HDPE Pipeline Pressure De-rating due to Solar Heating

[tomecki]

I'm working on an a 36" DR9 HDPE pipeline to carry warm (30 deg C) water. The pressure rating of the pipe is sufficient at 30 degrees, however I'm concerned about further heating of the pipe due to solar radiation. The Plastic Pipe Institute HDPE handbook says that the surface temperature of black HDPE pipe can get up to 65 deg C in the sun but doesn't go into much more detail.

At an average pipe wall temperature of 47.5 deg C the pipe fails. I hoped that due to the low thermal conductivity of PE, I could show that heat doesn't penetrate fast enough to heat up a significant portion of the wall thickness during the day. My calculations show that it does. I also hoped that the fact that only the portion of the pipe directly facing the sun would get that hot would help, but it doesn't seem to. The location of the project is far in the north, so the sun won't be directly overhead even during the summer, but applying Stefan-Boltzman law for the expected solar radiation and an emissivity of 0.95 gives me an even higher surface temperature than 65 degrees.

I'm wondering if anyone has any experience with something like this, or can point me to some design references that would help me analyze this problem better.

Perhaps the pipe isn't suitable for the application in which case I wonder if there is a simple way of protecting the pipe from the heat.

Thanks

 

[miningman]

Not sure of the supplier , but this type of pipe is used in the mining industry for tailings transfer. It is available with exterior insulation already applied. For us, its usage in freezing temperatures but ID think it would serve your purposes as well.

 

[SlideRuleEra]

Are you accounting for heat loss by convective cooling of the outer pipe wall to ambient air?

http://www.SlideRuleEra.net

 

[LittleInch]

Paint it white or bury it.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[cvg]

http://www.permapipe.com/uploads/products/documents/brochure/PPUSBrochures/XTRU-THERM®_Brochure.pdf

 

[LittleInch]

UHMWPE??

http://plastimnew.websitedesigntest...sheets/UHMWPE-PE1000-Technical-Data-Sheet.pdf

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[KernOily]

SlideRuleEra is correct. You need to account for the entire heat transfer picture, e.g. heat loss to the surroundings (don't forget wind speed and ambient temperature) as well as to the fluid inside the pipe. The fluid will remove a lot of the heat of solar gain. The pipe will achieve thermal equilibrium with surroundings and the fluid media. Easiest and most accurate thing to do is take actual measurements, if possible, of HDPE pipe at the location in question. Perhaps you can run a pilot test with smaller pipe and lower flowrate at same process temperature and then scale up the findings using similitude. At the minimum this will give you accurate heat transfer coefficients. If a pilot test is not possible, do the full theoretical heat transfer analysis and add at least 20% because the calcs are only an estimate. There is a pretty good discussion of this in a textbook called Practical Process Engineering by Sandler and Luckiewicz. Good luck; this is not a trivial problem. Pete