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Pressure rated dwv?

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Unread postAuthor: jimmy101 » Wed Jun 18, 2008 8:24 pm

joestue wrote:The PVC1120 means it is PVC type I grade 1. Hydraulic design stress of 2000 psi, or a safety factor of 2.5, industry standard. burst is 5600 psi.

the only other PVC i've seen is 2116 Type II grade 1, design stress of 1000 PSI.

DHW also means it is good to 140 Fahrenheit at some specific derating, i lost that pdf...trying to find it again

joestue wrote:absolutely, if the manufacturer don't want to guarantee a product but is sill kind enough the give the material properties of the product, feel free to use them

I don't believe those pressure ratings for PVC1120 are correct. I believe PVC1120 is the type of PVC pastic. The pressure rating of a particular pipe or fitting has to take into account the diameter of the pipe, characteristics of fittings, wall thickness etc.

You would be crazy to take a generic, pressure rated, piece of SCH 40 PVC up to 2000 PSI even if it does say PVC1120 on it. Why do you think the marked pressure rating is only 1/10th what you say PVC1120 is good for? That would be a 25X safety margin.

Here are some pressure ratings for various SDR pressure rated PVC1120 pipes. Notice that for the different SDR ratings the maximum pressure rating for the 2" pipe is different since the wall thicknesses are different, even though they are all PVC1120.

You can't say that the pressure rating of PVC1120 is XXX PSIG since you have not specified the wall thickness, pipe diameter etc.

You're going to get somebody killed telling them it's OK to take PVC1120 to 2000 PSI.

BTW, the derating for the pressure at 140F is a factor of 0.22, roughly 1/5th the pressure rating at 73F. The 200~300 PSI pressure rating for most pressure rated PVC pipe (PVC1120) may well be the pressure rating at ~140F. Regardless, it would be folly to expect pressure rated SCH40 PVC1120 to survive 2000 PSI.
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Unread postAuthor: psycix » Thu Jun 19, 2008 4:32 am

But what have those numbers to do with the pressure rating. Hydraulic design stress is not what he asked for.
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Unread postAuthor: jimmy101 » Thu Jun 19, 2008 12:18 pm

psycix wrote:But what have those numbers to do with the pressure rating. Hydraulic design stress is not what he asked for.

Which numbers? Joestue's (2000 PSI) or mine (~200 PSI)?
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Unread postAuthor: joestue » Thu Jun 19, 2008 4:12 pm

sorry, i meant the inherent strength of the plastic.

you need to take the diameter ratio into account, and correction factors for schedule 80 and higher.

before this flame gets any bigger.... if the manufacturing specifications are blatantly false, and your pipe bursts at a pressure more in line with pvc 2110.. or grade two or three.. you should get the manufacturer involved, immediately.
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Unread postAuthor: daxspudder » Thu Jun 19, 2008 4:26 pm

[flame]I personally think the blatant spreading/defending of poor and dangerous information is grounds enough for banning. Posting a gun that is nowhere close to safe and arguing that it is, to many more experienced people should have been a warning sign. Joestue, do you have a site that references your claim? anything at all? back of a cereal box? tattoo? cause it sounds like a load to me, and dont try to defend it, its wrong, and igpay's simple question has been terribly answered, with dangerous information, do more reading less writing, in fact I wouldnt write if I were you without citing sources.[/flame]
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Unread postAuthor: joestue » Thu Jun 19, 2008 5:04 pm

I have been doing a lot of reading, and i'm not convinced even pressure rated pvc is any safer than non pressure rated pvc.
Some sources indicate the difference is a safety factor of 2.0 vs. 2.5, but do your own research.

There is some massive discrepancies between what constitutes pressure rated pvc pipe and the service we demand of them. in the end everyone is playing dice with 1 in 10,000 odds that it will explode.

for starters you might want to take a look at...
http://www.uni-bell.org/faq.html#q9
http://www.harvel.com/pipepvc-sch40-80-derating.asp
http://books.google.com/books?id=LLaRlt ... Fx5tEa5wa4

http://www.google.com/url?sa=t&ct=res&c ... QNhF3YjnYA

Pressure vessel design manual, Dennis R. Moss
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Unread postAuthor: pat123 » Thu Jun 19, 2008 6:28 pm

basically to answer your question go by the pressure rating on the pipe. You are safe if you don't go over that. who knows a pipe rated to 200psi may be able to hold 600psi, but i wouldn't want to be the person beside it looking at the gauge.
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Unread postAuthor: jimmy101 » Fri Jun 20, 2008 1:35 am

joestue, it looks like you've done your homework but I think you are misinterpreting some things.

