AWWA M11 Pipe Buckling Question
AWWA M11 Pipe Buckling Question
(OP)
I'm reviewing a shop drawing from a tank builder which includes a vertical overflow pipe internal to the tank. The pipe will be empty and subjected to varying levels of external hydrostatic pressure varying from 0 feet to, say 20 feet at the bottom of the pipe as the water reaches the overflow weir.
I employed the calculation to calculate at what point the pipe would buckle from external pressure (equation 4-2 from M11). My calculations showed that buckling (for the pipe thickness they propose) could be a problem and I asked for justification.
The issue is what is "uniform and radial". I figured that the maximum "uniform and radial" pressure would occur at the bottom of the pipe. The tank guy contends that "uniform" means applying the average external pressure = (0 lb/sf at the top + max pressure at bottom)/2. Essentially, he's saying that the pipe would need to be horizontal and subjected to that max pressure at every point of the pipe in question.
They provided a justification and ultimately they are responsible so this is a relatively low risk question to answer. There are some flanges and bends that will stiffen the pipe that I acknowledged but didn't account for so I think we'll be fine either way. I am very curious about others' interpretation of "uniform and radial" and would appreciate some thoughts.
I employed the calculation to calculate at what point the pipe would buckle from external pressure (equation 4-2 from M11). My calculations showed that buckling (for the pipe thickness they propose) could be a problem and I asked for justification.
The issue is what is "uniform and radial". I figured that the maximum "uniform and radial" pressure would occur at the bottom of the pipe. The tank guy contends that "uniform" means applying the average external pressure = (0 lb/sf at the top + max pressure at bottom)/2. Essentially, he's saying that the pipe would need to be horizontal and subjected to that max pressure at every point of the pipe in question.
They provided a justification and ultimately they are responsible so this is a relatively low risk question to answer. There are some flanges and bends that will stiffen the pipe that I acknowledged but didn't account for so I think we'll be fine either way. I am very curious about others' interpretation of "uniform and radial" and would appreciate some thoughts.





RE: AWWA M11 Pipe Buckling Question
You are correct in your reasoning. You are determining the forces that the pipe will exposed to at 20 feet depth, so you should use the pressure of 8.67 psi (20 feet * ( 62.5/144)).
Having said that, one would expect that the standard pipe should not be affected by 8.67 psi external pressure.
Not sure what diameter of pipe that you have, but schedule 40 pipe should have a collapse pressure of several thousand psi.
http://www.engineeringtoolbox.com/stainless-steel-...
RE: AWWA M11 Pipe Buckling Question
It's a 48-inch pipe. Whether or not schedule 40 is applicable to that size is one of the contractual issues and 1/4" thick pipe is proposed in the absence of a defendable "schedule 40 standard".
You answered my question with the interpretation of uniform and radial.
RE: AWWA M11 Pipe Buckling Question
Further information is in the steel handbook:
http://www.steeltank.com/Portals/0/pubs/Welded%20S...
RE: AWWA M11 Pipe Buckling Question
I think there are multiple publications from this research, and perhaps some more applicable to your inquiry, but you may be interested e.g. in some of the results, relationships and factors involved e.g. testing on pages say 56 on in the report at https://www.google.com/url?sa=t&rct=j&q=&a....
RE: AWWA M11 Pipe Buckling Question
RE: AWWA M11 Pipe Buckling Question
RE: AWWA M11 Pipe Buckling Question
RE: AWWA M11 Pipe Buckling Question
48" and 0.25" walls and you're at 160
Good luck with that.
RE: AWWA M11 Pipe Buckling Question
RE: AWWA M11 Pipe Buckling Question
RE: AWWA M11 Pipe Buckling Question