Experimental study of the crack depth ratio threshold to analyze the slow crack growth by creep of high density polyethylene pipes

• Experimental data on pre-cracked rings featuring a longitudinally cracked HDPE pipe.
• Crack depth ratio threshold for slow crack growth study consecutive to oxidation.
• Investigation of the effects of the single/double notch(es) and of the strain rate.
• Original results obtained from tests performed with tensile and creep loadings.
• Correlation between creep initiation time and C* with DENT and ring specimens.

To assess the durability of drinking water connection pipes subjected to oxidation and slow crack growth, a comprehensive database was constructed on a novel specimen geometry: the pre-cracked NOL ring.135 tests were carried out consisting of initial crack depth ratio ranging from 0.08 to 0.6; single or double longitudinal cracks: tensile with steady strain rate and creep loading. A threshold value of the crack depth ratio of 0.2, induced by the oxidation was determined by analyzing several mechanical parameters. This threshold value was shown to be independent on the strain rate effects, single or double crack configuration and the kind of loading: tensile or creep. Creep test results with crack depth ratio larger than 0.2 were then utilized to establish a failure assessment diagram. A methodology allowing the prediction of residual lifetime of in-service pipes was proposed, using this diagram.