An Alternative to API 14E Erosional Velocity Limits for Sand Laden Fluids

Abstract

Abstract The current practice for eliminating erosional problems in piping systems is to limit the flow velocity (Ve) to that established by the recommended practice API RP 14E based on an empirical constant(C-factor) and the fluid mixture density (Pm) as follows:(available in full paper) The API criterion is specified for clean service (non-corrosive and sand-free) and it is noted that the C-factor should be reduced if sand or corrosive conditions are present. The validity of the equation has been challenged on the basis that the API RP 14E limits on the C-factor can be very conservative for clean service and is not applicable for conditions when corrosion or sand are present. Extensive effort has been devoted to develop an alterative approach for establishing erosional velocity limits for sand laden fluids. Unfortunately, none of these proposals have been adopted as a standard practice because of their complexity, This paper will review the results of these studies and proposes an alterativeequation that is as simple as the API 14 E equation. This alterative Equation has the following form:(available in full paper) The value of the S-factor depends on the pipe geometry, i.e. bend, tee, contraction, expansion, etc. Using the units for mixture flow velocity (Ve). in m/s, fluid mixture density (All) in kg/m3, pipe diameter (D) In rum and sand production (W) in kg/day, the value of the S-factor is 0.05 for pipe bends. The accuracy of the proposedequation for predicting erosion in pipe bends for fluids containing sand is demonstrated by a comparison with several multi-phase flow loop tests that cover a broad range of liquid-gas ratios and sand concentrations. Introduction Erosion is defined as the removal of material from a solid surface by the repeated application of mechanical forces. These forces are induced by solid particles, liquid droplets, or cavitations. Liquid impingement erosion occurs when liquid drops or liquid jet repeatedly impact the solid surface. Erosion may be attributed toremoval of the metal, the inhibited film, and/or protective corrosion scales. In order to avoid erosion damage, the current oil industry practice f()f sizing process piping, flow lines, pipelines, and tubing is to limit the now velocity to the maximum erosional velocity ascalculated by the following API RP 14 E equation (API, 1981, 1991)(available in full paper) The Original API criterion is specified for clean service (noncorrosive and sand-free), and it is noted that the C-factor should bereduced if sand or corrosive conditions are present. However no guidelines are provided for these reductions. It has been argued by several investigators that the API RP 14E relation is extremely conservative under these conditions and this led to the changes in the 1991 edition. However, the recent changes imply that a C-factor of 100 is acceptable for corrosive systems and a C-factor of 150 to 200 is acceptable for inhibited systems.