GPSA Ch. 7 API 1160 ASME B31.8
Slug formation, pipeline transients, finger vs. vessel design, and liquid holdup fundamentals
Pipeline slugs form from terrain undulations, pigging operations, or production rate changes. Volume depends on holdup and pipeline geometry.
During pigging, the pig sweeps liquid ahead of it. Slug volume equals pipeline liquid inventory times pig sweep efficiency (~80%).
A slug catcher is a vessel or set of pipes at a pipeline terminus that receives and separates liquid slugs from two-phase (gas-liquid) flow. It is needed to protect downstream equipment from transient liquid surges caused by terrain, pigging, or flow rate changes.
This calculator sizes slug catchers for three slug sources: terrain-induced slugs from hilly pipeline profiles, pigging slugs from pipeline maintenance operations, and ramp-up transients from flow rate changes per GPSA and API 1160.
The two main configurations are finger-type (multiple parallel pipes) and vessel-type (horizontal pressure vessel). Finger-type slug catchers are preferred for large slug volumes and high pressures, while vessel-type is more compact for smaller applications.