Good answer Hydrae.
In fact, HDPE will not hold roundness as well as others.
Lack of equipment is a problem too, although I find this less convincing because good equipment would be purchased if the customer perceived an advantage to switching to HDPE.
Poor quality of installation yes, good supervision by knowledgeable person is required. Installation error though is always there even with the others. I have seen operators out there with lead wool pounding the stuff into CI joints. C-900 I have seen not much but would suspect installation errors, hey, a fool can screw anything up.
PUMPDESIGNER