Experimental Slug Flow-Induced Fluid–Structure Interaction of a Pressurized Flexible Pipe

An experimental study into the fluid–structure interaction of gas–liquid flows as they pass through a pipeline riser, like those utilized in the oil and gas industry, was carried out. In this study, a 10-m-long pipe with inner diameter of 50 mm at 10 bar (gauge) pressure was used with operating fluids of water and nitrogen. A two-phase flow regime diagram is used to determine liquid and gas volume flow rates that fall within the slug flow regime, and this was further refined using PETEX GAP and finally CFD software, STAR-CCM+, to determine the experimental test matrix. Axial strain gauges were positioned close to the flanges at the ends of the riser to measure strain at the cardinal points of the pipe at both the top and bottom of the riser. At approximately 2 m and 3 m horizontal distance from the entrance to the riser, accelerometers were attached to monitor the motion of the pipe at these positions. The motion of the pipe was observed to be almost exclusively in-plane, with only small out-of-plane motion registered on the accelerometers. Strain gauge measurements demonstrated that the increase in mass flow rate of the liquid phase/decrease in mass flow rate of the gas phase served increases the mean values of stain at both the entrance and exit of the riser. A monotonic increase in the magnitude of the rms of the fluctuations of the strain was observed for an increase in the flow rate of either the liquid or the gas phase. The highest flow rates tested introduce an irregular cyclic whipping motion in the flexible pipe in addition to the smooth oscillation motion.