Wear Law Of Horizontal Straight Pipe For The Transport Of High Concentration Backfill Containing Coarse Aggregate By Gravity

The wear of the filling pipe is of great harm.The horizontal straight pipe accounts for the majority of the entire pipe length,and its long-term maintenance and replacement work is extensive.The research background of this paper is that coarse aggregate is added to the high concentration full tailings slurry to adjust the material balance in a lead-zinc mine.Taking 16Mn steel as the pipe material and the wear law of the horizontal straight filling pipe as the research object,the research aim is to prolong the pipe life.The key findings are as follows:(1)The characteristics of three basic wear forms of filling pipe were analyzed.The contact stress model between coarse aggregate and pipe wall was established,the bigger the size,density and velocity of particle,the more severe the pipe wear.Fatigue wear is the abrasion mechanism in the usual backfilling process,whereas cutting and fatigue wear are the erosion mechanisms during pipe flushing.Under the same circumstances,erosion wear during the flushing operation is more severe than abrasion wear during usual backfilling.The corrosion rate of pipe by flushing water and uncemented slurry is 3265.1 mg/m2d,and the corrosion rate increases as a quadratic function from 91.7 to 548.2 mg/m2d when the sand-cement ratio increases from 4 to 12.Corrosion products have a lower hardness than pipe,which accelerates pipe wear during slurry scouring.(2)The influence law of high concentration filling parameters on pipe wear were investigated based on the improved slurry pot tester.The wear rate increased exponentially with increasing slurry concentration,power-law with increasing flow velocity(<3 m/s),logarithmic with increasing coarse aggregate size,and gradually declined first then suddenly increased with increasing coarse aggregate content.Under constant slurry concentration,a suitable coarse aggregate content(≤25%)is advantageous in reducing pipe wear and resistance.Pure corrosion contributed less than 0.5%of total wear,but synergistic wear contributed 3.6%～59.4%.The wear rate regression models were established(mean error 3.8%).The power law index of concentration was larger than 6,while the power law index of flow velocity was less than 1.2,which differed considerably from those found in turbulent medium-and low-concentration slurry.The greater the pipe resistance,the more severe the pipe wear,and these two are strongly correlated.(3)The filling pipe wear rate prediction method and model were proposed.The surface shear stress model of the worn specimens was constructed,and the wear rate increases in a power-law function as shear stress increases.To solve the inner wall shear stress of the filling pipe,the modified Buckingham resistance formula(average error 11%)can be utilized.The total wear of the filling pipe is only weakly related to pipe pressure,and the wear rate of the high-pressure pipe can be predicted approximately by the wear test at atmospheric pressure.The prediction model for the total wear rate of filling pipe is composed of three parts:pipe wear in usual backfilling,pipe wear in flushing,and pipe corrosion by flushing water.The first component is calculated exactly based on the slurry pot wear test and pipe wall shear stress,the second part is estimated using the flow velocity of pipe flushing and usual backfilling,and the third part is calculated precisely based on the immersion corrosion test.(4)The wear mechanism of coarse aggregate on pipe wall was revealed by CFD-DEM simulation.When the full tailings slurry can support the coarse aggregate,the solid-liquid presents a plug-flow,otherwise the coarse aggregates form a sliding bed at the pipe bottom.In the case of plug-flow,the coarse aggregate is concentrated toward the pipe center,and the bigger particles are closer to the pipe center than smaller particles,resulting in uniform pipe wear.In a sliding bed,larger particles are closer to the pipe bottom than smaller particles,and the wear degree of the pipe bottom notably different from that of the top and sides,with pipe bottom wear is more severe than in a plug-flow.The motion trajectory of coarse aggregate near the pipe wall is similar to a sinusoidal curve,and the coarse aggregate not only slides but also rolls when contacting the pipe wall.The abrasion effect of coarse aggregate on the pipe wall is mainly tangential scraping at a small Angle.(5)Measures for controlling filling pipe wear based on filling parameters optimization and four-step pipe turning technology were proposed,and the reliability of pipe wear prediction model is acceptable.The filling rate is increased to 100 m3/h,and the filling efficiency is improved without excessive pipe wear.The maximum coarse aggregate size is 10 mm.The backfilling slurry concentration of 76%or 78%(coarse aggregate content≤20%)can meet the requirements of backfill strength,material balance,gravity transportation,and low pipe wear.A four-step pipe turning approach considering the pipe wear rate and pressure is proposed to increase the transportation volume of the straight horizontal pipe by at least 15×104 m3.The maen error of the pipe wear prediction model is 12.2%.