SDR 26 1

[johnwill65]

I am located in SE NY state upstae from NYC (Hudson Valley)I have been informed by both a local contractor and a local pipe supplier that SDR 26 is just not used for gravity sewer here because they cannot get it, at least unless they buy a truckload, but then no one seems to want to use it even if they have it in stock as everyone seems to prefer the SDR 35--easier to work with, more readily avaialble, cheaper. The local sewer district prefers SDR 26, and specifies it, for uses under high traffic areas like roads and parking lots. They require Class 52 DIP for applications where cover is less than four feet, but prefer the SDR 26 for deeper installation in those areas I noted above. My question is if others in this part of the country have had a similar problem in getting SDR 26, and if they have found that the SDR 35 will perform as well as the SDR 26 when used as stated for under roads and parking areas--that is will hold up as well over time agaisnt collpasing.

 

[stanier]

I presume you talking here of PE pipe. Please confirm? Of course SDR 35 is cheaper as it is thinner wall and hence less PE and energy to convert the pellets into a round pipe. If you quoted SDR 26 then you would have to give the council some money back for using SDR35.

The design of buried flexible pipelines needs to take into account the trench width and depth, the soil modulus, the backfill modulus, water table, dynamic and static loading. Councils and other authorities will specify a very conservative pipe wall thcikness to avoid contractors installing something that is going to fail in years to come. Do the calculations to whatever code you are working to and demonstrate that the SDR 35 will perform for the next 100 years. The calculations may cost more than the change in pipe SDR.

Generally the soil takes 90% of the load. The PE will deform when and external load is applied and the soil takes an even greater load.

You have not nominated a diameter so I cannnot quote wall thicknesses and advise.

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King

http://waterhammer.hopout.com.au/

 

[bimr]

I am in the midwest and of the opinion that your contractor and supplier opinions are off based. The SDR 35 and SDR 26 pipes are close to the same price.

In a perfect installation, the SDR 35 is designed to work. However, there is benefit to using the SDR 26. The cost is not much different. The heavier wall of the SDR 26 has increased durablity during the construction process. We have found that using the SDR 26 fittings to be more practical even if you use SDR 35 pipe as the fittings are more durable and break less often.

I have found that it is more common to specify PVC SDR 26 pipe instead of SDR 35 for gravity sanitary sewers. SDR 26 will perform better under less than perfect installation conditions. Contractors typically say that the price difference isn't significant and SDR26 is easier to install, so that it is common to use PVC SDR 26 even if SDR 35 is specified.

 

[jgailla]

My experience on this subject matches bimr's.
I actually had a contractor tell me they typically ordered SDR 26 when SDR 35 was specified because it was easier to handle and install without incident. They sent me SDR 26 backup for the shop review and I called to ask why.

 

[johnwill65]

Sorry I did not clarify--this is for PVC pipe. My understanding matches what you all have said though--although they just do not seem to stock the SDR 26 PVC here, or no one is using it, so they dont stock it at the two big suppliers here.

 

[rconner]

I believe “DR 26” and “DR 35” are really two somewhat different sort of animals, produced to different ASTM specifications. I suspect the DR 26 you are talking about is probably meant to refer to pvc pipe per ASTM D2241, and the DR 35 is e.g. per ASTM D3034 standard. The former is alleged to be pressure rated for water (many years ago quite commonly applied as “rural water pressure pipe”), whereas the latter
for “sewer”. To understand at least minimally what one is getting in the way of pvc, it would probably be advisable to at least glance at both of these standards. I believe D2241 requires compounding/manufacture etc. that is intended to result in some level of long-term or sustained pressure containment etc. strength, whereas D3034 pipe on the other hand has been compounded primarily for minimal short-term pipe (ring crushing) stiffness.

