Ductile Iron Compared to HDPE Pipe
Ductile iron pipe has tremendous advantages in strength and carrying capacity over HDPE pipe. The greater inside diameter of Ductile iron pipe means that comparable head loss substitute HDPE pipelines require larger sized pipe to compete. Check out the Resource Shelf to find out the many other advantages of Ductile iron pipe over HDPE.
Tensile Strength
Ductile iron has more than 24 times the tensile strength of HDPE pipe.
A pipe material’s tensile strength is a very important basic property because it resists the forces caused by internal hydrostatic pressure and water hammer.
Check out our Material Comparison publication for the full breakdown.
Installation Temperatures
Since Ductile iron pipe has a moderate and dependable coefficient of thermal expansion, few problems are created by changes in service temperatures. Ductile iron shows no significant difference in tensile strength in a typical range of waterworks operating temperatures (32°F to 95°F) or even a conceivable extreme range of installation temperatures (-10°F to 140°F).
Because of HDPE pipe’s thermoplastic polymeric nature, its performance is significantly related to its operating temperature. An indication of this is that HDPE manufacturers do not recommend their products for pressure service above 140°F.
Hydrostatic Burst Pressure
Ductile iron pipe resists up to 6.1 times the hydrostatic burst pressure of HDPE pipe.
Tests were conducted in accordance with ASTM D159912 by fitting the pipe specimens with gasketed, unrestrained end caps and securing them in a hydrostatic test structure to resist the end thrust. This arrangement produced stresses primarily in the circumferential direction in the walls of the pipes as internal hydrostatic pressure was applied.
All of the Ductile iron pipe specimens (6- and 24-inch diameter) burst in the form of a fracture 15- to 41-inches long.
All of the HDPE specimens (6- and 24-inch diameter) failed by “ballooning” with some also bowing and snaking, causing the pipe to pull away from the end closures and leak at the test seals.
To read the full findings after tests, access the publication.
Ductile Iron Pipe is the Right Decision!
Ductile iron pipe has long been recognized as the superior pipe material for water and wastewater applications. Its tremendous strength and durability allow it to be designed under conservative assumptions and installed with confidence that the actual service conditions it experiences will not compromise its ability to perform.
Regardless of the criteria — strength, durability, tapping, flow capacity, safety factor, or actual field experience — it is easy to understand what those who know pipe have long known.
