Burst behavior of CPVC compared to HDPE thermoplastic polymer under a controlled internal pressure

Abstract

Abstract: The HDPE (High Density Polyethylene) and CPVC (Chlorinated Polyvinyl Chloride) are extremely used in water piping systems. The CPVC have the particularity to support high temperatures of water. Those two materials are known for their different characteristics toward the internal pressure. To quantify their behavior we exposed pipe specimens, prepared according to ASTM 1599, to an increasing internal pressure and we registered the burst and the time of each specimen. To push further our analysis, we created groove notches over the same category of specimens and we exposed them to the same conditions. Then, we have noticed a drop of the internal pressure in function of the time and the life fraction which is the ratio of thickness and its fluctuation (Δe/e). Indeed, the burst pressure, and the time of failure are drastically dropping according to the notch depth. Besides, one important consequence is noticeable over the mechanical behavior which shift from a ductile one, for neat pipes, to a brittle one for the other HDPE pipes. Meanwhile, The CPVC pipes have a brittle behavior for both of the specimen's categories. The discrepancies can be explained by the nature of the two materials, the first one is an original polymer while the second is a Chlorinated PVC material. Furthermore, the comparison of the failure mode of the two polymers are slightly different compared to the linear damage of Miner. For HDPE pipes, the static damage is evaluating nearby the Miner one until getting to the critical life fraction (βc) of 52% and then get over it. However, the CPVC damage has a very weak evolution bellow the βc of 60% from which we notice a drastic increasing and an acceleration of the damage. The CPVC show good performances toward the supported internal pressure, support up to 160 bars, and a brittle behavior. Meanwhile, the HDPE pipe can support up to 70 bars and show a ductile behavior. Finally, this paper can be considered as a window to understand the difference between HDPE and CPVC polymers under burst pressure and the severity of the groove defects for researchers and industrials.