For your first link, note that that doesn't apply to SCH 40 pipe; "In closing, ASTM D1785 schedule pipe (40, 80 & 120) does not conform to the same design approach as the above-mentioned products. The products listed above offer a pressure capacity independent of pipe size, whereas the schedule product pressure ratings vary between different pipe diameters." (emphasis added)
So the AWWA and ASTM D2241 rating info in that sections does not apply to PVC pipe you get at the local hardware store.

Also note the "Once again, surge calculations are the designer’s responsibility. (emphasis added) Surge basically means you need to derate the pipe if there are rapid pressure changes. That eats into the pressure rating. Spudguns have rapid pressure changes and that means you need to derate the pipe.

For the Harvel link, nothing new there. A piece of SCH40 rated at 220 PSIG is for 70F. At 95F the pipe is derated to ~150 PSIG. Add in a fudge factor for rapid pressure changes (shock), particular for a combustion or hybrid gun, and the 220 PSIG original rating isn't looking all that good, you have to start counting on whatever the safety factor was in the pipe specification.

I haven't read the >160 pages in your third link. Perhaps you can point to a page that says typical SCH 40 PVC pipe has a working pressure limit of >1000 PSIG?

Your last link doesn't work for me. Can you get a different version of the URL? Perhaps go back through google and get rid of the google part of the URL. (Usually there is a link in the google frame to go directly to the page instead of showing the page as a frame in a google page.)
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Unread postAuthor: joestue » Fri Jun 20, 2008 4:17 pm

"Perhaps you can point to a page that says typical SCH 40 PVC pipe"

There is no such thing.

your question about the pressure rating shows you don't understand how they rate pvc. 5600 psi burst and a 2.5 safety factor means a schedule 40, 2 inch pvc pipe will be rated at 373 psi

pr=(2/diameter ratio-1) x (max stress or Hydrostatic design pressure/safety factor)
373 psi =(2/13-1) x (5600/2.5)

however, the hydrostatic design stress is not the same, and will differ according to things like temperature, surge and other considerations like falling anvils and exposure to shock.

A typical HDS is 4000psi
but here is a statement i found in a city of Madisonville water department pdf:
PVC water pipe shall conform, as a minimum, to AWWA C900, DR 18, Pressure Class 150.
PVC pipe shall be extruded from Class 12454-B polyvinyl chloride material with a hydrostatic design stress of 2000 psi for water at 73.4ºF, designated as PVC 1120, meeting ASTM Specifications D 1784-81 for material 40 as specified in ASTM D 1785-76.

HDS of 2000 psi, yet the pvc is designated the same. (type 1120)

here is another forum where a guy has a similar issues:
http://www.eng-tips.com/viewthread.cfm? ... 218&page=1

Either know what you have, or perform pressure tests to a safe standard, such as a safety factor of five.
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Unread postAuthor: jimmy101 » Fri Jun 20, 2008 6:30 pm

joestue wrote:"
your question about the pressure rating shows you don't understand how they rate pvc. 5600 psi burst and a 2.5 safety factor means a schedule 40, 2 inch pvc pipe will be rated at 373 psi

Yes, and if you remove the 2.5x safety factor the rating is 930 PSIG, NOT 5600 PSI. The difference between 5600 PSI and 930 PSI has nothing to do with safety, it is the structural affect on the burst pressure of the pipe. 5600 PSI is the burst pressure of the material without taking into consideration the geometry of the actual construction. It is an intensive property of the material.

