neqsim-relief-flare-network · diff
v1.0.0 to v1.0.0
139 added, 65 removed. Audit A to A.
---
name: neqsim-relief-flare-network
version: "1.0.0"
description: "Relief and flare design - PSV sizing per API 520 (gas/liquid/two-phase, fire), API 521 fire heat input, flare load summation, tip sizing, radiation contours, header back-pressure and Mach, and the TR3001 overpressure-study engine. USE WHEN: PSV sizing, relief contingency analysis, thermal relief of trapped liquid, flare hydraulics or radiation, PSV-to-flare integration, or a TR3001/API 521 study. Anchors on ReliefValveSizing, safety.overpressure, Flare, 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**.
+ Relief-system screening and simulation: individual PSV sizing, native valve response,
+ plant load summation, flare-tip selection and consequence estimates. References include
+ **API 520**, **API 521**, **API 537**, **ISO 4126** and **ISO 23251**; using these
+ APIs does not establish compliance, certified capacity or installation approval.
+ **PSV unit/API correction, 2026-11-05:** `ReliefValveSizing` pressures are **Pa absolute**,
+ not barg or bara. Native `SafetyValve` and `SafetyReliefValve` pressure settings use
+ **bara**. Convert explicitly at that boundary. Do not infer a capacity, orifice-area or
+ certified-coefficient basis from a dynamic model's Cv. Select accumulation, blowdown,
+ back-pressure and radiation limits from the applicable project/code/vendor basis;
+ the example fractions below are study inputs, not universal acceptance limits.
+
## 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)
+ ## Native PSV response and canonical P&ID feedback
+ Use `SafetyReliefValve` for a self-acting native pressure/hysteresis response with
+ declared lift lag, dwell and rate limits. Execute the UUID overload used by
+ `ProcessSystem`; a direct method-only ramp is not evidence that the process runner
+ exercises the same response. Keep opening at set pressure, full-open pressure and
+ reseat pressure distinct. Enable the native gas choked-flow capacity limit for credited gas relief response.
+ Record `getPressureReliefConfiguration()` and the actual
+ lift, flow and ordered pop/reseat observations. A cycle count is not an acoustic or
+ mechanical chatter model.
+
+ Algebraic `run()`/`run(UUID)` and steady-mode transient dispatch preserve the
+ connected source flow and fluid identity while evaluating outlet capacity on a
+ private inlet workspace. Finite transient mode publishes withdrawal at both
+ ports; give it a dedicated tee branch and aggregate downstream demands before
+ upstream inventory integration. Do not use algebraic capacity as a balanced
+ parallel withdrawal or dynamic-response result.
+
+ For a process/P&ID feedback study:
+
+ 1. Connect the actual valve to a protected-vessel gas branch and an explicit
+ downstream pressure boundary through a source-backed tee. Refresh branch
+ intensive state before valve hydraulics; aggregate both actual demands before
+ the vessel consumes its outlet boundary. Do not prescribe an arbitrary relief
+ split or reconcile inventory afterwards.
+ 2. Import it with `PidPressureReliefImporter` into the existing `PidDesignModel`.
+ The initial supported route is an exact CONVENTIONAL `SafetyReliefValve`, LINEAR trim and a
+ real two-outlet `Splitter`. Record a capacity-basis evidence reference; a
+ self-acting PSV receives no fabricated controller or SIF signal.
+ 3. Use `PidPressureReliefValidator` to apply canonical settings to an isolated
+ process copy, read them back, fingerprint the actual configuration and attach
+ strict native scenario evidence. Reject stale bindings, wrong endpoints,
+ unsupported trim, secondary valve controllers/travel and ignored settings.
+ 4. Check no-demand standby, actual relief demand, failed/limited relief,
+ back-pressure sensitivity, slow response and recovery/refinement as applicable.
+ Reseating requires an earlier observed opening and subsequent physical seating;
+ an initially closed sample cannot satisfy recovery. No-demand PASS is not
+ successful protection on a demand.
+ 5. Retain full-window sampled pressure checks, actual positive discharge and
+ unwanted-relief checks separately from per-vessel component, mass and energy
+ closure. A successful response cannot clear numerical FAIL/HOLD or establish
+ unobserved continuous peaks, certified sizing, SRS/SIL/IPL credit or construction
+ approval. Check actual snapshot coverage before claiming transactional rollback
+ of the entire process.
+
+ The synthetic `AdvancedV101PsvStudyTest`, `PidNativePressureReliefTest` and
+ `SafetyReliefValveUuidTest` provide executable examples and regression evidence.
+ See the [PSV workflow guide](../../../docs/process/safety/psv-pid-verification.md)
+ and [P&ID synthesis](../../../docs/pid-design-synthesis.md) for canonical authority,
+ source identities, explicit absolute-to-gauge references and separate engineering
+ review gates.
+
+ ## Pattern 1 — Gas-phase area screening
+
```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)
+ 5000.0 / 3600.0, // kg/s
+ 110.0e5, // set pressure, Pa absolute
+ 0.10, // explicit example overpressure fraction
+ 1.013e5, // back pressure, Pa absolute
+ 333.15, // K
+ 0.018, // kg/mol
+ 0.95, // compressibility factor
+ 1.30, // Cp/Cv
+ false, // balanced bellows
+ false // rupture disc upstream
);
- double area_m2 = psv.getRequiredArea();
- String orifice = psv.getRecommendedOrifice(); // API 526 letter
- String issues = ReliefValveSizing.validateSizing(psv, /*fire*/ false);
+ double area_m2 = psv.getRequiredArea();
+ String orifice = psv.getRecommendedOrifice();
```
- ## Pattern 2 — Fire Case (API 521)
+ This exact gas call and the following liquid, two-phase and fire calls are exercised
+ by `ReliefValveSizingDocumentationTest`. See the complete tested unit contract in
+ [`relief_valve_sizing_api.md`](../../../docs/safety/relief_valve_sizing_api.md).
