A Guideline to Calculate Erosional Velocity due to Liquid Droplets for Oil and Gas Industry

Abstract

Abstract In the oil and gas industry, pipe size and material are selected so that the flow velocity is below the so called "erosional velocity," presumably a flow velocity at which it is safe to operate. The American Petroleum Institute Recommended Practice 14E (API RP 14E) guide describes a method for calculating an erosional velocity for clean service. For oil and gas industry applications, some authors assume that the basis for API RP 14E is erosion due to liquid droplet impact. However, there is no experimental or theoretical evidence supporting this idea. The goal of present work is to provide a guideline to calculate erosional velocity due to liquid droplets in oil and gas production and transportation facilities. This paper describes how liquid droplet erosion can be calculated for a variety of materials that are commonly used in oil and gas industry pipelines. The calculation methodology developed previously has been extended to predict erosion of the oilfield materials due to water droplets with and without impurities using experimental data that was collected for specimens impacting a liquid jet. The erosion equation for liquid impact presented in American Society for Testing and Materials (ASTM) standard G73-10 has been modified based on experimental data to consider velocity exponent changes with droplet size. Based on the new erosion model, a procedure has been developed to predict erosional velocity due to liquid droplet impact utilizing the entrainment fraction and droplet size calculated from two-phase flow correlations and the impact velocity of the droplets within a pipe elbow or a tee that is estimated using stagnation length model which is basically a one-dimensional particle tracking model and an alternative for complex Computational Fluid Dynamic (CFD) simulation of multiphase flow and incorporated particle tracking scheme. Experimental data that was obtained at the Erosion/Corrosion Research Center (E/CRC) for several engineering materials such as stainless and carbon steels, chromium alloys and Inconel are used to calculate a threshold velocity using the data and method developed in this study. The erosional velocities computed using this model are compared with the erosional velocities computed using API RP 14E. It is shown that the trend of the erosional velocity calculated by the API guideline is extremely conservative as compared to the new model predictions for erosion due to liquid impact and does not correlate with erosion due to small entrained particles. Thus, oil and gas producers can use this method and provided equations and graphs to determine erosional velocities for cases when no sand is being produced or when small particles are entrained in the liquid.