I guess some might argue one unplasticized pvc pipe looks basically like another unplasticized pvc pipe. However, the ASTM standards for pvc pipes in general do not put many limits on the amount of “fillers” or additives that can or cannot be incorporated in the pipes (other than what is necessary to meet the minimal physical requirements of the
standards). In practice some spot analyses our laboratories have performed over the years have indicated at least some pvc manufacturers are more likely to put a whole lot more of cheapening fillers e.g. calcium carbonate (like limestone or “talc”) into the walls of the pvc solid and profile-walled gravity pipes, and often at least some less in the pressure-rated pipes. While such fillers can in fact enhance short-term ring stiffness while at the same time minimizing manufacturing cost/(maximizing at least price competitiveness or at least short-term profit?), some references indicate that can be at the expense of some other, and maybe particularly long-term properties. See the discussion also on filler loading of pvc pipe walls under “Importance of Volume Cost to the Plastics formulator” at the site

http://www.plastemart.com/Plastic-T...ormulator-unplasticised-PVC-plasticised-PVC..

To attempt to “put a number” on inferences others have made on this thread related to buried performance, I guess one can readily look at least at the theoretical, relative short-term pipe stiffnesses (PS) of pipes. Per ASTM plastic pipe standards,

PS = (E*I)/(.149*r^3)

Therefore, the short-term, calculated “pipe stiffness” (PS, sometimes used or considered in evaluations of installation, bedding, external loading, buckling/collapse scenarios etc.) e.g. of a 8” nominal size DR35 upvc pipe per ASTM D3034, with incidentally 8.40`” OD and 0.24” wall thickness, is in effect:

~ (400,000 lb/in^2) (0.24 in.)^3/12/((.149) (8.4-0.24 in)/2)^3) = 46 lb/in^2

In some contrast, PS of a 8” nominal size DR26 upvc pipe per ASTM D2241 with 8.625” OD and 0.332” wall thickness may be in effect:

~ (400,000 lb/in^2) (0.332 in.)^3/12/((.149) (8.625-0.332 in)/2)^3) = 115 lb/in^2, or this DR26 pvc pipe is about two and a half times as stiff as the DR35 pvc pipe.

Now as to 8” Special Thickness Class 52 ductile iron pipe (DIP) also mentioned in the OP, if one were to calculate the theoretical pipe stiffness in similar fashion,

PSDIP ~ (24,000,000 lb/in^2)(0.33 in.)^3/12/((.149)( 9.05-0.33 in)/2)^3) ~ 5,820 lb/in^2, or this class DIP in this size is more than 50 times as stiff than as the stiffer DR26 upvc pipe. It may not be hard to figure why this Authority prefers ductile iron pipe for shallow/potentially heavy-trafficked? sewer, and why some others prefer it also for quite deep and often nasty sewer constructions and
inexorable/unrelenting heavy earth loads there as well (where
differences in pipe cost are also often relatively quite insignificant in terms of total installed/constructed project cost). While I guess time will tell if the less stiff pvc is in the long-term adequate for what lies between, I have noticed “ageing” (perhaps non-obvious to some) has been reported in some European pvc sewers (e.g. see Table 2 at

http://www.sewer-rehabilitation.com/pdfs/baurherz.pdf

), that
generally have at least a little more age on them than pvc sewers in the New World.

Everyone have a good weekend!

 

[stanier]

rconner

Generally the pipe stiffness is of little consequence in respect of a combined pipe.soil structure at depths of 1.2m (4ft) as described. that is provided the embedment, teench width and native soil modulus are adequate. Refer AS 2566.

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King

http://waterhammer.hopout.com.au/

 

[jgailla]

rconner's comments on this subject should be taken with a grain of salt, as he works for a ductile iron pipe organization.
Regardless of the red herrings in his post, SDR 35 and SDR 26 PVC pipe are the predominant pipe used for gravity sewer piping, at least in my area in the Southeast US.
One good point that rconner makes is that SDR 26 and SDR 35 pipe should not be used for pressure piping, but I have not seen it used in this manner.

 

[rconner]

It is my understanding the OP basically asked if the lighter cheaper DR35 proposed by the Contractor should be considered a performance equal to DR26 pvc pipe. In this regard, I provided references and engineering calculations that illustrate that DR26 pipe is in fact 2-1/2 times as stiff as that DR35 the Contractor wishes to substitute.