+ The selected standard area is a screening result, not a vendor capacity certificate.
+ ## Pattern 2 — Wetted-area fire heat-input screening
+
```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%
- Kd
+ 80.0, // wetted area, m2
+ true, // adequate drainage
+ true // firefighting flag; current helper applies no firefighting credit
);
```
- API 521 fire equation: **Q = C × F × A_wet^0.82** with credit factors for drainage / insulation.
+ This helper is not a vessel energy-inventory simulation. Use an actual dynamic
+ vessel, declared heat input and a connected relief device to study pressure response.
+ Do not substitute an assumed latent heat for a phase/enthalpy calculation or invent
+ an insulation/firefighting credit not implemented and supported by project evidence.
- ## Pattern 3 — Liquid PSV (API 520 Part I §5.8)
+ ## Pattern 3 — Liquid area screening
```java
import neqsim.process.util.fire.ReliefValveSizing.LiquidPSVSizingResult;
LiquidPSVSizingResult lpsv = ReliefValveSizing.calculateLiquidReliefArea(
- volumeFlowRate_m3s,
- setPressure_barg,
- backPressure_barg,
- rho_kg_m3,
- viscosity_cP,
- Kd
+ 50.0 / 3600.0, // m3/s at relieving conditions
+ 850.0, // kg/m3
+ 25.0e5, // set pressure, Pa absolute
+ 0.10, // explicit example overpressure fraction
+ 1.013e5, // back pressure, Pa absolute
+ 0.004, // dynamic viscosity, Pa s
+ false // balanced bellows
);
```
- ## Pattern 4 — Two-Phase (Omega Method)
+ ## Pattern 4 — Two-phase area screening
```java
double area = ReliefValveSizing.calculateTwoPhaseReliefArea(
- massFlow_kgs, setP_barg, backP_barg, omega, rho_relief, Kd
+ 30000.0 / 3600.0, // kg/s
+ 80.0e5, // set pressure, Pa absolute
+ 0.10, // explicit example overpressure fraction
+ 5.0e5, // back pressure, Pa absolute
+ 373.15, // K
+ 0.30, // gas mass fraction
+ 50.0, // gas density, kg/m3
+ 700.0, // liquid density, kg/m3
+ 250000.0, // latent heat, J/kg
+ 2500.0 // liquid heat capacity, J/(kg K)
);
```
## 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).
+ - The engine's screening factors are not universal code limits. Record the protected
+ item's MAWP, gauge/absolute basis, contingency, number of installed devices,
+ governing edition and project-approved accumulation criterion separately.
- 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
+ double dSafe = flare.radiationDistanceForFlux(4730.0); // example 4.73 kW/m2 threshold
```
- API 521 §6.4 radiation criteria:
+ Illustrative radiation screening levels; verify the applicable exposure duration,
+ receptor location and governing project/standard basis before acceptance:
| 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)
+ Use the actual downstream stream/header pressure in the connected hydraulic model.
+ Distinguish superimposed from built-up back pressure and evaluate the selected valve's
+ certified operating envelope. A conventional/balanced/pilot label does not by itself
+ justify a fixed allowable percentage or correction factor.
- ```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
- ```
+ `SafetyReliefValve` exposes `setValveType`, `setBackpressureSensitivity` and `setKbMax`
+ for its empirical response model. These parameters do not replace certified vendor
+ curves. Legacy `SafetyValve` uses `setPressureSpec` in bara; it has no
+ `setSetPressure`, `setBackPressure` or `getBackPressureCorrectionFactor` APIs.
+ Do not call those nonexistent overloads or pass barg to a bara setter.
+ Check header hydraulics and project Mach/velocity criteria separately. Include the
+ actual relief line and disposal destination in the canonical P&ID; a drawn off-page
+ connector alone is not a simulated flare network or validated back-pressure model.
+
## 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°) |
+ | Treating a sample accumulation fraction as code approval | Establish the contingency, applicable code/edition and pressure basis; declare the approved criterion |
+ | Wetted area = total surface | Establish actual wetted geometry, fire exposure and applicable standard limits |
+ | Inventing drainage, insulation or firefighting credit | Verify project evidence and the exact helper implementation; the static fire helper applies no firefighting credit |
| 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 |
+ | Assuming a discharge coefficient from a service label | Obtain the applicable certified/vendor coefficient and correction-factor basis |
+ | Ignoring Mach and built-up pressure in the header | Evaluate actual compressible hydraulics; a project Mach margin is not the sonic choking condition |
+ | Ignoring inlet-line loss and valve/system interaction | Check applicable installation criteria and engineering-analysis requirements; a pressure-loss percentage alone does not prove chatter |
+ | Treating an API 526 letter as certified relief adequacy | Check selected area, service, certified coefficients and vendor capacity; apply project margin explicitly |
## Validation Checklist
- [ ] Each contingency has a documented worst-case mass flow
- - [ ] Wetted-area calculation shows boundary up to 7.6 m
+ - [ ] Wetted-area calculation records geometry, exposure and applicable limits
- [ ] 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)
+ - [ ] Header hydraulics meet the declared project Mach/velocity criteria at peak load
+ - [ ] Superimposed/built-up back pressure meets the selected device's approved envelope
+ - [ ] Inlet-line losses and stability meet applicable installation/vendor requirements
+ - [ ] Radiation meets the declared location, exposure-time and background criteria
- [ ] 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