Overview

Open-drain review in NeqSim combines two evidence streams:

Evidence stream	Source	Use in review
Calculated process evidence	NeqSim streams, equipment, and process systems	Liquid leak rate, liquid density, pressure, temperature, firewater load, and drain hydraulic capacity
Normalized document and operational evidence	STID/P&ID extracts, line lists, design-basis records, and optional tagreader summaries	Drain segregation, backflow prevention, seals, vents, fire-area separation, helideck and temporary-storage evidence

The central class for the calculated path is neqsim.process.safety.opendrain.OpenDrainProcessEvidenceCalculator. It builds OpenDrainReviewInput or OpenDrainReviewItem objects that are consumed by OpenDrainReviewEngine, so the same NORSOK S-001 Clause 9 checks can run on either calculated NeqSim evidence or externally normalized JSON.

The MCP runner run_open_drain_review accepts normalized JSON. It does not open a direct STID or tagreader connection; retrieval and historian reads should normalize evidence before calling the Java runner.

Calculated Values

OpenDrainProcessEvidenceCalculator writes these review keys into each OpenDrainReviewItem when the underlying stream contains enough thermodynamic and design-basis data:

Key	Unit	Meaning
neqsimLiquidMassFlowKgPerS	kg/s	Total liquid-like phase mass flow from oil, aqueous, liquid, and liquid-asphaltene phases
liquidLeakRateKgPerS	kg/s	Credible liquid leak rate, calculated from liquid flow, leak fraction, and maximum credible leak cap
liquidDensityKgPerM3	kg/m3	Mass-flow-weighted liquid density, or total fluid density if no liquid phase is present
pressureBara	bara	Stream operating pressure
temperatureC	deg C	Stream operating temperature
fireWaterCapacityKgPerS	kg/s	Firewater mass load from application area, application rate, and water density
drainageCapacityKgPerS	kg/s	Gravity-drain hydraulic capacity from density, drain diameter, head, discharge coefficient, and backpressure

The capacity check in OpenDrainReviewEngine compares:

\[\dot{m}_{required} = \dot{m}_{\mathrm{firewater}} + \dot{m}_{\mathrm{credible\ leak}}\]

against drainageCapacityKgPerS. The gravity-drain helper subtracts downstream backpressure as an opposing liquid head before calculating capacity.

Java Example

This example creates a liquid stream, derives open-drain evidence from NeqSim, and runs the review engine. The same API calls are covered by OpenDrainReviewEngineTest.testNeqSimStreamEvidenceDrivesOpenDrainReview.

import neqsim.process.equipment.stream.Stream;
import neqsim.process.safety.opendrain.OpenDrainProcessEvidenceCalculator;
import neqsim.process.safety.opendrain.OpenDrainReviewEngine;
import neqsim.process.safety.opendrain.OpenDrainReviewInput;
import neqsim.process.safety.opendrain.OpenDrainReviewItem;
import neqsim.process.safety.opendrain.OpenDrainReviewReport;
import neqsim.thermo.system.SystemInterface;
import neqsim.thermo.system.SystemSrkEos;

SystemInterface fluid = new SystemSrkEos(293.15, 8.0);
fluid.addComponent("n-heptane", 1.0);
fluid.setMixingRule("classic");

Stream liquidStream = new Stream("OD process liquid", fluid);
liquidStream.setFlowRate(8.0, "kg/sec");
liquidStream.run();

OpenDrainProcessEvidenceCalculator.DesignBasis basis =
    new OpenDrainProcessEvidenceCalculator.DesignBasis()
        .setAreaId("OD-NEQSIM-01")
        .setSourceReference("NeqSim process model: OD process liquid")
        .setFireWaterAreaM2(20.0)
        .setFireWaterApplicationRateLPerMinM2(18.0)
        .setDrainPipeDiameterM(0.20)
        .setAvailableDrainHeadM(1.0)
        .setCredibleLeakFractionOfLiquidFlow(1.0)
        .setMaximumCredibleLiquidLeakRateKgPerS(5.0);

OpenDrainReviewInput input = OpenDrainProcessEvidenceCalculator.createInputFromStream(
    "NeqSim calculated open drain review", liquidStream, basis);

OpenDrainReviewItem item = input.getItems().get(0);
double leakRateKgPerS = item.getDouble(Double.NaN, "liquidLeakRateKgPerS");
double drainCapacityKgPerS = item.getDouble(Double.NaN, "drainageCapacityKgPerS");

OpenDrainReviewReport report = new OpenDrainReviewEngine().evaluate(input);
String verdict = report.getOverallVerdict();

Process-System Workflow

Use createInputFromProcessSystem(process, basis) when a complete flowsheet is available. The helper walks process units, selects representative inlet or outlet streams, and creates one review item per stream-bearing unit.

For multi-area plants, create area-specific design bases where firewater area, drain diameter, available head, and safeguard evidence differ. The generic process-system helper is a screening shortcut, not a substitute for area-by-area STID and line-list evidence.

Normalized JSON Evidence

The review engine also accepts normalized items, openDrainAreas, drainAreas, or stidData. Use this when STID/P&ID extraction or tagreader summaries have already provided evidence values.

{
  "projectName": "Open drain review",
  "openDrainAreas": [
    {
      "areaId": "OD-A01",
      "areaType": "process area",
      "drainSystemType": "hazardous open drain",
      "standards": "NORSOK S-001; NORSOK P-002; ISO 13702",
      "sourceHasFlammableOrHazardousLiquid": true,
      "liquidLeakRateKgPerS": 5.0,
      "fireWaterCapacityKgPerS": 6.0,
      "drainageCapacityKgPerS": 12.0,
      "hasOpenDrainMeasures": true,
      "backflowPrevented": true,
      "closedOpenDrainInteractionPrevented": true,
      "hazardousNonHazardousPhysicallySeparated": true,
      "sealDesignedForMaxBackpressure": true,
      "ventTerminatedSafe": true,
      "openDrainDependsOnUtility": false
    }
  ]
}

Safeguards That Still Need Evidence

NeqSim can calculate process and hydraulic evidence, but it cannot infer all layout and design-basis requirements from a stream. Keep these values traceable to STID/P&ID, design basis, line list, area safety chart, or tagreader records:

Evidence key	Typical source
hasOpenDrainMeasures	STID/P&ID drain boxes, gutters, coamings, deck drainage
backflowPrevented	Drain hydraulics, non-return devices, elevation breaks, sump/caisson checks
closedOpenDrainInteractionPrevented	Drain philosophy, P&ID separation, seal design
hazardousNonHazardousPhysicallySeparated	Drain routing drawings and common-sump safeguards
sealDesignedForMaxBackpressure	Seal height and hydraulic grade-line calculation
ventTerminatedSafe	Vent routing drawings and hazardous-area review
openDrainDependsOnUtility	Utility-loss assessment and pump/sump design

Verification

The documented NeqSim stream workflow is exercised in OpenDrainReviewEngineTest. Focused verification command:

.\mvnw.cmd test "-Dtest=OpenDrainReviewEngineTest"

Use targeted Checkstyle when changing the package:

.\mvnw.cmd checkstyle:check "-Dcheckstyle.includes=**/opendrain/*.java,**/OpenDrainReviewEngineTest.java"