HDPE for Compressed Air?
HDPE for Compressed Air?
(OP)
I have been doing some research on this topic and I've found that there are mixed feelings.
My question is, can I use HDPE pipe (DR7) for an underground compressed air system at around 170psi? I'll start with what I found.
B31.8 has a limit of 100 psi on thermoplastic pipe. But this is for gas transmission and distribution, the question is with compressed air. Then again, why the limit?
B31.3 specifically states "No PVC in compressed air systems" period. But does not say anything about HDPE and it gives the formula to calculate the pressure rating on thermoplastics. Which for DR7 it's well above 170psi.
I have heard about detrimental effects from oxygen on thermoplastics... does it apply to HDPE?
I'd appreciate anyone's help/opinion on this. Thx.
My question is, can I use HDPE pipe (DR7) for an underground compressed air system at around 170psi? I'll start with what I found.
B31.8 has a limit of 100 psi on thermoplastic pipe. But this is for gas transmission and distribution, the question is with compressed air. Then again, why the limit?
B31.3 specifically states "No PVC in compressed air systems" period. But does not say anything about HDPE and it gives the formula to calculate the pressure rating on thermoplastics. Which for DR7 it's well above 170psi.
I have heard about detrimental effects from oxygen on thermoplastics... does it apply to HDPE?
I'd appreciate anyone's help/opinion on this. Thx.
RE: HDPE for Compressed Air?
RE: HDPE for Compressed Air?
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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RE: HDPE for Compressed Air?
I do not see this pipe going over 80°F.
Thx for your reply!
RE: HDPE for Compressed Air?
RE: HDPE for Compressed Air?
Anyhow, back to HDPE. I don't know whether oxygen will attack it, although I suspect, given long enough, most material will oxidise.
I guess what I am saying too is contact the vendor.
In my industry, almost all of our air lines (instrument and utility) are steel. Carbon steel for most headers and distribution, and SS to the instruments. I don't know why, but that's what we do. Most of our IA system is 100 psi, maximum of 120 psi.
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
RE: HDPE for Compressed Air?
If I can't go with HDPE then I will go with SS.
...it requires a 2" line from compressor to bollards. I was suprised as to how well the bollards hold up against impacts!
RE: HDPE for Compressed Air?
Have you looked at the new spoolable composite piping? This stuff has a layer of HDPE, a layer of kevlar, and a layer of carbon fiber. Pressure rating is similar to steel, corrosion resistance and surface roughness are similar to SDR7 (if you disregard the weld seams in the SDR7). It comes on spools in 1-inch through 4-inch. I would have no qualms about using it in air service. Take a look at http://www.futurepipe.com/usa/index.asp. Future Pipe purchased Hydril's spoolable composite line and has some good products. I've run them in natural gas and water service with good results.
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
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RE: HDPE for Compressed Air?
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
RE: HDPE for Compressed Air?
RE: HDPE for Compressed Air?
Also, if the pipe is buried, chances are that the soil temperature will be lower than 80°F, and depending on thermal conductivity of the pipe wall and soil, may act to further cool the air?
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
RE: HDPE for Compressed Air?
Below-ground installation is about twice the price of installation of steel.
David
RE: HDPE for Compressed Air?
The continuous coil nature of the material is a definite benefit for a buried piping system.
Recent experience would suggest that you avoid FRP piping below 2". Even at 2", all those buried joints would be worrisome. Small-bore FRP piping and fittings are expensive because they're difficult to make properly. We had a significant number of defective fittings supplied to us, and not by some fly-by-night supplier either: this was a major manufacturer of FRP piping components, and their fittings leaked through the body like a soaker hose.
The low pressure buried natural gas line that runs in front of my house is heavy schedule HDPE pipe. HDPE tubing is also used by the thousands of miles to connect instrument air users to supply headers etc.
RE: HDPE for Compressed Air?
Like Ashereng said. The air coming out of the compressor goes through an aftercooler, a pulsation bottle, a dryer and a filter. All of this piping will be galv. CS thus helping dissipate the heat. When it goes underground the temperature of the ground will help cool the pipe and not let it get too hot.
After speaking to the vendor the following was noted:
Experience has shown that HDPE can be successfully used in air systems. There are factors that must be evaluated. These are:
-Air temperature- often several lengths of metal pipe are needed from the compressor to transfer heat away from the air. - CHECK!
-Filtration to remove lubricate. - CHECK!
-Limited life (a good life expectation is ten years.) -MMM???
I will be installing SS pipe. This section of pipe will be in a well traveled area and I cannot afford for this pipe to fail.
Thanks for all of your input. Hopefully this thread helps someone in the future...
RE: HDPE for Compressed Air?
- Fusion-bonded epoxy external and internal coating on CS: shop-applied, bulletproof IF done properly and your contractor is skilled at installing it
- Plexcoat (HDPE extruded coating applied to CS) or its equivalent
Not sure I understand your cooling problems. If your compressor and aftercooler are working properly, you should have near-ambient air leaving your dryer skid or at least air within 15°-20° of the ambient dry bulb temperature.
Galvanized CS is no long-term panacea. We have gobs of those systems out here (central Cali) and plenty of them have internal corrosion after a few years. It only takes one or two dryer malfunctions for water to get in there, and then it's just a matter of time before internal corrosion sets in... If you are that critical, it might pay you to run SS the entire way. Use sch10S buttwelded to keep the cost down. If you have long runs, you can get DRL's from a special mill run and that will save a lot of welding $$$.
Thanks!
Pete
RE: HDPE for Compressed Air?
Sounds like some butt-covering on the part of the pipe manufacturer to me. But of course you can go with stainless, provided you have an open trench to lay it in. The other benefit of the polyethylene material is that it can be installed with trenchless technology (hydraulic rams etc.)
RE: HDPE for Compressed Air?
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
RE: HDPE for Compressed Air?
The fact that oxygen permiates into the wall of HDPE is the concern. Yellow HDPE pipe used for gas does not have a problem because there is no oxygen in Natural Gas.
I see what you are saying about internal corrosion. I had not thought about that. Either way, galv. CS or plain CS would still have to be coated and wrapped, as well as a cathodic system installed... in terms of cost and time, I believe stainless is a better option.
Trenchless technology is a neat idea. Although digging a trench is not a big deal in this project.
Stainless steel seemed like overkill at first.. but with the options I have, it's looking better and better.
FYI, at the bollards we are using Duratec pipe. It's an aluminum pipe with HDPE lining on the inside and the outside. So the Aluminum holds the pressure while HDPE protects against corrosion. Check it out:
http
Once, again. Thanks for all of your input.
RE: HDPE for Compressed Air?
Anonymous: In a buried pipeline I doubt there's much risk of HDPE degradation due to reaction with air. If oxygen diffuses through the HDPE wall, so what? You'll lose a trivial amount of oxygen from your air into the soil, and there's no UV light to do any embrittlement.
There's been lots of crosslinked HDPE used in hydronic heating systems over the past fifty years as well as the buried low pressure NG lines I mentioned. But again, I'm not in that biz, so what do I know? SS is safe, so go for it. It's only money...
RE: HDPE for Compressed Air?
RE: HDPE for Compressed Air?
RE: HDPE for Compressed Air?
I am not familiar with that method.
We usually plow it in:
http://www.spiderplow.com/
Or we dig an open trench and spool it in:
http
Much faster than the hydraulic ram method I think.
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
RE: HDPE for Compressed Air?
RE: HDPE for Compressed Air?
jdarco: I had not heard about this pipe. I will take a look. Thx for the link.
RE: HDPE for Compressed Air?
http:/
RE: HDPE for Compressed Air?
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