Analysis of Two-Phase Stratified Flow and Liquid Hold Up at Dead Ends of T-Sectioned Natural Gas Pipelines

T-sectioned configurations with a deadleg at the stopple are present in natural gas pipelines, where liquid water may accumulate, increasing the potential for internal corrosion. The objectives of the present study are to explore the pipeline operating conditions under which water enters the deadleg and define an operating protocol to prevent water accumulation in deadlegs. A combined computational fluid dynamics (CFD) experimental and analytical study was conducted to understand the behavior of liquid slugs at the T-junctions with dead ends. The flow equations were solved as an unsteady multiphase (gas and water) incompressible flow problem using the Volume of Fluid (VoF) Method. The analytical calculations were based on a modified form of the macroscopic mechanical energy balance equation. In order to computationally simulate the critical velocity at which water enters the deadleg, the inlet gas flow rate was specified to be a fixed value, while the water flow rate was gradually increased. The liquid entirely bypasses the deadleg until the liquid water velocity exceeds a critical value, which was noted as the critical superficial liquid velocity. The experimental study was conducted using a flow loop to understand the behavior of liquid water at the T-junction and determine the condition when liquid enters the deadleg. The analytical and computed solutions were compared with experimental observations. The computed results follow the same pattern as the experimental and analytical data. Solutions indicate that critical superficial liquid velocity is linearly dependent on superficial inlet gas velocity.