Buried steel pipe design: pressure influence??
Buried steel pipe design: pressure influence??
(OP)
Dear all,
I am designing a bruried steel pipe of 100" which can be subjected to a vacuum of 10 psi. I was going to use the Iowa-Spangler deflection formula in order to choose its thickness. But I have a doubt: The internal pressure of the pipe (in this case vacuum as I have told) shouldn't affect the deflection and, therefore, the thickness? I find it quite strange..
Perhaps it would be more appropiate to calculate it as a vessel subjected to an external pressure equivalent to the weight of backfill plus the internal vaccum of the pipe?
Any help or indication of any other calculation method will be welcomed.
Best regards,
I am designing a bruried steel pipe of 100" which can be subjected to a vacuum of 10 psi. I was going to use the Iowa-Spangler deflection formula in order to choose its thickness. But I have a doubt: The internal pressure of the pipe (in this case vacuum as I have told) shouldn't affect the deflection and, therefore, the thickness? I find it quite strange..
Perhaps it would be more appropiate to calculate it as a vessel subjected to an external pressure equivalent to the weight of backfill plus the internal vaccum of the pipe?
Any help or indication of any other calculation method will be welcomed.
Best regards,





RE: Buried steel pipe design: pressure influence??
thread161-101299
perhaps further explanation of problem can be provided, for example, fluid, application, service, etc.
good luck!
-pmover
RE: Buried steel pipe design: pressure influence??
Deflection isnt the only criteria. The controlling criteria for this diameter of steel pipe will be buckling.
RE: Buried steel pipe design: pressure influence??
Stanier says that "the controlling criteria for this diameter of steel pipe will be buckling". I suppose that it refers to the fact that this steel pipe must be considered as flexible.Is there any criteria (depending on thickness, diameter, elasticity modulus etc) to know if a steel pipe is flexible or rigid? I have to design other smaller buried pipes and I am not sure if they will be flexible enough...
And finally another question regarding AWWA: At first, I thought that the design of buried pipes would be similar to the design of vessels under external pressure, but I see that AWWA M11 says nothing about stifening rings, for example. Are not useful these stiffening rings for avoiding buckling of buried steel pipes? I do not understand it. Is there any reason not to use them in buried pipes?
Thanks a lot and best regards.
RE: Buried steel pipe design: pressure influence??
I am confused, what is your pipe dimensions? 100" does not say enough.
How deep are you going to bury the pipe?
Whats the service?
More data is needed
Regards
pennpoint
RE: Buried steel pipe design: pressure influence??
It has got other smaller branches. One of them is, for instance a 10" Sch. 40 pipe.
As you see they are very different, so my doubt is if the calculation method must be different (the bog one is likely to be flexible but the other one may be rigid, I do not know), and i do not know if using stiffening rings is useful according to AWWA M-11.
Thanks you all.
RE: Buried steel pipe design: pressure influence??
I see that Spangler equation includes a factor of soil resistance (0,061E'R^3). As far as I know E' dependes on the soil properties and the pipe radius, so this factor does not depend in any way on the "deformability" of the pipe.Is it reasonable? The reaction forces of the soil do not depend on pipe flexibility?
This matter is related to my previous question: when a steel pipe can be considered flexible and when it must be calculated as rigid, so, Spangler equation would not be applicabble?
Thanks and best regards,
RE: Buried steel pipe design: pressure influence??
Suggest you purchase AS 2566.1 & AS 2566.2
RE: Buried steel pipe design: pressure influence??
In practice, my results were very equal to the civil boys who use much more complicated analysis. I just consider the soil to act as an elastic foundation, that way you can use beam analysis to see exactly where the greatest moment occurs, hence the point of fracture.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada