Expanding capabilities for HDPE pipe
Originally published by Utility Magazine, April 26, 2019
High density polyethylene (HDPE) pipe has a track record spanning more than 60 years in Australia and is established as the system of choice for the transport of gas, pressurised sewerage, mining slurry and potable water. HDPE pipes are lightweight, corrosion free and feature an optimal strength-flexibility compromise, resulting in long service life and cost-effective installation.
The HDPE pipe industry is characterised by a collective drive for continuous improvement across the value chain, exemplified by the evolution of materials from HDPE Type 50 in the 1950s to the state-of-the-art PE100 resins available today. This drive for innovation has by no means come to an end and three examples are provided here on how HDPE pipe capabilities are expanding to larger pipe dimensions and longer design lifetimes.
Size does matter
Whilst HDPE pipes have traditionally dominated the diameter range up to 450mm, nowadays installation of DN/OD pipes of over 1800mm are becoming commonplace. The use of low slump materials, such as Alkadyne HDF145B (discontinued grade), coupled with advances in pipe extrusion technology, enable the efficient production of large diameter pipes with wall thicknesses in excess of 120mm while meeting tight dimensional tolerance specifications.
Qenos has been involved in a number of projects in the last two years that demonstrate the capability of large diameter HDPE pipe. Examples include a dual DN1200mm PN16 pipeline made from Alkadyne HDF145B, used to cross the Hunter River in NSW by horizontal directional drilling (HDD) as part of the Chichester Trunk Gravity Main upgrade. In greater Caloundra on Queensland’s Sunshine Coast, five sections of up to 1.6km length of DN900mm PN20 pipe made from the same material were used to upgrade Unitywater’s pressurised sewerage infrastructure, also using HDD. In both projects, high welding efficiencies were achieved by applying best practices in butt-fusion welding which was further aided by the high uniformity in the wall thickness of the pipes.
Extending design life
The design life of HDPE piping systems is at least 50 years at 20°C, with service life dictated by the hydrostatic strength of the material at a given design temperature. Condition assessment studies have shown life expectancies well in excess of 100 years are achievable. The use of non-conventional installation techniques such as HDD may put the pipe under additional stress and limit the service life. PE100 with high stress-crack resistance (PE100 HSCR) defined in PIPA Guideline POP016 is able to withstand these higher stresses and prolong the service life of trenchless installations.
The first PE100 HSCR pipeline in Australia was installed in 2017, where DN450mm and DN315mm PN20 pipes made from Alkadyne HCR193B were installed by HDD under the Causeway Lake estuary in Yeppoon QLD to expand the capacity of the existing water main. More recently, the same material powered a DN800mm PN20 pipe used in two HDD sections of up to 1.3km length for Perth’s groundwater replenishment scheme. Alkadyne HCR193B was selected by utilities in both cases to improve asset life and durability, thereby reducing whole-of-life costs and maintaining supply to their customers.
Another pathway to increasing the design life of HDPE piping systems, particularly when exposed to elevated temperature and presence of oxidative agents, is to select a pipe material that features not only high stress-crack resistance, but also higher resistance to oxidative degradation.
Hostalen CRP100 RCD Black combines both of these properties to increase pipe system longevity, whilst at the same time expanding the application range of HDPE pipes to include higher temperatures and media containing aggressive chemicals.