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themanufacturer'sguaranteedthicknessof0.969inchuntiltheDecember7,1985,reading.However,over 65percentofthematerialhandledduringthetest .7 millioncubicyards!hadbeenpumpedbythattime.From Table 3 and Figure 3, it is obvious that wear around the pipe was not uniform. Also, for all locations, wear was greaterinSection1.SlurryflowenteredtheHDPEpipesthroughSection1 andthenflowedintoSection2. Itispossiblethattheuniform,smoothinteriorofHDPESection1 reducedturbulenceenoughtocauseless wear in HPDE Section 2. Locations of greatest wear ,0! and least wear ,5! are the same in both sections. Inbothsectionsmorewearoccurredintheadjacentlocationsof7,0,1and2.However,asseeninTable2, only38.4percentofthetotalflowpassedthroughtheHDP Esectionswhentheselocationswereonthebottom. ThisrelationshipisillustratedbyFigure5,whichisa plotofthepercentofthedredgedmaterialthatpassed throughthepipewheneachofthelocationswasonthebottom,andthepercentofwearforeachlocation.If the amount of material was the major cause of wear, then the location of greatest wear would be the location that passed the greatest amount of material. This is not what the data show. Location on Pipe Section 1 01 2 35 7 4 6 Section 2 01 2 375 64 Average Thickness Start of Test inches 0.993 0.979 0.991 1.013 1.034 1.057 1.058 1.028 1.018 1.050 1.056 1.041 1,018 0.995 0.983 0.981 Average Thickness End of Test Inches 0.800 0.890 0,872 0.931 0.995 1.036 0,969 0.718 0.897 0.955 0.961 0.967 0.981 0.993 0.924 0,692 Difference Inches 0,193 0.089 0.'t19 0.082 0.039 0,021 0.089 0.310 0.121 0.095 0.095 0.074 0.037 0.002 0.059 0.289 Wear Percent of Original Thickness 19.4 9.1 12.0 8.1 3.8 2.0 8.4 30.2 11.9 9.0 9,0 7.1 3.6 0.2 6,0 29.5 Table 3. HDPE Pipe Wall Thickness Loss Before conclusions could be drawn, it was necessary to verify the data and the accuracy of the wall- thickness gage. A second set of final readings was taken on April 22, 1986. These two sets of data were comparable and verified the highest percent of wear in Location 7. The calibration of the wall thickness meter was also checked and found to be correct. During the course of the dredging season, the interior of the pipe was visually inspected by WES Hydraulics Laboratory personnel on three occasions, September 10 and October 19, 1985, and April 21, 1986. In September and October, the interior was smooth and unmarred with the finish going from highly glossy to a smooth satin. By April, the interior was marred with small, smooth nicks. The marring was uniform along the length of the pipe, but varied in intensity around the interior of the pipe, being most severe along Location 7 and least noticeable at Location 2. The butt weld bead a result of the fused joint! was still intact in some locations but completely worn away in others Figure 6!, Also noticed on the final inspection was the appearance of small, smooth, circumferential ridges around the inside of the pipe about every 2 inches along the length of the pipe Figure 7!. This "washboard" effect has been observed in polyethylene pipe, but no definite cause could be Identlfiedby the manufacturer's engineer. Itwas suggested that this might be a function of material creep and the fact that flow was always in the same direction.PDF Image | Dredging Applications of High Density Polyethylene Pipe
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