February 2022, Vol. 249, No. 2

Tech Notes

Polyethylene Pipe Proves Capable in High-Temperature Saltwater Disposal

Special to P&GJ  

Performance Pipe’s PlatinumStripe 1800 Series Pipe was recently utilized to convey water from wells to a saltwater disposal facility in Desert Hills, near Orla, a small town in West Texas.   

PlatinumStripe 1800 Series Pipe
PlatinumStripe 1800 Series Pipe

The pipe was made from Dow’s INTREPID 2499 NT Bimodal Polyethylene Resin – a high-density polyethylene (HDPE) resin produced with Polyethylene Raised Temperature (PE-RT) using UNIPOL II process technology and was initially developed for municipal and industrial pressure piping systems meant to withstand extreme temperatures of up to 180°F (82°C).   

PE-RT is typically used in municipal and industrial piping systems where extreme conditions, including high temperatures, aggressive chemicals and highly oxidative stressors, exist. Suitable uses include oil and gas gathering pipelines, mining pipelines, district energy municipal water distribution, biogas systems and other industrial applications.  

HDPE-based resins, like those used to manufacture the pipe for this Desert Hills project, feature various designs of molecular structures. They are used to make everything from plastic milk cartons to detergent bottles. They’re also used to manufacture pipe for stormwater, potable water and sanitary sewer systems, as well as pipe used for extruded electrical and telecommunications conduit and hydronic tubing.  

“The exceptional strength of PlatinumStripe 1800 Series Pipe is a direct result of the unique bimodal PE-RT resin we produced using our UNIPOL II Process Technology. It gives HDPE resin superior performance characteristics, which are critical for polyethylene pressure pipes like the one used in the Desert Hills project,” explained Dell Doyle, Ph.D., TS&D scientist at Dow and chair of the Energy Piping Systems Division of the Plastic Pipe Institute (PPI). “Compared to other PE-RT resins, the material used in this project is the only PE-RT that carries a PE4710 listing at high temperatures.”   

The long-term hydrostatic strength and its reduction to the hydrostatic design stress (HDS) of INTREPID 2499 NT Bimodal Polyethylene Resin was demonstrated in accordance with PPI Hydrostatic Stress Board (PPI HSB) policies. It also meets and exceeds the stringent American Society of Testing and Materials (ASTM) PE4710 requirements. A maximum operating pressure can be determined for a pipeline at various temperatures using the following ratings: hydrostatic design basis (HDB), hydrostatic design strength (HDS) obtained from HDB, minimum required strength (MRS), or categorized required strength (CRS).  

“PlatinumStripe pipe produced with the INTREPID 2499 resin has a 180° F pressure rating,” Doyle said, citing Doyle additional benefits of the process: “This outstanding high-temperature endurance, coupled with the best-in-class resistance to major pipe failure mechanisms, such as slow crack growth and rapid crack propagation, ensures safe operation of a prolonged service lifetime for the Desert Hills pipeline projects, which makes it more sustainable to the environment as it significantly reduces the need and frequency of repair and replacement-related issues.”   

The natural gas and oil coming from the wells are refined into ethane and propane, which are treated with high heat in a process known as cracking. This converts them into monomers such as ethylene and propylene. These monomers are then combined with a catalyst to create a polymer “fluff” that is fed into an extruder, where it is melted and fed into a die. As it cools, the resin forms a long strand that is cut into small pellets. Pellets are shipped to factories to be melted and molded into many products such as water bottles, food packaging, auto parts, medical devices and pipe.  

For this project, resins were extruded into pipe at one of Performance Pipe’s plants. The extrusion process forces melted HDPE resins through a die to form the diameter and wall thickness of the pipe. The PlatinumStripe 1800 Series PE-RT Pipe used in the Desert Hills project was 18- and 20-inch in diameter with a dimensional ratio (DR) of nine, which means the pipe had wall thicknesses of 2 and 2.2 inches, respectively.  

“The extremely hot temperatures of water coming from deep beneath the earth’s surface requires pipe and the materials used to make that pipe to be of exceptional quality and durability,” said Randy Knapp, engineering director of the Energy Piping Systems Division of PPI. “That is why HDPE resins produced with PE-RT are critical and can exceed the specifications for projects such as Desert Hills.”  

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