Pressure drop from Crane TP-410 Darcy-Weisbach: ΔP = f × (L/D) × (ρV²/2), with friction factor f from Colebrook-White solved iteratively. Equivalent length for fittings is user-supplied via the pipe length input.
Erosional velocity per API RP 14E: V_e = C / sqrt(ρ_mix) with mixture density from the gas and liquid mass flows at line conditions. Default C = 100 for continuous flow in non-corrosive service.
Two-phase pressure drop uses Beggs & Brill with flow-regime classification (segregated, intermittent, distributed) and inclination correction. Liquid holdup is the Mukherjee-Brill modification for the chosen regime.
Gas density from Peng-Robinson EOS with GPSA pseudo-critical mixing rules. CO₂, H₂S, and N₂ corrections per GPSA Section 23.