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Pure-Water Ice Ih Melting Temperature and Margin Calculator

Invert the IAPWS ice Ih melting curve at absolute pressure and compare it with a supplied pure-water temperature.

Inputs

Results

Calculate to view linked results. Default values are examples, not recommended operating inputs.

Calculation sequence

  1. Enter absolute pure-water pressure and temperature. This tool covers the ice Ih/liquid boundary, not the water boiling curve or methane hydrate boundary. Pressure depresses the ice Ih melting temperature over this branch; a familiar 0 C atmospheric rule cannot simply be held fixed at high pressure.
  2. Invert the explicitly attributed IAPWS equation with a bounded Brent root on 251.165-273.16 K. The application restricts pressure to 0.1-200 MPa, below the ice Ih/ice III/liquid triple point near 208.566 MPa. Root residual is checked in pascals rather than silently rounded in MPa.
  3. Subtract the pressure-dependent melting temperature from the actual supplied temperature. Negative margin favors ice Ih relative to liquid at equilibrium, positive margin favors liquid; neither gives ice mass, freezing time or nucleation probability. Plot the same branch across the permitted pressure interval to show its direction.
  4. IAPWS gives about 2 percent uncertainty for melting pressure. The root solver can close much more tightly than the physical correlation uncertainty; that computational precision must not be interpreted as a certified operating safety margin. Salts and inhibitors change the boundary and require other data.
  5. Calculations run locally in a dedicated WebAssembly worker. The advanced Python/scientific engine is a roughly 33 MB first download, separate from ordinary calculators; it is self-hosted and version pinned. No composition or measurements are sent to a calculation server. Save and file backups retain canonical inputs, while CSV/PDF include returned tables and source notes. The worker is released after idle time and failures never return partial results.

Worked check

At 10 MPa absolute, pure water melts below 273.16 K. Comparing a 273 K fluid temperature to that pressure-dependent root gives a positive margin, even though 273 K is slightly below the familiar atmospheric freezing temperature. The margin is not valid for seawater or inhibited produced water.

Synthetic examples for reproducibility, not measured field results.

Assumptions and limitations

  • Pure ordinary water only; no brine, dissolved gas, methanol/glycol inhibition, gas hydrate, pore-size effects or ice polymorph beyond Ih. This model must not be used as a natural-gas hydrate prediction.
  • Pressure 0.1-200 MPa absolute; the melting root is confined to the IAPWS Ih branch. Actual comparison temperature 251.165-300 K. No extension into the ice III/V/VI/VII branches or sublimation curve.
  • Equilibrium temperature margin only, not freezing kinetics, ice quantity, equipment protection or operational approval. Physical pressure uncertainty is much larger than the displayed numerical root residual.

Implemented equations

IAPWS R14-08(2011) ice Ih melting curve

pm611.657=1+∑i=13ai(1−θbi)θ=T/273.16ΔT=Tfluid−Tm(p)\begin{aligned}\frac{p_m}{611.657}&=1+\sum_{i=1}^{3}a_i(1-\theta^{b_i})\\\theta&=T/273.16\\\Delta T&=T_{\rm fluid}-T_m(p)\end{aligned}

Sources and maintenance

Published by PetroCalcHub Team. Implementation and source checks: . This does not claim independent expert review.

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