This video shows a field test we recently performed. In this test, liquid is being vented which results in “slug flow”. The resultant displacement demonstrates the need for good structural support and process design. Plant systems where slug flow could be of concern are process venting systems, emergency relief systems and condensate drainage systems.
Thermopedia and Wikipedia refer to "slug flow" as "liquid–gas two-phase flow in which the gas phase exists as large bubbles separated by liquid 'slugs'. Pressure oscillations within piping can be caused by slug flow."
In the book New Technologies in the Oil and Gas Industry, edited by Jorge Salgado Gomes, Chapter 5 "The Slug Flow Problem in Oil Industry and Pi Level Control" written by Airam Sausen, Paulo Sausen and Mauricio de Campos states: "The slug is a multiphase flow pattern that occurs in pipelines which connect the wells in seabed to production platforms in the surface in oil industry. It is characterized by irregular flows and surges from the accumulation of gas and liquid in any cross-section of a pipeline."
And, "The slug flow causes undesired consequences in the whole oil production such as: periods without liquid or gas production into the separator followed by very high liquid and gas rates when the liquid slug is being produced, emergency shutdown of the platform due to the high level of liquid in the separators, floods, corrosion and damages to the equipments of the process, high costs with maintenance. One or all these problems cause significant losses in oil industry. The main one has been of economic order, due to reduction in oil production capacity."
Plant managers and structural engineers both come to agreement where proper pressure venting is concerned. Without proper design for liquid and gas flow in piping, pressure builds and risks for catastrophic events can occur. The key is testing under all scenarios and conditions prior to relief system design and again periodically per regulations and your facility's formal procedures. Accounting for all events, including seismic is key in determining if the pressure flow is adequately addressed.
Fauske & Associates, LLC (FAI) designs, tests and provides analysis for structural engineering, plant analysis, gas and air intrusion accumulation, relief system design, seismic walkdowns and so much more. Prevention of runaway reactions, severe accidents and other threats to industrial facilities and plants are our specialty.