Effect of flow velocity on erosion-corrosion of 90-degree horizontal elbow

Erosion-corrosion is a serious problem in oil and gas gathering and transportation pipeline systems; specifically, the elbow is the weak part. Erosion-corrosion at different locations of a horizontal steel elbow through which a sand slurry was passed at different velocities was studied using weight loss measurement. Erosion samples were characterized using three-dimensional confocal microscopy and computational fluid dynamics was used to characterize the flow patterns and distribution of sand particles in the elbow. The erosion-corrosion rate increased most as the fluid velocity increased from 3.5 to 4.0 m/s. Increasing particle velocity increased the mechanical effects of the particles and induced secondary flow, leading to differing velocity contours in different cross-sections of the elbow, and thereby differing rates of erosion-corrosion. The maximum rate appeared in the outer part (annular angles φ=45, 90, and 135 degrees) and bottom of the inner part (annular angles φ=225, 270, and 315 degrees) of the elbow outlet with an axial angle between 75 and 90 degrees.