Using the burst pressure of the material (or the hydrostatic design pressure) is basically using an intensive property to charachterize an extensive property. Kind of like using temperature as the sole definition of the energy in a system. Temperature alone can not define the energy of a system because temperature is an intensive property. The energy of the system is an extensive property.
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Unread postAuthor: igpay » Fri Jun 20, 2008 8:40 pm

:shock: Wow, quite a flame-fest this has turned into. A lot of this is beyond me, so all I really took away from this discussion is, "even if its crap-core pvc, and its rated to 200 psi, you can probably use it to up to 200 psi." If a mod who knows his stuff could descend from the heavens and clear all of this up, there's less of a chance someone with the same question later down the road would take this info the wrong way and end up hurt, or at the very least confused. :D

Cheers,
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Unread postAuthor: daxspudder » Fri Jun 20, 2008 8:55 pm

<A HREF="http://books.google.com/books?id=xSwZK9yaKQ8C&pg=PA205&lpg=PA205&dq=hydrostatic+design+stress&source=web&ots=BRM8XkaKAb&sig=bnKmfnCUfwZRoq901HbGZ1uQdIs&hl=en&sa=X&oi=book_result&resnum=6&ct=result#PPA204,M1">Look here for all the answers on the subject, especially pages <B>204 and 205</B></A>
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Unread postAuthor: jimmy101 » Sat Jun 21, 2008 1:29 pm

Dsaxspuder: That reference gives the same numbers and equations that joestue posted.

My point is that HDB or HDS is not the pressure rating of the pipe. Using the HDB or the HDS you can calculate the pressure rating for a particular geometry of pipe. (As joestrue pointed out earlier.)


For PVC1120 (per ASTM D2241) HDB is 4,000 PSI, HDS is 2,000 PSI. It is very important to not confuse those two numbers with anything that might be considered the pressure rating of a piece of PVC pipe. The numbers are, very roughly speaking, ten to twenty times greater than the actual working pressure rating for typical PVC1120 ASTM D2441.

The difference between HDB and HDS is that the HDS has a safety factor built in (typical a factor of 2).

The difference between SDR PVC1120 pipes and SCH40 PVC1120 is that SDR pipes have a constant pressure rating for all pipe diameters with a given SDR number. Sch40 PV1120 pressure rated pipe has different pressure ratings depending on the diameter of the pipe. Same material, same nominal diameters, different pressure ratings.

Furthermore, as the discussion at http://www.eng-tips.com/viewthread.cfm? ... 218&page=1 (posted by joestue) points out, in particular the response from Harvel, people sometimes confuse Sch40 with a pressure rating. You can have SCH40 pressure rated pipe and SCH40 non-pressure rated pipe. DWV cell core pipe is not PVC1120 (though it is PVC) but it is still SCH40. It is not pressure rated and will not tolerate the same pressure as will PVC1120 in the same Schedule and diameter. All the schedule means is that the pipes and fittings are compatible. So SCH40 cell core pipe will fit properly into a SCH40 PVC1120 fitting of the same nominal dimension. In this example, the fitting will be pressure rated but the pipe is not. (Of course, the reverse is true also, pressure rated pipe fits into a non-pressure rated fitting.)

There is nothing wrong with quoting HDB or HDS except for the fact that some spudgun builders might misinterpret the PSI ratings as the actual working rating of the various types of PVC used in spudguns. We really don't want a noob to think that since the HDB of PVC1120 is 4,000 PSI that it'll survive being used in a 10X hybrid since the maximum peak pressure in a 10X is "only" ~1,400 PSI.
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Unread postAuthor: joestue » Sat Jun 21, 2008 1:47 pm

"The numbers are, very roughly speaking, ten to twenty times greater than the actual working pressure rating for typical PVC1120 ASTM D2441. "

and that's because the diameter ratio is ten to twenty.

in the case of my infamous cannon, the diameter ratio is ~39
so if you take (4000psi/safetyfactor of 3)x (2/39-1) = ~70 psi.

personally i don't know how you can mix up the two numbers, ie 4000 and 200 or in my case 70-80.

My point is: a safety factor of 3-5 is relatively safe, regardless of the material.

they always tell you to not to use hardware store variety "aircraft" cable for over head lifting. the safety factor for steel cable is typically 10. make your own decision please.
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Unread postAuthor: daxspudder » Sat Jun 21, 2008 2:49 pm

that site explains that HDS has nothing to do with pressure loads on the pipe... relative to spudding that is... unless you shooting your gun buried which kinda defeats the point...
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