All the basic types of pipe that have been mentioned thus far on this thread have been around for a long time. Of course, specifications for or selections of piping materials should be based on far more than “perception” and I think you are therefore prudent in seeking out experience as well as comparing all manner of engineering and maintenance etc. attributes. These matters have been discussed often on these forums (and discussions can be searched best with a few key words and the”Advanced Search” feature). There can obviously be a whole lot involved with prudent pipe material selection, including the two specific aspects/perceptions you’ve mentioned in your initial inquiry. Beyond that you might be interested in a hypothetical comparison of some current actual field pipeline hydrostatic testing requirements for say ductile iron and hdpe transmission pipelines, as follows:
Let’s say an Owner basically needs a transmission pipeline with a “20-inch” diameter flow area that is 12,000 feet long, and with a maximum working pressure (let’s say at the lowest point of the pipeline) of 170 psi (and with water etc. temperatures that will never exceed 80 degrees F. (thermal is of course an important consideration with plastic pipes) Let’s say that the Owner further likes to see a field hydrostatic test of say 250 psi (of course that is roughly 1-1/2 times the stated working pressure) after complete installation (involving pipe manufacture, shipping, handling, and finally complete burial/impacts etc.) for such a pipeline.
These working and testing conditions would appear to basically require, per Table 9 of AWWA C906 standard, a 24” DR 9-ish hdpe pipe that rates 193-200 psi working pressure etc. Per Table 6 of AWWA C906. It would further appear per Table 6 of that same standard that 24” DIOD (ductile iron O.D.) DR9 hdpe pipe would have a maximum possible flow diameter of 25.80” O.D. – 2(2.867) = 20.07” (OK for the hydraulic conditions stated). Per the proprietary field hydrostatic testing requirements for hdpe (I accessed today at
, it further appears that “Test Phase – Alternate 2” guidelines would perhaps be applicable, and per Table 2…”Make-Up Water Allowance” of this site they say 8.9 gallons per every 100 feet length of pipeline is allowable to be pumped back in after a 2 hour test. Of course this would in turn appear to mean (12,000 feet/100 feet)x8.9 gallons = 1,068 gallons pumped into the buried polyethylene line after the two hour test to get the pressure back up means the test is OK.
On the other hand lets say minimum Pressure Class 200 20” ductile iron pipe also rates some higher than a working pressure of 170 psi and can be field tested up to at least 300 psi (when all components in a system can withstand that level of test). Per Table No. 17-4 of the site at
the inside diameter of this 20” cementlined ductile iron pipe is 20.75” (of course OK and also larger than the above 24” even DIOD hdpe pipe). Per Table 5A of AWWA C600 standard for testing of ductile iron pipelines, a Contractor etc. is allowed a make-up water allowance of 2.24 gallons/1,000 feet length of pipeline per hour. Consequently, for a 2 hour test of the whole DI pipeline, no more than 2 hr x2.24 gal/hr (12,000 feet/1,000 feet) or 53.8 gallons of make-up water is allowable in field testing of this ductile iron pipeline.
I guess it is somehow conceivable (with all the weird things that can happen in pipeline profiles and durations of field testing etc.) that both pipelines are OK, but with allowable make-up water pumped back in to a buried hdpe pipeline of 1,068 gallons vs 53.8 gallons for DIP (nearly 20 times more for the hdpe), it is certainly not obvious that the hdpe is proven better, nor necessarily for that matter more actually proven “leak-tight” at joints, defects or damages, in this installation. I would recommend of course that you run your own numbers, and for your actual design/installation conditions.
As far as “brittle”(ness) is concerned, I guess it is possible that polyethylene is less brittle than pvc. However, what causes pipes to break can be a lot more complicated than that, and gets into detailed fracture mechanics and other fields. In this regard, however, ductile metals in general have far greater fracture toughness, and can also tolerate far greater “critical crack” or flaw/damage “lengths” etc., than the common plastics.
All have a good weekend.
