Experimental Investigation of Flow Behavior in a Bend and Sand Erosion Pattern Under Single-Phase and Multiphase Flow Conditions

Solid particle erosion in pipe fittings may cause pipe failure and major safety and environmental issues. Elbows are widely used in oil and gas production and transportation systems, and they are one of the most vulnerable fittings when presence of sand particles is anticipated in the system. An experimental apparatus was created to investigate the flow behavior in a 4-inch 90 degree bend under multiphase flow conditions in both horizontal-horizontal and vertical-horizontal elbow orientations. It was observed that in vertical annular flows, entrained droplets and liquid film are focused at the center of the outer bend, and as liquid velocity increases, the liquid film inside the elbow outer radius becomes thicker and it decreases the measured erosion. Observations were verified by comparison of erosion magnitudes in bends for different liquid velocities obtained utilizing a state-of-the-art ultrasonic thickness measurement technique. Erosion patterns and location of maximum erosion results were also examined through paint erosion experiments. It was concluded that regardless of particle size and gas and liquid flow rates, maximum erosion occurs in the range between 40° to 50° on the bend for gas dominant flows in low pressure gas environment studied here. A secondary erosion pattern caused by particle rebounds was observed to occur in the range between 60° to 90° in the bend. Erosion experimental results in the 4-inch elbow were compared with Computational Fluid Dynamics (CFD) predictions of erosion, and agreement was observed in terms of erosion pattern and 40% agreement in magnitude.