) |

| ---------------------------------- | --------------------------- |

| Personnel — emergency only | 9.46 |

| Personnel — escape (≤1 min) | 6.31 |

| Property line / 2-min escape | 4.73 |

| Solar background | ~1.0 (subtract from above) |

### Pattern 5b — Detailed Flare Flame & Sterile-Zone (API 537)

For sterile-zone radii, wind-tilted flame geometry, and flare noise, use

`Api537FlareFlameModel` (Kent 1968 flame length + tilt + iso-flux solver):

```java

import neqsim.process.safety.fire.Api537FlareFlameModel;

Api537FlareFlameModel flame = new Api537FlareFlameModel(

50.0, // relief mass flow [kg/s]

50.0e6, // heat of combustion [J/kg]

0.20, // radiant fraction

200.0) // tip exit velocity [m/s]

.setStackHeightM(40.0)

.setWindSpeedMPerS(10.0);

double lFlame = flame.flameLengthM();

double tilt = flame.flameTiltRad();

double r158 = flame.sterileZoneRadiusM(Api537FlareFlameModel.FLUX_1_58_KW); // ~personnel continuous

double r473 = flame.sterileZoneRadiusM(Api537FlareFlameModel.FLUX_4_73_KW); // property line

double r946 = flame.sterileZoneRadiusM(Api537FlareFlameModel.FLUX_9_46_KW); // emergency-only

double q75 = flame.heatFluxAtGroundDistance(75.0); // W/m²

double pwl = flame.soundPowerLevelDb();

double spl = flame.soundPressureLevelDb(100.0);

```

Verified by `Api537FlareFlameModelTest`. Radii are nested (lower flux reaches

further); flame tilts downwind and the tip moves horizontally with wind speed.

## Pattern 6 — Plant Load Summation

For each contingency (general power failure, total reflux failure, fire zone):

1. List PSVs that lift simultaneously

2. Sum mass flows at each PSV at its **relieving** conditions

3. Pick the **governing** contingency (highest header load)

4. Size the flare for that load

```java

double totalReliefLoad = psvs.stream()

.filter(p -> isActiveDuring(p, contingency))

.mapToDouble(p -> p.getMassFlowCapacity())

.sum();

```

For **simultaneous blowdown** contingencies (multiple BDVs into one header), use

`MultiVesselBlowdownStudy` (see `neqsim-depressurization-mdmt`) — it superimposes

the transient blowdown curves on a common time grid and reports the **peak**

combined header mass flow and the header Mach at that instant, which is the load

that actually sizes the header.

## Pattern 7 — Header Back-Pressure & Mach

For balanced-bellows / pilot-operated PSVs, verify:

- Built-up back-pressure ≤ 50% set (conventional 10%)

- Header Mach < 0.7 at any location (avoid critical flow choking design)

```java

import neqsim.process.equipment.valve.SafetyValve;

SafetyValve sv = new SafetyValve("PSV-101", inletStream);

sv.setSetPressure(120.0, "barg");

sv.setBackPressure(15.0, "barg");

sv.run();

double KbCorrection = sv.getBackPressureCorrectionFactor(); // > 0.6 for balanced PSV

```

## Pattern 8 — Dispersion of Unignited Release

```java

FlareDispersionSurrogateDTO disp = flare.getDispersionSurrogate();

// Use to bound H2S / SO2 ground concentration vs. IDLH/ERPG-2

```

For a governed production-readiness record, use

`neqsim.process.engineering.safety.FlareConsequenceCalculation`. It combines explicit

point-source radiation, neutral Gaussian centerline dispersion, spherical noise spreading,

and tip-Mach constraints in one typed result with uncertainty and provenance. Set

`productionQualification=true` only with standards/evidence references and

`consequenceMethodApplicability=approved`. This is a screening interface, not a substitute

for validated complex-terrain, stability-class, toxic, combustion, or detailed acoustic

modeling.

## Common Mistakes

| Mistake | Fix |

| --------------------------------------------------------- | -------------------------------------------------------------------- |

| Sizing fire PSV at 10% overpressure | Fire case uses 21%; non-fire is 10% (API 520) |

| Wetted area = total surface | API 521 wetted area is liquid-touching surface up to 7.6 m elevation |

| Ignoring drainage credit | F factor reduces Q_fire by 0.5 with adequate drainage (slope ≥ 1°) |

| Adding all PSV capacities for header | Use the governing **contingency**, not sum of nameplate capacities |

| K_d = 1.0 | Typical: gas/vapor 0.975, liquid 0.65, certified two-phase ≤ 0.85 |

| Ignoring Mach in header | Mach > 0.7 → choking, can dramatically raise back-pressure on PSVs |

| Using inlet line ΔP > 3% set | API 520 §7.3: > 3% inlet ΔP causes valve chatter, fix the piping |

| Picking smallest API 526 letter that meets area | Always pick the **next** letter for spare margin & spare-parts pool |

## Validation Checklist

- [ ] Each contingency has a documented worst-case mass flow

- [ ] Wetted-area calculation shows boundary up to 7.6 m

- [ ] Drainage / insulation credits supported by P&ID review

- [ ] Header sized so Mach < 0.7 at peak load

- [ ] Built-up back-pressure ≤ 10% (conventional) or ≤ 50% (balanced) of set

- [ ] Inlet line ΔP < 3% of set pressure

- [ ] Flare radiation ≤ 4.73 kW/m² at property line (incl. solar)

- [ ] Dispersion check at flame-out (toxic species)

- [ ] Results saved to `results.json` under `relief_system` with PSV table + flare load summary

## Related Skills

- [`neqsim-process-safety`](../neqsim-process-safety/SKILL.md) — when PSV is the IPL of last resort in LOPA

+ - [`neqsim-firewater-deluge-design`](../neqsim-firewater-deluge-design/SKILL.md) — fire-water demand for the area, which competes with the relief and flare load for the same simultaneous-demand budget

- [`neqsim-trapped-liquid-fire-rupture`](../neqsim-trapped-liquid-fire-rupture/SKILL.md) — blocked-in liquid fire rupture screening before thermal relief/PFP decisions

- [`neqsim-depressurization-mdmt`](../neqsim-depressurization-mdmt/SKILL.md) — blowdown transients + `MultiVesselBlowdownStudy` for coupled header loads

- [`neqsim-consequence-analysis`](../neqsim-consequence-analysis/SKILL.md) — `Api537FlareFlameModel` radiation/noise and hazardous-area zoning

- [`neqsim-dynamic-simulation`](../neqsim-dynamic-simulation/SKILL.md) — depressurization (blowdown) is separate from PSV

- [`neqsim-mechanical-design`](../neqsim-api-patterns/SKILL.md) — PSV mechanical via `SafetyValveMechanicalDesign`

- [`neqsim-standards-lookup`](../neqsim-standards-lookup/SKILL.md) — API 520 / 521 / 526 / 537