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The key physical design parameter for flexible buried non-pressure pipe is Pipe Stiffness. The ever broadening recognition of the inherent chemical resistance of polyvinyl chloride (PVC) pipe has led to a wide range of possible new applications. The effect of environment on PVC and other plastic pipe is typically measured by weight change or strength change on unstressed samples exposed to various environments such as described in ASTM D-1784, Standard Specification for Rigid Polyvinyl Chloride (PVC) Compounds or by stress or strain crack resistance. Herein a new method of measuring the long term pipe stiffness of samples exposed to various environments is proposed. This is accomplished by monitoring the instantaneous slope of the load deflection curve as a function of time. Six-inch (150mm) long pipe stiffness samples are tested to determine the initial stiffness by the method of ASTM D-2412-87, Standard Test Method for Determination of External Loading Characteristics of Plastic Pipe by Parallel Plate Loading. The sample is then clamped in a position of fixed deflection of either 5% or 7.5%. At time intervals of 1 day, 1 week, 2 weeks, 4 weeks, 8 weeks, 16 weeks and 32 weeks the load increment is increased to produce an added deflection increment to a total deflection of 7.5% or 10%. The slope of the load-deflection curve for this new load increment is calculated for each new time interval. Data from various PVC pipe samples in environments consisting of 5% sulfuric acid, 5% sodium hydroxide, tap water and air are presented. Results for up to two years exposure are included.
Polyvinyl Chloride (PVC) Pipe, Sewer Pipe, Pipe Stiffness, Stress Relaxation, Constant Strain
Bishop, Roland R.
Director of Technical Services, Carlon Division of Lamson & Sessions, Beachwood, OH