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Characterization of plastic Lay-flat irrigation tubing material properties and outlet flow performance as impacted by mil thickness and internal tubing pressure
Proceedings of the 2022 Mississippi Water Resources Conference

Year: 2022 Authors: Caey D.

Lay-flat irrigation tubing, or poly-pipe, has become a low-cost solution for flood irrigation on leveled-to-grade farmland through the Mid-South. Poly-pipe is available in a range of diameters and material thicknesses in lengths of up to one-quarter mile, providing the flexibility to be adapted to meet variable field conditions and flow requirements. System challenges include management of even flow distribution across the length of installed poly-pipe sections and poly-pipe failures from over-pressurization. Computerized hole selection (CHS) prescriptively determines the optimum outlet hole size for each furrow, providing the desired water output to maximize water use efficiency. Poly-pipe failures are common and are believed to result from improperly selected poly-pipe diameter and thickness and can also be influenced by incorrectly sized outlet holes at the furrows, creating elevated internal tubing pressures that result in material deformation. Theses failures can be identified as catastrophic, such as in a complete failure, or rupture, of the poly-pipe. However, over-pressurization can also result in stretching/elongation of outlet holes before complete material failure occurs, altering hole geometry and significantly affecting the flow dynamics of the hole. However, little research exists to quantify these factors and their relationships as causal agents for failure. The objectives of this study were to characterize poly-pipe performance by: 1) quantification of material properties of available poly-pipe mil. thicknesses, 2) evaluation of the interaction of poly-pipe thickness and internal pressure on failures. Virgin poly-pipe samples were analyzed in static conditions utilizing ASTM D882-18 "Standard Test Method for Tensile Properties of Thin Plastic Sheeting" in an MTI 2K Bench-Top Universal Testing System to capture the material properties in tension (modulus of elasticity, burst strength, and tensile strength) for each mil. thickness. Each thickness of poly-pipe was found to be significantly different (p<0.0001) across the assessed material properties analyzed. Further analysis was conducted in dynamic conditions simulating hole flow/pressure relationships to evaluate hole reaction to pressure changes. Single holes were punched in 44-inch sections of 7, 9, and 10 mil poly-pipe, and subjected to increasing pressures of up to 150% of yield tensile strength. Flow rates were captured at four pressures up to 100% of calculated yield tensile strength, at 150% of yield tensile strength, and the subsequent four pressures post 150%. Significant differences (p<0.0001) were observed between pre and post over-pressurization for all mil thicknesses, with differences being more pronounced in the 7 mil poly-pipe. No significant differences were observed between poly-pipe diameters of the same mil thicknesses. Further analysis is ongoing to assess the effects of over-pressurization in multi-hole poly-pipe configurations to assess if the effects are consistent across all holes.

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