HDPE failures are accelerated by aggressive conditions that result in the oxidative degradation of the material.
Failures of HDPE pipes have been documented in quite a few locations. DIPRA recently commented on premature failures of HDPE pipe in Hamilton, OH (
That being the case, the last thing we might expect from HDPE pipe would be a change in the design that increases the allowable stress in the pipe walls.
The Greater the Stress, the Sooner Plastic Pipe Fails
HDS = (HDB)(DF)
In the 2007 revision of the AWWA standard for polyethylene pipe
It is the HDS that is used to determine the pressure rating for HDPE pipe:
Where FT is a temperature factor, since higher temperatures (above 80°F) weaken the material. As a consequence, the pressure rating for DR 9 HDPE has risen from 200 psi to 250 psi just by increasing the allowable stress. But plastic pipe fails as the result of a stress applied over a period of time and the greater the stress, the sooner it fails.
Acceleration of Failures
The change to the Design Factor for PE 4710 HDPE is rationalized by the claim of a longer time to failure. Ultimately, failure occurs due to the degradation of the HDPE to the point that a very small strain results in a brittle failure
The recurring question: why choose a pipe with a history of vulnerability when a proven, resilient Ductile iron pipe is ready to serve when the demand is for safe water and reliable delivery.
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