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M AT E R I A L S S E L E C T I O N & D E S I G N FIguRE 1 (a) (b) (c) (a) Control valve cage eroded by black powder in 45 days, (b) typical black powder collected from sales gas transmission line, accumulated in metering stations, and (c) scanning electron microscope image of black powder particles. (v = 90 and 130 m/s) and six angles of impingement (angle between particle jet and surface (α = 15, 30, 45, 60, 75, and 90 degrees). These particle sizes and velocities are typical of feld-collected black powder and gas velocities in control valves, respectively. Three measurements were made using different dwell times. For all materials the set of dwell times was chosen to create erosion craters no deeper than the 350-μm depth suggested in ASTM G76-07. A microblaster for blasting the magnetite particles against the target materials was used in all erosion rate experiments.5 The target samples were clamped to a 100 by 300-mm aluminum plate that was scanned below the stationary nozzle using a computer-controlled two-dimensional motorized positioning stage. Figure 2 shows the schematic of the experimental set up. TAbLE 1 As-received average hardness values of target materials Sample Material(A) As-Received Vickers Hardness (HV) 17-4pH SS (17-4pH) 352 ± 3 A240 Type 2205 duplex SS (2205) 262 ± 1 Type 316L SS (316L) 164 ± 2 A515 Gr. 70 norm. (A515-70) 164 ± 1 A105 CS forging (A105) 161 ± 1 A53 Gr. B steel (A53-B) 157 ± 1 A240 Type 410 SS (410) 152 ± 1 (A) Three to six measurements were taken for each sample. FIguRE 2 Results and Discussion Figures 3 to 6 show the measured erosion rates for both tested particle velocities (90 and 130 m/s) and sizes (6.9 and 30.4 μm). As expected, for both particle sizes, the erosion rates at 130 m/s were between two and three times larger than those measured for the 90 m/s particle velocity. Two unexpected observations can be seen from these fgures: 1) smaller particles gave signifcantly higher erosion rates than the larger ones at the same velocity and 2) the erosion rates are not A schematic representation of the experimental setup. NACE International, Vol. 52, No. 5 May 2013 MATERIALS PERFORMANCE 71