With regard to the comment, “Generally the pipe stiffness is of little consequence in respect of a combined pipe.soil structure at depths of 1.2m (4ft) as described. that is provided the embedment, teench width and native soil modulus are adequate”, I do not recall the OP stating that they are only installing at 4 feet depth and frankly I guess this is a matter of specifier judgment. I believe that by that same “logic” of assumed adequacy of soil support it can be illustrated on paper that a pipe of ZERO stiffness would work! In the real world it of course doesn’t always
work like that, and there is risk, and who knows at some point perhaps also liability, in assumptions of substantial soil support. In writings of a former President of the American Society of Civil Engineers not long ago regarding problems with another very flexible as opposed to much more rigid pipes, I noticed the statement, “Some ASTM/AASHTO specifications place significant responsibility on the engineer regarding installation essentials to ensure service performance. Applicable sections in ASTM D2321-04 include requirements placed on the engineer with regard to installing thermoplastic pipe.“

As to the claim that I am just talking “red herrings”, I encourage all readers to do as I just did a quick Google search e.g. with the keywords “re-rounding pvc pipe”. I got one and a half million “hits”, that will quickly reveal that an entire industry has in fact arisen for equipment and services to attempt to re-round in reality even quite young pvc pipelines that in time have not performed as intended. In some cases (e.g. beyond the contractor’s warrantee period), it is no
doubt the tax and rate payers who often bear the cost of such equipment and services, and perhaps with questionable long-term efficacy.

Some of these re-rounding sites indicate that their equipment also has some alleged ability to minimize “sag” or appearances of undesirable vertical or profile undulations of the installed pvc pipeline, another arguable bane of very flexible and lightweight pipes. While lightweight has often been argued as an advantage by the plastic pipe industry, as perhaps foretold by a fellow named Archimedes a couple thousand years ago it is not an advantage with regard to control of vertical profile/alignment and also minimization of movement in high groundwater installation or soil liquefaction, e.g. in vibration or seismic events. In this regard I calculate the “bulk density” of an 8” DR35 pvc pipe even 1/3 its waterway depth full of sewage is only about 14.8 lb/ft^3. While still drastically less than a fluid water or soil environment, a comparable working DR26 pipeline is at least about 17% more dense, though I believe still more subject to move in ground than heavier pipes.

 

[stanier]

rconner,

I note that you have not denied working for a ductile pipe organisation. I wish you had the internal fortitude to add your title to your signature and be a bit more transparent.

In any buried pipe there are a number of criteria to be satisfied. These are not only deflection but strain, buckling, combined loading and stress. The codes allow for flexible pipes to deflect from their original diameter. As to a pipe with zero stiffness being adequate the codes have minimum stiffnesses.

So whether you are complying with AS 2566, ATV, ISO, EN or AWWA standards then the engineer has to design the combined soil/pipe structure. Importantly the field crew need to ensure that the native soil is within the design criteria.



“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King

http://waterhammer.hopout.com.au/

 

[rconner]

You are of course aware as I am of the impersonal nature of these forums. While I am aware of someones reported 30 year association with the design of plastic pipe systems, that industry, its standards and forensic work etc., I do not begrudge them what they do, and I refuse to attempt to use the perceived source of their livelihood against them in resorting to ad hominem or shoot the messenger attacks (as opposed to taking about the engineering issues).

While I guess you can write of me what you wish and I am likewise not hard to find, I prefer instead to keep discussions in this forum on an Engineering and technical basis. As there has been inference on this thread however that answers are in plastic pipe “standards”, I will however repeat a couple perhaps quite cogent quotes related to same from the aforementioned gentleman I have noticed in his presentations:

“These standards are not as comprehensive as standards for metallic materials. Therefore there is a need to use more esoteric approaches to meet design requirements.”

“International and national standards do not define the design requirements adequately for thermoplastic pipe systems”

Regardless of the source of solid information provided on these forums, I do not believe nuances of what is necessary to make pipe design and systems work, or for that matter why they do not work in particular case(s) etc. should be “esoteric” (or reserved to some select or secret clique), but instead/indeed should be out there for all to see.

 

[stanier]

Unfortunately standards are used to promote materials and denegrate others. There is a constant battle in committees to stop the manufacturers and their collective representative bodies from having undue influence.

