Experimental Determination of Impact Wear Coefficients for Modeling of Erosion in Highly Loaded Slurry Flows

Abstract

Empirical wear coefficients are used in concert with computational fluid dynamics (CFD) codes which model highly loaded slurry flows through centrifugal pumps in order to predict erosive wear in wet-end components. In practice, separate sets of wear coefficients are used to determine the contributions of sliding and impact wear to the total erosive wear at the wetted surface. In this study, experiments were performed in order to obtain the impact wear coefficients for sand in a water slurry impinging on high chrome white iron alloys that are commonly used in the construction of heavy duty centrifugal slurry pumps. Two separate sets of tests were completed using two different types of narrowly graded sand, with mass median particle diameters of approximately 600 μm and 300 μm respectively. The tests were performed in a closed loop containing a slurry pump, flow meter, inverted U loop for determination of the solids concentration, and 8 sample sections arranged serially. Each sample section was constructed from polyurethane, with rectangular flow cross sections of 1 inch (25.4 mm) width and 2 inch (50.8 mm) height and lengths of 1 foot (305 mm). One metal sample was placed into each sample holder so that it spanned across the 1 inch (25.4 mm) width and was exposed to the slurry flow, with its edges being supported by the flat polyurethane walls on either side. The samples were machined to have constant angles on the leading edge faces which varied from 10 to 60 degrees (from sample to sample), in order to obtain a range of impact angles (angle between the particle trajectory and the wetted surface) of the particles impinging on the sample leading edge faces. Tests were run at 12 % concentration by volume and at mean channel-sectional flow velocities of 10 m/s, with run times varying from 30 minutes to 180 minutes over the course of the test program. Slurry loop samples were taken at the beginning and end of each run in order to determine the particle size distribution and to monitor degradation of solids through sieve and micrograph analysis. The worn wedge face surfaces were scanned at intermittent times throughout the testing using an optical profilometer, and the local erosive wear was determined on the slanted face of, as well as at the tip of, the wedge-shaped samples. The progression of wear over the course of the test program was measured and analyzed in this manner. The local solids concentration, velocity, and impact angle was then predicted using in-house CFD codes formulated in the same manner as the pump wear models. The experimental wear profiles, together with the predicted local solids concentration, velocity, and impact angle, were then used to calculate the specific energy coefficient (or impact wear coefficient) at multiple impact angles. A formulation for the impact wear coefficient as a function of impact angle at a given particle size was then produced at each of the two different particle diameters. By comparing the data between the two different particle diameters, an adjustment factor for particle diameter was then formulated. This paper primarily focuses on the experimental test program, providing a description of the experiments, results, and data analysis, as well as a discussion of the results and some description of the test-derived wear coefficient formulations.