Stiffening rings in buried steel pipe? Useful??

[carletes]

Is it useful to install stiffening rings in a buried steel pipe? Designing it according to AWWA M11 I can't find any calculation where they influence in any way, but I have seen several buried pipes with these rings.
If a buried pipe is similar to a pipe under external pressure, why are they not considered in the same way as ASME sec. VIII div.1 UG-28 do?

Thanks a lot.

 

[JohnBreen]

Hello,

Maybe the real question is can the pipe function with reinforcing rings inside. The standing liquid between rings might lead to accelerated corrosion.

As a simply supported beam the pipe would want to ovalize under load thereby bringing the extreme fiber on the short axis side closer to the neutral axis (diminishing its section modulus (strength) and leading to collapse). The ring designs in M-11 are to keep the pipe round and thereby preventing it from losing section modulus (they (M-11) even show temporary wood "staves to keep the sections round while shipping). The Department of Reclamation has several design monographs addressing buried Penstocks. There is a classic very olde paper that was published by the Boston Engineering Society but I don't remember (CRS syndrome) the title. Given the standard wall thicknesses of standard pipe I think you have to go beyond NPS 36 before any of this really matters.

Of course the rings would help resist the external (overburden) loads but then you must address the very local membrane bending of the pipe wall at the rings (especially if the "pipe" is laying on a rock). Buried deep enough to be below the North American "frost line" the pipe will only see a part of the overhead vehicle loads.

Just some random thoughts.

Regards, John

 

[carletes]

Thank you JohnBreen for your help.

So, a copule of questions;

- If the stiffening rings are external, do you find any possible problem installing them?
- You refer to local membrane bending stresses due to stiffening rings. I suppose that if I use ASME Sec. VIII Div.1 for cylindical shells under external pressure I don't have to worry about it, do I?

My problem is that using ASME Sec. VIII or AWWA M11 I get quite different resultations.

Ah! Outside diameter of the pipe is 90".

Best regards,