In the interest of the engineering community if you have a role to represent the marketting of a product you should show your hand. If your posts are unbalanced and have been found by members of this forum then there is further need to avoid the perception of deceipt.

It may be that the ductile iron manufacturers feel threatened by the increased usage of thermoplastics in Europe and its spread into the USA.

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King

http://waterhammer.hopout.com.au/

 

[rconner]

I have no desire nor as far as I know any need to deceive. If there is something inaccurate or wrong with the many calculations and references I have provided, please advise and I will correct. You speak of a "spread" of plastic pipe as if it were a popular craze (or disease). In any case Engineering, and for that matter the pipe approval or selection part of same, should not be a popularity or nationality contest but should instead be based on sound technical grounds, and with all aspects that result in successful procurement, installation, service/operation, maintenance and nearby future work etc. reasonably considered.

 

[jgailla]

rconner,
If you do not realize you are being deceptive, you are deluded.
Your posts are clearly biased and you will not provide a caveat that you represent a certain type of pipe manufacturer. Your behavior is unethical.
I would expect it out of other professions, but as an engineer you have a higher ethical duty.

 

[dicksewerrat]

If you guys have such a problem with rconner's replies, don't read them. you waste a lot of our time to read your comments. We know he prefers DIP. Let it rest.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[stanier]

I for one will not let it rest!

I will continue to read these posts as some have value and need to be respected. Where my ire is raised is when the opinion is more towards marketing a specific product & reference is made to technical articles that are out dated and the product has moved on from there.

I have probably been involved in more projects with DIP pipelines than thermoplastics. There is a place for both in the market. DIP can survive on its merits and doesnt need stealth to gain market share.

I prefer a balanced view and if you come from a particular camp you should declare your hand so the newbies understand your position from the outset. The technical matters should be able to withstand critique and not need subtefuge.

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King

http://waterhammer.hopout.com.au/

 

[jgailla]

I agree with stanier. Here is the website policy below. The above poster has been breaking these rules repeatedly, as well as exhibiting unethical behavior by not being straightforward about his employer. There are other people besides myself who have observed this behavior. I have not brought this issue up to site management, but at some point I would expect engineers to be better than other professions and self-regulate their behavior. If this website is to remain a valuable source of information, as it has been to me and thousands of others, salesmen must be kept out, or least required to identify themselves as such.

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[stanier]

A Google search revealed Randy Conner PE research engineer American Cast Iron Pipe Company. Extensive postings can be found on pipingdesign.com, ASCE, etc promoting iron pipe and always negative comments about other materials.

Not much time spent in "research" I suspect other than for events that reflect negatively on products other than iron pipe.

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King

http://waterhammer.hopout.com.au/

 

[rconner]

Alas, it has been revealed, through I’m sure exhaustive investigation (for whatever reason by some dedicated Inquisitors), that rconner is in fact rconner, and maybe the same rconner who has contributed to many other technical and engineering organizations and forums with experience spanning a great many years. Furthermore, it has also been revealed that rconner is a “proponent” of iron pipes. I guess about all I care to say in defense is perhaps there are worse crimes, and I’m not sure readers with the modern marvels of the Web cannot otherwise read at least a little and determine on their own whether or not I know of what I write? Maybe so much however for the rule or promise, "ALL member identities are confidential, as members are known only by their "handle."

jgailla, with regard to the last sentence of your 28 Jul 12 7:25 post, I of course did not say that DR 26 should not be used for pressure pipe. I know SDR 26 or “DR 26” pvc pipe per ASTM D2241 has in fact been promoted in various areas of the USA for pressure service since on or before 1964, and believe it or not I have even seen even lighter DR’s since also promoted for pressure service (but most often in the Third World). In ASTM D2241 standard I believe this SDR 26 pipe was/is even called a 160 psi pressure rated pipe.

