Sch. 40 PVC vs. SDR21 PVC, how different are they?
Sch. 40 PVC vs. SDR21 PVC, how different are they?
(OP)
Has anyone ever heard the argument made that ASTM D-1785 Schedule 40 PVC pipe is manufactured differently or is more brittle than ASTM D-2241 SDR-21 PVC pipe?
I design lower pressure (<125 PSI) STEP collection systems and small community wastewater treatment systems. I was recently told by the state department of environmental quality (DEQ) that I could not specify Sch. 40 pipe because it is "not rated for burial" and that they had concern that it will not handle the soil load on the pipe (no more than 5' of cover typically).
I pointed out that both pipes are typically made with Type I, Grade I compund, Cell classification 12454-B per ASTM-D1784 (A.K.A. 1120). I also pointed out that for pipes <5" in diameter, Sch. 40 pipe has a thicker wall thickness than SDR21 pipe. For pipes 2-1/2" and smaller, it is over 150% thicker.
DEQ's reply was that they think Sch. 40 pipe is manufactured for "beam strength". And that they think it was manufactured differently to give it greater strength and less elasticity because the basis for Sch. 40 pipe is "non-pressure loading such as handling and supporting its own weight". Therefore it is too brittle to be buried in the ground.
Is this a valid statement, or is it a load of horse feathers? I have been told that this is their point of view, but they've not shown me anything to support it and they have basically told me to prove them wrong.
Thanks in advance for assistance!
I design lower pressure (<125 PSI) STEP collection systems and small community wastewater treatment systems. I was recently told by the state department of environmental quality (DEQ) that I could not specify Sch. 40 pipe because it is "not rated for burial" and that they had concern that it will not handle the soil load on the pipe (no more than 5' of cover typically).
I pointed out that both pipes are typically made with Type I, Grade I compund, Cell classification 12454-B per ASTM-D1784 (A.K.A. 1120). I also pointed out that for pipes <5" in diameter, Sch. 40 pipe has a thicker wall thickness than SDR21 pipe. For pipes 2-1/2" and smaller, it is over 150% thicker.
DEQ's reply was that they think Sch. 40 pipe is manufactured for "beam strength". And that they think it was manufactured differently to give it greater strength and less elasticity because the basis for Sch. 40 pipe is "non-pressure loading such as handling and supporting its own weight". Therefore it is too brittle to be buried in the ground.
Is this a valid statement, or is it a load of horse feathers? I have been told that this is their point of view, but they've not shown me anything to support it and they have basically told me to prove them wrong.
Thanks in advance for assistance!





RE: Sch. 40 PVC vs. SDR21 PVC, how different are they?
RE: Sch. 40 PVC vs. SDR21 PVC, how different are they?
RE: Sch. 40 PVC vs. SDR21 PVC, how different are they?
Same material and same process but with a different way to establish the pressure rating.
PVC has been buried in the ground since it was first manufactured! SDR 35 (very thin walls) was THE replacement for vitrified clay pipe! SCH 40 was first manufactured for pressure applications. Shortly thereafter drainage pattern fittings were developed for use under building slabs. Apparently someone felt SDR 35 wasn't good enough for underslab installation.
RE: Sch. 40 PVC vs. SDR21 PVC, how different are they?
On a related note... this whole thing has piqued my curiosity. Does anyone know the details of the history of the development of the standards? I am assuming Sch. 40 PVC showed up first and they just carried over the dimensions from iron pipe. But how were those dimensions developed and when?
RE: Sch. 40 PVC vs. SDR21 PVC, how different are they?
RE: Sch. 40 PVC vs. SDR21 PVC, how different are they?
Additionally, schedule pipe allows for up to 20% non PVC content, and SDR pipe doesn't.
I would appreciate any comment you may have on these items.
RE: Sch. 40 PVC vs. SDR21 PVC, how different are they?
SDR26 pipe has a pressure rating of 160 PSI. Every pipe diameter in a particular SDR is rated at the same pressure. This can be very useful if you are designing a system with a range of pipe sizes operating at the same pressure throughout.
Schedule 40 pipe on the other hand has a varying ratio of wall thickness to pipe diameter. Therefore, there is no way one can make the general statement that Schedule 40 pipe is rated at XX psi. Because the ratio varies, every pipe diameter is capable of withstanding a different pressure. However, due to the physical characteristics of the pipe, the "pressure rating" of Sch. 40 pipe tends to follow the trend of varying inversely proportional to the diameter. That is, the smaller the diameter of the pipe, the larger the pressure it is capable of withstanding.
http://www.harvel.com/tech-specs-pvc-pipe-40.asp
The systems that I design generally do not exceed 40,000 GPD. These systems have never required any pipe greater than 4" in diameter. I have no use in specifying a whole range of pipe diameters that are "pressure rated" at a constant pressure. Especially when I can specify a material that is far more robust than any readily available SDR product.
This might have some bearing on the argument they are making. Where does that statement come from? If I specify that the pipe be made of PVC 1120, Type I, Grade I Cell Classification 12454 per ASTM D1784 (as is typical of both types of pipe) are they not then made of the same material?
For anyone else following this thread that might find this information useful:
Here is what Harvel had to say on the matter:
Of particular interest was the attached engineering data pertaining to burial pressures. Here is a link to that information:
http://www.harvel.com/tech-support-eng-neg.asp
It shows a comparison of PVC duct, SDR 41, SDR 26, SDR 21, SCH 40, SCH 80, and SCH 120 pipe.
Thanks to everyone for all of the information and comments.
RE: Sch. 40 PVC vs. SDR21 PVC, how different are they?