diff --git a/app/simulation/components/amesim/flow/pipes.py b/app/simulation/components/amesim/flow/pipes.py
index 12d4b5b..8e72662 100644
--- a/app/simulation/components/amesim/flow/pipes.py
+++ b/app/simulation/components/amesim/flow/pipes.py
@@ -1667,6 +1667,16 @@ class AmesimPnl0003(DynamicComponent):
         viscosity = self._dynamic_viscosity(temperature)
         return 4.0 * abs(mass_flow) / (pi * self.diam * viscosity)
 
+    def reported_reynolds_number(
+        self,
+        mass_flow: float,
+        temperature: float,
+    ) -> float:
+        """Return AMESim's derived re without changing pipe dynamics."""
+
+        viscosity = self.medium.diagnostic_dynamic_viscosity(temperature)
+        return 4.0 * abs(mass_flow) / (pi * self.diam * viscosity)
+
     def friction_factor(self, reynolds_number: float) -> float:
         return AmesimPnl00r.friction_factor(self, reynolds_number)
 
@@ -1734,6 +1744,7 @@ class AmesimPnl0003(DynamicComponent):
         center_flow = self.resistance_mass_flow()
         upstream = port_1 if center_flow >= 0.0 else port_2
         reynolds = self.reynolds_number(center_flow, upstream.T)
+        reported_reynolds = self.reported_reynolds_number(center_flow, upstream.T)
         friction = self.friction_factor(reynolds)
         return {
             "m1": self.state_1.m,
@@ -1751,7 +1762,7 @@ class AmesimPnl0003(DynamicComponent):
             "u2": port_2.u,
             "h2": port_2.h,
             "dmctr": center_flow,
-            "re": reynolds,
+            "re": reported_reynolds,
             "cm": _bare_pipe_mass_flow_parameter(
                 center_flow,
                 area=self.area,
diff --git a/app/simulation/components/amesim/media/mediums.py b/app/simulation/components/amesim/media/mediums.py
index 8618e13..0256f4f 100644
--- a/app/simulation/components/amesim/media/mediums.py
+++ b/app/simulation/components/amesim/media/mediums.py
@@ -2,7 +2,7 @@ from __future__ import annotations
 
 from collections.abc import Callable, Sequence
 from dataclasses import dataclass
-from math import isfinite
+from math import exp, isfinite, log
 from typing import ClassVar
 
 from app.simulation.core.errors import RecoverableTrialStateError
@@ -55,6 +55,12 @@ class AmesimHeliumPengRobinsonMedium(IdealGasMedium):
     fluid: ClassVar[PengRobinsonFluid] = HELIUM_PR
     nasa_cp_over_R: ClassVar[float] = 2.5
     nasa_enthalpy_constant_K: ClassVar[float] = -745.375
+    nasa_viscosity_coefficients: ClassVar[tuple[float, float, float, float]] = (
+        0.7501594,
+        35.76324,
+        -2212.129,
+        0.9212635,
+    )
 
     name: str = "AMESimHeliumPengRobinson"
     R_gas: float = HELIUM_PR.specific_gas_constant
@@ -73,6 +79,19 @@ class AmesimHeliumPengRobinsonMedium(IdealGasMedium):
         del T
         return self.cv
 
+    def diagnostic_dynamic_viscosity(self, T: float) -> float:
+        """Return the AMESim NASA-table viscosity used by pipe diagnostics.
+
+        pn2pipefr reports Reynolds number with sagum viscosity. Keep this
+        separate from dynamic_viscosity so matching that diagnostic cannot
+        alter the already-validated pipe flow or friction dynamics.
+        """
+
+        if T <= 0.0:
+            raise ValueError("Temperature must be positive.")
+        a, b, c, d = self.nasa_viscosity_coefficients
+        return 1.0e-7 * exp(a * log(T) + b / T + c / (T * T) + d)
+
     @profile_property("density")
     @cache_property_calculation("density")
     def density(self, p: float, T: float) -> float:
diff --git a/app/simulation/core/medium.py b/app/simulation/core/medium.py
index e394fe8..fd6da1f 100644
--- a/app/simulation/core/medium.py
+++ b/app/simulation/core/medium.py
@@ -81,6 +81,8 @@ class GasMedium(Protocol):
 
     def dynamic_viscosity(self, T: float) -> float: ...
 
