Interesting thread. I suspect you may have already sought the assistance of the manufacturer (who it would appear has sold the pipe for this purpose) in this matter, but if you have not it might be interesting to find out exactly what they have to say. Sunlight is of course one of the environmental agents that can adversely affect plastics. I have noticed that a very large USA manufacturer of hdpe pipes (allegedly “the world's largest manufacturer of polyethylene pipe products”, but I suspect much for gravity and storage etc. services) states now at the site
, “Sunlight contains ultra-violet rays that reduce the tensile properties of plastics with time.” It appears a manufacturer of specialty compounds used to minimize these effects breaks the degradation phenomena down even further at the site
with the explanation, “The UV rays in the sunlight, on prolonged exposure, breaks the molecular chains of PE and produces free radicals. These free radicals continue the process further. As a result, polyethylene pipes lose their flexibility and toughness over a period of time.” They go on to say in effect that purposeful carbon black additions (and with many qualifications so as to be properly applied etc.) minimize the radiation degradation, and say that, “Carbon black has been proven to protect HDPE pipe for over three years with no change in tensile properties from UV effects.” I have seen other hdpe manufacturers claiming however outside exposure life of hdpe pipes up to 20 years. I have even seen some manufacturers of hdpe pressure pipes responding perhaps even more cagily to questions about exposed life, using words like “indefinitely” (while this may carry a connotation of infinitely to some, in reality my Webster’s defines this word as unidentified, not precise, vague, or having no exact limits etc.) While not necessarily denying some utility of even some exposed hdpe pipes, I wonder if a more accurate or at leastless deceptive answer might be “it depends…”?
Where I have seen some hdpe pipes used for example as some culverts etc. in my area, I have seen also that it is quite common to see that some exposed ends of these culverts exhibit damages. While I guess I have assumed in the past these damages are primarily a result of the basic gouge etc. vulnerability of the plastic to the equipment used to handle/install the sections, and/or later equipment like mowers etc. trying to do their job around same, in thinking about it I guess it may be kind of hard to sort out exactly how much of the damages are due to this basic gouge/impact vulnerability and how much may be due to some weakening by continual sun exposure in such areas etc. I have also noticed (e.g. at site
) and many other sites that many DOT’s etc. are conducting quite detailed studies and durabilities including of exposed ends, and such things as roadside fires have also reportedly occurred, destroying pipes, and that are at least also a stated concern to some authorities and DOT’s etc. I guess control burns, arson, or accidental brush fires from cigarettes or welding operations destroying pipes are indeed a most extreme example of problems “due to heat”!!
About the only other thing I would add about “heat” and hdpe pipes is that I believe it can drastically lower an already quite low “long-tem” elastic or bending modulus of the plastic material (see the photograph at the link below I took several years ago, of some large diameter, solid-wall hdpe pipes that were apparently sagging a few inches under only their own weight on a jobsite in the southern USA sun).
As a perhaps interesting contrast, and further to Ussuri’s post, I am aware of an actual case in the Carolinas, USA when a utility bought a shipment of (I think incidentally ~30”) ductile iron pipes back in the 1970’s, but as sometimes happens for various reasons were not able to immediately install the pipeline. To make a long story short, these particular ductile iron pipes were finally installed into a pipeline just a couple years ago, after withstanding direct sunlight and all manner of other outside weathering exposure on the ground for roughly 30 years after they were originally purchased! I understand that while the pipes themselves were in good shape, it was however necessary to obtain new gaskets from the manufacturer, and it was also decided to patch some end damages on the cement mortar linings and repaint the socket and spigot joint surfaces of the pipe prior to this successful 21st century installation. I also understand utilization of these stored pipes saved them considerable money compared to contemporary new pipe cost.
