Blocked-in liquid thermal expansion is one of the most severe overpressure scenarios in process plants: because liquids are nearly incompressible, even a modest temperature rise can produce extreme pressure increases when a segment is isolated with no vapor space and no relief path. BlockedInLiquidExpansionAnalysis (neqsim.process.util.fire) provides two complementary screening methods for this scenario, per API 521 7th Ed. Section 4.4.12.

When to Use This vs TrappedLiquidFireRuptureStudy

Tool Scope Use when
BlockedInLiquidExpansionAnalysis Pure thermal-expansion pressure rise for a blocked-in liquid (no fire, no pipe stress/flange checks) Quick check of whether a blocked-in liquid segment needs a thermal relief valve (TSV), or to size the magnitude of an expansion-pressure problem
TrappedLiquidFireRuptureStudy (docs) Full fire-exposure transient: wall heat-up, pipe/flange stress, rupture time, PFP demand Fire case screening for a blocked-in segment, including material strength derating and rupture-time estimation

Both classes provide complementary screening: use BlockedInLiquidExpansionAnalysis (neqsim.process.util.fire) first as a fast, fire-independent screening check, then move to TrappedLiquidFireRuptureStudy (neqsim.process.safety.rupture) when a fire scenario and material/flange checks are required.

Two Calculation Modes

  1. Rigorous isochoric pressure march — computeIsochoricPressureProfile(fluid, temperaturesK) re-flashes a clone of the fluid at each requested temperature, searching (bracket + bisection) for the pressure that reproduces the reference density recorded at the initial blocked-in state. This avoids the constant-property assumption of the simplified relation and is accurate over large temperature spans.
  2. Simplified screening relation — the classical $dP = (\beta / \kappa)\, dT$ relation from API 521 §4.4.12, where $\beta$ is the isobaric thermal expansion coefficient and $\kappa$ is the isothermal compressibility. Use estimateThermalExpansionCoefficient(fluid, dT) and estimateIsothermalCompressibility(fluid, dP) to estimate $\beta$ and $\kappa$ by central finite differences at the reference state, then simplifiedPressureRise(beta, kappa, deltaT) for the pressure rise. This relation is only accurate for small temperature steps around the reference state; for larger temperature changes prefer the isochoric pressure march.

Java Example

import neqsim.process.util.fire.BlockedInLiquidExpansionAnalysis;
import neqsim.thermo.system.SystemInterface;
import neqsim.thermo.system.SystemSrkEos;

SystemInterface oil = new SystemSrkEos(298.15, 10.0);
oil.addComponent("n-heptane", 100.0);
oil.setMixingRule("classic");

// 1. Rigorous isochoric pressure march from 25 C to 60 C
double[] temperaturesK = {298.15, 308.15, 318.15, 328.15, 333.15};
double[] pressuresPa =
    BlockedInLiquidExpansionAnalysis.computeIsochoricPressureProfile(oil, temperaturesK);

// 2. Simplified beta/kappa screening estimate for a quick cross-check
double beta = BlockedInLiquidExpansionAnalysis.estimateThermalExpansionCoefficient(oil, 1.0);
double kappa = BlockedInLiquidExpansionAnalysis.estimateIsothermalCompressibility(oil, 1.0e5);
double simplifiedDeltaPPa = BlockedInLiquidExpansionAnalysis.simplifiedPressureRise(beta, kappa, 35.0);

computeIsochoricPressureProfile returns pressures in Pa for each requested temperature (Kelvin); simplifiedPressureRise returns the estimated pressure rise in Pa. The simplified estimate should agree with the isochoric march to within roughly 30% for moderate temperature spans — use the isochoric march as the reference and the simplified relation only for a fast order-of-magnitude check.

Standards Basis

Topic Standard / method
Liquid thermal expansion overpressure scenario API 521 7th Ed., Section 4.4.12
Thermal relief valve sizing once a relief requirement is confirmed ReliefValveSizing (docs) — API 520
Full fire-exposure rupture screening for the same blocked-in segment TrappedLiquidFireRuptureStudy (docs)

Limitations

This is a screening tool. It does not replace a thermal relief valve sizing study, and it does not account for vapor space, trace heating, insulation credit, or non-uniform heating along a pipe run. Use ReliefValveSizing to size the thermal relief device once a relief requirement is confirmed.