+    def diagnostic_dynamic_viscosity(self, T: float) -> float: ...
+
     def specific_internal_energy(self, T: float) -> float: ...
 
     def specific_internal_energy_at_pressure(self, p: float, T: float) -> float: ...
@@ -182,6 +184,16 @@ class IdealGasMedium:
             / (T + self.sutherland_constant)
         )
 
+    def diagnostic_dynamic_viscosity(self, T: float) -> float:
+        """Return the viscosity convention used by derived diagnostics.
+
+        Most media use the same transport property for dynamics and reported
+        diagnostics. Reference-library media may override this without
+        changing a calibrated constitutive flow relation.
+        """
+
+        return self.dynamic_viscosity(T)
+
     @profile_property("specific_internal_energy")
     def specific_internal_energy(self, T: float) -> float:
         delta_T = T - self.T_ref
diff --git a/tests/test_amesim_helium_medium.py b/tests/test_amesim_helium_medium.py
index 0778e36..d4054e8 100644
--- a/tests/test_amesim_helium_medium.py
+++ b/tests/test_amesim_helium_medium.py
@@ -72,8 +72,33 @@ class AmesimHeliumPengRobinsonMediumTests(unittest.TestCase):
             temperature,
         )
         self.assertAlmostEqual(medium.dynamic_viscosity(293.15), 1.96e-5)
+        self.assertAlmostEqual(
+            medium.diagnostic_dynamic_viscosity(293.15),
+            1.9616132203938165e-5,
+        )
         self.assertEqual(medium.sutherland_constant, 79.4)
 
+    def test_pipe_diagnostic_viscosity_reproduces_amesim_nasa_table(self) -> None:
+        medium = AmesimHeliumPengRobinsonMedium()
+
+        self.assertEqual(
+            medium.nasa_viscosity_coefficients,
+            (0.7501594, 35.76324, -2212.129, 0.9212635),
+        )
+        self.assertAlmostEqual(
+            medium.diagnostic_dynamic_viscosity(233.92077861710192),
+            1.683135986478913e-5,
+            delta=1.0e-19,
+        )
+        self.assertNotAlmostEqual(
+            medium.diagnostic_dynamic_viscosity(233.92077861710192),
+            medium.dynamic_viscosity(233.92077861710192),
+            delta=1.0e-8,
+        )
+
+        with self.assertRaises(ValueError):
+            medium.diagnostic_dynamic_viscosity(0.0)
+
     def test_pressure_transport_enthalpy_includes_peng_robinson_departure(
         self,
     ) -> None:
diff --git a/tests/test_amesim_pnl0002_pnl0003_component.py b/tests/test_amesim_pnl0002_pnl0003_component.py
index e470f1b..8e4ef1e 100644
--- a/tests/test_amesim_pnl0002_pnl0003_component.py
+++ b/tests/test_amesim_pnl0002_pnl0003_component.py
@@ -1,9 +1,12 @@
 from __future__ import annotations
 
 import unittest
-from math import log10, sqrt
+from math import log10, pi, sqrt
 
 from app.simulation.components.amesim.flow.pipes import AmesimPnl0002, AmesimPnl0003
+from app.simulation.components.amesim.media.mediums import (
+    AmesimHeliumPengRobinsonMedium,
+)
 from app.simulation.core.medium import IdealGasMedium
 from app.simulation.registry import COMPONENT_MODEL_REGISTRY
 
@@ -462,6 +465,33 @@ class AmesimPnl0003ComponentTests(unittest.TestCase):
         self.assertIn("dmctr", values)
         self.assertIn("re", values)
 
+    def test_reported_reynolds_uses_amesim_helium_nasa_viscosity_only(self) -> None:
+        medium = AmesimHeliumPengRobinsonMedium()
+        pipe = AmesimPnl0003("pnl_3", medium, diam=0.02)
+        mass_flow = 0.04555349965141288
+        upstream_temperature = 233.92077861710192
+
+        # Frozen AMESim dense row: t=0.81 s, branch 2, D=0.02 m.
+        expected_amesim_reynolds = 172298.96343252173
+        reported = pipe.reported_reynolds_number(
+            mass_flow,
+            upstream_temperature,
+        )
+        dynamic = pipe.reynolds_number(mass_flow, upstream_temperature)
+
+        self.assertAlmostEqual(reported, expected_amesim_reynolds, delta=1.0e-9)
+        self.assertNotAlmostEqual(reported, dynamic, delta=1.0)
+        self.assertAlmostEqual(
+            dynamic,
+            4.0
+            * abs(mass_flow)
+            / (
+                pi
+                * pipe.diam
+                * medium.dynamic_viscosity(upstream_temperature)
+            ),
+        )
+
     def test_result_cm_excludes_center_resistance_flow_coefficient(self) -> None:
         pipe = AmesimPnl0003(
             "pnl_3",