SDR Rating for Pipe? 1

[TexasCHe]

Vertical sump 12 feet from surface to bottom and 4 feet in diameter. Design calls for a SDR of 21. If I am looking at this correctly, on a 48 inch pipe this would require a wall thickness of 2.28” for an SDR of 21. That seems like overkill. Thoughts?

TexChe

 

[zdas04]

You realize that gravity is a thing, right? Even with 2-1/4 inch wall thickness you have a big problem of the pipe trying to flatten out when lying horizontally and of collapsing when set on end (I wouldn't put any weight on top of piece of 48" HDPE set on end).

Then there is internal forces. If you look at the force over a 1 ft section of this pipe at the ASME B31.8 MAWP of 80 psig you have about 1000 lbf pushing on this plastic pipe. No, 2.28 inches does not seem to be overkill at all.

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[LittleInch]

I don't understand the question. SDR 21 is good for 8 bar / 115 psi internal pressure. If you don't need the pressure or strength then people make v low pressure SDR 33 pipe in that size.

[Edit]PE 100 means long term strength is 10 MpPa which means it has about 1/25 the astrength of basic steel.

PE tubes ability to withstand compressive forces is lower than internal pressure and needs to be pretty thick.

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[dik]

Can you use 'ribbed' piping?

Dik

 

[TexasCHe]

dik,

Funny that’s where this whole issue got started! Spec said 21 and contractor proposed corrugated pipe that was rejected.

 

[zdas04]

LittleInch,
That number really depends on the codes controlling. ASME B31.8 has a formula that limits the pressure of SDR 21 to 80 psig in water (about 58 psig in gas). B31.8 also says that no un-reinforced thermoplastic pipe can be rated above 100 psig. In Australia, one of the factors (which has values less than 1.0 in ASME) is removed and another has higher values than the ASME uses, and you get pressure ratings in the range you are talking about.

I think we'd need to define terms to understand your statement about the strength of PE to be 1/4 that of basic steel. If I do the standard coupon pull test, the numbers for HDPE are significantly less than 1% of steel for the same thickness. Manufacturers MAWP for Sched 40 6-inch pipe is 1210 psig. Even if you use your rating for SDR-21 (size is not a factor in MAWP, all sized of SDR-21 have the same MAWP) it has a MAWP of 115 psig, about 10%. Using ASME calcs it is about 5%.

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[dik]

Should provide mat'l as spec'd... unless you are the specifier, then use what is appropriate and issue a notice of change.

Dik

 

[bimr]

The rule of thumb for a concrete manhole is 1-Inch thickness per foot of depth. So you can compare the plastic to a 12-Inch thick concrete segment.

 

[cvg]

If I understand the OP correctly, this is a sump for a pump. there is likely to be no internal pressure other than 12 feet of standing water, open to atmosphere. It is basically a tank. the main pressure is earth pressure on the outside. Certainly the SDR21 can handle that. I would be worried about flotation more since the SG of HDPE is less than water.

 

[LittleInch]

Edited my post as I got the numbers wrong. Apologies. Pressure rating is dependant on location and codes used and especially temperature.

We still have no idea what the forces are that the pipe is exposed to.

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

 

[TexasCHe]

cvg,

You hit e nail on the head. It's to hold back the pressure exerted by the soil. Could probably assume saturated soil being that it's a sump.

Terry

 

[bimr]

https://books.google.com/books?id=8...e&q=can plastic be used for manholes&f=false