Pump Sizing Calculation
Template (Excel)

A pump sizing calculation determines the hydraulic duty (rated flow, differential head, NPSH-available), shaft power, motor rating, and applicable code (API 610 / ANSI B73.1 / ISO 13709) for a centrifugal or positive displacement pump. It uses process design data (fluid, temperature, specific gravity, viscosity, vapour pressure), suction system data (source pressure, static head, line losses), and discharge system data (destination pressure, static head, line losses, control valve drop). The output drives the pump datasheet, the Material Requisition (MR), and vendor selection. Sizing margins (typically 10% flow, 5% head over normal) are added per project basis of design.

Required columns: pump tag, service, P&ID reference, pump type, fluid identity and composition, operating temperature with min and max cases, specific gravity, viscosity, vapour pressure (needed for NPSH calculation), rated and normal and design flow rate, suction source plus pressure plus static head plus line loss, discharge destination plus pressure plus static head plus line loss plus control valve drop, total differential head, hydraulic power, pump efficiency, shaft power, motor sizing with sizing margin, NPSH-available, NPSH-required from vendor, NPSH margin, applicable code (API 610 / ANSI / ISO 13709). The template covers all required columns.

Pathnovo, an engineering document intelligence platform, extracts pump tags and service from the equipment list, pulls process data (fluid, temperature, flow, density, viscosity, vapour pressure) from the simulation heat and material balance, reads suction and discharge configuration from the P&ID extraction workflow (vessel tags, line numbers, elevations, control valve tags), computes line losses against the line list line size and length, and outputs a populated sizing calculation per the project basis of design. NPSH-available is computed; NPSH-required is held until vendor curves are received during TBE.

NPSH-available = (suction vessel pressure, absolute) plus (suction static head) minus (suction line loss) minus (fluid vapour pressure at operating temperature, absolute), all converted to metres of pumped fluid. The calculation must use absolute pressures, must use the maximum operating temperature case (vapour pressure rises with temperature, NPSH-available falls), and must use the minimum liquid level in the suction vessel (worst-case static head). The result is compared to vendor NPSH-required plus a margin (typically 1 m or 10% of NPSH-required, whichever is greater) per API 610.

API 610 (Centrifugal Pumps for Petroleum, Petrochemical, and Natural Gas Industries, currently 12th Edition) specifies pump types (OH, BB, VS), mechanical design requirements (casing thickness, bearing housing, mechanical seal per API 682), preferred operating region (between 80% and 110% of best efficiency point), allowable operating region, NPSH margin, hydrostatic test pressure (1.5 times maximum allowable working pressure), performance test tolerance, and minimum continuous stable flow. The sizing calculation must position the rated point inside the preferred operating region of the offered pump curve. Non-API pumps (ANSI B73.1, ISO 2858) follow simpler hydraulic checks.

Pump sizing computes the required duty point (rated flow, differential head, NPSH-available, shaft power) from process and piping data. Pump selection matches the duty point against vendor pump curves to choose a specific model, impeller diameter, motor rating, and accessories. Sizing is done by the process or systems engineer at FEED or early detailed engineering. Selection is done by the rotating equipment specialist after MR issue and vendor bids return. The sizing calculation is the input to the pump datasheet; the selected pump from TBE is recorded on the certified datasheet.

On a brownfield revamp, the existing pump curve and current operating point are the starting reference. The revamp duty (new rated flow and head) is plotted on the existing curve to check whether the existing pump can be re-rated (new impeller diameter, new motor, new mechanical seal) or whether a new pump is required. Pathnovo, an engineering document intelligence platform, ingests the as-built pump datasheet, the existing curve, and the new process data to flag re-rate versus replace decisions automatically. Output feeds the revamp Material Requisition. See the material requisition template.