Particle, Fluid Velocity, and Erosion Measurements for Viscous Liquids in a Submerged Direct Impingement Flow

Abstract

In the production and pipeline transport of various fluids, such as oil and natural gas, solid particles may be entrained in the fluid. These particles, commonly consisting of numerous types and sizes of sand, can travel apart from the streamlines of the fluid and impact the surface of the pipe. With time, enough particles may impinge a pipe wall at a sensitive location, such as an elbow or tee, to result in a measurable wall thickness loss. This may ultimately lead to severe erosion damage causing a leak in a pipeline, a dangerous and costly problem. As a result, a pipeline’s service life may often depend on the rate at which a pipe wall is eroded. The erosion rate, or amount of material loss over a certain time period, depends on a large number of factors. The target material, or material experiencing a thickness loss, such as a pipe wall, influences the rate at which damage occurs. Its density, hardness, yield strength, and microstructure combine to present a certain resistance toward erosion occurring from solid particle impact. Furthermore, the solid particle’s diameter, sharpness, and shape will influence its trajectory, speed, and momentum transfer into the target, thereby requiring the analysis of various particle types in predicting erosion. Finally, the carrier fluid being transported through a pipeline will further affect the solid particle’s movement as it approaches the target. As a result, the fluid’s density and viscosity must be carefully considered in particle tracking and erosion analysis. By considering the aforementioned properties of the target, solid particles, and carrier fluid, it is desirable to be able to predict the erosion rate from a single erosion equation. Other factors depending on these properties may be found in this expression, such as particle impact speed and impingement angle at the target. Velocity measurements by way of Laser Doppler Velocimetry (LDV) were made for particles entrained in a viscous liquid traveling in a submerged, direct impingement jet. In an attempt to obtain representative particle impact characteristics during material erosion, data was collected from the nozzle exit to the target surface in order to track fluid and particle velocities prior to impact with a wall. Average particle sizes of 120 and 550 μm were used to represent typical sand sizes, while much smaller particles with an average diameter of 3 μm were utilized in fluid velocity measurements. The carrier fluid viscosity was varied from 1 to 100 centiPoise, while the nozzle flow rate and fluid density were maintained constant. Changes in approach and estimated impingement velocity occurring due to fluid viscosity and particle size are then presented. For the same impingement geometry and flow situations, metal loss erosion measurements have been made by way of an Electrical-Resistance (ER) probe. Oklahoma #1 sand particles with an average diameter of 150 μm were suspended in a viscous carrier fluid at a measured sand concentration. The measured erosion rate and particle velocities at near target wall locations are then compared to observe the effect of viscosity on material erosion and impact speed. Particle tracking and erosion predictions made by Computational Fluid Dynamics (CFD) can then be experimentally validated.