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12-16-2008, 05:56 PM #1
OT-How much pressure can a PVC pipe take?
I need to make a pressure chamber for room temp curing of carbon fiber projects and would like to get anything between 20 to 100 psi. I have an 8 inch black PVC sewer pipe that would fit the bill but have no way of determining a reasonable level of pressure that this type of chamber will hold. I was thinking of using pins to hold the end cap and the insert for the threaded cap.
12-16-2008, 06:07 PM #2
PVC, I believe is outlawed for compressed air lines so I'd have thought a pressure vessels out the window as well.
There have been a lot of threads on this issue.
12-16-2008, 06:45 PM #3
Black PVC? Ehhh? You sure that's not ABS or HDPE pipe?
There is pressure-rated PVC and drain/waste/vent (DVW). Don't confuse them. It's important to know what you are dealing with. There are many different pressure ratings.
For home-brew, you can get away with a few liberties as long as you do it correctly. For commercial use, forget it.
12-16-2008, 06:47 PM #4
People aren't going to like this, but what the heck...
8in. Sch. 40:
Max. op: 93psi
8in. Sch. 80:
Max. op: 148psi
Their bursting pressures are higher by a factor of ~5, but don't push those operating pressures. They are there for good reason.
Be sure you have black PVC (this sounds fishy) and not ABS. ABS is another animal entirely (no pressure rating).
The end caps will need something mighty fierce to keep them on. With an 8in. Endcap at 50psi, you already have 1200lb of force trying to push that thing off.
Also, I'd wrap the section of pipe itself with several layers of fiberglass filament tape. While the joints are most likely to fail, the tape reduces the chances of shrapnel from a break in the long section of the pipe (think knocking it off the table onto something)
Don't blame me when you lose your face in a pipe explosion.
And don't trust my figures. Go find your own from a source you trust.
12-16-2008, 06:59 PM #5
I don't think the black pipe is pressure-rated at all. Don't use it. Sched-40 or 80 is marked on the pipe with a burst PSI number. I've got a chunk of 1" right here and it's marked 450 PSI at 70 degrees. If it's my face somewhere close to that pipe and the pressure is going to be cycled a lot and there are plasticizers and chemicals in the epoxy that may do something to the plastic, I'd use metal pipe.
12-17-2008, 10:06 PM #6
I was considering using 3/4" PVC for air line but everyone I talked to warned me to stay away from it. The factory reps said absolutly NOT to put compressed gas in PVC. Using PVC for compressed gas is much different than using with water pressure.
12-17-2008, 10:16 PM #7
We use a PVC pipe, C-900, which is a ductile grade/equivalent pipe for a lot of watermain installations. As far as I know, it comes in as small as 4" diameter and have seen it as large as 24". We typically have to perform a hydrostatic pressure test on watermains which entails 150-200psi for 2 hrs. For comparision,the same size ductile iron pipe is usually rated at pressure class 350 minimum.
FWIW, typical SDR 35/26 will be pressure tested at 3-5 psi (for a gravity sewer application)
Your joints will have to be correct(restrained) in order to hold pressure.
12-17-2008, 10:48 PM #8
At the very least, I'd pressurize it via a LOOOONG hose and locate it in my neighbors yard.....
12-17-2008, 10:59 PM #9
Also remember that most PVC pipe ratings are at a certain temperature, usually around 70 deg. F. If you fill it very quickly with gas, it could heat up substantially and be far weaker than you thought.
12-17-2008, 11:28 PM #10
I know that PVC is easier to go to Lowes or a plumbing supply store and get, but given that you are going to have to have a flange on at least one end (and maybe it's easiest if you put a flange on both, and use big ol' allthread rods to pull the end flanges tight), it might be safer and easier to just get some schedule 40 steel pipe, weld (or have a competent pressure-vessel welder weld) a cap on one end, a flange on the other, and go for it. A blind flange with a two threaded fittings on it (you could seal weld the threads), a 3/4 inch ball valve, a pressure gage, AND A PRESSURE RELIEF VALVE SET TO 110psi, and you'd be in pretty good shape.
If the eight inch size is about right, you might want to find a dead air compressor, the dual tube design, and salvage the pressure vessels. Flange on one end, salvage the relief valve (which is sized properly for that vessel - cool!) and youd be good to go more cheaply.
At eight inches diameter, and about three feet long, and 100 psi, you are getting pretty close to the 1.5 cubic foot/150psi exemption limit on ASME Boiler and Pressure vessel code (you'd have to be less than 4 foot long or so to avoid having to register the design and have a PE evaluate, approve, and stamp your drawing). There's a reason for those thresholds - the amount of energy released is limited. And you are getting close to those limits. An 8 inch diameter PVC pipe at 100psi would be, err, either memorable, or the last thing you remember.
I'd go with steel pipe myself.
PS I would think that you'd want a vacuum on your carbon layup to cure it. Or is the pressure used as a clamp?