Field and Laboratory Assessment of High-Density Polyethylene Slabs

Abstract This paper focuses on field and laboratory assessments conducted on HDPE slabs as an alternative solution for protecting oil and gas pipeline systems from external interference for use in northern climates. External interference is defined as external activities causing damage to the pipe or its components as per CSA Z662. It is one of the primary causes of failure for oil and gas pipeline systems. One of the mitigative methods to reduce the number of incidents resulting in damage and likelihood of failure due to external interference, is the installation of a physical barrier. Traditionally, concrete slabs, steel plates, or casings have been used as physical barriers to provide mechanical protection. In recent years, HDPE slabs have been chosen as an alternative product for mechanical protection by various pipeline operators around the world, including TC Energy. The effectiveness of these slabs to protect pipelines from excavator strikes was demonstrated previously in Europe by the PSG. Details of the PSG test results and other historical tests results, as well as success story of TC Energy’s implementation of HDPE slab will be presented in another TC paper in the IPC 2024 (IPC2024-133759). Canadian pipeline operators install pipelines year-round even in winter at temperatures well below freezing. According to the historical ground temperature data for Northern Alberta, the soil temperature at a depth of 1 m below ground remains above 0°C, even when the air temperature is below −20°C. Academic literature denotes the glass transition temperature for HDPE is well below −50°C (generally lower than −100°C). While the HDPE slabs are acknowledged as effective to protect pipelines even in cold winters in northern climates, TC Energy recognizes the importance of testing the HDPE slabs at low temperatures to confirm the material performance at such conditions. Hence, TC Energy has partnered with Overpipe to conduct bench impact tests at −23°C. Six (6) HDPE slabs with different formulations were tested. All tests displayed success at preventing and obstructing excavator strikes with minimal damage to the slabs, with no indications of rapid crack propagation. One slab did show a minor crack at the point of contact, but no significant propagation was noted. In addition to the bench impact testing, laboratory material tests have also been completed on these slabs. Based on Overpipe’s field impact and material tests, one of the slab formulations was recommended to be used in cold conditions. To further confirm the material properties, TC Energy has completed comprehensive material testing on the recommended slab formulation. This included Charpy-V-Notch testing, tensile testing and Dynamic Mechanical Analysis. While the overall results have provided positive indications regarding the slab’s performance in cold weather conditions, some irregularities and wider-than-expected variances were observed in certain properties measured. In response, TC Energy is looking to conduct additional testing and analysis to further investigate the current draft findings.