In this regard however on or before 1974 I know the USA plastic pipe industry lobbied strongly with AWWA et al to accept the first version of an AWWA standard for 4"-12" pvc pipes, that eventually issued as AWWA C900 in 1975. As the experience that had been amassed (worldwide) with ASTM style pvc pipes over at least a few years to that date was some good and frankly also some bad, the original at least some more conservatively designed (then thicker) 1975 C900 pipe proposed, with inclusion also of at least some small level of surge (of course shortly after the research per Robert Hucks and others in working pvc systems) as well as a reported 2.5 safety factor on the total pressure (working plus that defined surge) in thickness calculation, was instrumental in the successful balloting of this standard. It is also some interesting that a safety factor vs total pressure including surge and importance of consideration for surge was even highlighted in what appeared to be a promotional article I read sourced from the 1977 Uni-Bell "Handbook of PVC Pipe" entitled, "Water Hammer – Surge Pressure with Vengence" (their spelling). This more conservative original AWWA C900 design called a DR25 pipe (of course very close to the DR26 talked about here) only a 100 psi pressure class pipe.

In 1994 (of course 30 years after the first edition ASTM standard) and after nearly 20 years of the first design C900 pipes, I am aware that the American Water Works Association Research Foundation sponsored a "data gathering questionnaire" that was reportedly sent to many utilities. The reported results of this questionnaire revealed that approximately 80% of the aggregate utilities' installed pvc pipe was then "C900" and 20% was per ASTM D2241. While received results of this questionnaire revealed some positive perceptions and satisfaction with pvc pipe, it noted ovc pipe was "second in overall performance compared to other pipe materials" (I believe first was ductile iron pipe), and it also concluded that,

"An analysis of reported data shows that problems associated with pvc water pipe manufactured to the ASTM D2241 Standard is about twice as high as for pipe manufactured to the AWWA C900 standard."

More recently in 2007, the small standard surge allowance that was originally considered in addition to the class pressure in establishing the originally lesser C900 pressure classes, or greater original C900 wall thicknesses etc. was in effect removed from the AWWA C900 standard, and at the same time the safety factor on Hydrostatic Design Basis (HDB) was reduced from the original 2.5 to 2.0.

The sort of pressure rating philosophy of this new C900 standard appears now VERY similar to that early ASTM standard (e.g. with assumed, common unplasticized pvc compound strength per both standards), in that very early SDR26 pipe carried a 160 psi "pressure rating" and the new C900 promotion is that a quite similar DR25 is supposed to carry a 165 psi rating.

In other words, original C900 pressure class 100 pvc pipe has with the stroke of a pen (or contemporary computer keys) now become pressure class 165 psi pipe. More information is in the archives of these forums.

“It is the mark of an educated mind to be able to entertain a thought without accepting it”.
Aristotle

 

[stanier]

The use of a "surge allowance" in the design of any pipe system is negligent. Standards should not support such an approach whether it be for PVC, PE or DI. There are modern software tools where the system can be modelled. You cannot guess what the surge is going to be.
If there is column separtion and rejoining the pressure rise could be 7 to 10 times the operating pressure Refer Fluid Transients in Presure Systems by Prof ARD Thorley and Pressure Transients in Water Engineering by Ellis.

Standards committees the world over in the field of pipe materials are dominated by the manufacturers. Consultants can rarely afford to send along delegates. They have no interest in terms of $ for bums on seats. Authorities are under financial stress and have reduced involvement. It is left to the few committed individuals who want to keep the manufacturers honest.

The manufacturers use the standards as a marketting tool to get advantage of their product ahead of the competition. Do you see a similar thread in posts to this forum?

rconner,

The formulation of PVC has changed somewhat in the last 10 years let alone going back to 1977. Stabilisers and fillers have changed to improve quality. C test s have been introduced to censure the product is not subject to crack propogation. The formulation of PE has also changed and the properties are vastly difference. Continued reference to dated papers is erroneous and misleading. In Australia DI has been re-evaluated and is know manufactured based on class of pipe rather than using the legacy K9 & K12 designation. Products continually change.

The history of the introduction of thermoplastic pipe materials had certain design factors included to cover the unknowns. With hind sight and more long term test results the technology was such that the pressure ratings could be re- evaluated. I do find manufacturers abhorent who are party to the production of standards then hide behind the standard when there are failures. Perhaps we would be better off if the plastics and DI industry took the same approach as steel pipe as in ASME B31.1 & 31.3.

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King

http://waterhammer.hopout.com.au/