HDPE Pipe Failure 2

[esass13]

Anyone experience an HDPE failure due to heat? We have an above ground installation of 24" and 30" HDPE that should be ok, except that HDPE is greatly derated in the summer heat for exposed pipe.

I guess we could paint the black pipe to white to reduce some of the sun exposure and reduce heat. Anyone had any luck with painting HDPE?

Thanks

 

[ChipperB]

I think you may have a hard time getting paint to stick to HDPE.

 

[bimr]

Seems like you should be more concerned about the thermal expansion. Because of a lower modulus of elasticity and higher coefficient of thermal expansion, hdpe pipe tends to expand and contract much more from changes in temperature and/or pressure than other piping materials.

The applications that I am familiar with involved laying the piping on the ground between rows of stakes. Stakes were used to keep the piping from moving too far laterally.

Painting would not work with piping installed on top of the ground.

 

[PELS]

Here's some FAQ's on HDPE:

http://www.querycat.com/faq/369f3a2fff68ab6b8bdb880e835b7174

 

[stanier]

For a start what grade of PE are you referring to? The generic description HDPE is often confused with MDPE. Each has different properties.

HDPE , PE Type 80C, is a HDPE and suffers derating with temperature and shortened life span.

Whereas PE Type 80B & 100 are MDPE and have different characteristics.

In Australia we co extrude PE with a white covering. Not much use when it gets covered by dust in a mine site application as far as temperature is concerned.

You cant paint PE successfully. A wrapped sleeve in white doesn't last long. Best bury the stuff as it reduces the temperature of the pipe wall.

An alternative is ABS from Tyco Water. Has higher temperature characteristics and it is grey. It can also be painted with water based paints. Available to DN800 class 15. It has been used outdoors for more than 40 years with no problems with UV.

http://www.tycowater.com/__data/page/11643/DURAFLO_cover_content_iss_1_rev_3_0905.pdf

 

[Ussuri]

As I understood it the problem with PE pipes above ground is that ultraviolet radiation from sunlight causes degradation of the PE by breaking the material down.

Typically we usually terminate the PE pipe below ground and using something like an aquagrip coupling transition to DI pipework for the above ground sections.

 

[BarryEng]

There is no UV degradation (in the sun) in a PE pipe because of the carbon black used for the colour.

Coeffic of thermal expansion: -
steel 11.9 x 10^^-6
PVC 7 x 10^^-5
PE up to 18 x 10^^-5

PE expands about 11 times that for steel (& 2 or 3 times that for PVC) for the same thermal change. Pipes are usually laid below ground & 'snaked' to allow for thermal movement. Remember to snake the pipe & backfill as you go to keep thermal movements to a minimum. I was asked on one occasion to review an installation (water source at the bottom of a hill & to a tank at the top of the hill) where the PE pipe had been laid in a trench in the sun (about 40deg C & about 1 km long), connected up & then backfilled. When the pump was turned on (water at about 18deg C) the pipe just came up out of the ground.

Some mine sites in West Australia will lay PE above the ground for short term operation BUT the pipe can be damaged by being run over by drilling rigs & (occasionally) burnt in a bush fire. Most sites (even in remote areas) will bury PE.

 

[rconner]

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

http://www.ads-pipe.com/en/resources/productfaq.asp#question9

, “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

http://www.plastemart.com/upload/Literature/hdpe100.asp

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

http://168.166.124.22/RDT/reports/Ri07038a/or08002.pdf

) 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.

 

[bimr]

Since your post indicates that this HDPE material is already installed, the manufacturer should provide the material and design properties. But that is not the solution to your problem.

The solution is not paint, but rather to insulate or cover the pipe. Insulation will prevent the pipe from being exposed to the sun. You should use an inexpensive fiberglss insulation, which should be covered with plastic or metal insulation jacketing. As an alternative, you can put a sun shelter over the piping.

"It should be noted that surface temperatures in HDPE pipe exposed to direct sunlight exceed 150ºF. HDPE is colored black to offer maximum resistance to stress cracking which is a common failure mode for this product. The black color increases pipe temperature from radiant heat absorption.

HDPE pipe is rated at 70ºF. HDPE mechanical properties fall off immediately above 70ºF with about 1/2 the strength at 150ºF."

http://www.ips-frp.com/B5TechBulletins/TechBulletins/HDPE Versus FRP.pdf.

 

[stanier]

Readers should be aware that rconner is a DICL protagonist. That said his postings are always informative even if having a leaning towards the preferred product.

PE has been used successfully for many years in outback Australia & SE Asia fully exposed to the sun & UV. This is the PE100 or PE80B. HDPE has however a checkered history. This includes the Type 50, 63 & 80C.

PE is manufactured here using European standards and resins which may be altogether different to that in the USA.

Virgin PE without carbon black is susceptible to UV damage. Hence the carbon black needs to be dispersed in the PE so that it does not fail.

Some earlier grades of HDPE had problems when regrind was used. The problem is that the anti oxidant used in the extrusion process was damaged during the first extrusion to the point where when re extruded caused faults. To overcome this the other grades of PE were developed. You can always specify virgin PE for your pipeline.

Rural irrigation piping , rather than pressure pipe, has a higher degree of regrind. It is not considered so critical. Comments about PE failing may be attributed to such materials should not be confused with the performance of pressure pipe.

The coefficient of thermal expansion is about 18-20 times that for carbon steel. This is more of a nuisance factor due to the dimensional changes. The modulus of PE compared to metallic materials is orders of magnitude lower. Hence surge pressures and loads on equipment are lower. These are distinct advantages over steel and DICL.

The derating of PE is acknowledged by suppliers and manufacturers. Stick to the majors with their own R&D , QA etc and you can rely on the data.

 

[rconner]

I am pretty much an education and experience protagonist. I feel that when engineers, Owners, and installers etc. know a great deal about all features of all types of pipes, they are in a better position to make informed decisions. Owners and Engineers etc. have the choice of what types of pipes to specify and buy, and large manufacturing companies incidentally/likewise can produce what they feel is the best type of pipes for specific markets within which they choose to participate. In this regard I have tested and quite closely observed a great many different types of pipes over several decades, and I know that drastically different pipes are in fact not equal, in a great many respects. Some proliferation of problems and/or questions on these lists with regard to “use” appears to indicate that at least some good folks, and unfortunately often with the pipes already purchased and sitting in front of them, may not have had the benefit of adequate education into quite complicated factors, or maybe even quite simple behaviors/factors, that can be involved.
I did not advocate replacement of this pipeline with ductile iron or steel pipes, at least at this time (or for that matter Tyco ABS pipes, as I have happened to see folk advocate for some applications on these lists!), nor (though it may apparently be in keeping with the spirit of some ASTM recommendations for at least aboveground storage of polyethylene pipes, see e.g. page 12 at

http://www.dipra.org/pdf/DIPvsHDPE.pdf

) did I offer encasement of the line in ductile iron or steel pipes and e.g. blowing cool air through the interstice. This may be overkill in this case!

Since at least a few hundred years B.C. and the days of Sophocles (and I think later as immortalized by Shakespeare) it has been some popular strategy particularly when the message in uncomfortable to attack the messenger. I would prefer to keep the discussion on a technical/issues level. By all means see what the “majors” have to say (and/or put in writing?) as I believe I initially said, and maybe even such education/discussion will result in better unanimity among same with regard to this and other issues.

 

[dcasto]

The OP never stated anything about the material inside. pressureized Hydrocarbons and air both shorten the life of HDPE.