HDPE pipe is a type of flexible plastic pipe used for fluid and gas transfer and is often used to replace ageing concrete or steel mains pipelines. Made from the thermoplastic HDPE (high-density polyethylene), its high level of impermeability and strong molecular bond make it suitable for high pressure pipelines. HDPE pipe is used across the globe for applications such as water mains, gas mains, sewer mains, gas transfer lines, rural irrigation, fire system supply lines, electrical and communications conduit, and stormwater and drainage pipes. However, most United States municipal governments restrict its use on public works projects.
The toughness and resistance to chemicals of polyethylene, as well as the corrosion resistance and low weight have contributed to its growing use in situations where cost-effective and durable fluid and gas piping systems are required. According to a press release from the Plastics Pipe Institute, "PE piping has been used for water and other fluids in Europe and America since the 1950s due to its durability, leak free joints, resistance to corrosion, and long-term cost-effectiveness.

HDPE pipe can be joined by butt welding, electrofusion welding, socket welding, or extrusion welding. These joints heat the pipe during the joining process, creating a completely homogeneous joint so the weld becomes as strong, or stronger than the existing pipe on either side of the weld. There is no need to use rubber seals or jointing chemicals, as is used for joining PVC pipe, which cause environmental health issues and increase the chance of failure over time. PE is less likely to have problems with root intrusion, and provides integrity for the pipeline, even when installed in unstable soils.