Engineering context

Cavitation and flashing risk are screened as a diagnostic objective inside a steady-state model, not judged by hand one component at a time. They are driven by how local static pressure, temperature, and vapour pressure interact with pump suction conditions, valve and restriction pressure drops, and elevation changes. The practical method is to build a model configured to reproduce the suspected condition, solve it, and then identify where risk arises from the solver’s enunciated warnings, the pressure and NPSH results, and the relevant charts.

A practical workflow starts by defining the diagnostic objective and acceptance criteria (for example, a minimum NPSHA margin above NPSHR, and static pressure staying above vapour pressure) and setting the calculation basis — vapour pressure data and the NPSH margin philosophy. Engineers then build and connect the network, defining the boundary conditions and applying the fluid that is selected from the database, which carries its properties (including vapour pressure), and set up the operating cases that expose risk. After solving, risk is identified from the visual sweep and the Messages tab (cavitation, low static-pressure, and high-velocity warnings), from static pressure compared against vapour pressure and NPSHA against NPSHR, and from the pump’s Flow vs NPSHR chart and EGL/HGL plots. This workflow identifies risk within a steady-state model; it does not replace detailed equipment review or safety-critical assessment. For liquid-gas two-phase and slug-flow modelling, see the liquid-gas two-phase piping systems workflow.

Engineering workflow

1. Define the diagnostic objective and acceptance criteria — state whether you are screening for pump cavitation or flashing/vapour formation, and the criteria you will judge against (for example, an NPSH margin philosophy requiring a minimum NPSHA above NPSHR at the duty point, and static pressure staying above the fluid’s vapour pressure).
2. Set the calculation basis — select the correlations and solver options the screening depends on: the fluid’s vapour pressure data and the NPSH margin philosophy.
3. Build and connect the network — place and define the boundary conditions (the fluid is selected from the database, which carries its properties including vapour pressure, and applied at the boundary), then add pumps, valves, restrictions, fittings, and pipework and connect them with pipes. Pay particular attention to suction-side elevations and lengths, since small errors there materially change NPSH available.
4. Set up the operating cases that expose risk — as combinations of component settings, model the worst-case conditions: maximum flow toward end of curve, minimum suction level or pressure, hot versus cold, turndown, and similar.
5. Solve and run a visual sweep — confirm solution health on the status bar, check that flow-direction arrows appear on all open paths, and look for red component highlights; a missing arrow or a highlight is itself a diagnostic signal.
6. Work through the Messages tab — review the enunciated showstoppers, warnings, and hints; cavitation, low static-pressure / vapour-pressure, and high-velocity messages flag where and why risk arises. Resolve root causes and apply engineering judgement on which warnings are acceptable for the service.
7. Compare results against vapour pressure and NPSH — read static pressure across the network against the fluid’s vapour pressure to locate flashing or cavitation onset, and for pumps compare NPSH available against NPSH required at the duty point using the pump’s Flow vs NPSHR chart and the pump-versus-system curve.
8. Use charts to locate and characterise the risk, then document and compare — the pump’s Flow vs NPSHR chart and the pump-versus-system curve for cavitation margin, and EGL/HGL composite plots (where the elevation profile rises above the EGL, indicating vacuum or low margin). Document the basis, margins, and assumptions, and compare design or operating alternatives that restore margin.

How FluidFlow helps

FluidFlow screens cavitation and flashing risk within steady-state pipe network analysis — combining vapour pressure data, NPSH results, and its message and charting tools (NPSH charts and EGL/HGL plots) to show where risk arises in the connected system. For liquid-gas two-phase and slug-flow modelling, see the liquid-gas two-phase piping systems workflow. Do not position this page as full transient simulation or CFD-style local flow prediction.

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