WEAR RATE TO STAINLESS STEEL PIPE FROM LIQUID-SOLID SLURRY

摘要

The United States Department of Energy is building a Waste Treatment Plant (WTP) at the DOE Hanford Site in the state of Washington to process stored radioactive wastes for long-term storage and disposal. The Savannah River National Laboratory (SRNL) is helping resolve technical concerns with the WTP, which are related to piping erosion/corrosion (wear). SRNL is assisting in the design of a flow loop to obtain long term wear that will use prototypic simulant chemistry, operating conditions, and materials for total wear rate. The challenge is to accurately measure slurry wear to a pipe wall thickness tolerance of ～47 microns/year anywhere in the test flow loop in a timely manner. To help in the design of the flow loop a test was performed with a smaller loop, which contained many of the pipe fittings expected in WTP to determine where high wear locations exist. One aspect of this test was to understand the rate of wear to straight pipe and to protrusions from the surface of the pipe. Initially, wear to straight pipe was studied because wear in other flow loop situations, e.g., around bends, through tees, etc. will be higher. To measure such low wear rates requires sensitive measurement techniques. To that end, twelve wear coupons were placed in one section of the pipe system and at different protrusion heights into the flow stream. They were made of 316L stainless steel, which is the expected material of pipe to be utilized. From the wear coupons, an estimate of wear rate was obtained, as well as illustrating when a protrusion above a pipe surface no longer disturbs the flow streams with respect to slurry wear. It appears when a surface is just above the laminar sublayer it produces a wear rate equivalent to a surface with no protrusions. The slurry was a mixture of water and 30 wt% of sand, d_(50) ～ 200 microns. The test flow conditions were a velocity of 4 m/s in a 0.07793-m inside diameter (3-inch, Schedule 40) pipe system, resulting in Reynolds number just above 3 × 10~5, i.e., turbulent flow at a temperature of 25 °C. The wear was to a vertically oriented straight section of pipe that was 1.86 meter long. The twelve wear coupons were located on the inside surface starting from 10 diameters from the pipe entrance to 21 diameters, with a separation of 1-pipe diameter between each successive coupon. Furthermore, each set of two adjacent coupons were rotated 180 degrees apart which were then rotated 30 degrees from the next set to minimize disturbance to the flow for the downstream coupon. This paper describes the wear rates obtained, the effect of increasing a wear coupon's protrusion into the flow stream, and the overall operation of the test apparatus.