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New project on cracking in polyethylene and other polymer pipelines approved
Earlier this month the Energy Pipelines CRC Board approved a new project that studies cracking of polyethylene and other polymer pipe walls. This is an important failure mechanism of PE pipe.
Cracking is generally accepted to be mostly driven via slow crack growth (SCG) leading into rapid failure (including brittle failure). However, there is a lack of literature in relation to pipe ageing and predicting degradation mechanisms and the impact this has on service life and time to failure. This new project, RP1-07, will develop models based around this to allow more accurate replacement strategies to be developed.
The first phase of this project RP1-06 that was completed last month was directed at the first generation HDPE used in natural gas reticulation networks. Note that a significant part of the Australian gas pipe network was built during the mid-1970’s and 80s period and that HDPE grades PE50 and PE63 were predominantly used.
This research established a relative current condition ranking, and supported an informed asset replacement and management strategy for these older pipes in the network.
The role of squeeze-off in stress concentration formation and the subsequent impact on expected life was also examined for these PE pipe materials. Furthermore, this research project has shown that pipe age and regional geographic location are key factors in determining relative remaining lifetime for the vintage grade HDPE pipes.
While the data collected allows for replacement strategies, it is not clear as to the precise primary degradation factors and how these relate to newer HDPE and MDPE grades. Project RP1-07 aims to addresses these issues.
RP1-07 will expand the data set to include newer PE pipe grades, PE100 and PE80 as well as other plastic pipe materials. The research aims:
- To verify that the suite of tests developed in project RP1-06 are applicable to the newer grade materials being examined in this project (RP1-07);
- To determine if the factors responsible for degrading newer grade PE pipe materials are similar to those affecting vintage grade HDPE pipes;
- To establish the link between pipe degradation and geographically associated environmental factors for PE pipes, expanded the data set obtained for vintage HDPE and then applying this to new grades (eg climate, soil type); and
- To assess whether the suite of tests developed in RP1-06 and refined in this project for PE are also suitable for PA (nylon) and PVC (poly vinyl chloride) pipes.