Shock Behaviour of HDPE Pipes [PE]

In this paper, results of an investigation on behavior of HDPE pipes under internal shock pressure are presented. A number of HDPE pipe segments have been subjected to travelling shock wave of internal water pressure produced by an axial impacting mechanism. Three types of failure, consisting of ductile rupture, brittle fracture, and pipe buckling have been observed. Variations of internal pressure, hoop strain, and bursting pressure as well as internal buckling pressure have been measured and recorded. 

Polymeric pipes may become exposed to internal pressure gradients caused by some changes in the pressure within the piping system. The external blows can also generate pressure variations as well as dynamic stresses and premature collapses in the pipes. The phenomenon of water hammer is another example of internal dynamic loading of pipes. Brittle crack propagation is one of the phenomena that can occur in polymer pipes. Polymer pipes can also be susceptible to the buckling instability. These time varying factors could affect the behavior of the pipes drastically, and in some cases, could very well lead to failure piping systems. 

In this paper, results of an experimental and theoretical investigation on behavior of HDPE pipes under internal shock pressure are presented. In the course of this investigation, a number of HDPE pipe segments (D = 250 mm, L = 1.4 m, SDR 11) have been subjected to travelling shock wave of internal water pressure produced by an axial impacting mechanism. Time variations of internal pressure, hoop strain, and the bursting pressure as well as internal buckling pressure have been measured and the modes of failure have been recorded. The influence of pre-notch as well as the welds on the impact behavior of HDPE pipes have, to a limited extent, been investigated. 

A very interesting, and yet potentially dangerous, phenomenon which has occurred in pressurized polymer pipes tested herein has been the buckling instability of pipes. The so-called piston effect of internal pressure shocks (due to ram action) has induced an overall buckling of the pipes and so has rendered their initially straight configuration unstable. Through a simple theoretical modeling, the observed buckling phenomenon has been substantiated.