Liquid Pipeline Friction Loss and Pump Station Spacing

From the head available between MAOP and the minimum suction requirement. Liquid is incompressible, so unlike a gas line the pressure profile is a straight line falling at the friction gradient and tilted by terrain -- which makes the arithmetic simple and makes elevation matter enormously. A line climbing spends that lift regardless of flow, and on a mountain crossing the static term can exceed the friction term entirely, so the split between the two is reported here rather than buried in one combined number. Two constraints bracket every station. The discharge cannot exceed MAOP, and the suction must stay above the minimum required to keep the pump out of cavitation and, on a hot or volatile product, above the vapour pressure so the line does not go slack. That second one is why a downhill segment can be a problem rather than a gift: a line running downhill faster than friction holds it back goes to slack flow, and the column separation and rejoin that follows is a surge event. Friction goes roughly as the SQUARE of flow, so raising throughput raises the gradient quadratically and the station count with it. That is the shape of the economics -- capacity is bought with horsepower and stations, and the last increment of throughput is always the most expensive. The friction gradient is ENTERED, from a Darcy-Weisbach or Hazen-Williams calculation at the design flow, viscosity and roughness, because it depends on properties this does not take. This is a steady-state screen: it does not compute the friction gradient, size the pumps or their drivers, model batching and the different gradients each product produces, or -- most importantly -- analyse SURGE, whose transient pressures from a valve closure or pump trip routinely exceed the steady-state profile everywhere on the line. ASME B31.4, 49 CFR 195, a transient surge analysis, and the pipeline engineer of record govern.

available head = MAOP head - minimum suction head; elevation gradient = net elevation change / length; combined gradient = friction + elevation; maximum spacing = available head / combined gradient; stations = ceiling of length over spacing; and at another throughput the friction gradient scales as the SQUARE of the flow ratio.

The steady-state liquid pipeline head balance as ASME B31.4 and 49 CFR 195 practice writes it. The friction gradient is ENTERED, from a Darcy-Weisbach or Hazen-Williams calculation at the design flow, viscosity and roughness. It does not compute that gradient, size pumps or drivers, model batching and the different gradients each product produces, or analyse SURGE.

One head balance and one quadratic scaling; no code text is reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: total_length_mi, friction_gradient_ft_per_mi, elevation_change_ft, maop_head_ft, min_suction_head_ft, flow_bpd, alternate_flow_bpd, available_head_ft, elevation_gradient_ft_per_mi, combined_gradient_ft_per_mi, max_spacing_mi, station_count, alternate_gradient_ft_per_mi, alternate_spacing_mi

• The friction gradient is entered it depends on viscosity, roughness and flow, which this does not takea Darcy-Weisbach or Hazen-Williams calculation
• Steady state only surge transients from a valve closure or pump trip routinely exceed this profile everywherea transient surge analysis
• One product batching gives each product its own gradientthe operator's hydraulic model