Evaluation of Stress Crack Resistance of Corrugated High Density PE Pipes [PE]

In past ten years, there is a significant growth in the use of high density polyethylene (HDPE) corrugated pipes in transportation related applications in the United States. At the same time, the evaluation of stress crack resistance (SCR) of the HDPE corrugated pipes has also gone through many changes. A comprehensive SCR specification on pipe resins has been established recently; while no changes have been proposed for the finished pipes. The current SCR test on the corrugated pipe is impractical and ineffective. In this paper, the SCR of finished pipe was evaluated using the notched constant tensile load (NCTL) test. Five pipes with diameters from 460 to 900mm were tested together with their corresponding pure resins. The effects of pipe processing were investigated by testing specimens taken directly from the pipe liner and pipe crown locations at two different orientations. A large difference in the SCR was measured between the two locations. Furthermore, the SCR were affected by the orientation of the specimens and the notching position due to bending stress, residual stress and orientation of polymer chains. In all of the test configurations, the liner specimen oriented along the longitudinal direction of the pipe with an outer surface notch yielded the shortest failure time. The pipe processing decreased the SCR of the corresponding resin. The reduction factor varies from pipe to pipe ranging from 0.29 to 0.86.