Application of a CFD-Based Erosion Prediction Procedure for Sudden Expansions

Pipe fittings used in the production of oil and gas can experience erosion damage from solid particles such as sand present in the produced fluid. The fittings disturb the flow, which often results in erosion. Certain geometries are more susceptible to erosion damage than others; for example, a sudden expansion can experience severe erosion under certain operating conditions. A sudden expansion can promote erosion for two reasons. First, a radial velocity develops downstream of the expansion. This velocity component drives particles toward the wall. Second, the sudden expansion causes a zone of elevated turbulent kinetic energy. The high level of turbulent kinetic energy results in large turbulent fluctuations, and these fluctuations can also force particles to the wall. A comprehensive model for predicting sand erosion has been developed by utilizing a commercially available computational fluid dynamics (CFD) code. This procedure involves flow modeling, particle tracking, and applying erosion equations. Due to the low sand concentrations a one-way coupling is used between the fluid and the particles. The goal of this study is to use the procedure to calculate erosion in sudden expansions and determine if modifications to the existing procedure are necessary. Simulation results for sand in air flowing through sudden expansions with different diameter ratios (1.25 to 2.00) are compared with experimental data. Both the simulations and data show that the maximum erosion rate evaluated in thickness loss per mass of sand passing through the geometry decrease with increasing expansion ratio.