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.

 

[rconner]

While you make some good points I would be careful however to not paint all standards and the morphing of same with such broad brush and harsh language. While I guess I should not be personally offended (as I do not sit on these standards committees), I believe the USA history e.g. of ANSI/AWWA standards for iron piping materials goes back to at least 1908, with standards then of New England Water Works etc. Pipes were however actually installed for a century before that in our country, many of which are still in service today. I just have to think in seeing the results in sort of bottom line terms of USA public health, life expectancy and water cost/rates there were likely a whole lot of quite well-meaning folks, including some quite smart and capable Engineers involved in the more than century since, dealing as best they could with the technologies of the time. These USA iron pipe standards, unlike some other standards for other pipes or countries, have also been for the most part “consensus standards”. What this means to any not familiar is they are composed in some cases of quite large numbers of User, General Interest, as well as Producer members. Over much of this time as well, I believe some of the largest consulting Engineers and utilities, and with considerable experience, have been involved in these General Interest and User constituencies.
In the early days of our country including now pipes roughly 200 years old, in aggregate huge quantities of pipes have been put into the ground really without the benefit of anything resembling modern Engineering or “software”. Not saying it is right or wrong, and acknowledging that it is indeed now blasphemy to Engineers who derive fees and retainers for such modern service, it probably still goes on today to a greater extent than most realize with particularly many small installations e.g. of pvc and ductile iron pipes.
As to “negligent” design, I do not know exactly what that means in your part of the world; however, and while I realize mine is not any sort of formal nor legalistic definition, I suspect there is very little risk of one being charged with same as long as the pipes they put into the ground basically “work” and provide cost-effective service. USA iron pipe standards have for decades, and by standardized design, furnished extra wall thickness in the walls of standard class ductile iron pipes by adding a surge or water hammer allowance of now 100 psi (or nearly 7 bars) to the quite high working pressure “rating”, BEFORE that total pressure is multiplied by an explicit safety factor to determine required net thickness, then on top of that required net thickness also adding a service allowance (that I have always thought takes into account effects of at least minor corrosion or damages) and finally also a “casting tolerance” to come up with a total calculated thickness (to be compared to nominal thickness). Furthermore, in the area of the AWWA thickness design standard discussing the water hammer or surge “allowance”, I believe the thickness design standard also includes guidance to the effect that if the anticipated surge pressures are other than 100 psi, the actual surge pressure should be used.
While I guess I could hear such a design called many things, including over-conservative or anachronistic compared to standards for other pipes, I would not personally call such hell for stout outcome “negligent” (as smart as we think we are or as low a safety factor we feel we need in our designs, extra strength may still come in handy in the real world as even what comes out of the best software is after all dependent on the accuracy or dependable experience/knowledge of the input). Everyone have a good weekend.

 

[stanier]

"I believe the thickness design standard also includes guidance to the effect that if the anticipated surge pressures are other than 100 psi, the actual surge pressure should be used."

The problem with industry is that it perceives that it can add a safety factor whereas the quoted statement indicates that you should undertake a surge analysis as otherwise you have no idea what the anticipated surges are likely to be. You cannot guess that you will or will not have column seapration.

Unfortunately for ductile iron, cast iron or PVC pipes is that they have thrust blocks. The thrust blocks do not necessarily have the safety factors built into the pipe materials. If the designer purely uses the safety factor to design the thrust blocks then failures can occur. There are also other fittings in a system that do not have such safety factors such as gaskets, gibault joints, valves, air valves etc etc. It is rare for a pipe to burst due to wall failure it is all the other ancilliaries that are the casue of failure.

In the engineering world we do hear of failures as the contractor/designer/insurer/lawyers invariably sign up to confidentiality agreements when the matters are resolved commercially. try a GOogle search on pipeline failures. You wont find much. Let me tell you there are far more than you would imagine.

As for standards and their ethicicity, 1908 was a different era to 2012. We live in the world of economic rationalism where the engineer is considered a service industry to the commercial enterprises. Turn on the tap and engineers come out. How many consultant's specification avoid risk by trying to pass the detail desgin onto the contractor? How many material manufacturers claim their product complies with a standard so they are not at fault when they were party to writing the "rules" int he first place!

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

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