Pig Speed & Transit Time Calculator

Liquid pigs track fluid velocity: V = Q / A, with A = pi/4 x ID² (uses actual ID, not NPS). Gas converts standard to actual flow first - Q_actual = Q_std x (14.73/P_abs) x (T/520) x Z - then V = Q_actual/A less the bypass fraction. Transit time t = length / velocity. Optimal speed depends on pig type (foam best ~3-8 ft/s, ILI ~2-6 ft/s); most operators hold 2-15 ft/s to limit wear and surge. This is a continuity-based estimate - a real derivation, but line elevation, pig efficiency (0.85-0.95) and fluid properties shift it. Traces to the pig-speed fundamentals in NACE SP0102 / ASME B31.8 / API 1163 and vendor guides (TDW Guide to Pigging). Confirm with your operating data.